Episódios
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* This study uses data from the IceCube Neutrino Observatory, a massive detector at the South Pole, to study cosmic rays.
* The IceCube detector is primarily designed to detect high-energy neutrinos. However, it also collects a large amount of data on cosmic-ray muons.
* Muons are created when cosmic rays collide with the Earth's atmosphere.
* By studying the arrival directions of these muons, scientists can learn about the anisotropy of cosmic rays, meaning the variations in their arrival directions.
* This analysis used twelve years of data, from May 13, 2011, to May 12, 2023, resulting in the largest data sample ever collected by IceCube for this type of study.
* The analysis confirmed a change in the angular structure of cosmic-ray anisotropy between energies of 10 TeV and 1 PeV.
* This change is particularly noticeable in the 100 TeV to 300 TeV energy range.
* The researchers found that the anisotropy cannot be described as a simple dipole but is a complex pattern that changes with energy.
* They calculated the angular power spectrum of the anisotropy to understand the contribution of different angular scales to the overall pattern.
* The power spectrum analysis suggests that large-scale features of the anisotropy are relatively reduced at high energies compared to medium and small-scale features.
* This finding may provide insights into the origin and propagation of cosmic rays.
Reference: R. Abbasi et al., "Observation of Cosmic-Ray Anisotropy in the Southern Hemisphere with Twelve Years of Data Collected by the IceCube Neutrino Observatory." Submitted to ApJ (draft version December 9, 2024), arXiv:2412.05046v1.pdf.
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: IceCube collaboration
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* Orphan gamma-ray burst (GRB) afterglows occur when the gamma-ray emission from a GRB is not directed towards Earth, making the initial burst invisible. However, the afterglow, produced by the interaction of the GRB's blast wave with surrounding material, can be observed.
* Studying orphan afterglows provides valuable insights into GRB physics and their progenitors, and can enhance multi-messenger analyses with gravitational waves.
* The Vera C. Rubin Observatory, with its exceptional sensitivity and wide field of view, is expected to play a crucial role in detecting orphan afterglows.
* The anticipated high volume of alerts from the Rubin Observatory necessitates the use of alert brokers like Fink to filter and categorize events.
* Researchers are developing a machine learning classifier within Fink to identify orphan afterglows based on their distinct light curve characteristics.
* This classifier uses features like the duration, rise and decay rates, color, and fitted parameters of the light curve to distinguish orphan afterglows from other transient events.
* Initial tests using simulated data show promising results, with the classifier effectively excluding most non-orphan events while retaining a significant portion of orphan afterglows.
Reference: Masson, M., & Bregeon, J. (2024). Search for orphan gamma-ray burst afterglows with the Vera C. Rubin Observatory and the alert broker Fink. arXiv preprint arXiv:2412.05061v1.
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: LSST project/NSF/AURA
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Fast Radio Bursts (FRBs) are brief, powerful pulses of radio waves originating from distant galaxies. Their origins are still a mystery, with one leading theory pointing to magnetars, highly magnetized neutron stars, as the source. Astronomers have identified a small number of FRBs that emit repeated bursts, termed repeating FRBs (rFRBs). A subset of rFRBs have a persistent radio source (PRS) associated with them. PRSs are continuous sources of radio waves, distinct from the burst emission. The article discusses the discovery of the fourth known PRS associated with FRB 20240114A. This makes it a valuable case study for understanding the environments and mechanisms driving FRBs. Observations using the Very Long Baseline Array (VLBA) pinpointed the PRS to a location about 1 kpc away from the center of its host galaxy. The PRS's high brightness temperature suggests it originates from a non-thermal process like synchrotron radiation, where electrons are accelerated in magnetic fields.
