We show that the photospheres of "failed" Gamma-Ray Bursts (GRBs), whose bulk Lorentz factors are much lower than 100, can be outside of internal shocks. The resulting radiation from the photospheres is thermal and bright in UV/Soft X-ray band. The photospheric emission lasts for about one thousand seconds with luminosity about several times 10^46 erg/s. These events can be observed by current and future satellites. It is also shown that the afterglows of failed GRBs are peculiar at the early stage, which makes it possible to distinguish failed GRBs from ordinary GRBs and beaming-induced orphan afterglows.
We report our very early optical observations of GRB 110530A and investigate its jet properties together with its X-ray afterglow data. A peculiar broad onset bump followed by a plateau is observed in its early R band afterglow lightcurve. The optical data in the other bands and the X-ray data are well consistent with the temporal feature of the R band lightcurve. Our joint spectral fits of the optical and X-ray data show that they are in the same regime, with a photon index of $\sim 1.70$. The optical and X-ray afterglow lightcurves are well fitted with the standard external shock model by co…
Using the generic hydrodynamic model of Gamma-Ray Burst (GRB) afterglows, we calculate the radio afterglow light curves of low luminosity, high luminosity, failed and standard GRBs in different observational bands of FAST's energy window. The GRBs are assumed to be located at different distances from us. Our results rank the detectability of GRBs in descending order as high luminosity, standard, failed and low luminosity GRBs. We predict that almost all types of radio afterglows except that of low luminosity GRBs could be observed by the large radio telescope as long as the domains of time and…
We present the results of a detailed investigation of the prompt and afterglow emission in the HESS detected GRB 190829A. Swift and Fermi observations of the prompt phase of this GRB reveal two isolated sub-bursts or episodes, separated by a quiescent phase. The energetic and the spectral properties of the first episode are in stark contrast to the second. The first episode, which has a higher spectral peak of $\sim 120\:\text{keV}$ and a low isotropic energy $\sim 10^{50}\:\text{erg}$ is an outlier to the Amati correlation and marginally satisfies the Yonetoku correlation. However, the energe…
Context: The origin of GRBs' prompt emission is highly debated. Proposed scenarios involve dissipation processes above or below the photosphere of an ultra-relativistic outflow. Aims: We search for observational features that would favour one scenario over the others by constraining the dissipation radius, the outflow magnetization or by indicating the presence of shocks. Bursts showing peculiarities can emphasize the role of a specific physical ingredient, which becomes more apparent under certain circumstances. Methods: We study GRB 070110, which exhibited several remarkable features during …
We report on MASTER optical observations of an afterglow-like optical and X-ray transient AT2021lfa/ZTF21aayokph. We detected the initial steady brightening of the transient at 7σ confidence level. This allowed us to use smooth optical self-similar emission of GRBs model to constrain the explosion time to better than 14 min as well as to estimate its initial Lorentz factor Γ0 = 20 +/- 10. Taking into consideration the low Γ0 and non-detection in gamma-rays, we classify this transient as the first failed GRB afterglow.
