Detection of hard X-rays from V455 And

ATel #1372; F. Senziani (IUSS/INAF), G. Skinner (CRESST/GSFC/UMCP) and P. Jean (CESR/U. Toulouse)
on 29 Jan 2008; 14:01 UT
Credential Certification: G. Skinner (skinner@milkyway.gsfc.nasa.gov)

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We report the detection of hard X-ray emission from the dwarf nova V455 And shortly after its outburst on 2007 Sep 4 (CBET #1053). The emission was detected in an analysis of survey mode data from the Swift/BAT instrument. The 14-25 keV flux reached a peak on 2007 Sep 14.5 of 1.4e-10 ergs cm^2 s^-1 (7 sigma), corresponding to ~1e32 ergs s^-1 in this band at a distance of (90±15) pc (Araujo-Betancor et al. 2005, A&A, 430, 629). No data are available before 2007 Sept. 7.6, 2.8 day after the discovery. The flux declined, becoming undetectable by 2007 Sept. 24.

In XRT TOO observations made on 2007 Sep 17 the soft X-ray flux was strong (0.77 c/s) and highly variable, with a heavily cut-off spectrum. The level is consistent with the BAT 14-25 keV detection assuming a power law index of ~1.5 or a high bremsstrahlung temperature of (>50 keV), but either of these spectra would predict more flux above 25 keV than observed. Archival XRT observations show a very weak variable source at this position (0.002 to 0.005c/s) in observations between 2006 Feb 8 and 2006 May 28. In follow up observations made on 2007 Dec 27 and 28 the corresponding rate was (0.015±0.003) c/s and (0.022±0.003) c/s respectively.

A light curve is available here