Episodios
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Join us as we dive into the latest astronomical discovery! Scientists have identified a **new candidate pulsar wind nebula (PWN)**, named XMMU 034124.2+525720, which may be directly linked to **1LHAASO J0343+5254u**, a powerful "PeVatron" in our galaxy.
**What are PeVatrons?** They are the most energetic astrophysical objects in our galaxy, producing cosmic rays (CRs) with energies exceeding 1 PeV (10^15 eV), far surpassing what terrestrial accelerators can achieve. Understanding them is key to solving the mystery of the most energetic galactic cosmic rays and gamma rays.
This potential PWN, discovered through extensive **XMM-Newton observations**, exhibits key characteristics typical of other very high-energy PWNs like the "Eel" and "Boomerang" nebulae. Its X-ray emission shows an **extended, asymmetric morphology** and a **power-law spectrum (ΓX = 1.9)** that becomes notably softer farther from its center.
Using **multiwavelength modeling**, researchers demonstrated that a **fully leptonic model**—involving electron synchrotron radiation and inverse-Compton (IC) scattering of ambient photons—can explain the observed X-ray and gamma-ray emission, especially if there are **elevated infrared (IR) photon fields** in the region. While this model largely accounts for the LHAASO gamma-ray flux, future observations will help explore if hadronic processes in nearby molecular clouds also contribute to the gamma-ray emission and potential neutrino flux.
Though XMM-Newton observations didn't definitively resolve a central pulsar or detect X-ray pulsations, this discovery marks a crucial step in understanding galactic PeVatrons. Future, higher-resolution X-ray observations with missions like Chandra and NuSTAR, along with dedicated radio searches for a pulsar, are planned to solidify this PWN classification and provide deeper insights into these extreme cosmic accelerators.
**Article Reference:**
DiKerby, S., Zhang, S., Ergin, T., et al. 2025, *Discovery of a Pulsar Wind Nebula Candidate Associated with the Galactic PeVatron 1LHAASOJ0343+5254u*, The Astrophysical Journal, 983:21.
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Stephen DiKerby et al., 2025 ApJ 983 21
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In this episode, we dive into a fascinating new study that performs the **first direct consistency check** between two crucial measurements from the Large High Altitude Air Shower Observatory (LHAASO): the **cosmic-ray (CR) proton spectrum at the "knee"** and the **Galactic diffuse gamma-ray emission**.
The "knee" in the cosmic ray spectrum (around a few PeV) is thought to mark the maximum energy reached by Galactic CR accelerators. Diffuse gamma-ray emission, primarily from CR interactions with interstellar gas, provides a complementary view of the same underlying particle population.
The study reveals a **persistent mismatch**:
* The **predicted gamma-ray flux robustly overshoots the LHAASO data** in both inner and lateral Galactic regions.
* This discrepancy is evident in **both normalization and spectral shape**.
* This is particularly puzzling because while an excess of gamma-rays has been discussed before, **evidence of a deficit in observed emission represents a new and more puzzling feature**.
Key insights from the research:
* The disagreement **challenges conventional scenarios** linking the local cosmic-ray sea to Galactic gamma-ray emission.
* It **calls for a revision of current cosmic ray models** in the TeV-PeV sky.
* The mismatch is **not attributed to the hadronic interaction model** used for calculations; using alternative models would actually increase the tension.
* The findings suggest a **possible tension between the LHAASO gamma-ray observations and the CR proton flux measured by LHAASO itself**.
* One intriguing explanation is that the **CR spectrum measured locally might not be the same as the one responsible for the observed gamma-ray emission** throughout the Galaxy, possibly having a different "knee" location (e.g., around 300 TeV).
* Uncertainties also exist due to the **lack of helium flux measurements** between 100 TeV and a few PeV.
This research highlights the critical importance of evaluating the consistency between these two types of measurements and opens new avenues for understanding cosmic ray propagation in our Galaxy.
**Article Reference:**
Espinosa Castro, L. E., Villante, F. L., Vecchiotti, V., Evoli, C., & Pagliaroli, G. (2025). *LHAASO Protons versus LHAASO Diffuse Gamma Rays: A Consistency Check*. arXiv preprint arXiv:2506.06593.
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: LHAASO
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In this episode, we dive into the mysterious world of Fast Radio Bursts (FRBs) and the ongoing quest to understand their origins. We discuss a systematic search for **past supernovae (SNe) and other historical optical transients** at the positions of FRB sources, exploring a leading theory that links FRBs to **magnetars**.
The study **found no statistically significant associations** within the 5σ FRB localization uncertainties between the observed CHIME-KKO or literature FRBs and optical transients, *except* for a previously identified potential optical counterpart to FRB 20180916B, named AT 2020hur. AT 2020hur, however, occurred *after* the FRB was first detected, making it inconsistent with the "past SN" progenitor model, though it remains a potential association under other theories.
**Chance Coincidences:** The probability of a chance coincidence (Pcc) between an FRB and a transient was found to be **low (Pcc < 0.1)**. It's estimated that it would take **~22,700 subarcsecond-localized FRBs** to yield one chance association, which translates to roughly **30–60 years** at the projected CHIME/FRB Outrigger detection rate. This means that any robust match found in the near future is highly likely to be a **physical association**.
**Implications of Transparency Time:** The research estimates that **5–7% of matched optical transients** (if all were SNe) are old enough to be associated with a detectable FRB, assuming the 6.4-10 year transparency timescale. More broadly, **23–30% of all cataloged SNe and 32–41% of CCSNe** are currently old enough to have detectable FRB emission.
**The Future with Rubin Observatory:** The upcoming **Vera C. Rubin Observatory (LSST)** is expected to dramatically increase the number of known SNe and the volume over which they can be detected. This will significantly **increase the rate of potential FRB-SN associations** at redshifts below z~1, where most FRBs are discovered.
**Flexible Framework:** The systematic search machinery developed for this work is publicly available and flexible, allowing it to be applied to a wide range of transient timescales, FRB localization sizes, and different optical transient populations in future searches.
