We present a multi-wavelenght study of the recently discovered Ultraluminous X-ray transient XMMUJ004243.6+412519 (ULX2 hereafter) in M31, based on Swift data and the 1.8-m Copernico Telescope in Asiago (Italy). Undetected until January 2012, the source suddenly showed a powerful X-ray emission with a luminosity of 1038 erg s-1 (assuming a distance of 780 kpc). In the following weeks, its luminosity overcame 1039 erg s-1, remaining fairly constant for at least 40 days and fading below 1038 erg s-1 in the next 200 days. The spectrum can be well described by a single multi-color disk blackbody model which progressively softened during the decay (from kT= 0.9 keV to 0.4 keV). No emission from ULX2 was detected down to 22 \textit{mag} in the optical band and to 23-24 \textit{mag} in the near ultraviolet. We compare its properties with those of other known ULXs and Galactic black hole transients, finding more similarities with the latter
A stellar-mass BH in a transient, low luminosity ULX in M31?
PINTORE, FABIO;
2013-01-01
Abstract
We present a multi-wavelenght study of the recently discovered Ultraluminous X-ray transient XMMUJ004243.6+412519 (ULX2 hereafter) in M31, based on Swift data and the 1.8-m Copernico Telescope in Asiago (Italy). Undetected until January 2012, the source suddenly showed a powerful X-ray emission with a luminosity of 1038 erg s-1 (assuming a distance of 780 kpc). In the following weeks, its luminosity overcame 1039 erg s-1, remaining fairly constant for at least 40 days and fading below 1038 erg s-1 in the next 200 days. The spectrum can be well described by a single multi-color disk blackbody model which progressively softened during the decay (from kT= 0.9 keV to 0.4 keV). No emission from ULX2 was detected down to 22 \textit{mag} in the optical band and to 23-24 \textit{mag} in the near ultraviolet. We compare its properties with those of other known ULXs and Galactic black hole transients, finding more similarities with the latterI documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.