[vsnet-alert 10707] (fwd) Swift detection of Super Soft X-ray emission in nova CSS081007:030559+054715

[Taichi Kato]

The Astronomer's Telegram                   http://www.astronomerstelegram.org 
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Posted: Mon Nov 17 01:30:01 EST 2008 -- Tue Nov 18 01:30:01 EST 2008
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ATEL #1847							     ATEL #1847

Title:		Swift detection of Super Soft X-ray emission in nova CSS081007:030559+054715
Author:	G.J. Schwarz (West Chester), J.-U. Ness (Arizona State University),
		J.P. Osborne and K. Page (University of Leicester), R.M. Wagner (LBT/
		Ohio State University), S. Starrfield (Arizona State University),
		J. Prieto, O. Pejcha, and K. Denney (Ohio State University)
Queries:	julo at star.le.ac.uk
Posted:	17 Nov 2008;  14:30  UT
Subjects:	Ultra-Violet, X-ray, Novae

Swift obtained simultaneous X-ray and UV observations of the recent ONe
nova CSS081007:030559+054715 (ATEL #1825, ATEL #1835) on November 10
and 14, 2008.   The ~ 4 ks observation revealed a strong and variable source
in both the XRT   and UVOT detectors.  The average X-ray count rate was
0.183+/-0.009 counts/s   while the UVW2 band (lambda_c ~ 1928 Angstroms)
was 15.1+/-0.1 mag.  The   source is very soft in the X-ray spectrum with
most photons below 0.6 keV.   The X-ray spectrum can be modelled with an
absorbed blackbody with   kT ~ (38 +5/-7) eV and NH ~ (1.6 +0.9/-0.5)x10^21
cm^-2.  The 0.3-1 keV   X-ray flux is 6.3x10^-12 erg cm^-2 s^-1 (1.1x10^-10
unabsorbed).      

The unabsorbed bolometric flux of the model is 2.8x10^-9 erg cm^-2 s^-1.
To convert this to a bolometric luminosity we estimate the distance through
indirect methods since the initial outburst was not observed.  Converting
the SDSS ugriz photometry of the quiescent source to UBVRI photometry
using   the stellar transformations of Jester et al. (2005, AJ, 130, 873)
gives   V = 18.5 mag.  The extinction maps of Schlegel et al. (1998 ApJ,
500, 525)   show E(B-V) = 0.15 in the direction of CSS081007:030559+054715.

The first method assumes an absolute visual magnitude of M_V(max) ~
-9 mag   and an outburst amplitude between 12 and 15 magnitudes (e.g. Table
5.4 in   Warner's "Cataclysmic Variable Stars" 1995), both are typical
of very fast   novae and CSS081007:030559+054715 is likely to be a member
of this speed   class based on the similarity of its optical nebular spectrum
with the very   fast novae V838 Her and V4160 Sgr (see Schwarz et al. 2007,
ApJ, 657, 453).   These assumptions suggest a distance range of 2.5 to
10 kpc.  A second   method assumes that the absolute visual magnitude at
minimum for post-novae and   some cataclysmic variables is 7 > M_V(min)
> 4 mag (e.g. Fig. 4.20 in Warner   1995) for a wide range of orbital periods
and inclination angles.  The distance   based on this second method is
between 1.6 and 6.4 kpc.      

Therefore the bolometric luminosity ranges from 9x10^35 to 1.4x10^37
erg   s^-1   for distances of 2.5 and 6.4 kpc.  Note that luminosities
based on   blackbodies generally overestimate the true luminosity while
underestimating the   effective temperature.  Interestingly, our distance
estimate and the galactic   coordinates (l,b = 172.6,-43.7) imply that
the z-distance from the Galactic   plane exceeds 1.7 kpc which is well
above where most classical novae,   particularly the ONe type, are found.
Additional observations at other   wavelengths of this interesting nova
are strongly encouraged.      

We thank the Swift PI, Neil Gehrels, the Swift science team, and the
Swift   mission operations team for their support of these observations.

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