**Reference Article:**
* DONG, Y., KILPATRICK, C. D., FONG, W., et al. (2025). **Searching for Historical Extragalactic Optical Transients Associated with Fast Radio Bursts**. arXiv e-prints, arXiv:2506.06420v1.
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: NASA - JPL/Caltech
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In this episode, we discuss a significant new detection of the Geminga pulsar, a middle-aged, radio-quiet gamma-ray pulsar. The **Large-Sized Telescope (LST-1)**, the first of the Cherenkov Telescope Array Observatory (CTAO) Northern Array, has detected Geminga at energies down to 20 GeV.
Key takeaways from the study:
* The LST-1 detected the Geminga pulsar using 60 hours of data.
* The **second emission peak (P2)** of Geminga was detected with a high significance of **12.2σ** in the energy range between 20 and 65 GeV. This is a doubled significance compared to previous results by the MAGIC Collaboration, achieved with less observation time and a single telescope.
* The first peak (P1) was detected at a lower significance level of 2.6σ.
* The LST-1 analysis has an estimated energy threshold as low as 10 GeV for pulsar analysis, although the peak in reconstructed energy was around 20 GeV.
* The best-fit model for the P2 spectrum was a power law with a spectral index of Γ = 4.5 ± 0.4 (statistical uncertainty). When considering systematic uncertainties, the spectral index is Γ = (4.5 ± 0.4stat)+0.2sys −0.6sys. This is compatible with previous results from the MAGIC Collaboration.
* A joint fit of LST-1 and Fermi-LAT data preferred a power law with a sub-exponential cut-off (PLSEC) over a pure exponential cut-off (PLEC), although the PLSEC model didn't fully match the LST-1 points.
* While no curvature was detected in the LST-1-only spectrum, combining LST-1 and Fermi-LAT data showed a statistical preference for a curved log parabola model at lower minimum energies (10-20 GeV).
* Theoretical models, such as the synchro-curvature (SC) model from Harding et al. (2021), can explain the dominance of the SC component at high energies and the non-detection of the first peak above 20 GeV, although improvements are needed to match the LST-1 SED better.
* These results demonstrate the LST-1's excellent capabilities for observing pulsars at the upper end of their spectra and its overlap with the Fermi-LAT energy range. Future observations with the full CTAO Northern Array are expected to improve sensitivity and allow for more detailed studies of the pulsar peaks and spectra.
**Reference:**
* K. Abe et al. (CTAO LST Project). Detection of the Geminga pulsar at energies down to 20 GeV with the LST-1 of CTAO. *Astronomy & Astrophysics* manuscript no. aa54350-25 ©ESO 2025 May 29, 2025.
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Iván Jiménez (IAC)
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Astronomers have made a significant discovery, detecting X-ray emission from a rare type of cosmic object known as a **Long-Period Radio Transient (LPT)** for the very first time.
The object, designated **ASKAP J1832−0911**, is extraordinarily bright in radio, reaching flux densities of 10–20 Jy.Crucially, it exhibits **coincident radio and X-ray emission**, both pulsing with a regular period of **44.2 minutes** (2,656.2412 seconds in radio, 2,634 seconds in X-rays). This combination of properties – long period, bright coherent radio, and variable X-ray emission – makes ASKAP J1832−0911 **unlike any other known object in our galaxy**. Its luminosity is **highly variable**, with both radio and X-ray emission decreasing dramatically over a few months following a 'hyper-active' phase. This variability suggests that the lack of previous X-ray detections from other LPTs might be due to not observing them during such brief bright phases. The object is estimated to be located at a distance of approximately **4.5 kpc**. Current data suggest potential classifications like an old magnetar or an ultra-magnetized white dwarf, though both interpretations present **theoretical challenges** for existing models. It is not consistent with a classical rotation-powered pulsar or a typical isolated white dwarf.The discovery of X-ray emission from ASKAP J1832−0911 demonstrates that LPTs can be **more energetic** than previously believed. It also establishes a new class of hour-scale periodic X-ray transients linked to exceptionally bright radio emission.
Reference Article: "Detection of X-ray emission from a bright long-period radio transient" by Ziteng Wang et al..
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Alex Cherney
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A recent study utilized **15 years of observations** from the **Fermi Large Area Telescope (LAT)** to analyze the gamma-ray emission from the Sun in its quiet state, meaning when it's not flaring. This is the first study to separately analyze the flux variation of the two distinct components of this quiet-state gamma-ray emission over solar cycles.
According to theoretical understanding, the Sun's steady-state gamma-ray emission arises from interactions with Galactic cosmic rays (CRs). There are two main components:
* The hadronic component, which is primarily confined to the **solar disk**. It's thought to be produced by CR cascades in the solar atmosphere. This component's flux is expected to **anticorrelate with solar activity** (like sunspot number, SSN) and **correlate with the flux of cosmic rays**.
* The **leptonic component**, which is spatially **extended** beyond the solar disk. This is theorized to be an Inverse Compton (IC) component, where CR electrons scatter off solar photons. Like the disk component, its intensity was expected to **vary with the solar cycle**, being highest during solar minimum and lowest during solar maximum, thus anticorrelating with SSN and correlating with CR flux (specifically CR electron flux).
Previous Fermi-LAT observations had shown that the overall solar gamma-ray flux varies with solar activity, anticorrelating with SSN and changing by nearly a factor of two between solar maximum and minimum. However, these studies had not separated the contributions of the disk and extended components.
This new work analyzed Fermi-LAT data from August 2008 to June 2023, carefully selecting data and using an "off-source" method to evaluate background contamination. They were able to distinguish the two components and study their flux variations over Solar Cycle 24 and the beginning of Cycle 25.
The key findings from this analysis reveal both confirmation of expectations and **significant surprises**:
* For the **disk component**, the results align well with theoretical predictions. Its flux variation:
* **Anticorrelates strongly with the sunspot number (SSN)**.
* **Correlates strongly with the flux of cosmic-ray protons** measured near Earth.