The host galaxy is a dwarf galaxy exhibiting a high rate of star formation, termed a starburst galaxy. Its properties rule out an active galactic nucleus (AGN) as the source of the PRS. Studying the radio spectrum of FRB 20240114A's PRS reveals a potential spectral peak around a frequency of 1 GHz. Such a peak could provide constraints on the energy and distribution of electrons within the PRS. The observed properties of FRB 20240114A and its PRS align with a "nebular model," where the PRS is powered by synchrotron radiation from a surrounding nebula of charged particles. There is a theoretical correlation between the luminosity of a PRS and the Faraday rotation measure (RM) of its associated FRB, which quantifies the magnetic field and electron density along the line of sight. FRB 20240114A and its PRS fit well within this predicted relationship. Further high-resolution radio observations at various frequencies are needed to refine the spectral shape of the PRS. This will allow scientists to better understand the physical processes and conditions within the nebula and glean more insights into the nature of the FRB's central engine.
Reference: Bruni, G., Piro, L., Yang, Y.-P., et al. 2024, Astronomy & Astrophysics
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Wikipedia/user:Hajor
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The discovery of a new ultra-high-energy gamma-ray source, 1LHAASO J1857+0203u, by the Large High Altitude Air Shower Observatory (LHAASO) suggests the presence of a PeVatron, a cosmic accelerator capable of boosting particles to peta-electron volt energies. This source is particularly interesting because it is located in a region with complex multi-wavelength features, including the supernova remnant (SNR) G35.6−0.4 and the HII region G35.6−0.5.
The study, published in "An Enigmatic PeVatron in an Area around HII Region G35.6−0.5" by Cao et al., explores three possible origins for the observed gamma-ray emission:
HII region scenario: The gamma rays originate from the HII region G35.6−0.5, possibly accelerated by the stellar winds of massive stars. While no such stars have been directly observed yet, their presence cannot be ruled out, especially if they are embedded within molecular clouds. Supernova remnant scenario: The gamma rays are produced when protons that escaped from the SNR G35.6−0.4 interact with nearby molecular clouds. However, the current analysis suggests that the mass of the observed clouds is insufficient to explain the observed gamma-ray flux. Pulsar wind nebula (PWN) scenario: The gamma rays are emitted by a PWN powered by an as-yet undiscovered pulsar. This scenario is plausible given the potential for mature PWNe to be bright in gamma rays while remaining undetected at other wavelengths.Further observations across the electromagnetic spectrum are needed to definitively determine the origin of the gamma-ray emission from 1LHAASO J1857+0203u.** Future observations with instruments like the Large-Sized Telescope (LACT), ASTRI, and the Cherenkov Telescope Array (CTA) could help distinguish between these scenarios thanks to their enhanced angular resolution.
Reference:
Cao, Z., Aharonian, F., Axikegu, et al. "An Enigmatic PeVatron in an Area around HII Region G35.6−0.5". Draft version December 3, 2024. *Typeset using LATEX twocolumn style in AASTeX631.*
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: LHAASO
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The TAIGA-HiSCORE Cherenkov array, located in Siberia, is a unique instrument designed to study cosmic rays and gamma rays. However, scientists have realized that it can also be used to search for a variety of fascinating astronomical phenomena, including nanosecond optical transients.
What are nanosecond optical transients? These are extremely short bursts of light that last for only a few nanoseconds. The source of these transients is unknown, but there are several intriguing possibilities:
Evaporation of primordial black holes: Tiny black holes formed in the early universe could be evaporating today, releasing a burst of energy that includes optical light. Magnetic reconnection in black hole accretion disks: Sudden bursts of energy from these events could produce detectable nanosecond optical flashes. Signals from extraterrestrial civilizations: Advanced civilizations might be using powerful lasers to communicate across vast distances. TAIGA-HiSCORE could be sensitive enough to detect these signals.he TAIGA-HiSCORE array has a very large field of view (FOV) of about 0.6 steradians, making it ideal for searching for rare events. Researchers have been collecting data for several years and have developed sophisticated techniques to filter out background noise and identify potential transient signals.
So far, no definitive evidence of astrophysical nanosecond optical transients has been found. However, the search continues, and the TAIGA-HiSCORE array is pushing the boundaries of what we know about the universe.
Reference:
A. D. Panov et al. "Four Years of Wide-Field Search for Nanosecond Optical Transients with the TAIGA-HiSCORE Cherenkov Array." arXiv:2412.00159v1 (2024).
