arXiv subjects

M. Bulla

Publications and source records attributed to M. Bulla.

At least 19 recordsLinked to original sources

arXiv2026

Kilonova and progenitor properties of merger-driven gamma-ray bursts

Gamma-Ray Burst (GRB) prompt and afterglow emission, as well as a kilonova (KN), are the expected electromagnetic (EM) counterparts of Binary Neutron Star (BNS) and Neutron Star -- Black Hole (NSBH) mergers. We aim to infer the KN ejecta parameters and the progenitor properties by modeling merger-driven GRBs with a claim of KN, good data and robust redshift measurement. We model the afterglow and KN, and perform a Bayesian analysis, within the Nuclear physics and Multi-Messenger Astrophysics (NMMA) framework. The KN emission is modeled with the radiative transfer code POSSIS and for afterglow we use the afterglowpy library. In contrast to previous approaches, our methodology simultaneously models both afterglow and KN. We find that all GRBs in our sample have a KN, but we were unable to confirm or exclude its presence in GRB 150101B. A BNS progenitor is favored for GRB 160821B, GRB 170817A/AT2017gfo, GRB 211211A, and GRB 230307A. For GRB 150101B and GRB 191019A, we obtain a slight preference for NSBH scenario, while a BNS is also viable. For KN emission, we find that the median wind mass $\langle M_{\rm wind}\rangle=0.027^{+0.046}_{-0.019}$ $M_{\odot}$ is larger than the dynamical $\langle M_{\rm dyn}\rangle = 0.012^{+0.007}_{-0.006}$ $M_{\odot}$. We find that $M_{\rm wind}$ and the beaming corrected kinetic energy of the jet can be attributed as $log(M_{\rm wind})=-20.23+0.38\,log(E_{0,J})$. We confirm the results of numerical simulation that $\tildeΛ$ increases with decrease in $\mathcal{M}_{\rm \,Chirp}$. Our work shows that EM modeling can be effective for probing the progenitors, and for the first time presents the progenitor properties of a sizable sample of merger-driven GRBs.

astro-ph.HE↗

arXiv2026

A new $H_0$ measurement with SNe Requiem and Encore using $\texttt{Gravity.jl}$

We present a strong-lensing (SL) analysis of the galaxy cluster MACS J0138.0-2155 (z=0.336), the first known lens cluster discovered to host two distinct multiply imaged Type Ia supernovae (SNe): SN Requiem and SN Encore. Both SNe are located in the massive, multiply imaged red galaxy MRG-M0138 at z=1.949. The projected total mass of this cluster has been investigated with several independent lens models (Suyu+26; Pierel+26), using a sample of 23 spectroscopically confirmed multiple images from 8 background sources (0.767 10%). The forthcoming reappearance of SN Requiem offers an immediate opportunity to significantly improve constraints on H0, provided that lens-model systematics are controlled. These results establish M0138 as a premier anchor for high-precision cluster-scale TDC.

astro-ph.CO↗

arXiv2026

Nested, asymmetric H-He circumstellar shells in the Type Icn/Ibn SN 2024abvb

Interacting transients probe mass loss in the final stages of stellar evolution; however, the geometry and timing of multi-episode mass loss remain poorly constrained. SN 2024abvb is a nearby interacting event with transitional Ibn/Icn spectroscopic properties and multi-epoch polarimetry, offering a rare opportunity to study structured circumstellar material (CSM). We aim to characterise the kinematics, composition and geometry of the CSM around SN 2024abvb and to identify plausible progenitor/ejection scenarios that can produce the observed spectro-polarimetric evolution. We present high-resolution (VLT/UVES and VLT/X-Shooter) optical/NIR spectroscopy across several epochs, complemented by broadband polarimetry and spectropolarimetry (VLT/FORS2 and NOT/ALFOSC). Line identifications, velocity decompositions and polarimetric time-series are used to trace multiple kinematic components and changes in scattering geometry. The high-resolution spectra reveal multiple narrow CSM components composed of He, C and O with absorption minima at $\sim150 - 400$ km s$^{-1}$ and additional faster material up to $\sim2000$ \kms. Low-velocity Balmer absorptions are present, indicating distant H-rich material, a first in SNe Ibn/Icn. Polarimetry shows a marked evolution ($P\sim1\%$ near peak, $\lesssim0.5\%$ after $\sim1$ week, rising to $\sim1.5\%$ at $\sim20$ d with $\sim50^\circ$ position-angle rotation and to $\sim4\%$ at $\sim30$ d, stronger in the blue), implying a time-variable, wavelength-dependent scattering/obscuration component. The combination of kinematics and polarimetric behaviour is consistent with multiple, concentric toroidal shells with differing orientations and partial dust content.

