Issue |
A&A
Volume 373, Number 2, July II 2001
|
|
---|---|---|
Page(s) | 542 - 554 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20010537 | |
Published online | 15 July 2001 |
X-ray emission from classical and recurrent novae observed with ROSAT
1
Osservatorio Astronomico di Torino, Strada Osservatorio, 20, 10025 Pino Torinese (TO), Italy
2
Department of Astronomy, 475 N. Charter Str., Madison WI 53706, USA
3
Physics Department, 1150 University Avenue, Madison WI 53706, USA
Corresponding author: M. Orio, orio@cow.physics.wisc.edu
Received:
7
February
2000
Accepted:
10
April
2001
We have analysed 350 pointed and serendipitous observations
of 108 different classical and recurrent novae in outburst and in quiescence,
contained in the ROSAT archive. One aim was to
search for super-soft X-ray sources and we found only 3
of them among post-novae.
Thus, the super-soft X-ray phase of novae is relatively
short lived (up to 10 years) and is observed only for up to 20% of novae.
Most classical and recurrent novae instead emit hard X-rays
(in the ROSAT band) in the first months after the outburst, with peak
X-ray luminosity of a few times 1033 erg s-1.
The emission, which we attribute to
shocks in the nova ejecta, lasts at least 2 years and
even much longer under special circumstances (like preexisting circumstellar
material, or a prolonged wind phase).
We also investigated X-ray emission due to
the accretion mechanism in quiescent
novae. 81 Galactic classical and recurrent novae
were observed at quiescence, and only 11 were detected.
Some of them are variable in X-rays on time scales of years;
the X-ray spectra range from very soft
to hard. The average X-ray luminosity
is not larger than that of quiescent dwarf novae, even if
quiescent novae are at least 10 times more luminous
at optical wavelengths. There seems to be a missing boundary
layer problem: a possible explanation is that boundary layer
radiation in nova systems is emitted almost entirely in the
extreme ultraviolet.
There is no evidence of a large incidence of magnetic systems,
either of enhanced X-ray luminosity in novae
observed shortly before or after the outburst.
Key words: astronomical data bases: miscellaneous / stars: novae, cataclysmic variables / X-rays: stars
© ESO, 2001
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