The low-extinction afterglow in the solar-metallicity host galaxy of gamma-ray burst 110918A
J. Elliott, T. Krühler, J. Greiner, S. Savaglio, F. Olivares E., A. Rau, A. de Ugarte Postigo, R. Sánchez-Ramírez, K. Wiersema, P. Schady, D. A. Kann, R. Filgas… 展开作者
J. Elliott, T. Krühler, J. Greiner, S. Savaglio, F. Olivares E., A. Rau, A. de Ugarte Postigo, R. Sánchez-Ramírez, K. Wiersema, P. Schady, D. A. Kann, R. Filgas, M. Nardini, E. Berger, D. Fox, J. Gorosabel, S. Klose, A. Levan, A. Nicuesa Guelbenzu, A. Rossi, S. Schmidl, V. Sudilovsky, N. R. Tanvir, C. C. Thöne
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13 pages, 12 figures, 8 tables, accepted for publication in Astronomy & Astrophysics
Metallicity is theoretically thought to be a fundamental driver in gamma-ray burst (GRB) explosions and energetics, but is still, even after more than a decade of extensive studies, not fully understood. This is largely related to two phenomena: a dust-extinction bias, that prevented high-mass and thus likely high-metallicity GRB hosts to be detected in the first place, and a lack of efficient instrumentation, that limited spectroscopic studies including metallicity measurements to the low-redshift end of the GRB host population. The subject of this work is the very energetic GRB 110918A, for which we measure a redshift of z=0.984. GRB 110918A gave rise to a luminous afterglow with an intrinsic spectral slope of b=0.70, which probed a sight-line with little extinction (A_V=0.16 mag) typical of the established distributions of afterglow properties. Photometric and spectroscopic follow-up observations of the galaxy hosting GRB 110918A, including optical/NIR photometry with GROND and spectroscopy with VLT/X-shooter, however, reveal an all but average GRB host in comparison to the z~1 galaxies selected through similar afterglows to date. It has a large spatial extent with a half-light radius of ~10 kpc, the highest stellar mass for z<1.9 (log(M_*/M_sol) = 10.68+-0.16), and an Halpha-based star formation rate of 41 M_sol/yr. We measure a gas-phase extinction of ~1.8 mag through the Balmer decrement and one of the largest host-integrated metallicities ever of around solar (12 + log(O/H) = 8.93+/-0.13). This presents one of the very few robust metallicity measurements of GRB hosts at z~1, and establishes that GRB hosts at z~1 can also be very metal rich. It conclusively rules out a metallicity cut-off in GRB host galaxies and argues against an anti-correlation between metallicity and energy release in GRBs.
In order to study the effect of dust extinction on the afterglow of gamma-ray bursts (GRBs), we carry out numerical calculations with high precision based on rigorous Mie theory and latest optical properties of interstellar dust grains, and analyze the different extinction curves produced by dust grains with different physical parameters. Our results indicate that the absolute extinction quantity is substantially determined by the medium density and metallicity. However, the shape of the extinction curve is mainly determined by the size distribution of the dust grains. If the dust grains aggre…
We present optical photometry of the GRB 060912A afterglow obtained with ground-based telescopes, from about 100 sec after the GRB trigger till about 0.3 day later, supplemented with the Swift optical afterglow data released in its official website. The optical light curve (LC) displays a smooth single power-law decay throughout the observed epochs, with a power-law index of about -1 and no significant color evolution. This is in contrast to the X-ray LC which has a plateau phase between two normal power-law decays of a respective index of about -1 and -1.2. It is shown by our combined X-ray a…
In this paper we compute rest-frame extinctions for the afterglows of a sample of gamma-ray bursts complete in redshift. The selection criteria of the sample are based on observational high-energy parameters of the prompt emission and therefore our sample should not be biased against dusty sight-lines. It is therefore expected that our inferences hold for the general population of gamma-ray bursts. Our main result is that the optical/near-infrared extinction of gamma-ray burst afterglows in our sample does not follow a single distribution. 87% of the events are absorbed by less than 2 mag, and…
Context: GRB afterglows are excellent probes of gas and dust in star-forming galaxies at all epochs. It has been posited that dust in the early Universe must be different from dust at lower z. To date two reports directly support this contention, one of which is based on the spectral shape of GRB 050904 at z = 6.295. Aims: We reinvestigate the afterglow to understand dust at high z. We address the claimed evidence for unusual (SN-origin) dust in its host galaxy by simultaneously examining the X-ray and optical/NIR spectrophotometric data. Methods: We derive the intrinsic SED of the afterglow a…