The 2004-2012 X-ray time history of the NS LMXB GRS 1724-308 shows, along with the episodic brightenings associated to the low-high state transitions typical of the ATOLL sources, a peculiar, long lasting (about 300 d) flaring event, observed in 2008. This rare episode, characterised by a high-flux hard state, has never been observed before for GRS 1724-308 , and in any case is not common among ATOLL sources. We discuss here different hypotheses on the origin of this peculiar event that displayed the spectral signatures of a failed transition, similar in shape and duration to those rarely obse…
We discuss the potential of the eROSITA telescope on board the \emph{Spectrum-X-Gamma} observatory to detect gamma-ray burst (GRB) X-ray afterglows during its 4-year all-sky survey. The expected rate of afterglows associated with long-duration GRBs without any information on the bursts proper that can be identified by a characteristic power-law light curve in the eROSITA data is 4--8 events per year. An additional small number, $\lesssim 2$ per year, of afterglows may be associated with short GRBs, ultra hard (GeV) GRBs and X-ray flashes. eROSITA can thus provide the first unbiased (unaffected…
GRB 070610, which is also named Swift J195509.6+261406, is a peculiar Galactic transient with significant variability on short timescales in both X-ray and optical light curves. One possible explanation is that GRB 070610/Swift J195509.6 + 261406 is a soft gamma-ray repeater (SGR) in our Galaxy. Here we use the fireball model which is usually recognized as the standard model of gamma-ray burst (GRB) afterglows, and the energy injection hypothesis to interpret the X-ray and optical afterglow light curves of GRB 070610/Swift J195509.6 + 261406. It is found that the model is generally consistent …
We present the extensive follow-up campaign on the afterglow of GRB 110715A at 17 different wavelengths, from X-ray to radio bands, starting 81 seconds after the burst and extending up to 74 days later. We performed for the first time a GRB afterglow observation with the ALMA observatory. We find that the afterglow of GRB 110715A is very bright at optical and radio wavelengths. We use optical and near infrared spectroscopy to provide further information about the progenitor's environment and its host galaxy. The spectrum shows weak absorption features at a redshift z = 0.8225, which reveal a h…
Considering the contribution of the emission from the host galaxies of gamma-ray bursts (GRBs) to the radio afterglows, we investigate the effect of host galaxies on observations statistically. For the three types of events, e.g. low-luminosity, standard and high-luminosity GRBs, it is found that a tight correlation exists between the ratio of the radio flux (RRF) of host galaxy to the total radio peak emission and the observational frequency. Especially, toward lower frequencies, the contribution from the host increases significantly. The correlation can be used to get a useful estimate for t…
The short burst GRB 130912A was detected by Swift, Fermi satellites and several ground-based optical telescopes. Its X-ray light curve decayed with time normally. The optical emission, however, displayed a long term plateau, which is the longest one in current short GRB observations. In this work we examine the physical origin of the X-ray and optical emission of this peculiar event. We find that the canonical forward shock afterglow emission model can account for the X-ray and optical data self-consistently and the energy injection model that has been widely adopted to interpret the shallowly…
The X-ray afterglows of GRBs 060413, 060522, 060607A and 080330 are characterized by plateaus that are followed by very sharp drops. An X-ray plateau is interpretable within the framework of the external forward shock model but the sharp drop is not. In this work we interpret these peculiar X-ray afterglow data as the central engine afterglows from some magnetized central engines, plausibly magnetars. In this model, the X-ray afterglows are powered by the internal magnetic energy dissipation and the sudden drop is caused by the collapse of the magnetar. Accordingly, the X-ray plateau photons s…
Short gamma-ray bursts (sGRBs) are widely believed to result from the mergers of compact binaries. This model predicts an afterglow that bears the characteristic signatures of a constant, low density medium, including a smooth prompt-afterglow transition, and a simple temporal evolution. However, these expectations are in conflict with observations for a non-negligible fraction of sGRB afterglows. In particular, the onset of the afterglow phase for some of these events appears to be delayed and, in addition, a few of them exhibit late- time rapid fading in their lightcurves. We show that these…
