Swift and Chandra X-ray detections of nova M31N 2011-01b
ATel #3441; M. Henze, W. Pietsch, F. Haberl, V. Burwitz (Max-Planck-Institut fuer extraterrestrische Physik, MPE)
on 20 Jun 2011; 12:43 UT
Credential Certification: Martin Henze (mhenze@mpe.mpg.de)
We report the detection of the nova candidate M31N 2011-01b (see http://www.mpe.mpg.de/~m31novae/opt/m31/index.php ; also designated "PNV J00423907+4113258" at http://www.cbat.eps.harvard.edu/unconf/tocp.html ) as a supersoft X-ray source (SSS) in four Swift X-ray telescope (XRT) observations in June 2011, about 140 days after its optical outburst on 2011-01-16.52 UT. The SSS was already present in three Chandra High-Resolution Camera Imaging Detector (HRC-I) monitoring observations of the central region of M 31 in February 2011, as early as 32 days after outburst. Nothing was detected at the position of the source in two XMM-Newton observations taken on behalf of the XMM-Newton/Chandra M 31 nova monitoring collaboration (see http://www.mpe.mpg.de/~m31novae/xray/ao9/index.php ) 13 and 23 days earlier. Below we list details on the observations and the source light curve.
The combined spectrum of the X-ray source for the four Swift XRT observations contains only photons with energies below 0.9 keV, allowing us to classify the source as a SSS. Thereby, we can also confirm the optical candidate as a nova in M 31. Assuming an absorption of 6.7x1020 cm-2, the Galactic foreground, the low-count spectrum of the source can be fit using a blackbody model with best-fit temperature of 73 (+26,-21) eV. The unabsorbed luminosities given in the table below assume this model and a M 31 distance of 780 kpc. Exposure times are dead-time corrected and for XMM-Newton EPIC PN after screening for high background.
Telescope/ ObsID Exposure Day after Count rate Luminosity
Instrument [ks] outburst [E-3 ct/s] [E37 erg/s]
XMM-Newton EPIC PN 0650560501 6.2 8.8 < 2.7 < 0.07
XMM-Newton EPIC PN 0650560601 16.2 18.5 < 6.3 < 0.12
Chandra HRC-I 13178 17.5 31.7 7.1+-0.9 2.1+-0.3
Chandra HRC-I 13179 17.5 41.8 21+-2 6.3+-0.6
Chandra HRC-I 13180 17.3 52.6 34+-2 10.1+-0.6
Swift XRT 00032008001 4.5 137.5 6.1+-1.6 4.7+-1.2
Swift XRT 00032009001 4.1 141.5 7.3+-1.6 5.5+-1.2
Swift XRT 00032010001 2.5 145.7 7.2+-2.7 5.5+-2.0
Swift XRT 00032011001 3.8 150.3 7.4+-1.9 5.6+-1.5
Novae with fast SSS turn on are expected to be visible in X-rays for a relatively short time (see Hachisu & Kato,2010,ApJ,709,680; Henze et al. 2010 [arXiv:1010.1461]). Therefore, it would be important to monitor the X-ray light curve of M31N 2011-01b in order to determine the SSS turn-off time which is closely connected to the hydrogen mass burned on the white dwarf after the nova outburst.
We wish to thank the Swift team for scheduling the ToO observations.