Prompt optical emission of gamma-ray bursts (GRBs) is known to have important effects on the surrounding environment. In this paper, we study rotational disruption and alignment of dust grains by radiative torques (RATs) induced by GRB afterglows and predict their signatures on the observational properties of GRB afterglows. We first study grain disruption using RAdiative Torque Disruption (RATD) mechanism and find that large grains (size $>0.1 μ\rm m$) within a distance of $d< 40$ pc from the source can be disrupted into smaller grains. We then model the extinction curve of GRB afterglows and…
In this work we use gamma-ray burst (GRB) afterglow spectra observed with the VLT/X-shooter spectrograph to measure rest-frame extinction in GRB lines-of-sight by modeling the broadband near-infrared (NIR) to X-ray afterglow spectral energy distributions (SEDs). Our sample consists of nine Swift GRBs, eight of them belonging to the long-duration and one to the short-duration class. Dust is modeled using the average extinction curves of the Milky Way and the two Magellanic Clouds. We derive the rest-frame extinction of the entire sample, which fall in the range $0 \lesssim {\it A}_{\rm V} \less…
Galaxies selected through long gamma-ray bursts (GRBs) could be of fundamental importance when mapping the star formation history out to the highest redshifts. Before using them as efficient tools in the early Universe, however, the environmental factors that govern the formation of GRBs need to be understood. Metallicity is theoretically thought to be a fundamental driver in GRB explosions and energetics, but is still, even after more than a decade of extensive studies, not fully understood. This is largely related to two phenomena: a dust-extinction bias, that prevented high-mass and thus li…
We present observations and analysis of the broadband afterglow of Swift GRB 071025. Using optical and infrared (RIYJHK) photometry, we derive a photometric redshift of 4.4 < z < 5.2; at this redshift our simultaneous multicolour observations begin at ~30 s after the GRB trigger in the host frame and during the initial rising phase of the afterglow. We associate the light curve peak at 580 s in the observer frame with the formation of the forward shock, giving an estimate of the initial Lorentz factor Gamma_0 ~ 200. The red spectral energy distribution (even in regions not affected by the Lyma…
The redshift distribution of gamma-ray bursts (GRBs) is strongly biased by selection effects. We investigate, via Monte Carlo simulations, one possible selection effect that may be modifying the Swift GRB redshift distribution. We show how telescope response times to acquire a GRB redshift may, via the Malmquist effect and GRB optical afterglow brightness distribution, introduce a bias into the average of the observed redshift distribution. It is difficult to reconcile a recently reported correlated trend between telescope response time and average redshifts unless we employ a redshift-depende…
We present our optical observations of {\em Swift} GRB 070518 afterglow obtained at the 0.8-m Tsinghua University-National Astronomical Observatory of China telescope (TNT) at Xinglong Observatory. Our follow-up observations were performed from 512 sec after the burst trigger. With the upper limit of redshift $\sim$0.7, GRB 070518 is found to be an optically dim burst. The spectra indices $β_{ox}$ of optical to X-ray are slightly larger than 0.5, which implies the burst might be a dark burst. The extinction $A_{V}$ of the host galaxy is 3.2 mag inferred from the X-ray hydrogen column density w…
Extra-galactic X-ray absorption and optical extinction are often found in gamma-ray burst (GRB) afterglows and they could be tracers of both circumburst and host galaxy environments. By performing spectral analyses for spectral energy distribution of 9 short GRB (SGRB) afterglows with known redshift, we investigated a ratio of the equivalent hydrogen column density to the dust extinction, N^{rest}_{H}/A^{rest}_{V}, in the rest frame of each SGRB. We found that the distribution of N^{rest}_{H}/A^{rest}_{V} is systematically smaller than the one for long GRBs, and is roughly consistent with the …
Gamma-Ray Bursts can provide information about star formation at high redshifts. Even in the absence of a optical/near-infrared/radio afterglow, the high detection rate of X-ray afterglows by swift/XRT and its localization precision of 2-3 arcsec facilitates the identification and study of GRB host galaxies. We focus on the search for the host galaxies of a sample of 17 bursts with XRT error circles but no detected long-wavelength afterglow. Three of these events can also be classified as truly dark bursts: the observed upper limit on the optical flux of the afterglow was less than expected ba…
