D. H. Hartmann
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View article: Probing Evolution of Long GRB Properties through their Cosmic Formation History Aided by Machine Learning–predicted Redshifts
Probing Evolution of Long GRB Properties through their Cosmic Formation History Aided by Machine Learning–predicted Redshifts Open
Gamma-ray bursts (GRBs) are valuable probes of cosmic star formation reaching back into the epoch of reionization, and a large dataset with known redshifts ( z ) is an important ingredient for these studies. Usually, z is measured using sp…
View article: Unveiling the nature of the Einstein Probe transient EP 241021a
Unveiling the nature of the Einstein Probe transient EP 241021a Open
We present a multi-wavelength analysis of the fast X-ray transient EP 241021a, discovered by the Wide-field X-ray Telescope aboard the Einstein Probe satellite on 2024 October 21. The event was not detected in gamma-rays. Follow-up observa…
View article: The Radio Flare and Multiwavelength Afterglow of the Short GRB 231117A: Energy Injection from a Violent Shell Collision
The Radio Flare and Multiwavelength Afterglow of the Short GRB 231117A: Energy Injection from a Violent Shell Collision Open
We present the early radio detection and multiwavelength modeling of the short gamma-ray burst (GRB) 231117A at redshift z = 0.257. The Australia Telescope Compact Array automatically triggered a 9 hr observation of GRB 231117A at 5.5 and …
View article: A Multiwavelength View of the Multimessenger Sources NGC 1068 and PKS 1502+106
A Multiwavelength View of the Multimessenger Sources NGC 1068 and PKS 1502+106 Open
Multimessenger astronomy offers a powerful approach to studying high-energy radiative processes in astrophysical sources. A notable example was seen in 2017, when the IceCube Neutrino Observatory detected a high-energy neutrino event that …
View article: The Gamma-Ray Emission from Radio Galaxies and Their Contribution to the Isotropic Gamma-Ray Background
The Gamma-Ray Emission from Radio Galaxies and Their Contribution to the Isotropic Gamma-Ray Background Open
We evaluate the contribution to the isotropic gamma-ray background (IGRB) coming from radio galaxies (RGs), the subclass of radio-loud active galactic nuclei with the highest misalignment from the line of sight. Since only a small number o…
View article: Probing evolution of Long GRB properties through their cosmic formation history aided by Machine Learning predicted redshifts
Probing evolution of Long GRB properties through their cosmic formation history aided by Machine Learning predicted redshifts Open
Gamma-ray Bursts (GRBs) are valuable probes of cosmic star formation reaching back into the epoch of reionization, and a large dataset with known redshifts ($z$) is an important ingredient for these studies. Usually, $z$ is measured using …
View article: The gamma-ray emission from Radio Galaxies and their contribution to the Isotropic Gamma-Ray Background
The gamma-ray emission from Radio Galaxies and their contribution to the Isotropic Gamma-Ray Background Open
We evaluate the contribution to the Isotropic Gamma-Ray Background (IGRB) coming from Radio Galaxies (RGs), the subclass of radio-loud Active Galactic Nuclei (AGN) with the highest misalignment from the line of sight (l.o.s.). Since only a…
View article: Discovery and analysis of afterglows from poorly localized GRBs with the Gravitational-wave Optical Transient Observer (GOTO) All-sky Survey
Discovery and analysis of afterglows from poorly localized GRBs with the Gravitational-wave Optical Transient Observer (GOTO) All-sky Survey Open
Gamma-ray bursts (GRBs), particularly those detected by wide-field instruments such as the Fermi/GBM, pose challenges for optical follow-up because of their large initial localization regions, leaving many GRBs without identified afterglow…
View article: GRB 241105A: a test case for GRB classification and rapid <i>r</i> -process nucleosynthesis channels
GRB 241105A: a test case for GRB classification and rapid <i>r</i> -process nucleosynthesis channels Open
Gamma-ray bursts (GRBs) offer a powerful window to probe the progenitor systems responsible for the formation of heavy elements through the rapid neutron capture (r-) process, thanks to their exceptional luminosity, which allows them to be…
View article: Discovery and Analysis of Afterglows from Poorly Localised GRBs with the Gravitational-wave Optical Transient Observer (GOTO) All-sky Survey
Discovery and Analysis of Afterglows from Poorly Localised GRBs with the Gravitational-wave Optical Transient Observer (GOTO) All-sky Survey Open
