277 research outputs found
Gamma-ray Bursts: 15 Years of GRB Afterglows
Gamma-ray bursts (GRB) are amongst the most energetic phenomena in the Universe. In 1997 (more than 15 years ago), BeppoSAX allowed the detection of the first GRB X-ray afterglow, leading to the detection of afterglows at other wavelengths (optical, radio) in the following years, probing the cosmological distance scale. There are still many other open issues which still need to be addressed, regarding both theoretical and observational aspects: prompt emission and afterglow physics, progenitors (including Pop III stars), host galaxies, multi-messenger information, etc
On the nature of the short duration GRB 050906
The definitive version is available at www.blackwell-synergy.com. Copyright Blackwell Publishing DOI : 10.1111/j.1365-2966.2007.11953.xPeer reviewe
ILLUMINATING THE DARKEST GAMMA-RAY BURSTS WITH RADIO OBSERVATIONS
We present X-ray, optical, near-infrared (IR), and radio observations of gamma-ray bursts (GRBs) 110709B and 111215A, as well as optical and near-IR observations of their host galaxies. The combination of X-ray detections and deep optical/near-IR limits establish both bursts as "dark." Sub-arcsecond positions enabled by radio detections lead to robust host galaxy associations, with optical detections that indicate z ≾ 4 (110709B) and z ≈ 1.8-2.9 (111215A). We therefore conclude that both bursts are dark due to substantial rest-frame extinction. Using the radio and X-ray data for each burst we find that GRB 110709B requires A_V^(host) ≳ 5.3 mag and GRB 111215A requires A_V^(host) ≳ 8.5 mag (assuming z = 2). These are among the largest extinction values inferred for dark bursts to date. The two bursts also exhibit large neutral hydrogen column densities of N H, int ≳ 10^(22) cm^(–2) (z = 2) as inferred from their X-ray spectra, in agreement with the trend for dark GRBs. Moreover, the inferred values are in agreement with the Galactic A_V -N_H relation, unlike the bulk of the GRB population. Finally, we find that for both bursts the afterglow emission is best explained by a collimated outflow with a total beaming-corrected energy of E_γ + E_K ≈ (7-9) × 10^(51) erg (z = 2) expanding into a wind medium with a high density, Ṁ ≈ (6-20) x 10^(-5) M_☉ yr^(–1) (n ≈ 100-350 cm^(–3) at ≈ 10^(17) cm). While the energy release is typical of long GRBs, the inferred density may be indicative of larger mass-loss rates for GRB progenitors in dusty (and hence metal rich) environments. This study establishes the critical role of radio observations in demonstrating the origin and properties of dark GRBs. Observations with the JVLA and ALMA will provide a sample with sub-arcsecond positions and robust host associations that will help to shed light on obscured star formation and the role of metallicity in GRB progenitors
Spectroscopy and multiband photometry of the afterglow of intermediate duration gamma-ray burst GRB 040924 and its host galaxy
On the Afterglow of the X-ray Flash of 2003 July 23: Photometric evdence for an Off-Axis Gamma-Ray burst with an Associated Supernova
Peer reviewe
Slewing Mirror Telescope and the Data-Acquisition System for the UFFO-Pathfinder
The Ultra-Fast Flash Observatory (UFFO) aims to detect the earliest moment of Gamma-Ray
Bursts (GRBs) which is not well known, resulting into the enhancement of GRB mechanism
understanding. The pathfinder mission was proposed to be a scaled-down version of UFFO,
and only contains the UFFO Burst Alert & Trigger Telescope (UBAT) measuring the
X-ray/gamma-ray with the wide-field of view and the Slewing Mirror Telescope (SMT) with a
rapid-response for the UV/optical photons. Once the UBAT detects a GRB candidate with the
position accuracy of 10 arcmin, the SMT steers the UV/optical photons from the candidate
to the telescope by the fast rotatable mirror and provides the early UV/optical photons
measurements with 4 arcsec accuracy. The SMT has a modified Ritchey-Chrètien telescope
with the aperture size of 10 cm diameter including the rotatable mirror and the image
readout by the intensified charge-coupled device. There is a key board called the UFFO
Data Acquisition system (UDAQ) that manages the communication of each telescope and also
of the satellite and the UFFO overall operation. This pathfinder is designed and built
within the limited size and weight of  ~20 kg and the low power consumption up to
 ~30 W. We will discuss the design and performance of the UFFO-pathfinder, and its
integration to the Lomonosov satellite
A Systematic Study on Energy Dependence of Quasi-Periodic Oscillation Frequency in GRS 1915+105
Systematically studying all the RXTE/PCA observations for GRS 1915+105 before
November 2010, we have discovered three additional patterns in the relation
between Quasi-Periodic Oscillation (QPO) frequency and photon energy, extending
earlier outcomes reported by Qu et al. (2010). We have confirmed that as QPO
frequency increases, the relation evolves from the negative correlation to
positive one. The newly discovered patterns provide new constraints on the QPO
models
VLT/X-shooter spectroscopy of the GRB 120327A afterglow
We present a study of the environment of the Swift long gamma-ray burst GRB
120327A at z ~2.8 through optical spectroscopy of its afterglow. We analyzed
medium-resolution, multi-epoch spectroscopic observations (~7000 - 12000,
corresponding to ~ 15 - 23 km/s, S/N = 15- 30 and wavelength range
3000-25000AA) of the optical afterglow of GRB 120327A, taken with X-shooter at
the VLT 2.13 and 27.65 hr after the GRB trigger. The first epoch spectrum shows
that the ISM in the GRB host galaxy at z = 2.8145 is extremely rich in
absorption features, with three components contributing to the line profiles.
The hydrogen column density associated with GRB 120327A has log NH / cm^(-2) =
22.01 +/- 0.09, and the metallicity of the host galaxy is in the range [X/H] =
-1.3 to -1.1. In addition to the ground state lines, we detect absorption
features associated with excited states of CII, OI, SiII, FeII, and NiII, which
we used to derive information on the distance between the host absorbing gas
and the site of the GRB explosion. The variability of the FeI\lambda2396
excited line between the two epochs proves that these features are excited by
the GRB UV flux. Moreover, the distance of component I is found to be
dI=200+100-60 pc, while component II is located closer to the GRB, at
dII=100+40-30 pc. These values are among the lowest found in GRBs. Component
III does not show excited transitions, so it should be located farther away
from the GRB. The presence of H2 molecules is firmly established, with a
molecular fraction in the range f=4 X 10^(-7) - 10^(-4). This particularly low
value can be attributed to the small dust content. This represents the third
positive detection of molecules in a GRB environment.Comment: 18 pages, 12 figures, accepted by A&
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