A recent M 31 nova found as a supersoft X-ray source with Swift
ATel #5687; M. Henze, J.-U. Ness (both ESA/ESAC), M. F. Bode, M. J. Darnley, S. C. Williams (all LJMU), A. W. Shafter (SDSU)
on 24 Dec 2013; 12:05 UT
Credential Certification: Martin Henze (mhenze@mpe.mpg.de)
Subjects: Ultra-Violet, X-ray, Nova
We report the serendipitous detection of an M 31 nova in recent Swift X-ray telescope (XRT) data. Nova M31N 2013-11e (also designated PNV J00443928+4153491) was initially discovered in the optical by Koichi Itagaki on 2013 Nov 29.3778 UT (see the CBAT "Transient Objects Confirmation Page" entry here). Its coordinates were given as RA = 00:44:39.28, Dec = +41:53:49.1 (J2000). This is consistent (within the errors) with the position measured for a new X-ray source in M 31: RA = 00:44:39.71, Dec = +41:53:49.9 (90% uncertainty of 4.2 arcsec). No X-ray source was known at this position previously. The object became first visible in X-rays at (0.9±0.2) × 10-2 ct/s in a 3.8 ks XRT observation starting on 2013-12-10.44 UT. This date corresponds to approximately 11 d after the optical discovery.
After being below the detection limit during the majority of several subsequent XRT observations the source recently brightened in a 8 ks pointing starting on 2013-12-23.26 (approximately 24 d after the optical discovery). The count rate reached (1.9±0.2) × 10-2 ct/s. We extracted about 130 source photons and fitted the spectrum using an absorbed blackbody model. The best-fit parameters were kT = (61+6-8) eV and NH = (2.7+1.1-0.7) × 1021 cm-2 (1σ confidence ranges for the statistical uncertainty). All source photons were below 1 keV. This object is clearly a supersoft X-ray source.
The nova is also significantly detected in the simultaneous Swift UVOT data. We estimated a (Vega system) magnitude of 19.0±0.1 for an uvw2 filter (112-264 nm) pointing on day 11. This magnitude is in the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) and has not been corrected for extinction. Comprehensive ultraviolet photometry will be published soon.
We wish to thank the Swift Team for obtaining the observations.