Gamma-ray bursts (GRBs), particularly those detected by wide-field instruments such as the Fermi/GBM, pose a challenge for optical follow-up due to their large initial localisation regions, leaving many GRBs without identified afterglows. …
View article: The Day-long, Repeating GRB 250702B: A Unique Extragalactic Transient
The Day-long, Repeating GRB 250702B: A Unique Extragalactic Transient Open
γ -ray bursts (GRBs) are singular outbursts of high-energy radiation with durations typically lasting from milliseconds to minutes and, in extreme cases, a few hours. They are attributed to the catastrophic outcomes of stellar-scale events…
View article: Probing Evolution of Long Gamma-Ray Burst Properties through Their Cosmic Formation History
Probing Evolution of Long Gamma-Ray Burst Properties through Their Cosmic Formation History Open
The astrophysics of long gamma-ray burst (LGRB) progenitors as well as possible cosmological evolution in their properties still poses many open questions. Previous studies suggest that the LGRB rate density (LGRB-RD) follows the cosmic st…
View article: SVOM GRB 250314A at z $\simeq$ 7.3: an exploding star in the era of reionization
SVOM GRB 250314A at z $\simeq$ 7.3: an exploding star in the era of reionization Open
Most long Gamma-ray bursts originate from a rare type of massive stellar explosion. Their afterglows, while rapidly fading, can be initially extremely luminous at optical/near-infrared wavelengths, making them detectable at large cosmologi…
View article: JWST reveals a supernova following a gamma-ray burst at z $\simeq$ 7.3
JWST reveals a supernova following a gamma-ray burst at z $\simeq$ 7.3 Open
The majority of energetic long-duration gamma-ray bursts (GRBs) are thought to arise from the collapse of massive stars, making them powerful tracers of star formation across cosmic time. Evidence for this origin comes from the presence of…
View article: The day-long, repeating GRB 250702BDE / EP250702a: A unique extragalactic transient
The day-long, repeating GRB 250702BDE / EP250702a: A unique extragalactic transient Open
Gamma-ray bursts (GRBs) are singular outbursts of high-energy radiation with durations typically lasting from milliseconds to minutes and, in extreme cases, a few hours. They are attributed to the catastrophic outcomes of stellar-scale eve…
View article: EP240801a/XRF 240801B: An X-Ray Flash Detected by the Einstein Probe and the Implications of Its Multiband Afterglow
EP240801a/XRF 240801B: An X-Ray Flash Detected by the Einstein Probe and the Implications of Its Multiband Afterglow Open
We present multiband observations and analysis of EP240801a, a low-energy, extremely soft gamma-ray burst (GRB) discovered on 2024 August 1 by the Einstein Probe (EP) satellite with a weak contemporaneous signal also detected by the Fermi …
View article: EP 250108a/SN 2025kg: Observations of the Most Nearby Broad-line Type Ic Supernova Following an Einstein Probe Fast X-Ray Transient
EP 250108a/SN 2025kg: Observations of the Most Nearby Broad-line Type Ic Supernova Following an Einstein Probe Fast X-Ray Transient Open
With a small sample of fast X-ray transients (FXTs) with multiwavelength counterparts discovered to date, their progenitors and connections to γ -ray bursts (GRBs) and supernovae (SNe) remain ambiguous. Here, we present photometric and spe…
View article: The Kangaroo’s First Hop: The Early Fast Cooling Phase of EP250108a/SN 2025kg
The Kangaroo’s First Hop: The Early Fast Cooling Phase of EP250108a/SN 2025kg Open
Fast X-ray transients are a rare and poorly understood population of events. Previously difficult to detect in real time, the launch of the Einstein Probe with its Wide-field X-ray Telescope has led to a rapid expansionof the sample and al…
View article: First joint absorption and <i>Te</i>-based metallicity measured in a GRB host galaxy at <i>z</i> = 4.28 using <i>JWST</i>/NIRSpec
First joint absorption and <i>Te</i>-based metallicity measured in a GRB host galaxy at <i>z</i> = 4.28 using <i>JWST</i>/NIRSpec Open
We present the first gamma-ray burst (GRB) host galaxy with a measured absorption line and electron temperature (T$_e$) based metallicity, using the temperature sensitive [O iii]$\lambda$4363 auroral line detected in the JWST/NIRSpec spect…
View article: Multi-Model Framework for Reconstructing Gamma-Ray Burst Light Curves
Multi-Model Framework for Reconstructing Gamma-Ray Burst Light Curves Open
Mitigating data gaps in Gamma-ray bursts (GRBs) light curves (LCs) is crucial for cosmological research, enhancing the precision of parameters, assuming perfect satellite conditions for complete LC coverage with no gaps. This analysis impr…
