arXiv subjects

Péter Veres

Publications and source records attributed to Péter Veres.

At least 19 recordsLinked to original sources

arXiv2026

Predictions for Short Gamma-Ray Burst Detections by COSI

The Compton Spectrometer and Imager (COSI) is a soft gamma-ray telescope scheduled to launch in 2027. COSI will trigger onboard the spacecraft in response to short-duration transients, including gamma-ray bursts, and it will promptly disseminate alerts which include localizations to the community. This will enable rapid follow-up observations of the afterglow and associations with transients identified by other instruments. By simulating COSI observations of short gamma-ray bursts (sGRBs) and processing them with the trigger algorithm which will run onboard the spacecraft, we estimate the sensitivity of COSI to sGRBs. We then convolve this with a simulated set of sGRBs representing the intrinsic population in the universe to predict the rate that will be detected by COSI. We find that COSI is expected to trigger on $\sim$47-89 sGRBs per year with $\sim$7-10 localized to within 2.5°. With the gravitational wave sensitivity anticipated in the O5 run, we predict 0-3 joint detections with gravitational waves.

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arXiv2025

GRB 250702B: Discovery of a Gamma-Ray Burst from a Black Hole Falling into a Star

Gamma-ray bursts are the most luminous electromagnetic events in the universe. Their prompt gamma-ray emission has typical durations between a fraction of a second and several minutes. A rare subset of these events have durations in excess of a thousand seconds, referred to as ultra-long gamma-ray bursts. Here, we report the discovery of the longest gamma-ray burst ever seen with a ~25,000 s gamma-ray duration, GRB 250702B, and characterize this event using data from four instruments in the InterPlanetary Network and the Monitor of All-sky X-ray Image. We find a hard spectrum, subsecond variability, and high total energy, which are only known to arise from ultrarelativistic jets powered by a rapidly-spinning stellar-mass central engine. These properties and the extreme duration are together incompatible with all confirmed gamma-ray burst progenitors and nearly all models in the literature. This burst is naturally explained with the helium merger model, where a field binary ends when a black hole falls into a stripped star and proceeds to consume and explode it from within. Under this paradigm, GRB 250702B adds to the growing evidence that helium stars expand and that some ultra-long GRBs have similar evolutionary pathways as collapsars, stellar-mass gravitational wave sources, and potentially rare types of supernovae.

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arXiv2024

A Radio Flare in the Long-Lived Afterglow of the Distant Short GRB 210726A: Energy Injection or a Reverse Shock from Shell Collisions?

We present the discovery of the radio afterglow of the short $γ$-ray burst (GRB) 210726A, localized to a galaxy at a photometric redshift of $z\sim 2.4$. While radio observations commenced $\lesssim 1~$day after the burst, no radio emission was detected until $\sim11~$days. The radio afterglow subsequently brightened by a factor of $\sim 3$ in the span of a week, followed by a rapid decay (a "radio flare"). We find that a forward shock afterglow model cannot self-consistently describe the multi-wavelength X-ray and radio data, and underpredicts the flux of the radio flare by a factor of $\approx 5$. We find that the addition of substantial energy injection, which increases the isotropic kinetic energy of the burst by a factor of $\approx 4$, or a reverse shock from a shell collision are viable solutions to match the broad-band behavior. At $z\sim 2.4$, GRB 210726A is among the highest redshift short GRBs discovered to date as well as the most luminous in radio and X-rays. Combining and comparing all previous radio afterglow observations of short GRBs, we find that the majority of published radio searches conclude by $\lesssim 10~$days after the burst, potentially missing these late rising, luminous radio afterglows.