astro-ph.SR↗

arXiv2026

The hidden population of long gamma-ray bursts from compact object mergers

Context. The prompt-emission time profiles of GRB 230307A and other long-duration compact object merger (COM) candidates exhibit a unique set of temporal properties, characterised by a deterministic evolution of waiting times and pulse widths. Aims. We searched the Fermi/GBM catalogue for other unidentified long COM candidates exhibiting temporal properties similar to those observed in GRB 230307A. Methods. We examined the temporal and spectral prompt-emission properties of GRBs featuring at least eight light-curve peaks. For candidates, all with unknown redshifts, that exhibited properties similar to GRB 230307A, we analysed their trajectories in the Ep,i-Eiso plane as a function of redshift. We then evaluated the joint likelihood of their compatibility with the Ep,i-Eiso relation satisfied by the bulk of long GRBs. Furthermore, we calculated their minimum variability timescales (MVTs) for comparison against known COM and collapsar populations. Results. We identified 9 COM candidates with unknown redshifts and demonstrated that there are at least two outliers of the Ep,i-Eiso relation with 3.1 sigma (Gaussian) confidence level. Furthermore, their MVTs are more consistent with those of COM than with collapsar GRBs. Conclusions. These results indicate that this specific set of temporal properties can serve as a diagnostic tool to distinguish long-duration COMs from the broader collapsar population. Furthermore, our findings suggest that the fraction of unidentified COMs among long GRBs may be larger than previously assumed.

astro-ph.HE↗

arXiv2025

Revisiting the unification of tidal disruption events with polarimetry

Tidal disruptions of stars by supermassive black holes produce multi-wavelength emission, of which the optical emission is of ambiguous origin. A unification scenario of tidal disruption events (TDEs) has been proposed to explain the different classes of X-ray and optically selected events by introducing a dependence on the viewing angle and geometry. This work aims to test the unification scenario among optically bright TDEs using polarimetry. By studying the optical linear polarisation of 19 TDEs (of which 9 newly analysed in this work), we place constraints on their photosphere geometry, inclination, and the emission process responsible for the optical radiation. We study how these properties correlate with the relative X-ray brightness. We find that 14/16 non-relativistic events can be accommodated by the unification model. Continuum polarisation levels of optical TDEs lie most often in the range P ~ 1-2% (13 events), and for all except one event, remain below 6%. For those optical TDEs that have multi-epoch polarimetry, the continuum polarisation decreases after peak light for 5/10 events, increases for 3/10 events, and stays nearly constant for 2/10 events. When observed after +70 days (7/16 events), they become consistent with P = 0% within uncertainties (5/7 events). This implies the photosphere geometries of TDEs are at least initially asymmetric and evolve rapidly which, if tracing the formation of the accretion disk, suggests efficient circularisation. The polarisation signatures of emission lines of 7 TDEs directly support a scenario in which optical light is reprocessed in an electron-scattering photosphere. [...] However, a subset of events deviates from the unification model to some extent, suggesting this model may not fully capture the diverse behaviour of TDEs. Multi-epoch polarimetry plays a key role in understanding the evolution and emission mechanisms of TDEs.

astro-ph.HE↗

arXiv2025

GRB X-ray plateaus as evidence that the afterglow begins before the prompt gamma-ray emission