The peak time of optical afterglow may be used as a proxy to constrain the Lorentz factor Gamma of the gamma-ray burst (GRB) ejecta. We revisit this method by including bursts with optical observations that started when the afterglow flux was already decaying; these bursts can provide useful lower limits on Gamma. Combining all analyzed bursts in our sample, we find that the previously reported correlation between Gamma and the burst luminosity L_gamma does not hold. However, the data clearly shows a lower bound Gamma_min which increases with L_gamma. We suggest an explanation for this feature…
The "ultra-long" Gamma Ray Burst GRB 111209A at redshift z=0.677, is so far the longest GRB ever observed, with rest frame prompt emission duration of ~4 hours. In order to explain the bursts exceptional longevity, a low metallicity blue supergiant progenitor has been invoked. In this work, we further investigate this peculiar burst by performing a multi-band temporal and spectral analysis of both the prompt and the afterglow emission. We use proprietary and publicly available data from Swift, Konus Wind, XMM-Newton, TAROT as well as from other ground based optical and radio telescopes. We fin…
R-process nucleosynthesis from magnetar giant flares in neutron star--white dwarf mergers: A unified picture for peculiar long gamma-ray bursts
Guangxi University of Science and Technology（广西科技大学）；Nanchang University（南昌大学）；Xiangtan University（湘潭大学）；Hunan University of Science and Technology（湖南科技大学）
We present a process that accounts for the steep-decline-and-plateau phase of the Swift-XRT light curves, vexing features of GRB phenomenology. This process is an integral part of the "supercritical pile" GRB model, proposed a few years ago to provide an account for the conversion of the GRB kinetic energy into radiation with a spectral peak at $E_{\rm pk} \sim m_ec^2$. We compute the evolution of the relativistic blast wave (RBW) Lorentz factor $Γ$ to show that the radiation--reaction force due to the GRB emission can produce an abrupt, small ($\sim 25%$) decrease in $Γ$ at a radius which is …
We present the observations of the afterglow of gamma-ray burst GRB 090102. Optical data taken by the TAROT, REM, GROND, together with publicly available data from Palomar, IAC and NOT telescopes, and X-ray data taken by the XRT instrument on board the Swift spacecraft were used. This event features an unusual light curve. In X-rays, it presents a constant decrease with no hint of temporal break from 0.005 to 6 days after the burst. In the optical, the light curve presents a flattening after 1 ks. Before this break, the optical light curve is steeper than that of the X-ray. In the optical, no …
The peculiar short gamma-ray burst GRB 170817A has been firmly associated to the gravitational wave event GW170817, which has been unaninmously interpreted as due to the coalescence of a double neutron star binary. The unprecedented behaviour of the non-thermal afterglow led to a debate about its nature, which was eventually settled by high-resolution VLBI observations, which strongly support the off-axis structured jet scenario. Using information on the jet structure derived from multi-wavelength fitting of the afterglow emission and of the apparent VLBI image centroid motion, we compute the …
We report on a campaign of X-ray and soft gamma-ray observations of the black hole candidate H 1743-322 (also named IGR J17464-3213), performed with the RXTE, INTEGRAL and Swift satellites. The source was observed during a short outburst between 2008 October 03 and 2008 November 16. The evolution of the hardness-intensity diagram throughout the outburst is peculiar, in that it does not follow the canonical pattern through all the spectral states (the so called q-track pattern) seen during the outburst of black-hole transients. On the contrary, the source only makes a transition from the Hard S…
GRB 130925A is a peculiar event characterized by an extremely long gamma-ray duration ($\approx$7 ks), as well as dramatic flaring in the X-rays for $\approx$20 ks. After this period, its X-ray afterglow shows an atypical soft spectrum with photon index $Γ$$\sim$4, as observed by Swift and Chandra, until $\approx 10^7$ s, when XMM-Newton observations uncover a harder spectral shape with $Γ$$\sim$2.5, commonly observed in GRB afterglows. We find that two distinct emission components are needed to explain the X-ray observations: a thermal component, which dominates the X-ray emission for several…
