Volume 382, Number 2, FebruaryI 2002
|Page(s)||503 - 512|
|Section||Cosmology (including clusters of galaxies)|
|Published online||15 February 2002|
A half-a-day long thermonuclear X-ray burst from KS 1731-260
SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
2 Astronomical Institute, Utrecht University, PO Box 80000, 3508 TA Utrecht, The Netherlands
3 University of Michigan, Department of Physics, Ann Arbor, MI 48109, USA
4 Istituto di Astrofisica Spaziale (CNR), Area Ricerca Roma Tor Vergata, via del Fosso del Cavaliere, 00133 Roma, Italy
Corresponding author: E. Kuulkers, E.Kuulkers@sron.nl
Accepted: 6 November 2001
We report on an approximately twelve hour long X-ray flare from the low-mass X-ray binary KS 1731-260. The flare has a rise time of less than 13 min and declines exponentially with a decay time of 2.7 hours. The flare emission is well described by black-body radiation with peak temperature of 2.4 keV. The total energy release from the event is 1042 erg (for an assumed distance of 7 kpc). The flare has all the characteristics of thermo-nuclear X-ray bursts (so-called type I X-ray bursts), except for its very long duration and therefore large energy release (factor of 1500–4000 longer and 250–425 more energy than normal type I X-ray bursts from this source). The flare is preceded by a short and weak X-ray burst, possibly of type I. Days to weeks before the flare, type I X-ray bursts were seen at a rate of ~3 per day. However, after the flare type I X-ray bursting ceased for at least a month, suggesting that the X-ray flare affected the type I bursting behaviour. The persistent emission is not significantly different during the non-bursting period. We compare the characteristics of this event with similar long X-ray flares, so-called superbursts, seen in other sources (4U 1735-44, 4U 1820-30, 4U 1636-53, Ser X-1, GX 3+1). The event seen from KS 1731-260 is the longest reported so far. We discuss two possible mechanisms that might cause these superbursts, unstable carbon burning (as proposed recently) and electron capture by protons with subsequent capture of the resulting neutrons by heavy nuclei.
Key words: accretion, accretion disks / binaries: close / stars: individual (KS 1731-260) / stars: neutron / X-rays: bursts
© ESO, 2002
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.