* **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

**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

Introduction: This episode discusses the groundbreaking discovery of AT2019pim, the first spectroscopically confirmed afterglow of a relativistic explosion with no observed high-energy gamma-ray emission. This event challenges our understanding of gamma-ray bursts (GRBs) and suggests the existence of "orphan afterglows," which are afterglows not associated with typical GRB prompt emission. The discovery was serendipitous, occurring during follow-up observations of a gravitational-wave trigger and in a TESS sector.

Key Findings:

AT2019pim is characterized by a fast-rising, luminous optical transient with accompanying X-ray and radio emission. No gamma-ray emission was detected by Fermi-GBM or Konus, placing strong constraints on an associated GRB. The afterglow's properties are consistent with a moderately relativistic outflow with an initial Lorentz factor of Γ0 ≈ 10–30, significantly lower than in typical GRBs. This supports the “dirty fireball” scenario, where high-energy emission is suppressed by pair production. The event might also be explained by a structured jet model, where only the line-of-sight material was ejected at a low Lorentz factor, off-axis from a classical high-Γ jet core. The transient's light curve was constructed using data from ZTF and TESS, showing a rapid rise to peak brightness, followed by a decay. Spectroscopic analysis revealed a redshift of z = 1.2592, confirming its cosmological distance. The afterglow was observed across multiple wavelengths, including optical, X-ray, and radio. Radio observations show strong interstellar scintillation (ISS), suggesting a small source size and limiting the average Lorentz factor. Modeling of the afterglow supports a low Lorentz factor outflow as a possible explanation.

Implications:

AT2019pim demonstrates that luminous optical afterglows without detected GRB counterparts can be identified and spectroscopically confirmed in real-time. This discovery challenges the traditional GRB paradigm, suggesting that a population of GRB-like events exists with weak or no high-energy prompt emission. It opens new avenues for studying relativistic outflows and jet structures associated with collapsing stars. The event highlights the importance of wide-field surveys and multi-messenger astronomy for detecting and understanding such transients. Future observations of more orphan afterglows will allow for detailed studies of the structure of jets in GRBs, and help to determine if "dirty fireballs" exist.

Reference: Perley, D. A., et al. (2025). "The Luminous, Slow-Rising Orphan Afterglow AT2019pim as a Candidate Moderately Relativistic Outflow." MNRAS, arXiv:2401.16470v2

Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: B. Saxton, NRAO/AUI/NSF

**Reference:** Patel et al., "Direct evidence for r-process nucleosynthesis in delayed MeV emission from the SGR 1806-20 magnetar giant flare" (2025)

* **Introduction:**

* The origin of heavy elements, specifically those formed through the rapid neutron-capture process (**r-process**), has been a long-standing mystery in astrophysics.

* While neutron star mergers have been considered a primary site, evidence suggests additional sources are needed to explain the observed abundance of these elements.

* **Magnetar Giant Flares as r-process Sites:**

* Recent studies have proposed that magnetar giant flares can eject neutron star crust material at high velocities, creating the conditions necessary for the r-process.

* These flares are the most energetic outbursts from magnetars, releasing vast amounts of energy.

* **The ejected material is shock-heated, leading to r-process nucleosynthesis**.

* **Observational Evidence:**

* The 2004 giant flare from the magnetar SGR 1806-20 exhibited a previously unexplained **delayed MeV gamma-ray emission**.

* This emission, peaking around 10 minutes after the initial flare, is consistent with the radioactive decay of freshly synthesized r-process elements.

* The light curve, fluence, and spectrum of this emission match theoretical predictions for r-process material.

* The observed data suggests that approximately **10^-6 solar masses of r-process elements** were synthesized in this event.

* **The Mechanism:**

* The "α-rich freeze-out" mechanism, facilitated by high entropy and fast expansion rates, allows for the synthesis of heavy elements even when the initial material is not particularly neutron-rich.

* The radioactive decay of these nuclei releases gamma-ray lines, which are Doppler broadened by the high ejecta velocities, resulting in the observed MeV spectrum.

* **Implications:**

* Magnetar giant flares contribute at least **1-10% of the total Galactic r-process abundances**.

* They may be particularly significant in the early universe, contributing to the chemical enrichment of low-metallicity stars.

* These flares are also implicated as potential sources of heavy cosmic rays.

* The discovery of this r-process site has implications for understanding Galactic chemical evolution and the origin of heavy elements.

* The synthesized abundance distribution is predicted to be dominated by first-peak nuclei (A~90).

* **Future Observations:**

* Future missions like NASA's COSI nuclear spectrometer can resolve decay line features to provide further insight into r-process nucleosynthesis in magnetar flares.

* Detection of a kilonova-like UV/optical signal (nova brevis) is also predicted, which may be detectable with wide-field telescopes.