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: TAIGA-HiSCORE
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Kilonovae (KNe) are bright, rapidly fading astronomical events believed to be caused by the radioactive decay of heavy elements produced during the merger of neutron stars or a neutron star and a black hole.
While there are several candidate KNe events observed in association with short gamma-ray bursts (GRBs), there is only one confirmed KN associated with a gravitational wave (GW) event, AT2017gfo, detected in 2017.
The Kilonova and Transients Program (KNTraP) is a new survey project using the Dark Energy Camera (DECam) to search for KNe independent of GW and GRB triggers.
KNTraP is designed to be a deep, wide-field survey with a nightly cadence in the g and i filters, allowing it to probe a large volume of the sky and identify rapidly evolving transients. The first KNTraP observing run, conducted over 11 nights in 2022, did not detect any convincing KNe candidates but did identify several other interesting fast-evolving transients, including AT2022kak, a rapidly fading transient, and SN2022dmf, an early Type Ia supernova.
The KNTraP project offers several advantages over traditional GW and GRB follow-up searches:
It can probe volumes beyond the current detection range of GW detectors. It can search for KNe regardless of the merger orientation, unlike GW and GRB detectors that are sensitive to orientation. It allows for early detection of KNe, capturing their rise, peak, and fade, providing valuable data for theoretical models. Future KNTraP observing runs are expected to be more sensitive due to improved observing conditions and the availability of template images from this first run. Upcoming instruments like the Keck Wide-Field Imager (KWFI) could further enhance KNTraP's efficiency in detecting KNe.Reference Article: Van Bemmel, N., Zhang, J. et al. "An Optically Led Search for Kilonovae to z∼0.3 with the Kilonova and Transients Program (KNTraP)". MNRAS 000, 1–16 (2024).
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Dark Energy Camera
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In this episode, we explore the fascinating world of diffuse gamma rays emanating from the Galactic plane. A new study using the Large High Altitude Air Shower Observatory's Water Cherenkov Detector Array (LHAASO-WCDA) has provided unprecedented insights into these mysterious emissions.
What are diffuse gamma rays? These high-energy photons are produced when cosmic rays, energetic particles that constantly bombard our galaxy, interact with interstellar gas and radiation. Studying these gamma rays provides valuable information about the distribution and behavior of cosmic rays, helping us unravel their origins and propagation throughout the Milky Way.
LHAASO-WCDA's groundbreaking observations: The LHAASO-WCDA has detected diffuse gamma-ray emissions across a wide energy range, from 1 TeV to 25 TeV, bridging a crucial gap between previous observations by space-based and ground-based detectors.
Mapping the Galactic plane: The study focused on two distinct regions of the Galactic plane: the inner region (15° < l < 125°, |b| < 5°) and the outer region (125° < l < 235°, |b| < 5°). This wide coverage allowed scientists to create detailed maps of the diffuse gamma-ray emission, revealing intriguing patterns.
Surprising findings: The LHAASO-WCDA measurements show that the diffuse gamma-ray fluxes are significantly higher than predicted by conventional models that consider only interactions between cosmic rays and interstellar gas. This excess suggests the presence of additional, as yet unidentified sources of gamma rays in the Milky Way.
Possible explanations: Several hypotheses have been proposed to explain the unexpected gamma-ray excess.
One leading contender is the existence of a population of unresolved sources, such as pulsar wind nebulae or pulsar halos, that emit gamma rays at energies below tens of TeV. Other possibilities include contributions from young massive star clusters or modifications to our understanding of cosmic ray propagation.Future directions: Combining LHAASO-WCDA's observations with data from other experiments, such as neutrino detectors, will be crucial to pinpoint the origin of the diffuse gamma-ray excess and further illuminate the mysteries of cosmic rays and their journey through our galaxy.