Most GRB X-ray afterglow light curves are characterised by a plateau, followed by a normal power-law decay interpreted as afterglow emission. Despite the numerous alternative interpretations, the origin of the plateau remains unclear. In the early years of Swift, it was suggested that the plateau might be afterglow radiation, that started before the prompt gamma-ray emission, and its time profile would be an artefact of assuming the start time of the prompt gamma-ray emission as zero time (the so-called "prior activity model"). We aim to test this scenario by leveraging the current Swift sample of early X-ray afterglows of GRBs with measured redshifts. We modelled the GRB rest-frame X-ray afterglow luminosities assuming a simple power-law with the true reference time preceding the prompt gamma-ray emission trigger time by T_0 and the X-ray luminosity L_0 at the trigger time as free parameters. For 90% GRBs of our sample, the model provided a successful description. In 10 cases the afterglow peak is identified and modelled appropriately. Using the 300 GRBs with accurate parameters' estimates, we confirm the anti-correlation between L_0 and T_0 with 0.7 dex scatter. In addition, selecting the subsample of 180 from the literature with reliable estimates of isotropic-equivalent energy E_gamma,iso, peak luminosity L_gamma,iso, and intrinsic peak energy E_p,i of the nuFnu spectrum of the prompt gamma-ray emission, we find a correlation between L_0, T_0, and E_gamma,iso (0.4 dex scatter) over nine decades in L_0 and common to all kinds of GRBs. The afterglow likely begins in most cases before the start of the detected prompt gamma-ray emission. As also suggested by the recent discoveries of Einstein Probe of X-ray emission starting long before the prompt gamma-rays, our results suggest that the occurrence of prior activity could be much more frequent than what has tacitly been assumed so far.

astro-ph.HE↗

arXiv2025

A set of distinctive properties ruling the prompt emission of GRB 230307A and other long γ-ray bursts from compact object mergers

Short gamma-ray bursts (SGRBs), occasionally followed by a long and spectrally soft extended emission, are associated with compact object mergers (COMs). Yet, a few recent long GRBs (LGRBs) show compelling evidence for a COM origin, in contrast with the massive-star core-collapse origin of most LGRBs. While possible COM indicators were found, such as the minimum variability timescale (MVT), a detailed and unique characterisation of their gamma-ray prompt emission that may help identify and explain their deceptively long profile is yet to be found. Here we report the discovery of a set of distinctive properties that rule the temporal and spectral evolution of GRB 230307A, a LGRB with evidence for a COM origin. Specifically, the sequence of pulses that make up its profile is characterised by an exponential evolution of (i) flux intensities, (ii) waiting times between adjacent pulses, (iii) pulse durations, and (iv) spectral peak energy. Analogous patterns are observed in the prompt emission of other long COM candidates. The observed evolution of gamma-ray pulses would imply that a relativistic jet is colliding with more slowly expanding material. This contrasts with the standard internal shock model for typical LGRBs, in which dissipation occurs at random locations within the jet itself. We tentatively propose a few simple toy models that may explain these properties and are able to reproduce the overall time profile.

astro-ph.HE↗

arXiv2025

GRB minimum variability timescales with Fermi/GBM

Context. Gamma-ray bursts (GRBs) have traditionally been classified by duration into long (LGRBs) and short (SGRBs), with the former believed to originate from massive star collapses and the latter from compact binary mergers. However, events such as the SGRB 200826A (coming from a collapsar) and the LGRBs 211211A and 230307A (associated with a merger) suggest that duration-based classification could be sometimes misleading. Recently, the minimum variability timescale (MVT) has emerged as a key metric for classifying GRBs. Aims. We calculate the MVT, defined as the full width at half maximum (FWHM) of the narrowest pulse in the light curve, using an independent dataset from Fermi/GBM and we compare our results with other MVT definitions. We update the MVT-T90 plane and analyse peculiar events like long-duration merger candidates 211211A, 230307A, and other short GRBs with extended emission (SEE-GRBs). We also examine extragalactic magnetar giant flares (MGFs) and explore possible new correlations with peak energy. Methods. We used the MEPSA algorithm to identify the shortest pulse in each GRB light curve and measure its FWHM. We calculated the MVT for around 3700 GRBs, 177 of which with spectroscopically known redshift. Results. SEE-GRBs and SGRBs share similar MVTs (from few tens to a few hundreds of ms), indicating a common progenitor, while extragalactic MGFs exhibit even shorter values (from few ms to few tens of ms). Our MVT estimation method consistently yields higher values than another existing technique, the latter aligning with the pulse rise time. For LGRBs, we confirmed the correlations of MVT with peak luminosity and Lorentz factor. Conclusions. We confirmed that, although MVT alone cannot determine the GRB progenitor, it is a valuable tool when combined with other indicators, helping to flag long-duration mergers and distinguish MGFs from typical SGRBs.

