Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A stellar-mass BH in a transient, low luminosity ULX in M31?   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 1e38 erg/s (assuming a distance of 780 kpc). In the following
weeks, its luminosity overcame 1e39 erg/s, remaining fairly constant for at
least 40 days and fading below 1e38 erg/s 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 mag in the optical band and to 23-24
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.

15
The categories of this paper are: nucl-ex
1
The categories of this paper are: cs
2
The categories of this paper are: math
9
The categories of this paper are: nlin
20
The categories of this paper are: acc-phys
25
The categories of this paper are: patt-sol
33
The categories of this paper are: plasm-ph
13
The categories of this paper are: quant-ph
4
The categories of this paper are: cond-mat
35
The categories of this paper are: mtrl-th
3
The categories of this paper are: physics
24
The categories of this paper are: dg-ga
34
The categories of this paper are: chem-ph
14
The categories of this paper are: math-ph
17
The categories of this paper are: q-fin
31
The categories of this paper are: ao-sci