* Correlates with the gamma-ray flux from the Moon, supporting similar production mechanisms.
* The variation is **independent of energy** above 250 MeV.
This confirms that the hadronic emission mechanism for the disk component has been correctly identified.
* For the **spatially extended component**, the behavior was **unexpectedly complex**.
* It showed the expected anticorrelation with SSN and correlation with the disk component **only until approximately mid-2012**.
* **After 2013, there was no longer any significant correlation or anticorrelation observed** between the extended component's flux variation and either the SSN or the cosmic-ray electron flux. Correlation coefficients over the entire period are below 0.3.
* Like the disk component, the extended component's variation was also found to be independent of energy above 250 MeV.
This **surprising lack of correlation for the extended component after 2013** is a major finding. The change in behavior coincides with the start of the **reversal of the Sun's polar magnetic field**, which began at the end of 2012. This suggests that the transport and modulation of cosmic rays, particularly electrons, in the **inner heliosphere (close to the Sun)** may be **unexpectedly complex** and possibly different for electrons and protons.
Paper: https://arxiv.org/abs/2505.06348
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Solar Dynamics Observatory/GSFC/NASA
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The research investigates how supernovae exploding into dense circumstellar environments, specifically those with dense shells of material, can potentially accelerate particles to energies of a few PeV, thus acting as "PeVatrons" and contributing to the "knee" feature in the cosmic ray spectrum.
Supernova remnants (SNRs) have long been considered prime candidates for the sources of Galactic Cosmic Rays (CRs) up to energies of a few PeV. However, despite decades of gamma-ray astronomy, there hasn't been clear observational proof that standard SNR models can accelerate particles beyond approximately 100 TeV. Young SNRs like Tycho and Casiopeia A, initially expected to be strong accelerators, show even lower cutoff energies.
The presented study explores a different scenario: supernovae that expand into **much denser circumstellar material**, including dense shells ejected by the progenitor star shortly before explosion. These dense shells are thought to be present around massive stars like Luminous Blue Variables (LBVs), which can undergo brief episodes of very high mass-loss rates (up to 1 M⊙/yr). Type IIn supernovae, associated with LBVs, make up about 5% of core-collapse supernovae.
The researchers used spherically symmetric 1D simulations with their time-dependent acceleration code called **RATPaC** (Radiation Acceleration Transport Parallel Code). This code simultaneously solves the transport equations for cosmic rays, magnetic turbulence, and the hydrodynamical flow of the thermal plasma in the test-particle limit. Unlike models that assume a steady state for magnetic turbulence, RATPaC accounts for the time needed for turbulence to build up, which often leads to lower maximum energies in standard scenarios.
**The key finding is that the interaction of the supernova shock front with these dense circumstellar shells can significantly boost the maximum energy** of the accelerated particles.
Specifically, the simulations show that:
* **Interactions with shells that occur earlier post-explosion lead to a greater increase in maximum energy (Emax)**.
* If the interaction happens within the first **5 months (approximately 140 days)** after the explosion, the **Emax can increase to more than 1 PeV**.
* For very early interactions, around **0.1 years**, Emax can even surpass **10 PeV**.
This significant energy boost is attributed to several mechanisms during and after the shock-shell interaction:
1. **Enhanced Particle Escape:** The shock slows down considerably during the interaction with the dense shell, which temporarily enhances the "precursor scale" (the region upstream where particles diffuse back towards the shock, given by D(E)/v_shock). This increased scale provides more time for turbulence to grow. Enhanced particle escape also occurs during the onset of the interaction, boosting the CR current.
2. **Reacceleration in a Pre-amplified Field:** After passing through the shell, the shock propagates into a medium where the magnetic field has been pre-amplified by escaping cosmic rays during the interaction phase. The shock accelerating into this region with an enhanced field boosts Emax.
3. **Interaction with Reflected Shocks:** The collision with the dense shell creates reflected shocks. These can catch up with and interact with the forward shock from behind, leading to sharp increases in the forward shock's velocity and slightly boosting Emax.
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: ESO/L. Calçada
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The research presents **new observations of the gamma-ray binary system LS 5039 using the High Altitude Water Cherenkov (HAWC) observatory**, revealing significant insights into the nature of this high-energy source.
One of the most striking findings is that **HAWC detected gamma rays from LS 5039 extending up to 200 TeV with no apparent spectral cutoff**. This is a crucial extension of previous observations by the High Energy Stereoscopic System (H.E.S.S.), which had observed the system up to TeV energies. The spectral energy distribution (SED) presented in Figure 2 shows this extension, particularly during the inferior conjunction (INFC). The lower limit on the maximum energy measured by HAWC for LS 5039 is 208 TeV at a 68% confidence level during INFC.
Furthermore, the HAWC data **confirms with a 4.7σ confidence level that the gamma-ray emission between 2 TeV and 118 TeV is modulated by the orbital motion of the binary system**. This modulation, where the emission is more significant during the inferior conjunction (INFC) compared to the superior conjunction (SUPC), strongly suggests that these high-energy photons are produced within or very near the binary orbit. The study notes that despite a longer phase interval for the SUPC data, LS 5039 was more significantly detected during INFC due to a higher flux. This modulation up to 100 TeV provides strong evidence for gamma-ray production inside the binary.
These high-energy observations pose a challenge to purely **leptonic scenarios** for gamma-ray production. In a leptonic scenario, the highest energy photons would be produced by electrons inverse Compton scattering stellar photons. The detection of photons up to 200 TeV would require electrons to be accelerated to at least this energy, demanding an extremely efficient acceleration mechanism within LS 5039, especially given the dense radiation and potentially high magnetic fields within the binary system. The study suggests that achieving such high electron energies within the stellar photosphere would require an acceleration efficiency η close to 1 and a magnetic field not significantly larger than 0.1 Gauss to avoid substantial synchrotron losses.