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arXiv2024

Constraining possible $γ$-ray burst emission from GW230529 using Swift-BAT and Fermi-GBM

GW230529 is the first compact binary coalescence detected by the LIGO-Virgo-KAGRA collaboration with at least one component mass confidently in the lower mass-gap, corresponding to the range 3-5$M_{\odot}$. If interpreted as a neutron star-black hole merger, this event has the most symmetric mass ratio detected so far and therefore has a relatively high probability of producing electromagnetic (EM) emission. However, no EM counterpart has been reported. At the merger time $t_0$, Swift-BAT and Fermi-GBM together covered 100$\%$ of the sky. Performing a targeted search in a time window $[t_0-20 \text{s},t_0+20 \text{s}]$, we report no detection by the Swift-BAT and the Fermi-GBM instruments. Combining the position-dependent $γ-$ray flux upper limits and the gravitational-wave posterior distribution of luminosity distance, sky localization and inclination angle of the binary, we derive constraints on the characteristic luminosity and structure of the jet possibly launched during the merger. Assuming a top-hat jet structure, we exclude at 90$\%$ credibility the presence of a jet which has at the same time an on-axis isotropic luminosity $\gtrsim 10^{48}$ erg s$^{-1}$, in the bolometric band 1 keV-10 MeV, and a jet opening angle $\gtrsim 15$ deg. Similar constraints are derived testing other assumptions about the jet structure profile. Excluding GRB 170817A, the luminosity upper limits derived here are below the luminosity of any GRB observed so far.

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arXiv2023

The IXPE view of GRB 221009A

We present the IXPE observation of GRB 221009A which includes upper limits on the linear polarization degree of both prompt and afterglow emission in the soft X-ray energy band. GRB 221009A is an exceptionally bright gamma-ray burst (GRB) that reached Earth on 2022 October 9 after travelling through the dust of the Milky Way. The Imaging X-ray Polarimetry Explorer (IXPE) pointed at GRB 221009A on October 11 to observe, for the first time, the 2-8 keV X-ray polarization of a GRB afterglow. We set an upper limit to the polarization degree of the afterglow emission of 13.8% at a 99% confidence level. This result provides constraints on the jet opening angle and the viewing angle of the GRB, or alternatively, other properties of the emission region. Additionally, IXPE captured halo-rings of dust-scattered photons which are echoes of the GRB prompt emission. The 99% confidence level upper limit to the prompt polarization degree depends on the background model assumption and it ranges between ~55% to ~82%. This single IXPE pointing provides both the first assessment of X-ray polarization of a GRB afterglow and the first GRB study with polarization observations of both the prompt and afterglow phases.

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arXiv2022

The First Short GRB Millimeter Afterglow: The Wide-Angled Jet of the Extremely Energetic SGRB 211106A

We present the discovery of the first millimeter afterglow of a short-duration $γ$-ray burst (SGRB) and the first confirmed afterglow of an SGRB localized by the GUANO system on Swift. Our Atacama Large Millimeter/Sub-millimeter Array (ALMA) detection of SGRB 211106A establishes an origin in a faint host galaxy detected in Hubble Space Telescope (HST) imaging at $0.7\lesssim z\lesssim1.4$. From the lack of a detectable optical afterglow, coupled with the bright millimeter counterpart, we infer a high extinction, $A_{\rm V}\gtrsim2.6$ mag along the line of sight, making this the one of the most highly dust-extincted SGRBs known to date. The millimeter-band light curve captures the passage of the synchrotron peak from the afterglow forward shock and reveals a jet break at $t_{\rm jet}=29.2^{+4.5}_{-4.0}$~days. For a presumed redshift of $z=1$, we infer an opening angle, $θ_{\rm jet}=(15.5\pm1.4)$~degrees, and beaming-corrected kinetic energy of $\log(E_{\rm K}/{\rm erg})=51.8\pm0.3$, making this one of the widest and most energetic SGRB jets known to date. Combining all published millimeter-band upper limits in conjunction with the energetics for a large sample of SGRBs, we find that energetic outflows in high density environments are more likely to have detectable millimeter counterparts. Concerted afterglow searches with ALMA should yield detection fractions of 24-40% on timescales of $\gtrsim2$~days at rates $\approx0.8$-1.6 per year, outpacing the historical discovery rate of SGRB centimeter-band afterglows.

