@article {23914,
	title = {Three X-ray transients in M ;31 observed with Swift},
	volume = {489},
	year = {2008},
	month = {2008/10/1},
	pages = {707 - 711},
	abstract = {Aims: The purpose of this study is to find transient X-ray sources in M 31 and to investigate and classify their nature. <BR />Methods: Three X-ray transients were observed with Swift. For each of the three X-ray transients, we used the Swift X-ray and optical data with observations from XMM-Newton and Chandra to investigate the lightcurves and the spectra of the outburst, thereby identifying the source types. <BR />Results: The outburst of XMMU J004215.8+411924 lasted about one month. The source had a hard power-law spectrum with a photon index of 1.6. It was previously identified as a Be/X-ray binary based on the optical identification with a star. However, we show that, with improved source coordinates it is clear that the optical source is not the counterpart to the X-ray source. The source SWIFT J004217.3+411532 had a bright outburst, after which it slowly decayed over half a year. The spectrum was soft, corresponding to a thermal accretion disc with an innermost temperature of ~250-600 eV. The source was not seen in the optical, and the soft spectrum indicates that the source is most likely a black-hole low-mass X-ray binary. M31N 2006-11a is a nova that was previously observed in the optical. We detected it both in X-rays and UV with Swift ~half a year after the optical maximum, after which it decayed below the Swift detection threshold within a month. The spectrum of the X-ray transient can be modelled by a black-body with a temperature of 50 eV. We use catalogues of X-ray transients in M 31 to estimate their rate, and we find a lower limit of 9 yr<SUP>-1</SUP>.},
	keywords = {31, Astrophysics, galaxies: individual: M, X-rays: binaries, X-rays: galaxies},
	isbn = {0004-6361},
	url = {https://ui.adsabs.harvard.edu/abs/2008A\&A...489..707V},
	author = {Voss, R. and Pietsch, W. and Haberl, F. and Stiele, H. and Greiner, J. and Sala, G. and Hartmann, D. H. and Hatzidimitriou, D.}
}