Alternatively, the HAWC radiation can be interpreted through a **hadronic scenario**. In this case, protons are accelerated to peta-electronvolt (PeV) energies and then produce gamma rays through interactions with either the dense gas (stellar winds) or the intense radiation fields within and close to the binary orbit. The timescale for proton-proton collisions and subsequent pion decay is remarkably close to the binary period, making this a viable explanation. If the gamma rays are of hadronic origin, LS 5039 would be an astronomical accelerator capable of producing PeV-scale hadrons. The required jet power to produce the observed gamma-ray luminosity through proton-proton interactions is estimated, and the study suggests that binary jets powered by either Bondi-type accretion or colliding winds could potentially provide the necessary luminosity.
In conclusion, the HAWC observations provide compelling evidence for **gamma-ray emission beyond 100 TeV from LS 5039 and confirm the orbital modulation of this emission**, suggesting that the production of these very high-energy photons occurs within the binary system. These findings have significant implications for our understanding of particle acceleration and radiation processes in gamma-ray binaries, potentially hinting at a hadronic origin for the highest energy emission and establishing LS 5039 as a candidate PeVatron. Future observations at even higher energies could provide crucial evidence to further elucidate the underlying mechanisms at play.
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: J. Goodman
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* EP241021a was discovered as a soft X-ray trigger but was not detected at gamma-ray frequencies.
* The prompt soft X-ray emission spectrum is consistent with **non-thermal radiation**, suggesting a **mildly relativistic outflow with a bulk Lorentz factor Γ≳ 4**.
* The optical and near-infrared light curve shows a **two-component behavior**: an initial fading component (∼ t⁻¹) followed by a **rapid rise (steeper than ∼ t⁴)**, peaking at an absolute magnitude of **Mr ≈−22 mag**, before quickly returning to the initial decay. This peak magnitude is **the most luminous optical emission associated with an FXT**, surpassing EP240414a.
* Standard supernova models cannot explain either the **absolute magnitude or the rapid timescale (< 2 days rest frame)** of the rebrightening.
* The X-ray, optical, and near-infrared spectral energy distributions indicate a **red color (r− J ≈ 1 mag)** and suggest a **non-thermal origin (∼ ν⁻¹)** for the broadband emission.
* Considering a gamma-ray burst (GRB) as a possible scenario, the authors favor a **refreshed shock as the cause of the rebrightening**. This is consistent with the inferred mildly relativistic outflow.
* The results suggest a **likely link between EP-discovered FXTs and low-luminosity gamma-ray bursts**.
The source also compares EP241021a to another peculiar EP transient, **EP240414a**, which showed a roughly similar multi-wavelength behavior. Both events share features like the lack of gamma-ray emission, multiple optical emission components, a relatively flat X-ray light curve, and luminous, late-peaking radio emission. However, EP241021a has a **more luminous peak in its second optical component** and **longer timescales** for its light curve variations. Unlike EP240414a, which showed spectroscopic evidence of a supernova, **no clear supernova features were identified in the HET spectra of EP241021a**.
The authors explore various interpretations for the rebrightening, including off-axis structured jets and refreshed shocks. They disfavor a simple forward shock from an off-axis structured jet due to the steep rise observed but suggest that a **reverse shock from off-axis material in a shallow structured jet** or a **refreshed shock** are more plausible explanations. The consistency of the temporal and spectral indices with standard afterglow closure relations in a wind environment (expected for a massive star progenitor) supports the refreshed shock scenario.
The paper concludes that both EP241021a and EP240414a are likely produced by the **death of a massive star**. The non-thermal prompt emission necessitates at least a mildly relativistic outflow. The rapid optical rebrightening is challenging for supernova models and may be due to refreshed shocks or a reverse shock from off-axis material, both favoring a mildly relativistic outflow and non-thermal synchrotron radiation. The authors emphasize the need for future observations of similar events to better understand their nature.
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Chinese Academy of Sciences (CAS).
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**Introduction:**
What are Fast Radio Bursts (FRBs)? These millisecond bursts from distant galaxies have astrophysicists intrigued. We explore repeating FRBs (R-FRBs) and theories about their origins, including magnetars.
**AGILE's High-Energy Hunt:**
The Italian AGILE satellite, with its SuperAGILE (18-60 keV), MCAL (0.35-100 MeV), and GRID (0.03-50 GeV) detectors, searched for X- and gamma-ray counterparts to a sample of R-FRBs.
**The Search and Non-Detection:**
AGILE observed several bursts from R-FRBs with low dispersion measure (DMexc < 300 pc cm−3). However, no astrophysical signals were identified in the X- and gamma-ray bands.
**Upper Limits and Magnetar Models:**
The study derived upper limits on the flux, particularly with MCAL, which are now the most stringent in the 0.4-30 MeV range. Researchers compared these findings to the galactic magnetar SGR 1935+2154 (the source of FRB 200428) to test magnetar emission models for FRBs.
**Key Findings:**
* **No high-energy counterparts were detected by AGILE for the observed R-FRB sample**.
* **Stringent upper limits were placed on high-energy emission**, especially by MCAL.
* The study compared R-FRB energies with those extrapolated from **SGR 1935+2154**, providing constraints on the magnetar model.
**Conclusion:**
While AGILE didn't detect high-energy counterparts for this R-FRB sample, its observations provide valuable constraints for theoretical models, especially those involving magnetars. The archival AGILE data still holds potential for future discoveries.
**Reference:**
Casentini, C., Verrecchia, F., Tavani, M., Pilia, M., & Pacciani, L. (2025). AGILE observations of a sample of repeating Fast Radio Burst sources. *Draft version March 13, 2025*.
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: AGILE collaboration
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Welcome to this episode about the **Einstein Telescope (ET)**, a planned **third-generation gravitational-wave observatory** [see source].
* **ET will revolutionize gravitational-wave astronomy** with **higher sensitivity** and a **broader frequency range** compared to current detectors [see source].
* This allows deeper insights into **Fundamental Physics** (tests of General Relativity, search for dark matter), **Cosmology** (more precise Hubble constant measurement, early Universe studies), and the **Astrophysics of Compact Objects** (black holes, neutron stars, their formation and evolution) [see source].
