We present the SVOM (Space-based multi-band astronomical Variable Objects Monitor) mission that the Chinese National Space Agency and the French Space Agency have decided to jointly implement. SVOM has been designed to detect all known types of gamma
-ray bursts (GRBs), to provide fast and reliable GRB positions, to measure the broadband spectral shape and temporal properties of the GRB prompt emission, and to quickly identify the optical/near-infrared afterglows of detected GRBs, including high-redshift ones. Scheduled to be in orbit in the second half of the present decade, the SVOM satellite will carry a very innovative scientific payload combining for the first time a wide field X- and gamma-ray coded mask imager for GRB real-time localizations to few arcmin, a non-imaging gamma-ray monitor, and two narrow-field instruments for the study of the GRB early afterglow emission in the X-ray and visible bands. The SVOM payload is complemented by ground-based instruments including a wide-field camera to catch the GRB prompt emission in the visible band and two robotic telescopes to measure the photometric properties of the early afterglow. A particular attention is paid to the GRB follow-up in facilitating the observation of the SVOM detected GRB by the largest ground based telescopes.
GRBs are the most energetic events in the Universe, associated with the death of massive stars (core-collapse supernovae) or the merging of neutron stars or black holes. Discovered in the early 1970s, their cosmological origin was demonstrated only i
n 1997, when the first distance was measured. Theoretical models predict that the very energetic processes at work in GRBs accelerate charged particles to such energies that they could contribute to the observed high energy neutrinos. These processes will be discussed and the observational consequences, in particular for current and forthcoming neutrino telescopes, presented.
We report the serendipitous detection by GALEX of fast (<1 day) rising (>1 mag) UV emission from two Type II plateau (II-P) supernovae (SNe) at z=0.185 and 0.324 discovered by the Supernova Legacy Survey. Optical photometry and VLT spectroscopy 2 wee
ks after the GALEX detections link the onset of UV emission to the time of shock breakout. Using radiation hydrodynamics and non-LTE radiative transfer simulations, and starting from a standard red supergiant (RSG; Type II-P SN progenitor) star evolved self-consistently from the main sequence to iron core collapse, we model the shock breakout phase and the 55 hr that follow. The small scale height of our RSG atmosphere model suggests that the breakout signature is a thermal soft X-ray burst (lambda_peak ~ 90AA) with a duration of <~ 2000 s. Longer durations are possible but require either an extended and tenuous non-standard envelope, or an unusually dense RSG wind with dot{M} ~ 10^(-3) Msun yr^(-1). The GALEX observations miss the peak of the luminous (M_FUV ~ -20) UV burst but unambiguously capture the rise of the emission and a subsequent 2 day long plateau. The postbreakout, UV-bright plateau is a prediction of our model in which the shift of the peak of the spectral energy distribution (SED) from ~100 to ~1000AA and the ejecta expansion both counteract the decrease in bolometric luminosity from ~10^11 to ~10^9 L_sun over that period. Based on the observed detection efficiency of our study we make predictions for the breakout detection rate of the GALEX Time Domain Survey.