astro-ph.HE↗

arXiv2025

A search for periodic activity in multi-peaked long gamma-ray bursts

A sizeable fraction of gamma-ray burst (GRB) light curves (LCs) features a sequence of peaks, which holds information on the unknown way energy is dissipated into gamma-rays over time. Traditional searches for periodic signals in GRB LCs turned out to be inconclusive, partly because they are challenging as a consequence of the short-lived, coloured-noise, and non-stationary nature of the LCs themselves. Yet, recent claims have revived the issue. We searched for periodic components in GRB LCs through a new approach to GRBs, that avoids most of the issues faced by traditional techniques. We identified peaks through a well tested algorithm and selected GRBs with at least 10 peaks out of 5 GRB catalogues (Swift/BAT, CGRO/BATSE, Fermi/GBM, Insight-HXMT, BeppoSAX/GRBM). Each GRB was simply treated as a discrete point process, whose realisation coincides with the sequence of peak times. We searched for possible periodic recurrences based on the multinomial distribution, after accounting for the clustering of peaks due to the non-stationarity of the GRB signals. The best candidate has a p-value of 3e-4 that there is no periodic recurrence. However, accounting for the multiple trials of 555 searched GRBs, its statistical significance is demoted to 17%. The overall distribution of the p-values obtained for all GRBs is compatible with a uniform distribution in [0,1]. We found no robust evidence for multi-peaked GRBs with periodic recurrences. We can exclude that a sizeable fraction (>~ 0.75) of peaks of each GRB with at least 10 peaks are periodic. While our result does not necessarily clash with claimed periodicities based on Fourier techniques, it constrains the putative recurrent behaviour, which would not manifest itself through the sequence of peaks, but, evidently, in a more elusive way.

astro-ph.HE↗

arXiv2025

Limits on the Ejecta Mass During the Search for Kilonovae Associated with Neutron Star-Black Hole Mergers: A case study of S230518h, GW230529, S230627c and the Low-Significance Candidate S240422ed

Neutron star-black hole (NSBH) mergers, detectable via their gravitational-wave (GW) emission, are expected to produce kilonovae (KNe). Four NSBH candidates have been identified and followed-up by more than fifty instruments since the start of the fourth GW Observing Run (O4), in May 2023, up to July 2024; however, no confirmed associated KN has been detected. This study evaluates ejecta properties from multi-messenger observations to understand the absence of detectable KN: we use GW public information and joint observations taken from 05.2023 to 07.2024 (LVK, ATLAS, DECam, GECKO, GOTO, GRANDMA, SAGUARO, TESS, WINTER, ZTF). First, our analysis on follow-up observation strategies shows that, on average, more than 50% of the simulated KNe associated with NSBH mergers reach their peak luminosity around one day after merger in the $g,r,i$- bands, which is not necessarily covered for each NSBH GW candidate. We also analyze the trade-off between observation efficiency and the intrinsic properties of the KN emission, to understand the impact on how these constraints affect our ability to detect the KN, and underlying ejecta properties for each GW candidate. In particular, we can only confirm the kilonova was not missed for 1% of the GW230529 and S230627c sky localization region, given the large sky localization error of GW230529 and the large distance for S230627c and, their respective KN faint luminosities. More constraining, for S230518h, we infer the dynamical ejecta and post-merger disk wind ejecta $m_{dyn}, m_{wind}$ $<$ $0.03$ $M_\odot$ and the viewing angle $θ>25^\circ$. Similarly, the non-astrophysical origin of S240422ed is likely further confirmed by the fact that we would have detected even a faint KN at the time and presumed distance of the S240422ed event candidate, within a minimum 45% credible region of the sky area, that can be larger depending on the KN scenario.

