0000000000268079
AUTHOR
D. Malesani
Detection of GRB 060927 at z = 5.47: Implications for the Use of Gamma-Ray Bursts as Probes of the End of the Dark Ages
We report on follow-up observations of the GRB 060927 using the ROTSE-IIIa telescope and a suite of larger aperture ground-based telescopes. An optical afterglow was detected 20 s after the burst, the earliest rest-frame detection of optical emission from any GRB. Spectroscopy performed with the VLT about 13 hours after the trigger shows a continuum break at lambda ~ 8070 A produced by neutral hydrogen absorption at z~5.6. We also detect an absorption line at 8158 A which we interpret as SiII at z=5.467. Hence, GRB 060927 is the second most distant GRB with a spectroscopically measured redshift. The shape of the red wing of the spectral break can be fitted by a damped Lyalpha profile with a…
Swift GRBs: The early afterglow spectral energy distribution
We present the first results of a program to systematically study the optical-to-X-ray spectral energy distribution (SED) of Swift GRB afterglows with known redshift. The goal is to study the properties of the GRB explosion and of the intervening absorbing material. In this report we present the preliminary analysis on 23 afterglows. Thanks to Swift, we could build the SED at early times after the GRB (minutes to hours). We derived the Hydrogen column densities and the spectral slopes from the X-ray spectrum. We then constrained the visual extinction by requiring that the combined optical/X-ray SED is due to synchrotron, namely either a single power law or a broken power law with a slope ch…
GRB 070311: a direct link between the prompt emission and the afterglow
We present prompt gamma-ray, early NIR/optical, late optical and X-ray observations of the peculiar GRB 070311 discovered by INTEGRAL, in order to gain clues on the mechanisms responsible for the prompt gamma-ray pulse as well as for the early and late multi-band afterglow of GRB 070311. We fitted with empirical functions the gamma-ray and optical light curves and scaled the result to the late time X-rays. The H-band light curve taken by REM shows two pulses peaking 80 and 140 s after the peak of the gamma-ray burst and possibly accompanied by a faint gamma-ray tail. Remarkably, the late optical and X-ray afterglow underwent a major rebrightening between 3x10^4 and 2x10^5 s after the burst …
Variable Ly alpha sheds light on the environment surrounding GRB 090426
Long duration gamma-ray bursts are commonly associated with the deaths of massive stars. Spectroscopic studies using the afterglow as a light source provide a unique opportunity to unveil the medium surrounding it, probing the densest region of their galaxies. This material is usually in a low ionisation state and at large distances from the burst site, hence representing the normal interstellar medium in the galaxy. Here we present the case of GRB 090426 at z=2.609, whose optical spectrum indicates an almost fully ionised medium together with a low column density of neutral hydrogen. For the first time, we also observe variations in the Ly alpha absorption line. Photoionisation modeling sh…
XMM-Newton and VLT observations of the afterglow of GRB040827
The field of the Gamma-Ray Burst GRB 040827 was observed with XMM-Newton and with the ESO/VLT starting ~6 and ~12 hours after the burst, respectively. A fading X-ray afterglow is clearly detected with the XMM-Newton/EPIC instrument, with a time decay t^(-delta), with delta=1.41+/-0.10. Its spectrum is well described by a power law (photon index Gamma=2.3+/-0.1) affected by an absorption largely exceeding (by a factor ~5) the expected Galactic one, requiring the contribution of an intrinsic, redshifted absorber. In the optical/NIR range, the afterglow emission was observed in the Ks band, as a weak source superimposed to the host galaxy, with magnitude Ks=19.44+/-0.13 (12 hours after the GRB…
GRB 050904 at redshift 6.3: observations of the oldest cosmic explosion after the Big Bang
We present optical and near-infrared observations of the afterglow of the gamma-ray burst GRB 050904. We derive a photometric redshift z = 6.3, estimated from the presence of the Lyman break falling between the I and J filters. This is by far the most distant GRB known to date. Its isotropic-equivalent energy is 3.4x10^53 erg in the rest-frame 110-1100 keV energy band. Despite the high redshift, both the prompt and the afterglow emission are not peculiar with respect to other GRBs. We find a break in the J-band light curve at t_b = 2.6 +- 1.0 d (observer frame). If we assume this is the jet break, we derive a beaming-corrected energy E_gamma = (4-12)x10^51 erg. This limit shows that GRB 050…
The THESEUS space mission concept: science case, design and expected performances
THESEUS is a space mission concept aimed at exploiting Gamma-Ray Bursts for investigating the early Universe and at providing a substantial advancement of multi-messenger and time-domain astrophysics. These goals will be achieved through a unique combination of instruments allowing GRB and X-ray transient detection over a broad field of view (more than 1sr) with 0.5¿1 arcmin localization, an energy band extending from several MeV down to 0.3¿keV and high sensitivity to transient sources in the soft X-ray domain, as well as on-board prompt (few minutes) follow-up with a 0.7¿m class IR telescope with both imaging and spectroscopic capabilities. THESEUS will be perfectly suited for addressing …