Issue |
A&A
Volume 426, Number 1, October IV 2004
|
|
---|---|---|
Page(s) | 257 - 265 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20040522 | |
Published online | 05 October 2004 |
Superbursts at near-Eddington mass accretion rates
1
SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands e-mail: jeanz@sron.nl
2
Astronomical Institute, Utrecht University, PO Box 80000, 3508 TA Utrecht, The Netherlands
3
Dept. of Physics and Astronomy, University of Southampton, Hampshire SO17 1BJ, UK
4
Dept. of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA
Received:
25
March
2004
Accepted:
29
June
2004
Models for superbursts from neutron stars involving carbon
shell flashes predict that the mass accretion rate should be anywhere
in excess of one tenth of the Eddington limit. Yet, superbursts have
so far only been detected in systems for which the accretion rate is
derived to be between 0.1 and 0.25 times that limit. The question arises
whether this is a selection effect or an intrinsic property.
Therefore, we have undertaken a systematic study of data from the
BeppoSAX Wide Field Cameras on the luminous source GX 17+2, comprising
10 Msec of effective observing time on superbursts. GX 17+2 contains a
neutron star with regular Type-I X-ray bursts and accretes matter
within a few tens of percents of the Eddington limit. We find four
hours-long flares which reasonably match superburst
characteristics. Two show a sudden rise (i.e., faster than 10 s), and
two show a smooth decay combined with spectral softening. The implied
superburst recurrence time, carbon ignition column and quenching time
for ordinary bursts are close to the predicted values. However, the
flare decay time, fluence and the implied energy production of
(2–4) 1017 erg g-1 are larger than expected from
current theory.
Key words: X-rays: binaries / X-rays: bursts / X-rays: individuals: GX 17+2 / nuclear reactions, nucleosynthesis, abundances
© ESO, 2004
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