* A key focus is exploring the **physics of extreme matter** in neutron stars by observing mergers [see source].
* **Multi-messenger astronomy** will be significantly advanced through improved event localization in combination with electromagnetic and neutrino telescopes [see source].
* **Data analysis** of the expected large data volumes and **overlapping signals** presents a significant challenge, for which new methods are being developed [see source].
**Reference:**
* arXiv:2503.12263
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Marco Kraan, Nikhef
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* **Introduction:** Astronomers have discovered a new celestial object, PSR J0311+1402, a radio pulsar with an unusual spin period of **41 seconds**. This discovery bridges the gap between normal pulsars (millisecond to seconds) and long-period radio transients (LPTs) (minutes to hours).
* **The Discovery:** PSR J0311+1402 was first detected by the **Australian Square Kilometre Array Pathfinder (ASKAP)** during commissioning tests of the CRACO system in January 2024. It exhibited pulses with a duration of about 0.5 seconds.
* **Intermediate Nature:** Unlike normal pulsars and LPTs, PSR J0311+1402's **41-second spin period** falls in a previously under-explored range. Traditional pulsar searches were less sensitive to these periods, and image-based LPT searches missed shorter pulses.
* **Pulsar-like Properties:** Despite its long period, PSR J0311+1402 shows characteristics similar to normal pulsars, including **low linear (∼25%) and circular (∼5%) polarisation** and a **steep spectral index (∼ −2.3)**. It also has a double or potentially triple-peaked pulse profile.
* **Below the Death Line:** Intriguingly, its spin-down properties place PSR J0311+1402 **below the pulsar death line**, a theoretical boundary where radio emission is expected to cease due to insufficient particle production. This challenges current understanding of pulsar emission mechanisms.
* **Relation to Long-Period Transients (LPTs):** Known LPTs have much longer periods and often exhibit radio luminosities too high to be powered by rotation alone, along with high polarisation. PSR J0311+1402's properties, such as its luminosity being potentially powered by rotation and its low polarisation, suggest it is more likely a pulsar. Its duty cycle also aligns better with the trend observed in typical pulsars.
* **Implications:** The discovery suggests the existence of a **previously undetected population of neutron stars with intermediate spin periods**. Finding more such objects will help bridge the gap between pulsars and LPTs and improve our understanding of neutron star evolution.
* **Future Research:** Ongoing observations and timing studies are crucial to refine PSR J0311+1402's spin-down properties and shed light on its emission mechanism and evolutionary state. The ASKAP CRACO system is expected to discover more such intermediate period objects.
**Reference:**
* Wang, Y., Uttarkar, P. A., Shannon, R. M., et al. (2025). The discovery of a 41-second radio pulsar PSR J0311+1402 with ASKAP. *arXiv preprint arXiv:2503.07936*.
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Alex Cherney
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**Introduction**
* The podcast discusses the search for **diffuse photons** with energies above tens of PeV, using data from the **Pierre Auger Observatory**.
* These photons are produced by interactions between cosmic rays and interstellar matter or background radiation.
* The measurement of a diffuse photon flux can help us understand the distribution of cosmic rays in the Galaxy and probe models of super-heavy dark matter.
**The Pierre Auger Observatory**
* The observatory uses a surface detector (SD) and an underground muon detector (UMD).
* The SD array consists of **water-Cherenkov detectors (WCDs)**, and the UMD uses **buried scintillators**.
* The study focuses on data from a 2 km² area with 19 WCDs and 11 UMD stations.
* The combination of SD and UMD measurements allows for a more accurate analysis of air showers.
**The Search for Photons**
* Primary photons are difficult to distinguish from the background of charged cosmic rays.
* Photon-initiated air showers are mostly electromagnetic, while hadron-initiated showers have more muons.
* The analysis uses a **muon content estimator (Mb)** to discriminate between photon and hadron events.
* The study uses **15 months of data** collected during the construction of the array.
* A photon-equivalent energy scale is developed for comparing events initiated by different primary species.
**Results and Implications**
* No photon candidate events were identified in the data.
* Upper limits on the integral photon flux were set between 13.3 and 13.8 km−2 sr−1 yr−1 above tens of PeV.
* These limits are the only ones based on measurements from the **Southern Hemisphere** in this energy domain.
* The analysis extends the Pierre Auger Observatory photon search program to lower energies.
* The results provide constraints on models of super-heavy dark matter.
* Future data from the observatory is expected to improve the upper limit by a factor of ~20.
**Article Reference:**
* A. Abdul Halim et al., Search for a diffuse flux of photons with energies above tens of PeV at the Pierre Auger Observatory, 2024,
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Pierre Auger Observatory
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**Introduction:**
* This episode discusses the search for the sources of high-energy neutrinos using the example of the blazar B3 2247+381.
* The IceCube Neutrino Observatory detects astrophysical neutrinos, and scientists are working to find their origins by looking for correlations between neutrino alerts and electromagnetic radiation from objects like blazars.
**The IceCube Alert and B3 2247+381:**
* IceCube detected a multiplet of muon neutrino events, which appeared to be coming from the direction of the blazar B3 2247+381 between May and November 2022.
* This triggered a multiwavelength observational campaign, including observations by the VERITAS telescope.
* The Gamma-ray Follow-Up (GFU) program is a method used by IceCube to enable follow up investigations of known gamma-ray sources for which IceCube has detected a cluster of candidate neutrino events.
**VERITAS and Multiwavelength Observations:**
* VERITAS did not detect B3 2247+381 during the time period of the neutrino alert.
* The source was in a low-flux state in the optical, ultraviolet, and gamma-ray bands during the neutrino event.
* B3 2247+381 was detected in the hard X-ray band with NuSTAR during this time.
* Data from Swift-XRT, Swift-UVOT, ASAS-SN, ATLAS, and the 48” optical telescope at the FLWO were also used in this study.
* The multiwavelength spectral energy distribution (SED) was modeled using a one-zone leptonic synchrotron self-Compton (SSC) radiation model.
