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New and recurrent X-ray transients in M31 observed with XMM-Newton in January 2016 - part 2

ATel #8827; M. Henze (IEEC/CSIC), M. Sasaki (IAAT), F. Haberl (MPE), B. F. Williams (U. Washington), D. Hatzidimitriou (U. Athens / NOA), for a larger collaboration
on 16 Mar 2016; 12:47 UT
Credential Certification: Martin Henze (henze@ice.cat)

Subjects: X-ray, Transient

Here we report the second set of new and recurrent X-ray transients found in two XMM-Newton 100-ks pointings of the M31 northern disk on Jan 1 and 21 (see ATels #8825, #8826).

2E 161: We report a new outburst of a recurrent X-ray transient first observed with the Einstein satellite (Trinchieri & Fabbiano 1991 McDowell 1994). Since then, multiple other outbursts have been described e.g. by Supper et al. 2001 (RX J0043.7+4124) or Hofmann et al. 2013 (source 313). In the Jan 21 observation the source is very bright with an EPIC count rate of (4.13±0.05) × 10-1 ct s-1 (all given uncertainties indicate 1σ confidence ranges unless otherwise noted). All count rates are given in the 0.2-4.5 keV band. The X-ray spectrum can be fitted using an absorbed powerlaw with best-fit parameters Γ = 1.6±0.1 and NH = (1.1±0.1) × 1021 cm-2. Nothing was detected at this position in Jun 2015 (cf. ATel #8227).

XMMU J004522.6+414802 is a new X-ray source at RA = 00:45:22.64, Dec = +41:48:02.4 (J2000; 3σ statistical uncertainty of 2.4 arcsec). No X-ray source is known within 10 arcsec around this position in CDS/VizieR or in the catalogues of Pietsch et al. (2005) or Stiele et al. (2011). We estimated an EPIC count rate of (5.4±0.5) × 10-3 ct s-1. The source has a hard X-ray spectrum. It was already detected in Aug 2015 (ObsID 0763120301; cf. ATel #8227) with a consistent count rate of (5.7±0.5) × 10-3 ct s-1.

XMMU J004421.0+414656 is a new X-ray source at RA = 00:44:21.05, Dec = +41:46:56.4 (J2000; 3σ statistical uncertainty of 2.7 arcsec). No X-ray source is present in the catalogues of Pietsch et al. (2005) or Stiele et al. (2011) or in the CDS/VizieR data base within a radius of 10 arcsec. The new source has a hard spectrum with an EPIC count rate of (5.5±0.7) × 10-3 ct s-1. It was already detected with a comparable count rate of (6.2±0.5) × 10-3 ct s-1 during the Aug 2015 observation described in ATel #8227.

All sources reported here and in ATels #8825 and #8826 will be studied in detail in a forthcoming paper.