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Register a new userDetailed multi-wavelength modelling of the dark GRB 140713A and its host galaxy
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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 relatively wide jet opening angle and an electron energy distribution slope $p$ below 2. Most importantly, the model predicts an optical flux about two orders of magnitude above the observed limits. We calculated that the required host extinction to explain the observed limits in the $r$, $i$ and $z$ bands was $A^{rm host}_{V} > 3.2$ mag, equivalent to $E(B-V)^{rm host} > 1.0$ mag. From the X-ray absorption we derive that the GRB host extinction is $A^{rm host}_{rm V} = 11.6^{+7.5}_{-5.3}$ mag, equivalent to $E(B-V)^{rm host} = 3.7^{+2.4}_{-1.7}$ mag, which is consistent with the extinction required from our BOXFIT derived fluxes. We conclude that the origin of the optical darkness is a high level of extinction in the line of sight to the GRB, most likely within the GRB host galaxy.
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We study the dark nature of GRB 130528A through multi-wavelength observations and conclude that the main reason for the optical darkness is local extinction inside of the host galaxy. Automatic observations were performed at BOOTES-4/MET robotic telescope. We also triggered target of opportunity (ToO) observation at the OSN, IRAM PdBI and the GTC+OSIRIS. The host galaxy photometric observations in optical to near-infrared (nIR) wavelengths were achieved through large ground-based aperture telescopes, such as the 10.4m GTC, the 4.2m WHT, 6m BTA, and the 2m LT. Based on these observations, spectral energy distributions (SED) for the host galaxy and afterglow were constructed. Thanks to mm observations at PdBI, we confirm the presence of a mm source within the XRT error circle that faded over the course of our observations and identify the host galaxy. However, we do not find any credible optical source within early observations with BOOTES-4/MET and 1.5m OSN telescopes. Spectroscopic observation of this galaxy by GTC showed a single faint emission line that likely corresponds to [OII] 3727{AA} at a redshift of 1.250+/-0.001 implying a SFR(M_sun/yr) > 6.18 M_sun/yr without correcting for dust extinction. The probable extinction was revealed through analysis of the afterglow SED, resulting in a value of AV >= ~ 0.9 at the rest frame, this is comparable to extinction levels found among other dark GRBs. The SED of the host galaxy is explained well (chi2/d.o.f.=0.564) by a luminous (MB=-21.16), low-extinction (AV =0, rest frame), and aged (2.6 Gyr) stellar population. We can explain this apparent contradiction in global and line-of-sight extinction if the GRB birth place happened to lie in a local dense environment. In light of having relatively small specific SFR (SSFR) ~ 5.3 M_sun/yr (L/L_star)-1, this also could explain the age of the old stellar population of host galaxy.
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 microphysical parameters of the GRB blast wave. By combining the broadband modeling results with our nIR upper limits we have put constraints on the extinction in the host galaxy. This is consistent with the optical extinction we have derived from the excess X-ray absorption, and higher than in other dark bursts for which similar modeling work has been performed. We also present deep imaging of the host galaxy with the Keck I telescope, Spitzer Space Telescope, and Hubble Space Telescope (HST), which resulted in a well-constrained photometric redshift, giving credence to the tentative spectroscopic redshift we obtained with the Keck II telescope, and estimates for the stellar mass and star formation rate of the host. Finally, our high resolution HST images of the host galaxy show that the GRB afterglow position is offset from the brightest regions of the host galaxy, in contrast to studies of optically bright GRBs.
We present UBVRIZJsHKs broad band photometry of the host galaxy of the dark gamma-ray burst (GRB) of February 10, 2000. These observations represent the most exhaustive photometry given to date of any GRB host galaxy. A grid of spectral templates have been fitted to the Spectral Energy Distribution (SED) of the host. The derived photometric redshift is z=0.842^+0.054_-0.042, which is in excellent agreement with the spectroscopic redshift (z=0.8463+/-0.0002) proposed by Piro et al. (2002) based on a single emission line. Furthermore, we have determined the photometric redshift of all the galaxies in an area of 6x6 around the host galaxy, in order to check for their overdensity in the environment of the host. We find that the GRB 000210 host galaxy is a subluminous galaxy (L ~ 0.5+/-0.2 L*), with no companions above our detection threshold of 0.18+/-0.06 L*. Based on the restframe ultraviolet flux a star formation rate of 2.1+/-0.2 Solar Masses per year is estimated. The best fit to the SED is obtained for a starburst template with an age of 0.181^+0.037_-0.026 Gyr and a very low extinction (Av~0). We discuss the implications of the inferred low value of Av and the age of the dominant stellar population for the non detection of the GRB 000210 optical afterglow.
Very-high-energy (VHE; $geq 10$ GeV) photons are expected from the nearest and brightest Gamma-ray bursts (GRBs). VHE photons, at energies higher than 300 GeV, were recently reported by the MAGIC collaboration for this burst. Immediately, GRB 190114C was followed up by a massive observational campaign covering a large fraction of the electromagnetic spectrum. In this paper, we obtain the LAT light curve of GRB 190114C and show that it exhibits similar features to other bright LAT-detected bursts; the first high-energy photon ($geq$ 100 MeV) is delayed with the onset of the prompt phase and the flux light curve exhibits a long-lived emission (lasting much longer than the prompt phase) and a short-lasting bright peak (located at the beginning of long-lived emission). Analyzing the multi-wavelength observations, we show that the short-lasting LAT and GBM bright peaks are consistent with the synchrotron self-Compton reverse-shock model and the long-lived observations with the standard synchrotron forward-shock model that evolves from a stratified stellar-wind like medium to a uniform ISM-like medium. Given the best-fit values, a bright optical flash produced by synchrotron reverse-shock emission is expected. From our analysis we infer that the high-energy photons are produced in the deceleration phase of the outflow and some additional processes to synchrotron in the forward shocks should be considered to properly describe the LAT photons with energies beyond the synchrotron limit. Moreover, we claim that an outflow endowed with magnetic fields could describe the polarization and properties exhibited in the light curve of GRB 190114C.
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. The host galaxy exhibits red optical/near-IR colors. Equally important, JVLA observations at 0.9-11 d reveal a constant 5.8 GHz flux density and an optically-thin spectrum, unprecedented for GRB afterglows, but suggestive instead of emission from the host galaxy. The optical/near-IR and radio fluxes are well fit with the scaled spectral energy distribution of the local ultra-luminous infrared galaxy (ULIRG) Arp 220 at z~1.3, with a resulting star formation rate of ~300 Msun/yr. The inferred extinction and small projected offset (2.2+/-1.2 kpc) are also consistent with the ULIRG scenario, as is the presence of a companion galaxy at a separation of about 11 kpc. The limits on radio afterglow emission, in conjunction with the observed X-ray and optical emission, require a circumburst density of ~10^-3 cm^-3 an isotropic-equivalent energy scale of E_gamma,iso ~ E_K,iso ~ 7x10^51 erg, and a jet opening angle of >8 deg. The expected fraction of luminous infrared galaxies in the short GRB host sample is ~0.01-0.3 (for pure stellar mass and star formation weighting, respectively). Thus, the observed fraction of 2 events in about 25 hosts (GRBs 120804A and 100206A), provides additional support to our previous conclusion that short GRBs track both stellar mass and star formation activity.
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