Multi-messenger astrophysics

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Discussions around tools and discoveries in the novel domain of multi-messenger and time domain astrophysics. We'll highlight recent publications, discuss tools to faciliate observations and generally talk about the cool science behind the most violent explosions in the universe.

  1. The Super PeVatron: LHAASO Unlocking the High-Energy Secrets of Cygnus X-3

    DEC 23

    The Super PeVatron: LHAASO Unlocking the High-Energy Secrets of Cygnus X-3

    In this episode, we dive into a groundbreaking discovery from the **Large High Altitude Air Shower Observatory (LHAASO)**. For decades, the microquasar **Cygnus X-3** has been "an astronomical puzzle," but new data has finally confirmed its status as a **Super PeVatron**—a cosmic engine capable of accelerating protons to tens of petaelectronvolt (PeV) energies. **Key Discussion Points:** **The Iconic Microquasar:** Cygnus X-3 is a unique high-mass X-ray binary consisting of a compact object (a black hole or neutron star) and a massive **Wolf–Rayet donor star**. It features a relativistic jet and a remarkably short 4.8-hour orbital period. **Breaking the Energy Barrier:** LHAASO detected variable gamma-rays reaching up to **3.7 PeV**, the highest-energy photons ever recorded from such an astrophysical source. **The Hardest Spectrum:** The source exhibits the **hardest ultra-high-energy (UHE) spectrum** ever detected by LHAASO, with a distinct "hump" or spectral hardening around 1 PeV.**Protons vs. Electrons:** While lower-energy GeV gamma-rays are often produced by electrons, researchers explain that **leptonic origins are robustly excluded** for these PeV emissions due to intense synchrotron cooling. Instead, the signal likely comes from **photomeson processes**, where protons accelerated in the jet collide with the dense ultraviolet and X-ray photon fields of the binary system.**Temporal Puzzles:** We discuss the **month-scale variability** of the signal and the 3.2$\sigma$ evidence for orbital modulation, which strongly suggests the PeV radiation is born deep within the innermost regions of the jet. The Big Picture: This discovery provides the first compelling evidence that a microquasar can act as a **super-PeVatron**, generating transient PeV gamma-ray emission in close proximity to the central engine. This shifts our understanding of how cosmic rays are accelerated within our own galaxy. ### Article Reference **Title:** *Cygnus X-3: A variable petaelectronvolt gamma-ray source* **Authors:** The LHAASO Collaboration **Journal:** *National Science Review (NSR)* **Source PDF:** 2512.16638v1.pdf Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: LHAASO Collaboration

    14 min
  2. Chasing Cosmic Ghosts: The Global Multi-Messenger Hunt for Neutrino Sources

    DEC 22

    Chasing Cosmic Ghosts: The Global Multi-Messenger Hunt for Neutrino Sources

    In this episode, we dive into the cutting-edge world of multi-messenger astronomy. We explore how scientists are using a global network of specialized telescopes to solve one of the greatest mysteries in physics: the origin of high-energy cosmic rays. By tracking "ghost particles" called neutrinos from the depths of the South Pole to the highest mountain peaks where gamma-ray telescopes wait, researchers are building a new map of the most violent processes in our universe. Key Discussion Points: What are Neutrinos? Learn why these secondary particles are the "smoking gun" signature of hadronic acceleration processes in space.The Multi-Messenger Approach: Why detecting neutrinos alone isn't enough and how simultaneous observations of very-high-energy (VHE) gamma-rays help pinpoint source locations.The IceCube-IACT Partnership: A look at how the IceCube Neutrino Observatory at the South Pole coordinates with the "Big Four" imaging atmospheric Cherenkov telescopes—FACT, H.E.S.S., MAGIC, and VERITAS—to react to cosmic alerts in real-time.Target-of-Opportunity (ToO) Programs: How telescopes automatically repoint within seconds or minutes to catch a glimpse of a neutrino’s source.Case Studies & Legacy Results: We review the famous coincidence of the blazar TXS 0506+056 and discuss the latest findings from follow-up observations conducted between 2017 and 2021.The Future of the Hunt: What the next generation of detectors, like IceCube-Gen2 and the Cherenkov Telescope Array Observatory (CTAO), will mean for the next decade of discovery. Featured Reference: FACT, H.E.S.S., MAGIC, VERITAS, Fermi-LAT, and IceCube Collaborations. (2025). Prompt Searches for Very-High-Energy $\gamma$-Ray Counterparts to IceCube Astrophysical Neutrino Alerts. Accepted at the Astrophysical Journal, arXiv: https://arxiv.org/abs/2512.16562 Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: IceCube/NASA