* **Conclusion:**

* The study of the delayed MeV emission from SGR 1806-20 has provided direct observational evidence for **r-process nucleosynthesis in magnetar giant flares**.

* This finding challenges current models of heavy element formation and opens new avenues for research.

Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: NASA

* **Introduction:**

* The Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) will soon produce an unprecedented amount of transient astronomical data, with around 10 million alerts every night.

* This data deluge requires intelligent tools to prioritize the most scientifically valuable events for follow-up, especially spectroscopic observations.

* This podcast discusses AAS2RTO, a new tool designed to address this challenge.

* Reference: Sedgewick et al. (2025) "AAS2RTO: Automated Alert Streams to Real-Time Observations"

* **What is AAS2RTO?**

* AAS2RTO is a Python-based tool for prioritizing transient candidates for follow-up observations.

* It uses a **greedy algorithm** to rank candidates based on a user-defined "score".

* The score is calculated from various factors that consider observed properties of the transients, their visibility from a given location, and user specified criteria.

* AAS2RTO is not a broker but rather works with data streams that have already been pre-filtered by brokers.

* AAS2RTO is designed to be flexible and adaptable to different telescopes and scientific goals.

* **How AAS2RTO Works:**

* AAS2RTO ingests transient data from alert brokers like fink, ALeRCE and Lasair, which process data from surveys like the Zwicky Transient Facility (ZTF).

* It can also incorporate data from other sources like the Asteroid Terrestrial-impact Last Alert System (ATLAS) and the Transient Name Server (TNS).

* AAS2RTO filters candidates based on preliminary scores before fitting models to the lightcurves, such as SALT2 models for Type Ia Supernovae (SNe Ia), in order to estimate the time of peak brightness.

* It calculates a final score for each candidate, considering factors like brightness, age, proximity to peak brightness, and visibility from the observing site.

* AAS2RTO generates a ranked list of candidates that is continuously updated.

* **Example Science Case: Type Ia Supernovae**

* The tool was tested on the prioritization of Type Ia Supernovae (SNe Ia) close to their peak brightness.

* AAS2RTO uses lightcurve fitting to predict the time of peak brightness.

* It uses factors such as the latest magnitude, the number of detections, the proximity to peak brightness, the rising light curve, and the time since the first observation to prioritize candidates.

* It also takes into account the visibility of the candidate from the observing site.

* The tests with archival ZTF data show the tool can estimate the time of peak brightness with a precision of ±1.3 - 2.1 days.

* **AAS2RTO in the Context of Other Schedulers**

* AAS2RTO uses a greedy algorithm similar to other telescope schedulers, and is very flexible, quickly responding to new data and conditions.

* AAS2RTO is different from schedulers for facilities with competing programs, as it is designed for a single scientific goal, and does not normalize priority scores.

* Other schedulers use different approaches, such as integer linear programming solutions to provide globally optimal solutions.

* AAS2RTO’s visibility factor accounts for how long a candidate will be visible during the night.

* **Conclusion:**

* AAS2RTO is a valuable tool for prioritizing transient candidates from LSST for spectroscopic follow-up.

* Its flexible design allows for adaptation to different telescopes and scientific objectives.

* It will be used to help optimize observations with the Danish 1.54m telescope, among others.

Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Rubin Obs/NSF/Aura

* **Introduction**:

* This episode discusses the search for continuous gravitational waves (CWs) emitted by neutron stars, specifically known pulsars, using data from the LIGO-Virgo-KAGRA (LVK) collaboration's fourth observing run (O4a).

* CWs are distinct from transient gravitational waves (GWs) like those from black hole mergers; they are nearly monochromatic signals with small variations over long periods.

* **Detecting CWs can provide insights into the internal structure of neutron stars, their equations of state, and help test general relativity.**

* **What are Pulsars?**

* Pulsars are extremely dense, rapidly rotating objects with strong magnetic fields that emit beams of electromagnetic radiation.

* Their stability and predictable behavior make them ideal for CW searches.

* Electromagnetic (EM) observations of pulsars help predict and correct for modulations of any CW signal, like the Doppler effect from Earth's motion.

* **The Search for Continuous Gravitational Waves:**

* CWs are expected from neutron stars due to non-axisymmetric mass distributions. This can be caused by strain in the star's crust, accretion, strong magnetic fields, or fluid oscillations.

* The search focuses on known pulsars using "targeted searches," where the GW signal is assumed to be locked to the pulsar’s rotation as determined by EM observations.

* This paper presents results from three independent search methods (Bayesian, 5-vector, and F/G/D-statistic). These methods are used to look for both single-harmonic (at twice the pulsar's spin frequency) and dual-harmonic (at both the spin frequency and twice the spin frequency) emissions.

