We report the discovery of the nearby long, soft GRB 100316D, and the subsequent unveiling of its host galaxy and associated supernova. We study the extremely unusual prompt emission with time-resolved gamma-ray to X-ray spectroscopy and find that a
thermal component in addition to the synchrotron spectrum is required. The host galaxy is a bright, blue galaxy with a highly disturbed morphology. From optical photometry and spectroscopy we provide an accurate astrometry and redshift, and derive the key host properties of star formation rate and stellar age. We compare our findings for this GRB-SN with the well known previous case of GRB 060218. GRB 100316D is an important addition to the current sparse sample of spectroscopically confirmed GRB-SNe, from which a better understanding of long GRB progenitors and the GRB-SN connection can be gleaned.
The small subset of hyper-luminous X-ray sources with luminosities in excess of ~1E41 erg/s are hard to explain without the presence of an intermediate mass black hole, as significantly super-Eddington accretion and/or very small beaming angles are r
equired. The recent discovery of HLX-1, the most luminous object in this class with a record breaking luminosity of ~1E42 erg/s in the galaxy ESO 243-49, therefore currently provides some of the strongest evidence for the existence of intermediate mass black holes. HLX-1 is almost an order of magnitude brighter than the other hyper-luminous sources, and appears to exhibit X-ray spectral and flux variability similar to Galactic stellar mass black hole X-ray binaries. In this paper we review the current state of knowledge on this intriguing source and outline the results of multi-wavelength studies from radio to ultra-violet wavelengths, including imaging and spectroscopy of the recently identified optical counterpart obtained with the Very Large Telescope. These results continue to support an intermediate mass black hole in excess of 500 Msun
In this Letter we report a spectroscopic confirmation of the association of HLX-1, the brightest ultra-luminous X-ray source, with the galaxy ESO 243-49. At the host galaxy distance of 95 Mpc, the maximum observed 0.2 - 10 keV luminosity is 1.2E42 er
g/s. This luminosity is ~400 times above the Eddington limit for a 20 Msun black hole, and has been interpreted as implying an accreting intermediate mass black hole with a mass in excess of 500 Msun (assuming the luminosity is a factor of 10 above the Eddington value). However, a number of other ultra-luminous X-ray sources have been later identified as background active galaxies or foreground sources. It has recently been claimed that HLX-1 could be a quiescent neutron star X-ray binary at a Galactic distance of only 2.5 kpc, so a definitive association with the host galaxy is crucial in order to confirm the nature of the object. Here we report the detection of the Halpha emission line for the recently identified optical counterpart at a redshift consistent with that of ESO 243-49. This finding definitively places HLX-1 inside ESO 243-49, confirming the extreme maximum luminosity and strengthening the case for it containing an accreting intermediate mass black hole of more than 500 Msun.