    14 min
  3. V1723 Sco and V6598 Sgr: Decoding the Fastest and Brightest Gamma-Ray Eruptions

    DEC 18

    V1723 Sco and V6598 Sgr: Decoding the Fastest and Brightest Gamma-Ray Eruptions

    Classical novae, thermonuclear eruptions on the surface of a white dwarf in a binary system, are known sources of high-energy gamma-rays detected by the Fermi-LAT. This episode explores a multi-wavelength analysis of two recent novae, **V1723 Sco 2024** and **V6598 Sgr 2023**, aiming to constrain the mechanism behind this intense gamma-ray emission. **V1723 Sco** proved to be a very bright gamma-ray source, with emission lasting 15 days, allowing scientists to constrain the total energy and spectral properties of accelerated protons. Intriguingly, V1723 Sco also showed unexpected gamma-ray and thermal hard X-ray emission more than 40 days after its initial outburst, suggesting that particle acceleration can occur even several weeks post-eruption. In contrast, **V6598 Sgr** was detected by Fermi-LAT for only two days, marking one of the shortest gamma-ray emission durations ever recorded for a classical nova. Its brief gamma-ray signal coincided with a rapid decline in optical brightness. V6598 Sgr also exhibits peculiar characteristics, including no significant gamma-ray emission below 1 GeV and the possibility that it is an Intermediate Polar (IP) system, which may hint at a different particle acceleration region due to potentially strong magnetic fields. The detailed analysis, which combined Fermi-LAT data with optical (AAVSO) and X-ray (NuSTAR) observations, strongly supports the hypothesis that the gamma-ray generation in both novae is more consistent with the **hadronic scenario** (involving accelerated protons) than the leptonic scenario. However, the long-standing challenge remains: no non-thermal X-ray emission has been detected simultaneously with the gamma-rays. **Article Reference:** Fauverge, P., Jean, P., Sokolovsky, K., et al. (2025). *Fermi-LAT detections of the classical novae V1723 Sco and V6598 Sgr in a multi-wavelength context.* submitted to Astronomy & Astrophysics, arXiv: 2512.14198 Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: NASA's Goddard Space Flight Center/S. Wiessinger

    14 min
  4. Exploding Star in the Early Universe: The SVOM Discovery of GRB 250314A

    DEC 10

    Exploding Star in the Early Universe: The SVOM Discovery of GRB 250314A

    Join us as we explore the remarkable cosmic event, **GRB 250314A**, an exploding star detected deep within the early Universe. This long gamma-ray burst (LGRB), observed by the SVOM satellite, was spectroscopically measured at a redshift of approximately **$z \approx 7.3$**, meaning it occurred when the Universe was only about 5% of its current age, placing it firmly in the era of reionization. The observation campaign was critical, identifying the GRB as a classical long (Type II) event, consistent with the explosion of a rare massive star. Initial ground-based follow-up, triggered by the SVOM detection, led to the discovery of the near-infrared afterglow and the crucial redshift measurement via the Lyman-$\alpha$ break observed using the VLT/X-shooter. The investigation reached a major milestone when **JWST/NIRCAM** observations were obtained, revealing both the faint, blue host galaxy and the likely presence of an associated **Supernova (SN)**. Researchers found that the luminosity and spectral shape of this ancient SN are strikingly similar to **SN 1998bw**, the canonical GRB SN prototype observed locally. This similarity is profound, suggesting that despite the vast differences in physical conditions in the early Universe, the massive star that created GRB 250314A was not significantly more massive than local progenitors, implying a surprisingly limited scope for evolution in GRB and SN properties across much of cosmic history. Studying such events is key to exploring star formation and chemically characterizing the interstellar medium in the highest-redshift galaxies. *** ### Reference Articles * **Cordier, B., et al. (2025). SVOM GRB 250314A at $z \approx 7.3$: An exploding star in the era of re-ionization.** *Astronomy & Astrophysics, 704, L7*. * **Levan, A. J., et al. (2025). JWST reveals a supernova following a gamma-ray burst at $z \approx 7.3$.** *Astronomy & Astrophysics, 704, L8*. Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: CNSA/CNES

