28 research outputs found
Constrains on the physics of the prompt emission from a distant and energetic gamma-ray burst GRB 220101A
No full textThe emission region of -ray bursts (GRBs) is poorly constrained.
The uncertainty on the size of the dissipation site spans over 4 orders of
magnitude ( cm) depending on the unknown energy
composition of the GRB jets. The joint multi-band analysis from soft X-rays to
high energies (up to 1 GeV) of one of the most energetic and distant
GRB 220101A (z = 4.618) allows us for an accurate distinction between prompt
and early afterglow emissions. The enormous amount of energy released by GRB
220101A ( erg) and the spectral cutoff at
MeV observed in the prompt emission spectrum
constrains the parameter space of GRB dissipation site. We put stringent
constraints on the prompt emission site, requiring and
cm. Our findings further highlights the
difficulty of finding a simple self consistent picture in the
electron-synchrotron scenario, favoring instead a proton-synchrotron model,
which is also consistent with the observed spectral shape. Deeper measurements
of the time variability of GRBs together with accurate high-energy observations
(MeV-GeV) would unveil the nature of the prompt emission.Comment: 16 pages, 7 figures. Accepted for ApJ publicatio
The short gamma-ray burst population in a quasi-universal jet scenario
No full textWe describe a model of the short gamma-ray burst (SGRB) population under a
`quasi-universal jet' scenario in which jets can differ in their on-axis peak
prompt emission luminosity , but share a universal angular luminosity
profile as a function of the viewing angle
. The model is fitted, through a Bayesian hierarchical approach
inspired by gravitational wave (GW) population analyses, to 3 observed SGRB
samples simultaneously: the Fermi/GBM sample of SGRBs with spectral information
in the catalogue (367 events); a flux-complete sample of 16 Swift/BAT SGRBs
also detected by GBM, with a measured redshift; and a sample of SGRBs with a
binary neutron star (BNS) merger counterpart, which only includes GRB~170817A
at present. The results favour a narrow jet core with half-opening angle
deg (90\% credible intervals from our fiducial
`full sample' analysis) whose on-axis peak luminosity is distributed as with above a minimum luminosity
erg s. For ,
the luminosity scales as a power law with
, with no evidence for a break. While the model
implies an intrinsic `Yonetoku' correlation between and the peak photon
energy , its slope is somewhat shallower than
the apparent one, and the normalization is offset towards larger , due to
selection effects. The implied local rate density of SGRBs is between about 100
up to several thousands of events per Gpc yr, in line with the BNS merger
rate density inferred from GW observations. Based on the model, we predict 0.2
to 1.3 joint GW+SGRB detections per year by the Advanced GW detector network
and Fermi/GBM during the O4 observing run.Comment: 30 pages, 23 figures, submitted to A&A. Comments are welcome
Gravitational lensing in gamma-ray bursts
No full textGravitationally lensed gamma-ray bursts (GRBs) offer critical advantages over other lensed sources. They can be detected via continuously operating detectors covering most of the sky. They offer extremely high time resolution to determine lensing delays and find short time delays accurately. They are detectable across most of the visible Universe. However, they are also rare and frequently poorly localized. In this article, we review searches for gravitational lensing in GRBs and comment on promising avenues for the future. We note that the highly structured jets in GRBs can show variations on sufficiently small scales that, unlike lensing of most transient sources, gravitational lensing in GRBs may not be achromatic. Such behaviour would weaken the stringent requirements for identifying lensed bursts but would also make robust identification of lensing more challenging. A continuously running search that could identify candidate lensed events in near real-time would enable afterglow searches with current and near-future wide-field optical/infrared surveys that could yield the first unambiguous detection of a lensed GRB. The new generation of sensitive X-ray and γ-ray detectors, such as the Einstein Probe and SVOM, will complement Swift and significantly enhance the number of well-localized γ-ray and X-ray transients. Tuned strategies could dramatically improve the probability of observing a lensed GRB. This article is part of the Theo Murphy meeting issue 'Multi-messenger gravitational lensing (Part 1)'.</p