The gamma-ray burst that followed the first detection of gravitational waves from the merger of a Binary Neutron Stars and its low energy counterparts were in many respects unusual and challenge our understanding of mechanisms involved in their production. In a previous work we used a phenomenological formulation of relativistic shocks and synchrotron emission to analyse the prompt gamma-ray emission of GW/GRB 170817A. Here we use the same model to analyse late afterglows of this event. The main goal is to see whether synchrotron emission alone can explain late afterglows. We find that collisi…
The recently-discovered Fundamental Metallicity Relation (FMR), which is the tight dependence of metallicity on both mass and SFR, proves to be a very useful tool to study the metallicity properties of various classes of galaxies. We have used the FMR to study the galaxies hosting long-GRBs. While the GRB hosts have lower metallicities than typical galaxies of the same mass, i.e., they are below the mass-metallicity relation, they are fully consistent with the FMR. This shows that the difference with the mass-metallicity relation is due to higher than average SFRs, and that GRBs with optical a…
[Abridged] We report the discovery of the near-infrared and optical afterglow of the short-duration gamma-ray burst GRB070724A. The afterglow is detected in i,J,H,K observations starting 2.3 hr after the burst with K=19.59+/-0.16 mag and i=23.79+/-0.07 mag, but is absent in images obtained 1.3 years later. Fading is also detected in the K-band between 2.8 and 3.7 hr at a 4-sigma significance level. The optical/near-IR spectral index, beta_{O,NIR}=-2, is much redder than expected in the standard afterglow model, pointing to either significant dust extinction, A_{V,host}~2 mag, or a non-afterglo…
The unprecedentedly bright optical afterglow of GRB 130606A located by Swift at a redshift close to the reionization era (z = 5.913) provides a new opportunity to probe the ionization status of intergalactic medium (IGM). Here we present an analysis of the red Ly alpha damping wing of the afterglow spectrum taken by Subaru/FOCAS during 10.4-13.2 hr after the burst. We find that the minimal model including only the baseline power-law and HI absorption in the host galaxy does not give a good fit, leaving residuals showing concave curvature in 8400-8900 A with an amplitude of about 0.6% of the fl…
Context: Thirteen years after the discovery of the first afterglows, the nature of dark gamma-ray bursts (GRB) still eludes explanation: while each ng-duration GRB typically has an X-ray afterglow, optical/NIR emission is only seen for 40-60% of them. Aim: Here we use the afterglow detection statistics of the systematic follow-up observations performed with GROND since mid-2007 in order to derive the fraction of "dark bursts" according to different methods, and to distinguish between various scenarios for "dark bursts". Method: Observations were performed with the 7-channel "Gamma-Ray Optical …
Dust is known to be produced in the envelopes of AGB stars, the expanded shells of supernova (SN) remnants, and in situ grain growth in the ISM, although the corresponding efficiency of each of these dust formation mechanisms at different redshifts remains a topic of debate. During the first Gyr after the Big Bang, it is widely believed that there was not enough time to form AGB stars in high numbers, so that the dust at this epoch is expected to be purely from SNe, or subsequent grain growth in the ISM. The time period corresponding to z ~5-6 is thus expected to display the transition from SN…
We present the optical discovery and sub-arcsecond optical and X-ray localization of the afterglow of the short GRB 120804A, as well as optical, near-IR, and radio detections of its host galaxy. X-ray observations with Swift/XRT, Chandra, and XMM-Newton to ~19 d reveal a single power law decline. The optical afterglow is faint, and comparison to the X-ray flux indicates that GRB 120804A is "dark", with a rest-frame extinction of A_V~2.5 mag (at z~1.3). The intrinsic neutral hydrogen column density inferred from the X-ray spectrum, N_H~2x10^22 cm^-2, is commensurate with the large extinction. T…
We perform a detailed study of the gamma-ray burst GRB091127/SN2009nz host galaxy at z=0.490 using the VLT/X-shooter spectrograph in slit and integral-field unit (IFU). From the analysis of the optical and X-ray afterglow data obtained from ground-based telescopes and Swift-XRT we confirm the presence of a bump associated with SN2009nz and find evidence of a possible jet break in the afterglow lightcurve. The X-shooter afterglow spectra reveal several emission lines from the underlying host, from which we derive its integrated properties. These are in agreement with those of previously studied…