    17 min
  5. Satellite megaconstellations will threaten space-based astronomy

    DEC 8

    Satellite megaconstellations will threaten space-based astronomy

    The rapid expansion of Low Earth Orbit (LEO) satellite megaconstellations is creating a growing threat to space-based astronomy, challenging the long-held perception that space telescopes are immune to light contamination. If all proposals for new telecommunication satellite launches are fulfilled, projections indicate that Earth could be orbited by **half a million artificial satellites by the end of the 2030s**. Currently, the total number of satellites is only a small fraction (less than 3%) of those planned for the next decade. This episode delves into a study forecasting the devastating impact of these constellations on vital observatories: * **Current Impact:** Satellite trails already affect astronomical images across the complete electromagnetic spectrum. A recent study demonstrated that 4.3% of images obtained by the **Hubble Space Telescope** between 2018 and 2021 already contained artificial satellite trails. * **Future Contamination:** If the planned constellations are completed (approximately 560,000 satellites), light contamination becomes critical for LEO observatories. * The forecast shows that **more than one-third (39.6% $\pm$ 4.6%) of Hubble Space Telescope images will be contaminated**. * Newer LEO telescopes, such as the SPHEREx, ARRAKIHS, and Xuntian space telescopes, are predicted to have **more than 96% of their exposures affected**. * The Xuntian Space Telescope, due to its lower orbit (450 km), will be the most affected, potentially seeing 92 satellite trails per average exposure. * **Trail Brightness:** Reflections from satellites are extremely bright for professional telescopes. The typical surface brightness of detectable trails is forecasted to range from $\mu = 18$ to $\mu = 23$ mag arcsec⁻². This is orders of magnitude above the detectability limit for these telescopes. The scientific community is urging action to address this growing threat. Proposed mitigation measures include setting an optimal upper limit for large satellite constellations' orbits, maintaining updated and precise open archives of orbital solutions for active and derelict spacecraft (avoidance), and implementing correction techniques for unwanted light pollution. *** **Reference to the article discussed:** Borlaff, A. S., Marcum, P. M. & Howell, S. B. Satellite megaconstellations will threaten space-based astronomy. *Nature*. Published online 3 December 2025. **DOI:** https://doi.org/10.1038/s41586-025-09759-5 Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Borlaff, A.S., Marcum, P.M. & Howell, S.B., Nature 648, 51–57 (2025)

    14 min
  6. AT2022zod: An Unusual Tidal Disruption Event

    DEC 5

    AT2022zod: An Unusual Tidal Disruption Event

    **Topic:** Tidal Disruption Events (TDEs) are short-lived optical flares that occur when a black hole shreds a star, offering valuable insight into black hole demographics. This episode dives into the unusual characteristics and implications of the event AT2022zod. **The Event:** * AT2022zod was identified as an extreme, short-lived optical flare in an elliptical galaxy at a redshift of 0.11. * The event lasted roughly 30 days, with a rapid rise time of approximately 13 days. * It reached a high peak luminosity, positioning it at the extreme end compared to most supernovae. **The Puzzle:** * The host galaxy is estimated to contain a massive central Supermassive Black Hole (SMBH) of about $1.0 \times 10^8 M⊙$. * However, AT2022zod’s short duration and luminosity are **inconsistent** with a TDE powered by this central SMBH. * Modeling and comparison with other TDEs suggest AT2022zod originated from a lower-mass black hole within the system. * The event is highly unlikely to be an AGN flare, as it was the only significant flaring activity detected across five years of monitoring. Alternative explanations like kilonovae, compact-binary mergers, and supernovae were also strongly disfavored by the light-curve analysis. **The Conclusion:** * Lightcurve modeling points to a Massive Black Hole (MBH) in the **intermediate-mass range** (IMBH, $10^4-10^6 M⊙$) as the source of the disruption. * The most plausible origin proposed is the tidal disruption of a star by an MBH embedded in an **Ultra-Compact Dwarf galaxy (UCD)** acquired by the host galaxy. * This discovery highlights the need for flexible search strategies to accommodate unusual events, especially as the Vera C. Rubin Observatory’s Legacy Survey of Space and Time begins. **Article Reference:** * Kristen C. Dage et al. (for the COIN collaboration). "AT2022zod: An Unusual Tidal Disruption Event in an Elliptical Galaxy at Redshift 0.11." Draft version December 3, 2025. Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: NASA / CXC / M. Weiss.

    14 min
  7. The Next Frontier in Astronomical Text Mining: Parsing GCN Circulars with LLMs.

    DEC 1

    The Next Frontier in Astronomical Text Mining: Parsing GCN Circulars with LLMs.

