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:

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

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:

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

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:

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

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.

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

Publication: arXiv:2411.06996

Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Y. Xing et al. (arXiv:2411.06996)

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

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

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

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

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