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arXiv2021

External Inverse-Compton Emission from Low-Luminosity Gamma-Ray Bursts: Application to GRB 190829A

The detection of TeV gamma-ray bursts (GRBs) brought new opportunities for studying the physics of particle acceleration at relativistic shocks. The \hess telescopes recently observed very-high-energy (VHE) emission from a nearby low-luminosity GRB, GRB 190829A. Follow-up observations with, e.g., Swift-XRT, revealed unusual flare activities at $\sim 10^3\rm~s$, which can be caused by a long-lasting central engine. We show that the VHE emission during the H.E.S.S. observation time is naturally produced in the external inverse-Compton (EIC) scenario, where seed photons supplied by the flares or other late-time dissipation are upscattered to VHE energies by the non-thermal electrons accelerated at the external forward shock. Our calculations show that the EIC flare nearly coincides with the late-prompt flare, but extends $\sim3-4$ times longer than the duration of the late-prompt flare. The preferred kinetic energy and initial Lorentz factor used in our model are $\sim 10^{52}\rm~erg$ and $\sim 20$, respectively. Understanding the mechanisms of the VHE emission from low-luminosity GRBs will help us constrain the properties of the outflow and the central engine activities, as well as the particle acceleration mechanism.

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arXiv2021

GRB 191016A: A Long Gamma-Ray Burst Detected by TESS

The TESS exoplanet-hunting mission detected the rising and decaying optical afterglow of GRB 191016A, a long Gamma-Ray Burst (GRB) detected by Swift-BAT but without prompt XRT or UVOT follow-up due to proximity to the moon. The afterglow has a late peak at least 1000 seconds after the BAT trigger, with a brightest-detected TESS datapoint at 2589.7 s post-trigger. The burst was not detected by Fermi-LAT, but was detected by Fermi-GBM without triggering, possibly due to the gradual nature of rising light curve. Using ground-based photometry, we estimate a photometric redshift of $z_\mathrm{phot} = 3.29\pm{0.40}$. Combined with the high-energy emission and optical peak time derived from TESS, estimates of the bulk Lorentz factor $Γ_\mathrm{BL}$ range from $90-133$. The burst is relatively bright, with a peak optical magnitude in ground-based follow-up of $R=15.1$ mag. Using published distributions of GRB afterglows and considering the TESS sensitivity and sampling, we estimate that TESS is likely to detect $\sim1$ GRB afterglow per year above its magnitude limit.

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arXiv2019

Reverse Shock Emission Revealed in Early Photometry in the Candidate Short GRB 180418A

We present observations of the possible short GRB 180418A in $γ$-rays, X-rays, and in the optical. Early optical photometry with the TAROT and RATIR instruments show a bright peak ($\approx$ 14.2 AB mag) between $T+28$ and $T+90$ seconds that we interpret as the signature of a reversal shock. Later observations can be modeled by a standard forward shock model and show no evidence of jet break, allowing us to constrain the jet collimation to $θ_j> 7^\circ$. Using deep late-time optical observations we place an upper limit of $r>24$ AB mag on any underlying host galaxy. The detection of the afterglow in the \textit{Swift} UV filters constrains the GRB redshift to $z<1.3$ and places an upper bound on the $γ$-ray isotropic equivalent energy $E_{\rm{γ,iso}} < 3 \times 10^{51}$ erg. The properties of this GRB (e.g. duration, hardness ratio, energetic, and environment) lie at the intersection between short and long bursts, and we can not conclusively identify its type. We estimate that the probability that it is drawn from the population of short GRBs is 10\%-30\%.