The recent discovery of a faint gamma-ray burst (GRB) coincident with the gravitational wave (GW) event GW 170817 revealed the existence of a population of low-luminosity short duration gamma-ray transients produced by neutron star mergers in the nearby Universe. These events could be routinely detected by existing gamma-ray monitors, yet previous observations failed to identify them without the aid of GW triggers. Here we show that GRB150101B was an analogue of GRB170817A located at a cosmological distance. GRB 150101B was a faint short duration GRB characterized by a bright optical counterpa…
Using high-quality, broad-band afterglow data for GRB 091029, we test the validity of the forward-shock model for gamma-ray burst afterglows. We used multi-wavelength (NIR to X-ray) follow-up observations obtained with the GROND, BOOTES-3/YA and Stardome optical ground-based telescopes, and the UVOT and the XRT onboard the Swift satellite. To explain the almost totally decoupled light curves in the X-ray and optical/NIR domains, a two-component outflow is proposed. Several models are tested, including continuous energy injection, components with different electron energy indices and components…
The jet compositions, central engines, and progenitors of gamma-ray bursts (GRBs) remain open questions in GRB physics. Applying broadband observations, including GRB prompt emission and afterglow properties derived from {\em Fermi} and {\em Swift} data, as well as from Keck host-galaxy observations, we address these questions for the peculiar, bright GRB 110731A. By using the pair-opacity method, we derive $Γ_{0}>190$ during the prompt emission phase. Alternatively, we derive $Γ_{0} \approx 580$ and $Γ_{0} \approx 154$ by invoking the early-afterglow phase within the homogeneous density and w…
Gamma-ray bursts (GRBs) are intense bursts of high-energy photons (prompt emissions) caused by relativistic jets. After the emissions, multi-wavelength afterglows, from radio to very-high-energy (VHE) gamma-ray, last for more than a few days. In the past three years, the VHE gamma-ray photons from four GRBs (GRBs 180720B, 190114C, 190829A and 201216C) were detected by ground-based Imaging Atmospheric Cherenkov Telescopes, such as the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescopes and the High Energy Stereoscopic System (H.E.S.S.). One of them, GRB 190829A, had some peculiar featu…
The gamma-ray burst GRB 180720B is very peculiar. On one hand, some interesting features have been found by performing the detailed time-resolved spectral analysis in the prompt phase. First, the `flux-tracking' pattern is exhibited both for the low energy spectral index $α$ and the peak energy $E_{p}$ in the Band function. Second, some parameter relations show strong monotonous positive correlations, include $E_{p}-F$, $α-F$, $E_{p}-α$, and $E_{p}-L_{γ,iso}$ for all time-resolved spectra. Lastly, it should be noted that the values of $α$ do not exceed the synchrotron limits (from $-\frac{3}{2…
We present X-ray and multi-band optical observations of the afterglow and host galaxy of GRB 180418A, discovered by ${\it Swift}$/BAT and ${\it Fermi}$/GBM. We present a reanalysis of the GBM and BAT data deriving durations of the prompt emission of $T_{90}\approx$2.56s and $\approx$1.90s, respectively. Modeling the ${\it Fermi}$/GBM catalog of 1405 bursts (2008-2014) in the Hardness-$T_{90}$ plane, we obtain a probability of $\approx$60% that GRB 180418A is a short-hard burst. From a combination of ${\it Swift}$/XRT and ${\it Chandra}$ observations, the X-ray afterglow is detected to $\approx…
Short gamma-ray bursts (GRBs) are believed to be produced by relativistic jets from mergers of neutron-stars (NS) or neutron-stars and black-holes (BH). If the Lorentz-factors $Γ$ of jets from compact-stellar-mergers follow a similar power-law distribution to those observed for other high-energy astrophysical phenomena (e.g. blazars, AGN), the population of jets would be dominated by low-$Γ$ outflows. These jets will not produce the prompt gamma-rays, but jet energy will be released as x-ray/optical/radio transients when they collide with the ambient medium. Using Monte Carlo simulations, we s…
It is generally believed that long-duration gamma-ray bursts (GRBs) are associated with massive star core-collapse, whereas short-duration GRBs are associated with mergers of compact star binaries. However, growing observations have suggested that oddball GRBs do exist, and multiple criteria (prompt emission properties, supernova/kilonova associations, and host galaxy properties) rather than burst duration only are needed to classify GRBs physically. A previously reported long-duration burst, GRB 060614, could be viewed as a short GRB with extended emission if it were observed at a larger dist…