Reference: Zhen Cao et al. "Measurement of Very-high-energy Diffuse Gamma-ray Emissions from the Galactic Plane with LHAASO-WCDA" (arXiv:2411.16021v1)
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: LHAASO Collaboration
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IACTs (Imaging Atmospheric Cherenkov Telescopes) are typically used for gamma-ray astronomy. Muons are produced in hadronic showers and IACTs can detect these muons, which are normally considered background noise. The information from these muons can be used to study cosmic ray showers. One way to study cosmic rays is by observing the muon lateral distribution, which is the muon density as a function of the distance from the shower core. Another way is by determining the muon slant height, which is the distance from the muon production point along the shower axis to the telescope. Studying muon lateral distribution and slant height may help us to better understand hadronic interaction models.
Challenges: One challenge is that IACTs have a low effective area for muons. Also, IACTs typically only detect one muon per shower event. To reconstruct a muon lateral distribution, you need to know the effective area of the telescope array, which is difficult to determine. Current methods for determining the muon production height underestimate the true height.
These challenges may be overcome with the use of future IACT arrays, such as the Cherenkov Telescope Array (CTA). CTA will have a much larger effective area for muons, with more telescopes in a denser configuration. CTA will also have a higher data rate, which will allow for more precise measurements. Improvements to current muon identification algorithms, including machine learning and citizen science approaches, could also help to improve muon detection.
Publication: A.M.W. Mitchell et al., "Potential for measuring the longitudinal and lateral profile of muons in TeV air showers with IACTs", Astroparticle Physics 111, 2019, Pages 23-34, arXiv:1903.12040
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: IN2P3/HESS
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Ultra-high-energy cosmic rays (UHECRs) are the most energetic particles ever detected, with energies exceeding 10^18 eV. Their origin remains a mystery, as their paths are deflected by magnetic fields in space, making it difficult to trace them back to their sources. Scientists use models of the Galactic magnetic field (GMF) to account for these deflections and try to pinpoint the sources of UHECRs. A recent study used a new suite of GMF models called UF23, which provides a more accurate representation of the Milky Way's magnetic field. The study found that the dipole amplitude of UHECRs, which is a measure of the anisotropy in their arrival directions, is significantly smaller than predicted by previous models. This discrepancy is attributed to the demagnification effect of the GMF, where the magnetic field deflects UHECRs coming from certain directions so strongly that they never reach Earth.
The study also highlighted the importance of considering the inhomogeneous distribution of UHECRs arriving at the Milky Way. The flux of UHECRs is enhanced in the direction of the Virgo cluster, which is a massive cluster of galaxies.
The combination of the demagnification effect and the inhomogeneous flux distribution significantly affects the predicted dipole amplitude and direction of UHECRs. This finding has important implications for the search for UHECR sources, as it suggests that some popular source candidates, such as M87, may be hidden from our view due to demagnification.
Publication: T. Bister et al., "The large-scale anisotropy and flux (de-) magnification of ultra-high-energy cosmic rays in the Galactic magnetic field", arXiv:2408.00614
Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: BBC
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Swift's New Capability: Continuous Commanding
A new capability of the Neil Gehrels Swift Observatory, called "continuous commanding", allows Swift to respond to targets of opportunity within 10 seconds. This capability allows Swift to receive commands in real-time because the spacecraft is now constantly in contact with the ground. This capability was developed to allow Swift to respond to early warning gravitational wave detections. Specifically, it will allow Swift to point the Burst Alert Telescope (BAT) at the origin of the gravitational waves before or at the time of merger.
Simulations show that 60 seconds of early warning can double the rate of prompt GRB detection with arcminute localization, and 140 seconds guarantees observation anywhere on the unocculted sky. The latency of the LIGO/Virgo cyberinfrastructure is now the limiting factor in the detection yield.
Swift's new continuous commanding capability was demonstrated by responding to an external Fast Radio Burst (FRB) trigger. Swift was able to start slewing to the location of the FRB only 9 seconds after receiving the command.
Publication: A. Tohuvavohu et al., "Swiftly chasing gravitational waves across the sky in real-time", arXiv: 2410.05720
Acknowledgements: Podcast created with Google/NotebookLM. Illustration credits: NASA
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The Pierre Auger Observatory, situated in Argentina, is designed to detect UHE cosmic rays. The observatory is also sensitive to UHE photons and has been used to search for photons from various sources. This study looked for coincidences between UHE photon events and a selection of GW events detected by the LIGO/Virgo observatories. No UHE photon events were observed in coincidence with any of the selected GW events. This is the first study to place limits on UHE photon emission from GW sources.