**Analysis and Findings:**
* The observed neutrino excess had a significance of 3.2σ but was likely not fully corrected for trials. The corresponding false alert rate was 0.0355 per year.
* The neutrino events associated with B3 2247+381 had energies primarily between 0.5 TeV and 6 TeV, making them likely to be atmospheric neutrino background.
* The lack of detection by VERITAS, combined with the low multiwavelength flux levels during the neutrino alert period, suggests that B3 2247+381 is an unlikely source of the IceCube multiplet.
* The neutrino excess is likely a background fluctuation.
* The study highlights some of the challenges in searching for neutrino-emitting blazars, such as the limited localization precision of the IceCube Observatory and the effect of weather on IACT observations.
* The one-zone leptonic model reasonably fits the SED, suggesting that no hadronic component is needed to explain the data.
**Conclusion:**
* This study is an example of a follow-up to an IceCube alert within the framework of the GFU program.
* Further multiwavelength observations, especially during flaring periods, and improved understanding of instrument uncertainties, are needed to identify neutrino sources.
* Future neutrino detectors are expected to improve sensitivity to high-energy neutrino events.
**Reference:**
* Acharyya, A., et al. "VERITAS and multiwavelength observations of the Blazar B3 2247+381 in response to an IceCube neutrino alert." *Draft version February 7, 2025*
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: CfA/Rick Peterson
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**Introduction:**
* A recent ultra-high-energy neutrino event, named KM3-230213A, was detected by the KM3NeT/ARCA detector.
* This event has sparked interest in the scientific community, as its origin is still unclear.
* The neutrino's high energy suggests it may have come from a very powerful cosmic source.
* The event was detected on February 13, 2023.
* The podcast explores two potential origins for this neutrino event: galactic sources and cosmogenic neutrinos.
**Galactic Origin:**
* The study investigates potential galactic sources such as supernova remnants (SNRs), X-ray binaries, and microquasars.
* **No nearby sources from HAWC or LHAASO were found, imposing stringent constraints on potential astrophysical sources**.
* The study also looks at known gamma-ray sources from catalogs such as 4FGL-DR4, 3HWC, and 1LHAASO.
* Researchers explored the possibility of the neutrino originating from blazars, which are active galactic nuclei (AGN) with jets pointed towards Earth.
* **Seventeen blazar candidates were identified within the 99% confidence region of the neutrino event**.
* The study examined multiwavelength data, including radio, X-ray, and gamma-ray observations, to characterize these blazars.
* **A major radio flare from blazar PMN J0606-0724 was found to be coincident with the neutrino event, with a time difference of five days**, which is considered statistically uncommon.
* The chance probability of this coincidence is estimated to be 0.26%, which suggests a possible association, but is not conclusive.
* Other blazars, such as MRC0614-083, also showed flaring activity in the X-ray band around the time of the neutrino detection.
* **It is not possible to conclusively associate the neutrino with a specific blazar due to the size of the neutrino direction uncertainty region, encompassing seventeen blazar candidates**.
**Cosmogenic Origin:**
* The study explores the possibility that the neutrino is cosmogenic, produced by the interaction of ultra-high-energy cosmic rays (UHECRs) with the cosmic microwave background (CMB) or the extragalactic background light (EBL).
* Cosmogenic neutrinos are expected from the interactions of cosmic rays with photons.
* The paper examines how the expected cosmogenic neutrino flux can be enhanced, starting from a minimal scenario.
* The study considers the effects of different models for the EBL and the photo-disintegration cross section, and concludes that these uncertainties do not significantly impact the results.
* **The study compares the spectra of neutrinos produced in the nearby and far-away Universe**.
**Conclusion:**
* The origin of KM3-230213A remains an open question.
* While a specific source cannot be pinpointed, the study provides valuable insights into potential galactic and cosmogenic origins of such high-energy neutrino events.
* Further studies and observations are needed to determine the precise origin of this neutrino.
**Reference:**
* The information presented is based on the following three articles:
* "On the Potential Galactic Origin of the Ultra-High-Energy Event KM3-230213A"
* "Characterising Candidate Blazar Counterparts of the Ultra-High-Energy Event KM3-230213A"
* "On the potential cosmogenic origin of the ultra-high-energy event KM3-230213A"
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: KM3NeT
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**Introduction**
* A recent detection by the KM3NeT/ARCA telescope of an ultra-high-energy neutrino, named KM3-230213A, is discussed. This event has an estimated energy in the hundreds of PeV, surpassing previous observations by the IceCube Neutrino Observatory.
* The observed neutrino's high energy suggests an astrophysical origin, as it's unlikely to be from atmospheric sources.
**Key Concepts**
* The study explores the compatibility of the KM3NeT event with previous data from IceCube and the Pierre Auger Observatory.
* The analysis assumes the neutrino originates from an isotropic diffuse flux, exploring scenarios such as steady sources, transient sources, cosmogenic origins, or physics beyond the Standard Model.
* The research uses both single power law (SPL) and broken power law (BPL) models to fit the neutrino flux. A single power law assumes the flux follows a consistent pattern, while a broken power law allows for a change in the pattern at a certain energy level.
**Findings**
* **Initial analysis of the KM3NeT event suggests a per-flavor isotropic diffuse flux of E2Φ1f ν+ν̄(E) = 5.8+10.1 −3.7 × 10−8 GeV cm−2 s−1 sr−1, assuming an E−2 spectrum**.
* Combining the KM3NeT observation with non-observations from IceCube (IC-EHE) and Auger, the best-fit flux normalisation becomes E2Φ1f ν+ν̄ = 7.5 × 10−10 GeVcm−2s−1sr−1.
* The joint fit of all experiments under the assumption of an isotropic E−2 flux shows a preference for a break in the PeV regime when the IceCube "High-Energy Starting Events" (HESE) data is included, with a tension of 2.5σ − 3σ.
* The analysis explores if the KM3NeT event is an outlier compared to the IceCube and Auger data.