* A subset of pulsars were analyzed with a "narrowband search," which relaxes the assumption that the GW phase evolution exactly matches the EM solution, and searches in a narrow band around the expected frequencies.

* **Results**

* **No CW signal was detected in the O4a data.**

* The search set upper limits on the signal amplitude and the ellipticity (a measure of asymmetry in the star’s mass distribution) for each target.

* For 29 targets, the upper limit on the amplitude is below the theoretical "spin-down limit," which is calculated by assuming all the pulsar's rotational energy loss is due to GW emission.

* The lowest upper limit on the amplitude is 6.4 x 10^-27 for pulsar J0537-6910.

* The lowest constraint on the ellipticity is 8.8 x 10^-9 for pulsar J0437-4715.

* **No evidence was found for non-standard polarizations predicted by the Brans-Dicke theory**.

* The narrowband search also found no signals.

* **Comparison with Past Searches**:

* The results from this search are comparable to previous searches using data from the second and third observing runs (O2 and O3).

* The improved sensitivity of the detectors during O4a is balanced by a shorter observation period, resulting in similar overall sensitivity.

* Some pulsars have improved upper limits compared to previous searches and some have worse, which is expected, with low frequency searches showing more improvement.

* **Significance of the Findings:**

* These results continue to push into the regime of astrophysical interest for neutron star parameters, such as ellipticity, which is related to the "mountain" size on the neutron star.

* **The fact that these searches are not detecting signals yet is important, as it places constraints on the properties of these objects**.

* **Future Directions:**

* The full O4 dataset, when analyzed, will provide improved sensitivity.

* Ongoing improvements in detectors and data analysis techniques will enhance future search capabilities.

* **Reference:** A. G. Abac et al. (2025). Search for continuous gravitational waves from known pulsars in the first part of the fourth LIGO-Virgo-KAGRA observing run. https://arxiv.org/abs/2501.01495

Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: C. Reed, PennState

**Introduction:**

* This episode discusses the **Markarian Multiwavelength Data Center (MMDC)**, a new web-based tool designed to access and model multiwavelength data from blazar observations.

* MMDC is designed to enhance blazar research by providing a comprehensive framework for data accessibility, analysis, and theoretical interpretation.

* The tool integrates archival data, optical data from all-sky surveys, and newly analyzed datasets in optical/UV, X-ray, and high-energy γ-ray bands.

* **MMDC distinguishes itself from other online platforms by the large quantity of available data and its ability to enable theoretical modeling using machine learning algorithms**.

**What are Blazars?**

* Blazars are a type of active galactic nuclei (AGN) with powerful emissions from relativistic jets oriented at small angles relative to the observer.

* Their emissions are highly variable across many bands, making them interesting subjects for study.

* Blazars' spectral energy distributions (SEDs) typically exhibit a double-peaked morphology.

* The first peak, in the infrared to X-ray range, is due to synchrotron emission. The second, in the X-ray to VHE γ-ray range, is due to inverse Compton scattering or hadronic processes.

* Blazars are classified based on the peak frequency of their synchrotron emission.

**Key Features of MMDC:**

* MMDC allows users to build time-resolved multiwavelength SEDs of blazars.

* It uses data from multiwavelength catalogs and newly analyzed data in optical/UV, X-ray, and high-energy γ-ray bands.

* **It provides interactive visualization of SEDs and theoretical modeling using machine learning.**

* MMDC incorporates data from various sources such as:

* **Archival data** from catalogs using the VOU-Blazars tool.

* **Optical/UV data** from ASAS-SN, ZTF, Pan-STARRS1, and Swift-UVOT.

* **X-ray data** from Swift-XRT and NuSTAR.

* **γ-ray data** from Fermi-LAT.

* MMDC facilitates the study of blazar emissions and their variability over time.

* **It uses convolutional neural networks (CNNs) for theoretical modeling of SEDs.**

* The tool provides access to different theoretical models such as Synchrotron Self-Compton (SSC) and External Inverse Compton (EIC).

**Significance of MMDC**

* MMDC addresses the challenge of extracting maximum information from astrophysical data accumulated by different instruments and observatories.

* It provides a robust framework for data management and analysis and enhances the ability to interpret vast amounts of heterogeneous data.

* MMDC’s modeling capabilities using machine learning allow for a more comprehensive understanding of blazar physics.

* The tool promotes scientific discovery by making data more accessible.

* **It combines data accessibility with advanced interpretation tools.**

* Future plans for MMDC include an interface with the astroLLM artificial intelligence tool.

**Reference:**

* Sahakyan, N., Vardanyan, V., Giommi, P., et al. 2024, AJ, 168, 289. https://doi.org/10.3847/1538-3881/ad8231

Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: MMDC

* 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

* 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

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