Publication: Abdul Halim, A., et al. "Search for UHE Photons from Gravitational Wave Sources with the Pierre Auger Observatory.", 2023 ApJ 952 91
Acknowledgements: Podcast prepared with Google/NotebookLM. Illustration credits: A.Chantelauze/S.Staffi/L.Bret
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Astronomers discovered a new long-period (21-minute) radio transient called GPM J1839–10, with the Murchison Widefield Array (MWA). Follow-up observations were done using other telescopes, including the Australia Telescope Compact Array (ATCA), Parkes/Murriyang radio telescope, the Australian Square Kilometre Array Pathfinder (ASKAP), and MeerKAT. The pulses from GPM J1839–10 vary in brightness, last between 30 and 300 seconds, and have quasiperiodic substructure. Archival data revealed that this source has been repeating since at least 1988.
Publication: Hurley-Walker, N. et al. A long-period radio transient active for three decades. Nature , 57–62 (2023)
Acknowledgements: Podcast created with Google/NotebookLM. Image credits: Olena Shmahalo
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Microquasars, like V4641 Sgr, are binary star systems with a black hole that pulls material from a companion star. They are fascinating objects for astronomers because they can produce jets of relativistic particles. The High-Altitude Water Cherenkov (HAWC) Observatory observed TeV gamma-ray emissions from V4641 Sgr. These observations suggest that the microquasar is accelerating particles far from the black hole, in a region much larger than the binary system itself. It supports the idea that microquasars may be more common sources of galactic cosmic rays than previously thought.
Future observations, particularly with neutrino detectors, could provide further evidence for the hadronic scenario and confirm the role of microquasars as cosmic ray accelerators.
Publication: HAWC collaboration, "Very high energy particle acceleration powered by the jets of the microquasar SS 433", Nature 562 (2018), 82-85 (arXiv:1810.01892)
Acknowledgements: The podcast has been prepared using Google/NotebookLM. Image credits: HAWC Collaboration
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Astronomers using LOFAR detected a short, coherent radio flash at 144 MHz, 76.6 minutes after observing a short gamma-ray burst (GRB) called GRB 201006A. The probability of finding an unrelated transient is less than 1 in a million and it is thus likely the radio counterpart to GRB 201006A.
The discovery of this radio flash suggests that searches for similar emissions could be helpful for multi-messenger campaigns following neutron star mergers and associated gravitational wave events. Identifying coherent radio emission from a gravitational wave detection would significantly improve the localization of the event, enabling more precise follow-up observations.
Publication: A. Rowlinson et al., "A candidate coherent radio flash following a neutron star merger", MNRAS stae2234
Acknowledgements: Illustration from ESO/A. Roquette. The podcast was produced with Google/NotebookLM
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The paper examines the "Matthew Effect" in science, where more well-known scientists or institutions tend to receive a disproportionate amount of credit for discoveries, even in collaborative efforts. This effect extends to large research collaborations, as demonstrated by the case of the LIGO, Virgo, and KAGRA collaborations.
While LIGO, Virgo, and KAGRA have been working together since 2007 and co-author all their gravitational-wave observation papers, the wider scientific community often overlooks the contributions of Virgo and KAGRA, attributing most of the credit to LIGO.
The paper identifies three main types of issues:
Attributing the first gravitational wave detection, GW150914, solely to LIGO, even though the discovery was a collaborative effort. Downplaying the crucial role of Virgo in the discovery of GW170817, the first confirmed merger of compact stars. While the signal was detected only by LIGO, Virgo's data enabled precise sky localization, crucial for multimessenger observations. Attributing overall science results and future projections in the field to LIGO alone.The authors' efforts resulted in about half of the problematic papers being corrected. However, the study found no significant difference in the citation impact of corrected versus uncorrected papers. This suggests that more work is needed to understand the social dynamics of this cognitive bias and to promote a more equitable recognition of scientific contributions in large collaborations.