Four years after the launch the Swift satellite the nature of the GRBs broadband afterglow behaviour is still an open issue. The standard external shock fireball model cannot easily explain the combined temporal and spectral properties of Optical to X-ray afterglows. We analysed the rest frame de-absorbed and K-corrected Optical and X-ray light curves of a sample of 33 GRBs with known redshift and optical extinction at the host frame. We modelled their broadband behaviour as the sum of the standard forward shock emission due to the interaction of a fireball with the circum-burst medium and an …
Dark gamma-ray bursts (GRBs) are sources with a low optical-to-X-ray flux ratio. Proposed explanations for this darkness are: i) the GRB is at high redshift ii) dust in the GRB host galaxy absorbs the optical/NIR flux iii) GRBs have an intrinsically faint afterglow emission. Within this framework, GRB 100614A and GRB 100615A are extreme. In fact, they are bright in the X-rays, but no optical/NIR afterglow has been detected for either source, despite several follow-up campaigns began early after the triggers. We build optical-to-X-ray spectral energy distributions (SEDs) at the times at which t…
Dark gamma-ray bursts (GRBs) are sources with a low optical-to-X-ray flux ratio. Proposed explanations for this darkness are: i) the GRB is at high redshift ii) dust in the GRB host galaxy absorbs the optical/NIR flux iii) GRBs have an intrinsically faint afterglow emission. Within this framework, GRB 100614A and GRB 100615A are extreme. In fact, they are bright in the X-rays, but no optical/NIR afterglow has been detected for either source, despite several follow-up campaigns began early after the triggers. We build optical-to-X-ray spectral energy distributions (SEDs) at the times at which t…
We report on strong H2 and CO absorption from gas within the host galaxy of gamma-ray burst (GRB) 080607. Analysis of our Keck/LRIS afterglow spectrum reveals a very large HI column density (NHI = 10^22.70 cm^-2) and strong metal-line absorption at z_GRB = 3.0363 with a roughly solar metallicity. We detect a series of A-X bandheads from CO and estimate N(CO) = 10^16.5 cm^-2 and T_ex^CO > 100K. We argue that the high excitation temperature results from UV pumping of the CO gas by the GRB afterglow. Similarly, we observe H2 absorption via the Lyman-Werner bands and estimate N(H2) = 10^21.2 cm^-2…
We present cm-band and mm-band afterglow observations of five long-duration $γ$-ray bursts (GRBs; GRB 130131A, 130420B, 130609A, 131229A, 140713A) with dust-obscured optical afterglow emission, known as "dark" GRBs. We detect the radio afterglow of two of the dark GRBs (GRB 130131A and 140713A), along with a tentative detection of a third (GRB 131229A) with the Karl G. Jansky Very Large Array (VLA). Supplemented by three additional VLA-detected dark GRBs from the literature, we present uniform modeling of their broadband afterglows. We derive high line-of-sight dust extinctions of $A_{V, \rm G…
Extensive multi-band afterglow data are available for GRB 980703. Especially, its radio afterglow was very bright and was monitored until more than 1000 days after the trigger time. Additionally, there is no obvious special feature, i.e., no rebrightenings, no plateau, and no special steep decay or slow decay in the multi-band afterglow light curves. All these conditions make GRB 980703 a precious sample in gamma-ray burst research. Here we use the observational data of GRB 980703 to test the standard fireball model in depth. It is found that the model can give a satisfactory explanation to th…
Aims: GRB 050502B is well known for the very bright flare displayed in its X-ray light curve. Despite extensive studies, however, the optical light curve has never been discussed and its redshift is unconstrained. Possible correlations between optical and X-ray data are analysed. Methods: Photometric data from TNG in the R and I bands were used to compare the optical afterglow with the X-ray light curve. The HyperZ package and a late time VLT host observation were used to derive redshift estimates. Results: The I-band afterglow decay followed a power-law of index α = 2.1 $\pm$ 0.6, after a lat…