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arXiv2019

The rare extended radio-loud narrow-line Seyfert 1 galaxy SDSS J1030+5516 at high resolution

Recently, Rakshit et al. (2018) reported the discovery of SDSS J103024.95$+$551622.7, a radio-loud narrow-line Seyfert 1 galaxy having a $\sim 100$ kpc scale double-lobed radio structure. Here we analyse archival radio interferometric imaging data taken with the Very Large Array (VLA) at 5 GHz, and with the Very Long Baseline Array (VLBA) at 4.3 and 7.6 GHz. Two hotspots and a compact core are detected with the VLA at arcsec scale, while a single milliarcsec-scale compact radio core is seen with the highest resolution VLBA observations. The Fermi Large Area Telescope did not detect $γ$-ray emission at the position of this source. In the mid-infrared, the Wide-field Infrared Survey Explorer satellite light curve, covering more than 7 years and including the most recent data points, hints on flux density variability at 3.4 $μ$m. Our findings support the notion that this source is a young version of Fanaroff-Riley type II radio galaxies.

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arXiv2019

Multi-Messenger Astrophysics Opportunities with Stellar-Mass Binary Black Hole Mergers

The conventional view of stellar-mass binary black hole (sBBH) mergers is that there should not be enough matter present to produce a detectable electromagnetic transient. However, there ARE a number of mechanisms for producing such a counterpart through accretion of matter from various reserves, charged black holes, or interactions with magnetic or exotic fields. After reviewing these mechanisms, we describe what we can learn from multi-messenger observations of sBBH mergers in the areas of stellar evolution and compact binary formation, cosmological measurements, searches for charged black holes, and tests of general relativity and fundamental physics. We end with some remarks about the need to support both observing capabilities and modeling in the next decade and beyond.

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arXiv2016

High-Energy Non-Thermal and Thermal Emission from GRB141207A detected by Fermi

The bright long gamma-ray burst GRB 141207A was observed by the {\it Fermi Gamma-ray Space Telescope} and detected by both instruments onboard. The observations show that the spectrum in the prompt phase is not well described by the canonical empirical Band function alone, and that an additional power-law component is needed. In the early phase of the prompt emission, a modified blackbody with a hard low-energy photon index ($α$ = +0.2 -- +0.4) is detected, which suggests a photospheric origin. In a finely time-resolved analysis, the spectra are also well fitted by the modified blackbody combined with a power-law function. We discuss the physical parameters of the photosphere such as the bulk Lorentz factor of the relativistic flow and the radius. We also discuss the physical origin of the extra power-law component observed during the prompt phase in the context of different models such as leptonic and hadronic scenarios in the internal shock regime and synchrotron emission in the external forward shock. In the afterglow phase, the temporal and spectral behaviors of the temporally extended high-energy emission and the fading X-ray emission detected by XRT on-board {\it Swift} are consistent with synchrotron emission in a radiative external forward shock.

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arXiv2016

The Fermi GBM gamma-ray burst time-resolved spectral catalog: brightest bursts in the first four years

We aim to obtain high-quality time-resolved spectral fits of gamma-ray bursts (GRBs) observed by the Gamma-ray Burst Monitor (GBM) on board the Fermi Gamma-ray Space Telescope. We perform time-resolved spectral analysis with high temporal and spectral resolution of the brightest bursts observed by Fermi GBM in its first 4 years of mission. We present the complete catalog containing 1,491 spectra from 81 bursts with high spectral and temporal resolution. Distributions of parameters, statistics of the parameter populations, parameter-parameter and parameter-uncertainty correlations, and their exact values are obtained and presented as main results in this catalog. We report a criterion that is robust enough to automatically distinguish between different spectral evolutionary trends between bursts. We also search for plausible blackbody emission components and find that only 3 bursts (36 spectra in total) show evidence of a pure Planck function. It is observed that the averaged time-resolved low-energy power-law index and peak energy are slightly harder than the time-integrated values. Time-resolved spectroscopic results should be used when interpreting physics from the observed spectra, instead of the time-integrated results.