View article: A large, chemically enriched, neutral gas reservoir in a galaxy at z = 6.782
A large, chemically enriched, neutral gas reservoir in a galaxy at z = 6.782 Open
The chemical characterization of galaxies in the first billion years after the Big Bang is one of the central goals of current astrophysics. Optical/near-infrared spectroscopy of long gamma-ray bursts (GRBs) have been heralded as an effect…
View article: Revisiting the Intergalactic Medium around GRB 130606A and Constraints on the Epoch of Reionization
Revisiting the Intergalactic Medium around GRB 130606A and Constraints on the Epoch of Reionization Open
Gamma-ray bursts (GRBs) are excellent probes of the high-redshift Universe due to their high luminosities and the relatively simple intrinsic spectra of their afterglows. They can be used to estimate the fraction of neutral hydrogen (i.e.,…
View article: Enhancing Compton telescope imaging with maximum a posteriori estimation
Enhancing Compton telescope imaging with maximum a posteriori estimation Open
We present a modified Richardson-Lucy (RL) algorithm tailored for image reconstruction in MeV gamma-ray observations, focusing on its application to the upcoming Compton Spectrometer and Imager (COSI) mission. Our method addresses key chal…
View article: Enhancing Compton telescope imaging with maximum a posteriori estimation: a modified Richardson-Lucy algorithm for the Compton Spectrometer and Imager
Enhancing Compton telescope imaging with maximum a posteriori estimation: a modified Richardson-Lucy algorithm for the Compton Spectrometer and Imager Open
We present a modified Richardson-Lucy (RL) algorithm tailored for image reconstruction in MeV gamma-ray observations, focusing on its application to the upcoming Compton Spectrometer and Imager (COSI) mission. Our method addresses key chal…
View article: The brightest GRB ever detected: GRB 221009A as a highly luminous event at <i>z</i> = 0.151
The brightest GRB ever detected: GRB 221009A as a highly luminous event at <i>z</i> = 0.151 Open
Context. The extreme luminosity of gamma-ray bursts (GRBs) makes them powerful beacons, thus effective probes of the distant Universe. The most luminous bursts are typically detected at moderate and high redshift, where the volume for seei…
View article: Panning for gold with the <i>Neil Gehrels Swift Observatory</i>: an optimal strategy for finding the counterparts to gravitational wave events
Panning for gold with the <i>Neil Gehrels Swift Observatory</i>: an optimal strategy for finding the counterparts to gravitational wave events Open
The LIGO, Virgo, and KAGRA (LVK) gravitational wave observatories are currently undertaking their O4 observing run offering the opportunity to discover new electromagnetic counterparts to gravitational wave events. We examine the capabilit…
View article: Neutral fraction of hydrogen in the intergalactic medium surrounding high-redshift gamma-ray burst 210905A
Neutral fraction of hydrogen in the intergalactic medium surrounding high-redshift gamma-ray burst 210905A Open
The Epoch of Reionization (EoR) is a key period of cosmological history in which the intergalactic medium (IGM) underwent a major phase change from being neutral to almost completely ionized. Gamma-ray bursts (GRBs) are luminous and unique…
View article: Discovering High-$z$ BL Lacs Using Swift/UVOT and SARA Observations with the Dropout Technique
Discovering High-$z$ BL Lacs Using Swift/UVOT and SARA Observations with the Dropout Technique Open
Measuring spectroscopic redshifts for BL Lacertae (BL Lac) objects, a class of blazar, is challenging because their optical spectrum lacks, or has weak, emission lines ( equivalent width $\leqslant5Å$). In this situation, alternative techn…
View article: Characterizing the γ-Ray Emission from FR0 Radio Galaxies
Characterizing the γ-Ray Emission from FR0 Radio Galaxies Open
FR0 galaxies constitute the most abundant jet population in the local Universe. With their compact jet structure, they are broadband photon emitters and have been proposed as multimessenger sources. Recently, these sources have been detect…
View article: Varying linear polarisation in the dust-free gamma-ray burst 210610B
Varying linear polarisation in the dust-free gamma-ray burst 210610B Open
Context. Long gamma-ray bursts (GRBs) are produced by the collapse of some very massive stars, that emit ultra-relativistic jets. When the jets collide with the interstellar medium they decelerate and generate the so-called afterglow emiss…