astro-ph.HE↗

arXiv2025

The puzzling long GRB 191019A: Evidence for Kilonova Light

GRB 191019A was a long Gamma-ray burst (GRB) lasting about 65 s and, as such, originally thought to be linked to a core-collapse supernova. However, even though follow-up observations identified the optical counterpart close to the bright nucleus of a nearby ancient galaxy (z=0.248), no associated supernova was found. This led to the suggestion that the burst was caused by the merger of two compact stellar objects, likely in a dense circumnuclear environment. By using a recently developed diagnostic tool based on prompt emission temporal properties, we noticed that GRB 191019A falls among those long GRBs which are associated with compact mergers and with evidence of kilonova light. We thus re-analyzed unpublished GROND multi-color (g'r'i'z'JHK_s) data obtained between 0.4 and 15 days post trigger. Image subtraction confirmed the optical counterpart in all four optical bands, with GROND tracking its fading until 1.5 days post-burst. Incorporating publicly available Swift-XRT data, a joint fit of an afterglow plus a kilonova model revealed a better match than an afterglow-only scenario. The resulting kilonova properties resemble those of AT2017gfo associated with the binary neutron star merger GW170817, with a total ejected mass of about 0.06 solar mass. Contrary to previous findings inferring a high-density circumburst environment (n0=10^7-10^8 cm^-3), our analysis finds standard conditions (n0 = 1 cm^-3), suggesting the long duration of GRB 191019A was intrinsic rather than due to jet interaction with a dense external medium.

astro-ph.HE↗

arXiv2024

New results on the gamma-ray burst variability-luminosity relation

At the dawn of the gamma-ray burst (GRB) afterglow era, a Cepheid-like correlation was discovered between time variability V and isotropic-equivalent peak luminosity Liso of the prompt emission of about a dozen long GRBs with measured redshift available at that time. Soon afterwards, the correlation was confirmed against a sample of about 30 GRBs, despite being affected by significant scatter. Unlike the minimum variability timescale (MVT), V measures the relative power of short-to-intermediate timescales. We aim to test the correlation using about two hundred long GRBs with spectroscopically measured redshift, detected by Swift, Fermi, and Konus/WIND, for which both observables can be accurately estimated. For all the selected GRBs, variability was calculated according to the original definition using the 64-ms background-subtracted light curves of Swift/BAT (Fermi/GBM) in the 15-150 (8-900) keV energy passband. Peak luminosities were either taken from literature or derived from modelling broad-band spectra acquired with either Konus/WIND or Fermi/GBM. The statistical significance of the correlation has weakened to <~2%, mostly due to the appearance of a number of smooth and luminous GRBs characterised by a relatively small V. At odds with most long GRBs, 3 out of 4 long-duration merger candidates have high V and low Liso. Luminosity is more tightly connected with shortest timescales measured by MVT rather than short-to-intermediate ones, measured by V. We discuss the implications on internal dissipation models and the role of the e+- photosphere. We identified a few, smooth GRBs with a single broad pulse and low V, that might have an external shock origin, in contrast with most GRBs. The combination of high variability (V>~0.1), low luminosity (Liso<~10^51 erg s^-1) and short MVT (<~ 0.1 s) could be a good indicator for a compact binary merger origin.

astro-ph.HE↗

arXiv2024

Distribution of the number of peaks within a long gamma-ray burst: The full Fermi/GBM catalogue