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arXiv2016

Modeling the early multiwavelength emission in GRB130427A

One of the most powerful gamma-ray bursts, GRB 130427A was swiftly detected from GeV $γ$-rays to optical wavelengths. In the GeV band, the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope observed the highest-energy photon ever recorded of 95 GeV, and a bright peak in the early phase followed by emission temporally extended for more than 20 hours. In the optical band, a bright flash with a magnitude of $7.03\pm 0.03$ in the time interval from 9.31 s to 19.31 s after the trigger was reported by RAPTOR in r-band. We study the origin of the GeV $γ$-ray emission, using the multiwavelength observation detected in X-ray and optical bands. The origin of the temporally extended LAT, X-ray and optical flux is naturally interpreted as synchrotron radiation and the 95-GeV photon and the integral flux upper limits placed by the HAWC observatory are consistent with synchrotron self-Compton from an adiabatic forward shock propagating into the stellar wind of its progenitor. The extreme LAT peak and the bright optical flash are explained through synchrotron self-Compton and synchrotron emission from the reverse shock, respectively, when the ejecta evolves in thick-shell regime and carries a significant magnetic field.

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arXiv2015

Early-time VLA observations and broad-band afterglow analysis of the Fermi-LAT detected GRB 130907A

We present multi-wavelength observations of the hyper-energetic gamma-ray burst (GRB) 130907A, a Swift-discovered burst with early radio observations starting at $\approx 4$ hr after the $γ$-ray trigger. GRB 130907A was also detected by the Fermi/LAT instrument and, at late times, showed a strong spectral evolution in X-rays. We focus on the early-time radio observations, especially at $>10 $ GHz, to attempt identifying reverse shock signatures. While our radio follow-up of GRB 130907A ranks among the earliest observations of a GRB with the Karl G. Jansky Very Large Array (VLA), we did not see an unambiguous signature of a reverse shock. While a model with both reverse and forward-shock can correctly describe the observations, the data is not constraining enough to decide upon the presence of the reverse-shock component. We model the broad-band data using a simple forward-shock synchrotron scenario with a transition from a wind environment to a constant density interstellar medium (ISM) in order to account for the observed features. Within the confines of this model, we also derive the underlying physical parameters of the fireball, which are within typical ranges except for the wind density parameter ($A_*$), which is higher than those for bursts with wind-ISM transition, but typical for the general population of bursts. We note the importance of early-time radio observations of the afterglow (and of well sampled light curves) to unambiguously identify the potential contribution of the reverse shock.

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arXiv2015

Hints of the jet composition in gamma-ray bursts from dissipative photosphere models

We present a model for gamma-ray bursts where a dissipative photosphere provides the usual spectral peak around MeV energies accompanied by a subdominant thermal component. We treat the initial acceleration of the jet in a general way, allowing for magnetic field- and baryon dominated outflows. In this model, the GeV emission associated with GRBs observed by Fermi LAT, arises as the interaction of photospheric radiation and the shocked electrons at the deceleration radius. Through recently discovered correlations between the thermal and non-thermal peaks within individual bursts, we are able to infer whether the jet was Poynting flux or baryon dominated.

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arXiv2013

Gamma-ray burst models with general dynamics and fits to Fermi LAT bursts

We present a dissipative photospheric model for gamma-ray bursts where the usual Band peak around MeV energies arises as synchrotron emission from around the photosphere. We treat the initial acceleration in a general way and the GeV emission arises as the interaction of photospheric radiation and the shocked electrons at the deceleration radius. We show some applications of this model.

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arXiv2012

Magnetically and Baryonically Dominated Photospheric Gamma-Ray Burst Model Fits to Fermi LAT Observations

We consider gamma-ray burst models where the radiation is dominated by a photospheric region providing the MeV Band spectrum, and an external shock region responsible for the GeV radiation via inverse Compton scattering. We parametrize the initial dynamics through an acceleration law Gamma \propto r^μ, with μbetween 1/3 and 1 to represent the range between an extreme magnetically dominated and a baryonically dominated regime. We compare these models to several bright Fermi LAT bursts, and show that both the time integrated and the time resolved spectra, where available, can be well described by these models. We discuss the parameters which result from these fits, and discuss the relative merits and shortcomings of the two models.

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