    This episode dives into how astronomers are leveraging cutting-edge AI to make sense of decades of critical astronomical observations, focusing on the General Coordinates Network (GCN). The GCN, NASA’s time-domain and multi-messenger alert system, distributes over 40,500 human-generated "Circulars" which report high-energy and multi-messenger astronomical transients. Because these Circulars are flexible and unstructured, extracting key observational information, such as **redshift** or observed wavebands, has historically been a challenging manual task. Researchers employed **Large Language Models (LLMs)** to automate this process. They developed a neural topic modeling pipeline using tools like BERTopic to automatically cluster and summarize astrophysical themes, classify circulars based on observation wavebands (including high-energy, optical, radio, Gravitational Wave (GW), and neutrino observations), and separate GW event clusters and their electromagnetic (EM) counterparts. They also used **contrastive fine-tuning** to significantly improve the classification accuracy of these observational clusters. A key achievement was the successful implementation of a zero-shot system using the **open-source Mistral model** to automatically extract Gamma-Ray Burst (GRB) redshift information. By utilizing prompt-tuning and **Retrieval Augmented Generation (RAG)**, this simple system achieved an impressive **97.2% accuracy** when extracting redshifts from Circulars that contained this information. The study demonstrates the immense potential of LLMs to **automate and enhance astronomical text mining**, providing a foundation for real-time analysis systems that could greatly streamline the work of the global transient alert follow-up community. *** **Reference to the Article:** Vidushi Sharma, Ronit Agarwala, Judith L. Racusin, et al. (2025). **Large Language Model Driven Analysis of General Coordinates Network (GCN) Circulars.** *Draft version November 20, 2025.*. (Preprint: 2511.14858v1.pdf). Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: arXiv:2511.14858v1

    15 min
  8. CHIME’s Cosmic Echo: The First Detection of the 21 cm Auto-Power Spectrum.

    NOV 27

    CHIME’s Cosmic Echo: The First Detection of the 21 cm Auto-Power Spectrum.

    Reference Article: Detection of the Cosmological 21 cm Signal in Auto-correlation at z ∼ 1 with the Canadian Hydrogen Intensity Mapping Experiment, by The CHIME Collaboration. Summary: We delve into a groundbreaking astronomical achievement: the **first detection of the cosmological 21 cm intensity mapping signal in auto-correlation at $z \sim 1$** using the Canadian Hydrogen Intensity Mapping Experiment (CHIME). This discovery utilizes 94 nights of observation data, covering a frequency range from 608.2 MHz to 707.8 MHz, corresponding to a mean redshift of approximately $z \sim 1.16$. The detection was highly significant, measured at **$12.5\sigma$**. This marks a major milestone, as it establishes the 21 cm auto-power spectrum as a direct and potent cosmological probe, eliminating the dependence on external galaxy surveys to study large-scale structure. Key Discussion Points: The Challenge: Detecting the cosmological 21 cm signal is extremely challenging because astrophysical radio foregrounds are several orders of magnitude brighter.Pipeline Advancements: The success relies on significant improvements to the CHIME data processing pipeline. These advancements include novel RFI (Radio Frequency Interference) detection and masking algorithms, achromatic beamforming techniques, and applying foreground filtering *before* time averaging to minimize spectral leakage. The Hybrid Foreground Residual Subtraction (HyFoReS) algorithm was also deployed to correct residual bandpass errors.Robustness and Validation: The measurement is exceptionally reliable, having been established through a comprehensive suite of validation tests. Key checks demonstrated that the signal is consistent across independent right ascension bins, declination bins, and different baseline configurations, ruling out baseline-dependent, RA-dependent, or declination-dependent systematics. Crucially, the consistency of the signal in Stokes-Q data with noise rules out significant polarized foreground leakage.Consistent Results: The auto-correlation result is statistically consistent with previous cross-correlation measurements performed using the same CHIME data stacked on eBOSS quasars, providing strong evidence against contamination from systematics.Cosmological Implications: The measurement constrains the clustering amplitude of neutral hydrogen (HI). For the full band, the derived amplitude parameter is $A^2_{\text{HI}} = 2.59^{+1.26}_{-0.78}(\text{stat.})^{+2.45}_{-0.47}(\text{sys.})$. Independent detections were also made in two sub-bands (9.2$\sigma$ at $z \sim 1.24$ and 8.7$\sigma$ at $z \sim 1.08$), showing consistency between the different redshift slices.Future Outlook:This detection sets the stage for precision 21 cm cosmology. Future work aims to include the nearly 7 years of archival CHIME data to reduce statistical uncertainties, push measurements to higher redshifts (400–600 MHz band), and develop new techniques to recover linear scales in the power spectrum, potentially enabling measurements of Baryon Acoustic Oscillations (BAOs). Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: CHIME/Andre Recnik

    16 min
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Discussions around tools and discoveries in the novel domain of multi-messenger and time domain astrophysics. We'll highlight recent publications, discuss tools to faciliate observations and generally talk about the cool science behind the most violent explosions in the universe.

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