* **When considering only KM3NeT and IceCube HE measurements, the data shows a significant preference for a broken power law model, which suggests a break at a certain energy**.
* However, this model would be inconsistent with null observations from IceCube and Pierre Auger.
* The study notes that more statistics are required to resolve the tension and better characterise the neutrino landscape at ultra-high energies.
**Implications and Future Research**
* The study highlights the importance of combining data from different experiments.
* Future observations with larger detectors and increased exposures from various observatories are crucial to determine the shape of the neutrino spectrum and to differentiate between different models of neutrino production. This includes the KM3NeT/ARCA detector configuration, IceCube, Auger, and upcoming radio instruments.
**Reference:**
* The KM3NeT Collaboration, "The ultra-high-energy event KM3-230213A within the global neutrino landscape," (Dated: February 2025).
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: KM3NeT
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* **Introduction**: A recent groundbreaking discovery by the KM3NeT Collaboration has detected an exceptionally high-energy cosmic neutrino. This event, named KM3-230213A, is significant because its energy far exceeds any neutrino previously observed.
* **What are Cosmic Neutrinos?**: Cosmic neutrinos are electrically neutral particles that travel vast distances without being deflected by magnetic fields or significantly absorbed by matter. They are produced when cosmic rays interact with matter or photons, making their detection a key to understanding high-energy astrophysical processes.
* **The KM3NeT Experiment**: The KM3NeT is a deep-sea neutrino telescope located in the Mediterranean Sea. It consists of two detector arrays: ARCA, optimized for high-energy cosmic neutrinos, and ORCA, for neutrino oscillations. These detectors utilize optical sensors to detect Cherenkov light produced by charged particles resulting from neutrino interactions.
* **The Ultra-High-Energy Event**: The detected event, KM3-230213A, is a muon with an estimated energy of **120 PeV**. The neutrino that produced this muon is estimated to have had an even higher energy. The muon was detected traversing the ARCA detector on February 13, 2023.
* **How it was Detected**: The muon's trajectory was reconstructed using the arrival times and positions of the first hits recorded on the photomultiplier tubes (PMTs). The energy was estimated by counting the number of PMTs that triggered. The large amount of light detected saturated the PMTs closest to the muon trajectory, and large showers resulting from energy loss processes were observed along the track.
* **Significance**: This event may indicate a different source of cosmic neutrinos or could be the first detection of a cosmogenic neutrino, produced by interactions of ultra-high-energy cosmic rays with background photons. The detected energy significantly exceeds previous detections, suggesting new astrophysical phenomena.
* **Background and Analysis**: The possibility of the event being caused by atmospheric muons or neutrinos was considered. The probability of an atmospheric origin is extremely low, especially given the near-horizontal direction and high energy. The direction of the neutrino matches expectations for an isotropic flux of ultra-high-energy neutrinos, where downgoing neutrinos are obscured by atmospheric muons, and upgoing neutrinos are absorbed by the Earth.
* **Searches for Source**: Extensive searches were conducted for a source counterpart within a 3° radius of the event using multiwavelength data. Various catalogs of gamma-ray, X-ray, infrared, and radio sources were examined, but no conclusive source association has been made.
* **Flux Measurement:** The steady isotropic flux that would produce one event like KM3-230213A is **5.8 x 10^-8 GeV cm^-2 s^-1 sr^-1**. This flux measurement exceeds current limits from IceCube and Auger, possibly indicating an upward fluctuation or a new component in the flux. This event could be from cosmogenic neutrino production or from transient emitters such as gamma-ray bursts or tidal-disruption events.
* **Conclusion**: The detection of KM3-230213A provides significant evidence for the existence of ultra-high-energy neutrinos and enhances our understanding of the universe's most energetic phenomena.
* **Reference**: The KM3NeT Collaboration. "Observation of an ultra-high-energy cosmic neutrino with KM3NeT." *Nature* (2025).
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: KM3NeT
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The Mystery of ANITA: Investigating Anomalous Radio Pulses with the Pierre Auger Observatory
* **Introduction**: The Antarctic Impulsive Transient Antenna (ANITA) has detected some unusual radio pulses that don't fit with the standard model of particle physics. These "anomalous" pulses, which appear to come from below the horizon, could potentially be caused by air showers developing in an upward direction. This podcast discusses a search using the Pierre Auger Observatory to either confirm or constrain the possibility of upward-going air showers.
* **The ANITA Anomalies**: ANITA, which flies on NASA balloons, has detected radio pulses consistent with ultra-high-energy cosmic ray air showers. Most of these pulses are reflected from the ice, but some anomalous ones have been observed with strong horizontal polarization but without the expected polarity inversion. These could be caused by upward-going air showers, possibly from tau lepton decays, but this interpretation faces significant challenges.
* **The Pierre Auger Observatory**: The Pierre Auger Observatory, a large cosmic ray detector, was used to search for these upward-going air showers. It combines a Surface Detector (SD) and a Fluorescence Detector (FD) which uses telescopes to collect the fluorescence light emitted by nitrogen as a shower develops. The search focused on data from the FD, as upward-going air showers are unlikely to trigger the SD.
* **The Search**: A dedicated search was conducted for upward-going air showers with zenith angles greater than 110 degrees and energies above 0.1 EeV. The search analyzed data collected between 2004 and 2018, using simulations of both regular cosmic ray showers and upward-going events to distinguish potential candidates from background. The analysis also employed a Global Fit (GF) reconstruction to eliminate misidentified events.
* **Background and Challenges**: A key challenge was distinguishing genuine upward-going showers from mis-reconstructed cosmic ray showers and other sources of background such as laser pulses. Several selection cuts were implemented to filter out background, including cuts based on time sequence of triggered pixels, the shower profile, and zenith angle. A discrimination variable, *l*, was defined to differentiate between upward and downward reconstructions based on the likelihood ratio.
* **Results**: After analyzing the data, only one event was found that passed all selection criteria. This was consistent with an expected background of 0.27 ± 0.12 events from mis-reconstructed cosmic ray showers. This result was used to calculate an upper bound on the integral flux of upward-going showers.
