Query : 2008A&A...489..707V

2008A&A...489..707V - Astronomy and Astrophysics, volume 489, 707-711 (2008/10-2)

Three X-ray transients in M 31 observed with Swift.


Abstract (from CDS):

The purpose of this study is to find transient X-ray sources in M 31 and to investigate and classify their nature. 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. 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 ∼250-600eV. 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 50eV. We use catalogues of X-ray transients in M 31 to estimate their rate, and we find a lower limit of 9/yr.

Abstract Copyright:

Journal keyword(s): galaxies: individual: M 31 - X-rays: binaries - X-rays: galaxies

Simbad objects: 6

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Number of rows : 6
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 XMMU J004215.8+411924 X 00 42 15.88 +41 19 24.4           ~ 8 0
2 SWIFT J004217.3+411532 X 00 42 17.3 +41 15 32           ~ 2 0
3 SWIFT J004217.4+411532 X 00 42 17.4 +41 15 32           ~ 4 0
4 M 31 G 00 42 44.330 +41 16 07.50 4.86 4.36 3.44     ~ 12390 1
5 M31N 2006-11a No* 00 42 56.60 +41 06 18.0       16.0   ~ 10 0
6 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 10857 1

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