The Radio to GeV Afterglow of GRB 221009A
No full textGRB 221009A ( z = 0.151) is one of the closest known long γ -ray bursts (GRBs). Its extreme brightness across all electromagnetic wavelengths provides an unprecedented opportunity to study a member of this still-mysterious class of transients in exquisite detail. We present multiwavelength observations of this extraordinary event, spanning 15 orders of magnitude in photon energy from radio to γ -rays. We find that the data can be partially explained by a forward shock (FS) from a highly collimated relativistic jet interacting with a low-density, wind-like medium. Under this model, the jet’s beaming-corrected kinetic energy ( E _K ∼ 4 × 10 ^50 erg) is typical for the GRB population. The radio and millimeter data provide strong limiting constraints on the FS model, but require the presence of an additional emission component. From equipartition arguments, we find that the radio emission is likely produced by a small amount of mass (≲6 × 10 ^−7 M _⊙ ) moving relativistically (Γ ≳ 9) with a large kinetic energy (≳10 ^49 erg). However, the temporal evolution of this component does not follow prescriptions for synchrotron radiation from a single power-law distribution of electrons (e.g., in a reverse shock or two-component jet), or a thermal-electron population, perhaps suggesting that one of the standard assumptions of afterglow theory is violated. GRB 221009A will likely remain detectable with radio telescopes for years to come, providing a valuable opportunity to track the full lifecycle of a powerful relativistic jet
Spectral index-flux relation for investigating the origins of steep decay in γ-ray bursts
No full textγ-ray bursts (GRBs) are short-lived transients releasing a large amount of energy (1051 − 1053 erg) in the keV-MeV energy range. GRBs are thought to originate from internal dissipation of the energy carried by ultra-relativistic jets launched by the remnant of a massive star's death or a compact binary coalescence. While thousands of GRBs have been observed over the last thirty years, we still have an incomplete understanding of where and how the radiation is generated in the jet. Here we show a relation between the spectral index and the flux found by investigating the X-ray tails of bright GRB pulses via time-resolved spectral analysis. This relation is incompatible with the long standing scenario which invokes the delayed arrival of photons from high-latitude parts of the jet. While the alternative scenarios cannot be firmly excluded, the adiabatic cooling of the emitting particles is the most plausible explanation for the discovered relation, suggesting a proton-synchrotron origin of the GRB emission
Gravitational lensing in gamma-ray bursts
No full textGravitationally lensed gamma-ray bursts (GRBs) offer critical advantages over other lensed sources. They can be detected via continuously operating detectors covering most of the sky. They offer extremely high time resolution to determine lensing delays and find short time delays accurately. They are detectable across most of the visible Universe. However, they are also rare and frequently poorly localized. In this article, we review searches for gravitational lensing in GRBs and comment on promising avenues for the future. We note that the highly structured jets in GRBs can show variations on sufficiently small scales that, unlike lensing of most transient sources, gravitational lensing in GRBs may not be achromatic. Such behaviour would weaken the stringent requirements for identifying lensed bursts but would also make robust identification of lensing more challenging. A continuously running search that could identify candidate lensed events in near real-time would enable afterglow searches with current and near-future wide-field optical/infrared surveys that could yield the first unambiguous detection of a lensed GRB. The new generation of sensitive X-ray and γ-ray detectors, such as the Einstein Probe and SVOM, will complement Swift and significantly enhance the number of well-localized γ-ray and X-ray transients. Tuned strategies could dramatically improve the probability of observing a lensed GRB.