Context. The dissipation process responsible for the long gamma-ray burst (GRB) prompt emission and the kind of dynamics that drives the release of energy as a function of time are still key open issues. We recently found that the distribution of the number of peaks per GRB is described by a mixture of two exponentials, suggesting the existence of two behaviours that turn up as peak-rich and peak-poor time profiles. Aims. Our aims are to study the distribution of the number of peaks per GRB of the entire catalogue of about 3000 GRBs observed by the Fermi Gamma-ray Burst Monitor (GBM) and to make a comparison with previous results obtained from other catalogues. Methods. We identified GRB peaks using the MEPSA code and modelled the resulting distribution following the same procedure that was adopted in the previous analogous investigation. Results. We confirm that only a mixture of two exponentials can model the distribution satisfactorily, with model parameters that fully agree with those found from previous analyses. In particular, we confirm that (21 +- 4)% of the observed GRBs are peak-rich (8 +- 1 peaks per GRB on average), while the remaining 80% are peak-poor (2.12 +- 0.10 peaks per GRB on average). Conclusions. We confirm the existence of two different components, peak-poor and peak-rich GRBs, that make up the observed GRB populations. Together with previous analogous results from other GRB catalogues, these results provide compelling evidence that GRB prompt emission is governed by two distinct regimes.

astro-ph.HE↗

arXiv2024

Evidence for bipolar explosions in Type IIP supernovae

Recent observations of core-collapse supernovae (SNe) suggest aspherical explosions. Globally aspherical structures in SN explosions are regarded as the key for understanding their explosion mechanism. However, the exact explosion geometries from the inner cores to the outer envelopes are poorly understood. Here, we present photometric, spectroscopic and polarimetric observations of the Type IIP SN 2021yja and discuss its explosion geometry, in comparison to those of other Type IIP SNe that show large-scale aspherical structures in their hydrogen envelopes (SNe 2012aw, 2013ej and 2017gmr). During the plateau phase, SNe 2012aw and 2021yja exhibit high continuum polarization characterized by two components with perpendicular polarization angles. This behavior can be interpreted to be due to a bipolar explosion, composed of a polar (energetic) and an equatorial (bulk) components of the SN ejecta. In such a bipolar explosion, an aspherical axis created by the polar ejecta would be dominating at early phases, while the perpendicular axis along the equatorial ejecta would emerge at late phases after the receding of the photosphere in the polar ejecta. The interpretation of the bipolar explosions in SNe 2012aw and 2021yja is also supported by other observational properties, including the time evolution of the line velocities and the line shapes in the nebular spectra. The polarization of other Type IIP SNe that show large-scale aspherical structures in the hydrogen envelope (SNe 2013ej and 2017gmr) is also consistent with the bipolar-explosion scenario, although this is not conclusive.

astro-ph.HE↗

arXiv2024

Distribution of number of peaks within a long gamma-ray burst

The variety of long duration gamma-ray burst (LGRB) light curves (LCs) encode a wealth of information on how LGRB engines release energy following the collapse of the progenitor star. Attempts to characterise GRB LCs focused on a number of properties, such as the minimum variability timescale, power density spectra (both ensemble average and individual), or with different definitions of variability. In parallel, a characterisation as a stochastic process was pursued by studying the distributions of waiting times, peak flux, fluence of individual peaks within GRB time profiles. Yet, the question remains as to whether the diversity of profiles can be described in terms of a common stochastic process. Here we address this issue by studying for the first time the distribution of the number of peaks in a GRB profile. We used four different GRB catalogues: CGRO/BATSE, Swift/BAT, BeppoSAX/GRBM, and Insight-HXMT. The statistically significant peaks were identified by means of well tested algorithm MEPSA and further selected by applying a set of thresholds on signal-to-noise ratio. We then extracted the corresponding distributions of number of peaks per GRB. Among the different models considered (power-law, simple or stretched exponential) only a mixture of two exponentials models all the observed distributions, suggesting the existence of two distinct behaviours: (i) an average number of 2.1+-0.1 peaks per GRB ("peak poor") and accounting for about 80% of the observed population of GRBs; (ii) an average number of 8.3+-1.0 peaks per GRB ("peak rich") and accounting for the remaining 20% of the observed population. We associate the class of peak-rich GRBs with the presence of sub-second variability, which seems to be absent among peak-poor GRBs. The two classes could result from two different regimes through which GRB engines release energy or through which energy is dissipated into gamma-rays.