Gamma-ray burst (GRB) 111215A was bright at X-ray and radio frequencies, but not detected in the optical or near-infrared (nIR) down to deep limits. We have observed the GRB afterglow with the Westerbork Synthesis Radio Telescope and Arcminute Microkelvin Imager at radio frequencies, with the William Herschel Telescope and Nordic Optical Telescope in the nIR/optical, and with the Chandra X-ray Observatory. We have combined our data with the Swift X-Ray Telescope monitoring, and radio and millimeter observations from the literature to perform broadband modeling, and determined the macro- and mi…
We modelled dust grain-size distributions for carbonaceous and silicates dust, as well as for free-flying iron nanoparticles in the environment of a $γ$-ray burst (GRB) afterglow, GRB 180325A. This GRB, at $z=2.2486$, has an unambiguous detection of the 2175 Å extinction feature with $R_V=4.58$ and $A_V=1.58$. In addition to silicates, polycyclic aromatic hydrocarbons (PAH), and graphite, we used iron nanoparticles grain-size distributions for the first time to model the observed extinction curve of GRB 180325A. We fit the observed extinction for four model permutations, using 232 sets of sili…
Instruments such as the ROTSE, TORTORA, Pi of the Sky, MASTER-net, and others have recorded single-band optical flux measurements of gamma-ray bursts starting as early as $\thicksim$ 10 seconds after gamma-ray trigger. The earliest measurements of optical spectral shape have been made only much later, typically on hour time scales, never starting less than a minute after trigger, until now. Beginning only 58 seconds after the \emph{Swift} BAT triggerred on GRB201015A, we observed a sharp rise in optical flux to a peak, followed by a power law temporal decay, $\propto t^{-0.81 \pm 0.03}$. Flux …
The class of long gamma-ray bursts (LGRBs) is associated with the collapse of the most massive stars, making them a tool to investigate star formation in the early Universe. Furthermore, thanks to their exceptional brightness, LGRB afterglows can be used as extra-galactic background sources capable of unveiling the properties of the cold/warm gas of their hosting galaxies, up to the highest redshifts. Therefore LGRBs allow, uniquely, the combination of the information on different phases of the gas, through the absorption lines present in the afterglow spectra and the emission (continuum and l…
The metallicity and dust-to-metals ratio of the Galaxy are fundamental parameters in understanding the ISM, but there is still uncertainty surrounding these parameters. In this paper, the dust-to-metals ratio in the Galaxy is determined using the photoelectric absorption of the X-ray afterglows of a sample of several hundred gamma-ray bursts (GRBs) to determine the metal column density in combination with Galactic dust maps to determine the line-of-sight dust extinction through the Galaxy in the direction of the GRB. GRB afterglows often have large extragalactic soft X-ray absorptions and ther…
We present spectroscopic observations of the host galaxy and explosion site of the long-duration gamma-ray burst GRB 020819. We determine a metallicity for this host environment of log(O/H) + 12 = 9.0 +/- 0.1, by far the highest metallicity determined for a long-duration GRB to date. We compare the metallicity and other properties of the GRB 020819 host environment to existing observations of long-duration GRB host galaxies, and consider the implications that this metallicity has for our understanding of long-duration GRB progenitor scenarios. We also consider how this unusually high metallici…
Fermi can measure the spectral properties of gamma-ray bursts over a very large energy range and is opening a new window on the prompt emission of these energetic events. Localizations by the instruments on Fermi in combination with follow-up by Swift provide accurate positions for observations at longer wavelengths leading to the determination of redshifts, the true energy budget, host galaxy properties and facilitate comparison with pre-Fermi bursts. Multi-wavelength follow-up observations were performed on the afterglows of four bursts with high energy emission detected by Fermi/LAT : GRB09…
Astrophysics Research Institute, Liverpool John Moores University（利物浦约翰摩尔斯大学天体物理研究所）；School of Systems Information Science, Future University Hakodate（函馆未来大学系统信息科学学院）；Astronomical Institute, Graduate School of Science, Tohoku University（东北大学理学研究科天文研究所）；Department of Astrophysics/IMAPP, Radboud University（拉德堡德大学天体物理学系/IMAPP）；Department of Physics, University of Warwick（华威大学物理系）；School of Physics and Astronomy, University of Leicester（莱斯特大学物理与天文学院）；Space Science Data Center (SSDC) Agenzia Spaziale Italiana (ASI)（意大利航天局空间数据中心）；DARK, Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯玻尔研究所DARK中心）；INAF, Osservatorio Astronomico di Capodimonte（意大利国家天体物理研究所卡波迪蒙特天文台）
