374 research outputs found
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Another short-burst host galaxy with an optically obscured high star formation rate: The case of GRB 071227
We report on radio continuum observations of the host galaxy of the short
gamma-ray burst 071227 (z=0.381) with the Australia Telescope Compact Array
(ATCA). We detect the galaxy in the 5.5 GHz band with an integrated flux
density of Fnu = 43 +/- 11 microJy, corresponding to an unobscured
star-formation rate (SFR) of about 24 Msun/yr, forty times higher than what was
found from optical emission lines. Among the ~30 well-identified and studied
host galaxies of short bursts this is the third case where the host is found to
undergo an episode of intense star formation. This suggests that a fraction of
all short-burst progenitors hosted in star-forming galaxies could be physically
related to recent star formation activity, implying a relatively short merger
time scale.Comment: 6 pages, ApJ, accepted for publicatio
Afterglow rebrightenings as a signature of a long-lasting central engine activity? The emblematic case of GRB 100814A
In the past few years the number of well-sampled optical to NIR light curves
of long Gamma-Ray Bursts (GRBs) has greatly increased particularly due to
simultaneous multi-band imagers such as GROND. Combining these densely sampled
ground-based data sets with the Swift UVOT and XRT space observations unveils a
much more complex afterglow evolution than what was predicted by the most
commonly invoked theoretical models. GRB 100814A represents a remarkable
example of these interesting well-sampled events, showing a prominent late-time
rebrightening in the optical to NIR bands and a complex spectral evolution.
This represents a unique laboratory to test the different afterglow emission
models. Here we study the nature of the complex afterglow emission of GRB
100814A in the framework of different theoretical models. Moreover, we compare
the late-time chromatic rebrightening with those observed in other well-sampled
long GRBs. We analysed the optical and NIR observations obtained with the
seven-channel Gamma-Ray burst Optical and Near-infrared Detector at the 2.2 m
MPG/ESO telescope together with the X-ray and UV data detected by the
instruments onboard the Swift observatory. The broad-band afterglow evolution,
achieved by constructing multi-instrument light curves and spectral energy
distributions, will be discussed in the framework of different theoretical
models. We find that the standard models that describe the broad-band afterglow
emission within the external shock scenario fail to describe the complex
evolution of GRB 100814A, and therefore more complex scenarios must be invoked.
[abridged]Comment: 11 pages, 7 figures, 2 tables; Astronomy & Astrophysics, in pres
Multiwavelength analysis of three SNe associated with GRBs observed by GROND
After the discovery of the first connection between GRBs and SNe almost two
decades ago, tens of SN-like rebrightenings have been discovered and about
seven solid associations have been spectroscopically confirmed to date. Using
GROND optical/NIR data and Swift X-ray/UV data, we estimate the intrinsic
extinction, luminosity, and evolution of three SN rebrightenings in GRB
afterglow light curves at z~0.5. The SNe 2008hw, 2009nz, and 2010ma exhibit
0.80, 1.15, and 1.78 times the optical (r band) luminosity of SN 1998bw,
respectively. While SN 2009nz evolves similarly to SN 1998bw, SNe 2008hw and
2010ma show earlier peak times. The quasi-bolometric light curves were
corrected for the contribution of the NIR bands using data available in the
literature and blackbody fits. The large luminosity of SN 2010ma (1.4x10^43
erg/s) is confirmed, while SNe 2008hw and 2009nz reached a peak luminosity
closer to SN 1998bw. Physical parameters of the SN explosions, such as
synthesised nickel mass, ejecta mass, and kinetic energy, are estimated using
Arnett's analytic approach, which resulted in nickel masses of around 0.4-0.5
Msun. By means of the a very comprehensive data set, we found that the
luminosity and the nickel mass of SNe 2008hw, 2009nz, and 2010ma resembles
those of other known GRB-associated SNe. This findings strengthens previous
claims of GRB-SNe being brighter than type-Ic SNe unaccompanied by GRBs.Comment: 11 pages, 9 figures, accepted for publication in Astronomy &
Astrophysics, abstract abridge
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