Long-duration GRBs are the most luminous sources of electromagnetic radiation known in the Universe. Their initial prompt flashes of MeV gamma rays are followed by longer-lasting afterglow emission from radio waves to GeV gamma rays. Emission at TeV energies had been theoretically predicted, but never confirmed by observations. Here we report the detection of a huge signal from GRB 190114C in the TeV energy range by the MAGIC imaging atmospheric Cherenkov telescopes. Starting one minute after the onset of the burst, gamma rays in the energy range 0.2 -1 TeV were observed at more than 50 sigma …
Swift J164449+573451 is a peculiar outburst which is most likely powered by the tidal disruption of a star by a massive black hole. Within the tidal disruption scenario, we show that the periastron distance is considerably smaller than the disruption radius and the outflow should be launched mainly via magnetic activities (e.g., Blandford-Znajek process) otherwise the observed long-lasting X-ray afterglow emission satisfying the relation $L_{X}\propto\dot{M}$ can not be reproduced, where $L_{X}$ is the X-ray luminosity and $\dot{M}$ is the accretion rate. We also suggest that $L_{X}\propto\dot…
The observations of jet breaks in the afterglows of short gamma-ray bursts (SGRBs) indicate that the jet has a small opening angle of < 10°. The collimation mechanism of the jet is a longstanding theoretical problem. We numerically analyze the jet propagation in the material ejected by double neutron star merger, and demonstrate that if the ejecta mass is > 10^{-2} M_{sun}, the jet is well confined by the cocoon and emerges from the ejecta with the required collimation angle. Our results also suggest that there are some populations of choked (failed) SGRBs or low-luminous new types of event. B…
We study the late-time (t>0.5 days) X-ray afterglows of nearby (z<0.5) long Gamma-Ray Bursts (GRB) with Swift and identify a population of explosions with slowly decaying, super-soft (photon index Gamma_x>3) X-ray emission that is inconsistent with forward shock synchrotron radiation associated with the afterglow. These explosions also show larger-than-average intrinsic absorption (NH_x,i >6d21 cm-2) and prompt gamma-ray emission with extremely long duration (T_90>1000 s). Chance association of these three rare properties (i.e. large NH_x,i, super-soft Gamma_x and extreme duration) in the same…
From a comprehensive statistical analysis of $Swift$ X-ray light-curves of gamma-ray bursts (GRBs) collected from December 2004 to the end of 2010, we found a three-parameter correlation between the isotropic energy emitted in the rest frame 1-10$^4$ keV energy band during the prompt emission (E$_{\rm{γ,iso}}$), the rest frame peak of the prompt emission energy spectrum (E$_{\rm{pk}}$), and the X-ray energy emitted in the rest frame 0.3-30 keV observed energy band (E$_{\rm{X,iso}}$), computed excluding the contribution of the flares. In this paper, we update this correlation with the data coll…
A self-consistent explanation of the MeV line in GRB 221009A unveils a dense circum-stellar medium
INAF – Osservatorio Astronomico di Brera（意大利国家天体物理研究所布雷拉天文台）；INFN – sezione di Milano-Bicocca（意大利国家核物理研究所米兰-比可卡分部）；SISSA（国际高等研究学院）；INFN – sezione di Trieste（意大利国家核物理研究所的里雅斯特分部）；IFPU – Institute for Fundamental Physics of the Universe（宇宙基础物理研究所）；Gran Sasso Science Institute（格兰萨索科学研究所）；INFN – Laboratori Nazionali del Gran Sasso（意大利国家核物理研究所格兰萨索国家实验室）；Institute of Space Sciences (ICE, CSIC)（空间科学研究所）
Gamma-ray bursts (GRBs) are among the brightest and most energetic events in the universe. The duration and hardness distribution of GRBs has two clusters, now understood to reflect (at least) two different progenitors. Short-hard GRBs (SGRBs; T90 <2 s) arise from compact binary mergers, while long-soft GRBs (LGRBs; T90 >2 s) have been attributed to the collapse of peculiar massive stars (collapsars). The discovery of SN 1998bw/GRB 980425 marked the first association of a LGRB with a collapsar and AT 2017gfo/GRB 170817A/GW170817 marked the first association of a SGRB with a binary neutron star…
In the early Universe, most of the cold neutral gas that will later form into individual stars and galaxies is practically invisible to us. These neutral gas reservoirs can, however, be illuminated by bright cosmic lightsources such as gamma-ray bursts (GRBs) and quasars. The aim of this thesis is to use these luminous objects as tools to study the environments of intervening or host galaxy absorption systems through cosmic time. Part I is dedicated to examining the gas, dust and metals in the immediate region surrounding GRBs. Part II presents a search for and the study of cold and molecular …