We present X-ray and optical observations of the short duration gamma-ray burst GRB 071227 and its host at $z=0.381$, obtained using \textit{Swift}, Gemini South and the Very Large Telescope. We identify a short-lived and moderately bright optical transient, with flux significantly in excess of that expected from a simple extrapolation of the X-ray spectrum at 0.2-0.3 days after burst. We fit the SED with afterglow models allowing for high extinction and thermal emission models that approximate a kilonova to assess the excess' origins. While some kilonova contribution is plausible, it is not f…
Context. Gamma-ray burst (GRB) afterglows originate from the interaction between the relativistic ejecta and the surrounding medium. Consequently, their properties depend on several aspects: radiation mechanisms, relativistic shock micro-physics, circumburst environment, and the structure and geometry of the relativistic jet. While the standard afterglow model accounts for the overall spectral and temporal evolution for a number of GRBs, its validity limits emerge when the data set is particularly rich and constraining, especially in the radio band. Aims. We aimed to model the afterglow of the…
We use a parent sample of 118 gamma-ray burst (GRB) afterglows, with known redshift and host galaxy extinction, to separate afterglows with and without signatures of dominant reverse-shock emission and to determine which physical conditions lead to a prominent reverse-shock emission. We identify 10 GRBs with reverse shock signatures - GRBs 990123, 021004, 021211, 060908, 061126, 080319B, 081007, 090102, 090424 and 130427A. By modeling their optical afterglows with reverse and forward shock analytic light curves and using Monte Carlo simulations, we estimate the parameter space of the physical …
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…
GRB120711A, discovered and rapidly localized by the INTEGRAL satellite, attracted particular interest due to its high gamma-ray fluence, very bright X-ray afterglow, and the detection of a prompt optical transient and of long-lasting emission at GeV energies. A follow-up observation carried out with the XMM-Newton satellite has provided an X-ray spectrum in the 0.3-10 keV with unprecedented statistics for a GRB afterglow 20 hours after the burst. The spectrum is well fit by a power-law with photon index 1.87+-0.01, modified by absorption in our Galaxy and in the GRB host at z=1.4. A Galactic a…
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…
We investigate the afterglow of GRB 140713A, a gamma-ray burst (GRB) that was detected and relatively well-sampled at X-ray and radio wavelengths, but was not present at optical and near-infrared wavelengths, despite searches to deep limits. We present the emission spectrum of the likely host galaxy at $z = 0.935$ ruling out a high-redshift explanation for the absence of the optical flux detection. Modelling the GRB multi-wavelength afterglow using the radiative transfer hydrodynamics code BOXFIT provides constraints on physical parameters of the GRB jet and its environment, for instance a rel…
In order to constrain the broad-band spectral energy distribution of the afterglow of GRB 100621A, dedicated observations were performed in the optical/near-infrared with the 7-channel "Gamma-Ray Burst Optical and Near-infrared Detector" (GROND) at the 2.2m MPG/ESO telescope, in the sub-millimeter band with the large bolometer array LABOCA at APEX, and at radio frequencies with ATCA. Utilizing also Swift X-ray observations, we attempt an interpretation of the observational data within the fireball scenario. The afterglow of GRB 100621A shows a very complex temporal as well as spectral evolutio…
Context. Gamma-ray burst (GRBs) afterglows probe sightlines to star-forming regions in distant star-forming galaxies. Here we present a study of the peculiar afterglow spectrum of the z = 0.889 Swift GRB 140506A. Aims. Our aim is to understand the origin of the very unusual properties of the absorption along the line-of-sight. Methods. We analyse spectroscopic observations obtained with the X-shooter spectrograph mounted on the ESO/VLT at two epochs 8.8 h and 33 h after the burst as well as imaging from the GROND instrument. We also present imaging and spectroscopy of the host galaxy obtained …
We report the detection of the radio afterglow of a long gamma-ray burst (GRB) 111005A at 5-345 GHz, including the very long baseline interferometry observations with the positional error of 0.2 mas. The afterglow position is coincident with the disk of a galaxy ESO 580-49 at z= 0.01326 (~1" from its center), which makes GRB 111005A the second closest GRB known to date, after GRB 980425. The radio afterglow of GRB 111005A was an order of magnitude less luminous than those of local low-luminosity GRBs, and obviously than those of cosmological GRBs. The radio flux was approximately constant and …