This article is part of the Theo Murphy meeting issue ‘Multi-messenger gravitational lensing (Part 1)’.</p
Spectral index-flux relation for investigating the origins of steep decay in γ-ray bursts
No full textγ-ray bursts (GRBs) are short-lived transients releasing a large amount of energy (10 − 10 erg) in the keV-MeV energy range. GRBs are thought to originate from internal dissipation of the energy carried by ultra-relativistic jets launched by the remnant of a massive star’s death or a compact binary coalescence. While thousands of GRBs have been observed over the last thirty years, we still have an incomplete understanding of where and how the radiation is generated in the jet. Here we show a relation between the spectral index and the flux found by investigating the X-ray tails of bright GRB pulses via time-resolved spectral analysis. This relation is incompatible with the long standing scenario which invokes the delayed arrival of photons from high-latitude parts of the jet. While the alternative scenarios cannot be firmly excluded, the adiabatic cooling of the emitting particles is the most plausible explanation for the discovered relation, suggesting a proton-synchrotron origin of the GRB emission.The research leading to these results has received funding from the European Union’s Horizon 2020 Programme under the AHEAD2020 project (Grant agreement n. 871158). G. Ghir. acknowledges the support from the ASI-Nustar Grant (1.05.04.95). M.B., P.D., and G.G. acknowledge support from PRIN-MIUR 2017 (Grant 20179ZF5KS). G.O. acknowledges financial contribution from the agreement ASI-INAF n.2017-14-H.0. S.A. acknowledges the PRIN-INAF “Towards the SKA and CTA era: discovery, localization, and physics of transient sources” and the ERC Consolidator Grant “MAGNESIA” (nr. 817661). M.G.B. and P.D. acknowledge ASI Grant I/004/11/3. O.S.S. acknowledges the INAF-Prin 2017 (1.05.01.88.06) and the Italian Ministry for University and Research Grant “FIGARO” (1.05.06.13) for support. G.O. and S.R. are thankful to INAF—Osservatorio Astronomico di Brera for kind hospitality during the completion of this work. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester
A bright megaelectronvolt emission line in -ray burst GRB 221009A
No full textThe highly variable and energetic pulsed emission of a long gamma-ray burst
(GRB) is thought to originate from local, rapid dissipation of kinetic or
magnetic energy within an ultra-relativistic jet launched by a newborn compact
object, formed during the collapse of a massive star. The spectra of GRB pulses
are best modelled by power-law segments, indicating the dominance of
non-thermal radiation processes. Spectral lines in the X-ray and soft
-ray regime for the afterglow have been searched for intensively, but
never confirmed. No line features ever been identified in the high energy
prompt emission. Here we report the discovery of a highly significant () narrow emission feature at around MeV in the brightest ever GRB
221009A. By modelling its profile with a Gaussian, we find a roughly constant
width MeV and temporal evolution both in energy ( MeV
to MeV) and luminosity ( erg/s to erg/s) over 80 seconds. We interpret this feature as a blue-shifted
annihilation line of relatively cold ()
electron-positron pairs, which could have formed within the jet region where
the brightest pulses of the GRB were produced. A detailed understanding of the
conditions that can give rise to such a feature could shed light on the so far
poorly understood GRB jet properties and energy dissipation mechanism.Comment: Submitte
A mega–electron volt emission line in the spectrum of a gamma-ray burst
No full textA long gamma–ray burst (GRB) is observed when the collapse of a massive star produces an ultrarelativistic outflow pointed toward Earth. Gamma-ray spectra of long GRBs are smooth, typically modeled by joint power-law segments describing a continuum, with no detected spectral lines. We report a significant (>6σ) narrow emission feature at ~10 mega–electron volts (MeV) in the spectrum of the bright GRB 221009A. Over 80 seconds, it evolves in energy (~12 to ~6 MeV) and in luminosity (~1.1 to <0.43 × 1050 erg second−1) but has a constant width of ~1 MeV. We interpret this feature as a blueshifted spectral line produced by the annihilation of electron-positron pairs, potentially in the same location responsible for emitting the brightest GRB pulses.M.E.R. acknowledges support from the research program Athena with project number 184.034.002, which is financed by the Dutch Research Council (NWO). O.S.S. acknowledges funding by the European Union-Next Generation EU, PRIN 2022 RFF M4C21.1 (202298J7KT- PEACE). S.A. is supported by the H2020 ERC Consolidator Grant “MAGNESIA” (grant no. 817661; principal investigator: Rea) and National Spanish grant PGC2018-095512-BI00. A.J.L. and D.B.M. are supported by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant no. 725246). D.B.M. thanks the Cosmic Dawn Center, supported by the Danish National Research Foundation (grant DNRF140), for kind hospitality. G.O. and M.B. acknowledge financial support from the European Union’s Horizon 2020 Programme under the AHEAD2020 project (grant no. 871158). B.B. and M.B. acknowledge financial support from the Italian Ministry of University and Research (MUR) for the PRIN grant METE under contract no. 2020KB33TPPeer reviewe
Supplementary material: Multi-wavelength view of the close-by GRB~190829A sheds light on gamma-ray burst physics
No full textThis repository contains supplementary data regarding the article "Multi-wavelength view of the close-by GRB~190829A sheds light on gamma-ray burst physics" published by the Astrophysical Journal Letters.
In particular, the repository contains:
Markov Chain Monte Carlo samples for both the afterglow modelling and the circular gaussian fits to VLBI data
clean radio images, residuals and UV coverage plots for all our VLBI epochs
Data formats should be self-explanatory. Do not hesitate to contact us at [email protected] for any question