Publication: P. Barneo et al., "Addressing the problem of the LIGO-Virgo-KAGRA visibility in the scientific literature", The European Physical Journal H, (2024) 49:2 (arXiv:2402.03359)
Acknowledgements: Image credit ICRR, Univ. of Tokyo/LIGO Lab/Caltech/MIT/Virgo Collaboration. The podcast was created with Google/NotebookLM.
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Ultra-high-energy cosmic rays (UHECRs) are a mystery. Scientists still don’t know where or how they are created. A new study combines three kinds of data measured at the Auger Observatory: the energy spectrum, shower maximum depth distributions, and arrival directions of UHECRs.
Publication: A.A. Halim et al., "Constraining models for the origin of ultra-high-energy cosmic rays with a novel combined analysis of arrival directions, spectrum, and composition data measured at the Pierre Auger Observatory", JCAP 01 (2024) 022
Acknowledgements: Image credits Pierre Auger Observatory. The podcast was created with Google/NotebookLM
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GRB 201216C, a long GRB, was observed by numerous instruments, including Swift-BAT, Fermi-GBM, and the MAGIC telescopes. MAGIC detected GRB 201216C at a redshift of z = 1.1, making it the farthest known source detected at VHE gamma rays.
Modeling of GRB 201216C's multiwavelength data, including the MAGIC observations, favors a scenario where the GRB jet is expanding into a wind-like medium shaped by the progenitor star. This is consistent with the observed light curves and SEDs.
Publication: H. Abe et al., "MAGIC detection of GRB 201216C at z = 1.1", MNRAS 527, 3 (2024), 5856–5867
Acknowledgement: Illustration credits Gabriel Pérez Díaz (IAC). The podcast was produced by Google/NotebookLM
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This episode explores the search for Galactic PeVatrons, powerful cosmic accelerators that boost cosmic rays to PeV energies (1 PeV = 10^15 eV). The study, conducted by researchers using the HAWC gamma-ray observatory and the IceCube Neutrino Observatory, focuses on identifying neutrino emission from known gamma-ray sources.
The study focused on 22 gamma-ray sources detected by HAWC. The researchers first used HAWC data to create a detailed spatial and spectral model for each gamma-ray source. They then combined this information with IceCube neutrino data, looking for evidence of neutrino emission from the same locations. The researchers did not find any significant evidence of neutrino emission from any of the 22 gamma-ray sources.
Publication: R. Alfaro et al., "Search for joint multimessenger signals from potential Galactic PeVatrons with HAWC and IceCube", arXiv:2405.03817
Acknowledgements: Illustration credits WIPAC, Department of Physics, UW–Madison. Podcast created with Google/NotebookLM.
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Millisecond pulsars (MSPs) are incredibly stable rotators and can be used as extremely precise clocks. Pulsar Timing Arrays (PTAs) monitor a collection of these pulsars to detect gravitational waves (GWs). GWs affect the arrival times of pulses from these pulsars, causing tiny, correlated fluctuations.
There are four main PTAs:
The European Pulsar Timing Array (EPTA) combines data from five major European radio telescopes and the synthesized Large European Array for Pulsars (LEAP). The Indian Pulsar Timing Array (InPTA), focusing on low-frequency observations, uses data from the upgraded Giant Metrewave Radio Telescope (GMRT). The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) utilizes data from the Arecibo Observatory, Green Bank Telescope, Very Large Array, and the Canadian Hydrogen Intensity Mapping Experiment (CHIME). The Parkes Pulsar Timing Array (PPTA) in Australia employs the Parkes radio telescopeThe most recent PTA data sets have yielded promising results. They have all detected CRN and the PPTA, NANOGrav, EPTA, and InPTA have found evidence of quadrupolar correlations in this noise, suggesting the presence of a GW background. This is a major step towards a definitive GW detection and opens up exciting possibilities for understanding the universe through GWs in the nanohertz frequency range.
Publication: J. Verbiest et al., "Status Report on Global Pulsar-Timing-Array Efforts to Detect Gravitational Waves", arXiv:2404.19529
Acknowledgements: Image credit: David J. Champion. Podcast created by Google/NotebookLM
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