* **Implications**: The non-observation of upward-going air showers by the Pierre Auger Observatory puts constraints on the interpretation of the anomalous ANITA events as being produced by upward-going showers. The study found that the sensitivity of the Auger Observatory exceeds that of the ANITA-III flight, making the results particularly significant. The results suggest that if the ANITA events are caused by upward-going air showers, then those showers likely originated at very high altitudes, or have unusual shower profiles inconsistent with known particle decays or interactions.
* **Conclusion**: The search for upward-going air showers at the Pierre Auger Observatory did not find evidence to support the interpretation of the anomalous ANITA events as being caused by upward-going air showers. This implies either the ANITA events are caused by something else, or there is a need for new theoretical models beyond the Standard Model of particle physics to explain the data.
* **Reference**: A. Abdul Halim et al. (Pierre Auger Collaboration), "A search for the anomalous events detected by ANITA using the Pierre Auger Observatory", 2502.04513v1.pdf.
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Pierre Auger Observatory
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* **Introduction:** This episode discusses the search for extremely-high-energy neutrinos (EHEν) using 12.6 years of data from the IceCube Neutrino Observatory. EHEνs are unique messengers from the distant universe, traveling without being deflected by magnetic fields or attenuated by interactions with background photons.
* **IceCube Detector:** The IceCube detector, located at the South Pole, consists of 5160 Digital Optical Modules (DOMs) distributed on 86 strings, instrumenting a cubic kilometer of ice. The detector observes Cherenkov light produced by charged particles from neutrino interactions. A surface array called IceTop measures cosmic-ray air showers.
* **EHEν Detection:** EHEν events in IceCube are observed as tracks (from muon or tau neutrinos) or cascades (from all-flavor neutral-current interactions and electron neutrinos). The search focuses on downgoing or horizontal neutrinos because higher energy neutrinos are absorbed by the Earth.
* **Backgrounds:** The main background is from downgoing atmospheric muon bundles. Other backgrounds include atmospheric neutrinos, which are divided into conventional and prompt components, and astrophysical neutrinos.
* **Analysis:** The analysis uses quality cuts of high-energy events and an IceTop veto to improve the signal-to-noise ratio. The event direction is reconstructed, and energy loss profiles are used to distinguish between single muons and muon bundles.
* **Results:** The non-observation of cosmogenic neutrinos places constraints on the cosmological evolution of ultra-high-energy cosmic ray (UHECR) sources. The study constrains the proton fraction of UHECRs above approximately 30 EeV to be less than 70% at a 90% confidence level, assuming that the source evolution is comparable to or stronger than the star formation rate. This result disfavors the "proton-only" hypothesis for UHECRs.
* **Significance:** This research complements direct air-shower measurements by being insensitive to uncertainties associated with hadronic interaction models. The study also provides the most stringent limit on cosmogenic neutrino fluxes to date.
* **Methodology:** The analysis fits data using a binned Poisson likelihood in the space of reconstructed direction and energy. The study uses the CRPropa package to model cosmogenic fluxes and includes energy losses from photo-pion production and pair production on the cosmic microwave background (CMB) and extragalactic background light (EBL).
* **Event Selection:** The event selection involves several steps including: charge and hit cuts, track quality cuts, muon bundle cuts, and IceTop veto.
* **Differential Limit**: The differential upper limit on the neutrino flux above 5 x 10^6 GeV is presented in the study and compared to various cosmogenic neutrino models.
* **Systematics**: Systematic uncertainties are taken into account through pseudo-experiments. Parameters considered include: the optical efficiency of the DOMs, the neutrino cross section, average neutrino inelasticity, and atmospheric muon and neutrino fluxes.
* **Reference:** The research is detailed in the article "A search for extremely-high-energy neutrinos and first constraints on the ultra-high-energy cosmic-ray proton fraction with IceCube".
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: NSF, IceCube
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**Article Reference:**
* Thakore, B., et al. (2024). "High-Significance Detection of Correlation Between the Unresolved Gamma-Ray Background and the Large Scale Cosmic Structure."
**Introduction:**
* The universe is filled with a mysterious glow of gamma rays, known as the **unresolved gamma-ray background (UGRB)**. This background could contain clues about the faintest gamma-ray sources and the nature of dark matter.
* This podcast episode explores a recent study that has found a significant correlation between the UGRB and the distribution of mass in the universe, as traced by gravitational lensing.
**Key Findings:**
* Researchers detected a correlation between the UGRB and **weak gravitational lensing** with a signal-to-noise ratio of 8.9.
* This is the first time a significant correlation has been observed at **large scales**, indicating that a substantial portion of the UGRB aligns with the mass clustering of the universe.
* **Blazars**, a type of active galactic nuclei (AGN), are a likely source for this signal.
* The study suggests that blazars contributing to this correlation are likely located in **massive halos** (around 10^14 solar masses).
* The research indicates a preference for a **curved gamma-ray energy spectrum**, specifically a log-parabolic shape, over a simple power-law. This implies that the gamma-ray sources have a complex energy distribution.
* The signal is stronger at **high energies and high redshifts**. This suggests that the sources are located far away and emit higher energy photons.
**Significance:**
* The cross-correlation technique can help in distinguishing between gamma-ray emissions from astrophysical sources and those potentially caused by **dark matter annihilation** or decay.
* This method provides insights into the properties of unresolved gamma-ray sources, such as their **redshift distribution and clustering**.
* The findings refine the understanding of **blazars** and their contribution to the UGRB, but also point towards modifications in the current understanding of blazar models.
**Implications and Future Research:**
* The study opens the door to the possibility of additional gamma-ray sources such as **star-forming galaxies or particle dark matter**.
* Future research will include cross-correlating the gamma-ray sky with galaxy clustering data to further confirm the source populations that are responsible for the signal. This will also allow for more detailed characterization of the signal's redshift dependence and absorption.
* This analysis can also help refine the **extragalactic background light (EBL)** model.
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Fermi-LAT, DES
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