astro-ph.HE↗

arXiv2024

Multi-band analyses of the bright GRB 230812B and the associated SN2023pel

GRB~230812B is a bright and relatively nearby ($z =0.36$) long gamma-ray burst (GRB) that has generated significant interest in the community and has thus been observed over the entire electromagnetic spectrum. We report over 80 observations in X-ray, ultraviolet, optical, infrared, and sub-millimeter bands from the GRANDMA (Global Rapid Advanced Network for Multi-messenger Addicts) network of observatories and from observational partners. Adding complementary data from the literature, we then derive essential physical parameters associated with the ejecta and external properties (i.e. the geometry and environment) of the GRB and compare with other analyses of this event. We spectroscopically confirm the presence of an associated supernova, SN2023pel, and we derive a photospheric expansion velocity of v $\sim$ 17$\times10^3$ km s$^{-1}$. We analyze the photometric data first using empirical fits of the flux and then with full Bayesian Inference. We again strongly establish the presence of a supernova in the data, with a maximum (pseudo-)bolometric luminosity of $5.75 \times 10^{42}$ erg/s, at $15.76^{+0.81}_{-1.21}$ days (in the observer frame) after the trigger, with a half-max time width of 22.0 days. We compare these values with those of SN1998bw, SN2006aj, and SN2013dx. Our best-fit model favours a very low density environment ($\log_{10}({n_{\rm ISM}/{\rm cm}^{-3}}) = -2.38^{+1.45}_{-1.60}$) and small values for the jet's core angle $θ_{\rm core} = 1.54^{+1.02}_{-0.81} \ \rm{deg}$ and viewing angle $θ_{\rm obs} = 0.76^{+1.29}_{-0.76} \ \rm{deg}$. GRB 230812B is thus one of the best observed afterglows with a distinctive supernova bump.

astro-ph.HE↗

arXiv2024

Distributions of energy, luminosity, duration, and waiting times of gamma-ray burst pulses with known redshift detected by Fermi/GBM

Discovered more than 50 years ago, gamma-ray burst (GRB) prompt emission remains the most puzzling aspect of GRB physics. Its complex and irregular nature should reveal how newborn GRB engines release their energy. In this respect, the possibility that GRB engines could operate as self-organized critical (SOC) systems has been put forward. Here, we present the energy, luminosity, waiting time, and duration distributions of individual pulses of GRBs with known redshift detected by the Fermi Gamma-ray Burst Monitor (GBM). This is the first study of this kind in which selection effects are accounted for. The compatibility of our results with the framework of SOC theory is discussed. We found evidence for an intrinsic break in the power-law models that describe the energy and the luminosity distributions.

astro-ph.HE↗

arXiv2024

Science with a small two-band UV-photometry mission I: Mission description and follow-up observations of stellar transients

This is the first in a collection of three papers introducing the science with an ultra-violet (UV) space telescope on an approximately 130~kg small satellite with a moderately fast re-pointing capability and a real-time alert communication system approved for a Czech national space mission. The mission, called Quick Ultra-Violet Kilonova surveyor - QUVIK, will provide key follow-up capabilities to increase the discovery potential of gravitational wave observatories and future wide-field multi-wavelength surveys. The primary objective of the mission is the measurement of the UV brightness evolution of kilonovae, resulting from mergers of neutron stars, to distinguish between different explosion scenarios. The mission, which is designed to be complementary to the Ultraviolet Transient Astronomy Satellite - ULTRASAT, will also provide unique follow-up capabilities for other transients both in the near- and far-UV bands. Between the observations of transients, the satellite will target other objects described in this collection of papers, which demonstrates that a small and relatively affordable dedicated UV-space telescope can be transformative for many fields of astrophysics.

astro-ph.HE↗