The multi-messenger discovery of gravitational waves (GWs) and light from the binary neutron star (NS) merger GW170817, associated with Gamma-Ray Burst (GRB) 170817A and kilonova AT2017gfo, has marked the start of a new era in astrophysics. GW170817 has confirmed that binary NS mergers are progenitors of at least some short GRBs. The peculiar properties of the GRB 170817A radio afterglow, characterized by a delayed onset related to the off-axis geometry, have also demonstrated how some nearby short GRBs may not be identified as such with standard short-timescale electromagnetic follow-up obser…
GRB 090709A is a long gamma-ray burst (GRB) discovered by Swift, featuring a bright X-ray afterglow as well as a faint infrared transient with very red and peculiar colors. The burst attracted a large interest because of a possible quasi-periodicity at P=8.1 s in the prompt emission, suggesting that it could have a different origin with respect to standard, long GRBs. In order to understand the nature of this burst, we obtained a target of opportunity observation with XMM-Newton. X-ray spectroscopy, based on XMM-Newton and Swift data, allowed us to model the significant excess in photoelectric…
Due to the peculiar properties of ultra-diffuse galaxies (UDGs), understanding their origin presents a major challenge. Previous X-ray studies demonstrated that the bulk of UDGs lack substantial X-ray emission, implying that they reside in low-mass dark matter halos. This result, in concert with other observational and theoretical studies, pointed out that most UDGs belong to the class of dwarf galaxies. However, a subset of UDGs is believed to host a large population of globular clusters (GCs), which is indicative of massive dark matter halos. This, in turn, hints that some UDGs may be failed…
Multiwavelength properties of short gamma ray bursts with extended emission observed by Swift
Università degli Studi di Milano（米兰大学）；INAF – Osservatorio Astronomico di Brera（意大利国家天体物理研究所布雷拉天文台）；Ioffe Institute（约费研究所）；INFN Sezione di Milano（意大利国家核物理研究所米兰分部）
Understanding the origin and diversity of emission processes responsible for Gamma-ray Bursts (GRBs) remains a pressing challenge. While prompt and contemporaneous panchromatic observations have the potential to test predictions of the internal-external shock model, extensive multiband imaging has been conducted for only a few GRBs. We present rich, early-time, multiband datasets for two \swift\ events, GRB 110205A and GRB 110213A. The former shows optical emission since the early stages of the prompt phase, followed by the steep rising in flux up to ~1000s after the burst ($t^{-α}$ with $α=-6…
We report on a 63ks Chandra observation of the X-ray transient Swift J195509.6+261406 discovered as the afterglow of what was first believed to be a long duration Gamma-Ray Burst (GRB 070610). The outburst of this source was characterized by unique optical flares on timescales of second or less, morphologically similar to the short X-ray bursts usually observed from magnetars. Our Chandra observation was performed ~2 years after the discovery of the optical and X-ray flaring activity of this source, catching it in its quiescent state. We derive stringent upper limits on the quiescent emission …
A milli-Tidal Disruption Event Model for GRB$\;$250702B: Main Sequence Star Disrupted by an IMBH
The Open University of Israel（以色列开放大学）；The George Washington University（乔治华盛顿大学）；Technion - Israel Institute of Technology（以色列理工学院）；Universidad Nacional Autónoma de México（墨西哥国立自治大学）
GRB 250702B的毫 tidal 破坏事件模型表明，主序星被中间质量黑洞破坏可解释其持续时间和能量特征。
GRB 110709B presented a peculiar three-peak lightcurve; this burst twice triggered the BAT detector onboard Swift. The two triggers were separated by $\sim 10$ minutes. In order to explain such an event, we unify into a single description the millisecond (ms) protomagnetar and the collapsar central-engine models. We find that such a scenario could produce GRBs with three peaks. One for the ms-protomagnetar stage, a second one for the BH-formation event and a third one for the collapsar phase. We show that the three peaks for GRB 110709B originate from different phases of the same collapsing ob…
The bipolarity of Supernova 1987A can be understood through its very early light curve observed from the CTIO 0.4-m telescope and IUE FES, and following speckle observations of the `Mystery Spot' by two groups. These indicate a highly directional beam/jet of light/particles, with initial collimation factors in excess of 10,000 and velocities in excess of 0.95 c, as an impulsive event of up to 1e-5 solar masses interacting with circumstellar material. These can be produced by a model proposed in 1972, by Bolotovskii and Ginzburg, which employs pulsar emission from polarization currents induced/…
