EDP Sciences Journals List
Advanced Search
Subscriber Authentication Point
Home All issues Volume 382/2 Article
Free access article

Issue A&A
Volume 382, Number 2, February I 2002
Page(s) 503 - 512
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20011654



A&A 382, 503-512 (2002)
DOI: 10.1051/0004-6361:20011654

A half-a-day long thermonuclear X-ray burst from KS 1731-260

E. Kuulkers1, 2, J. J. M. in 't Zand2, 1, M. H. van Kerkwijk2, R. Cornelisse1, 2, D. A. Smith3, J. Heise1, A. Bazzano4, M. Cocchi4, L. Natalucci4 and P. Ubertini4

1  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

(Received 4 September 2001 / Accepted 6 November 2001)

Abstract
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 10 42 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

Offprint request: E. Kuulkers, E.Kuulkers@sron.nl

SIMBAD Objects



© ESO 2002


What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.