Chandra observations of the neutron star soft X-ray transient RX J170930.2-263927 returning to quiescence

P G Jonker, M Mendez, G Nelemans, R Wijnands, M van der Klis

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35 Citations (Scopus)

Abstract

We present our analysis of Chandra observations obtained when the soft X-ray transient RXJ170930.2-263927 (XTE J1709-267) returned to quiescence after an outburst. Using the type I burst peak luminosity found by Cocchi et al. and the value of N-H we derived from our spectral fits, the distance to RX J170930.2-263927 can be constrained to 2.5-10 kpc. RX J170930.2-263927 is probably associated with the low-metallicity globular cluster NGC 6293, which has a tidal radius of 14.2 arcmin, as the projected distance to the centre of the cluster is approximately 25 pc (9-10 arcmin). If the association is correct, RX J170930.2-263927 would be at similar to8.5 kpc. We determined that L-outburst/L-quiescence greater than or similar to 10(5) for this outburst. If the quiescent luminosity is caused by cooling of the neutron star core then enhanced core cooling processes were at work, implying a neutron star mass of similar to1.7-1.8 M-circle dot . Combining our Chandra observations with archival ROSAT observations we show that the source very probably exhibits periods of sustained low-level accretion. Variable, low-level activity could provide an alternative explanation for some of the sources in the recently proposed category of faint soft X-ray transients. We found excess emission at similar to0.6 keV. If such an excess is a unique feature of ultracompact systems, as was recently proposed, RX J170930.2-263927 must have a short orbital period as well. From the constraints on the distance and the non-detection of the optical counterpart with m(V) 20.5, we conclude that this system must have a low-mass companion.

Original languageEnglish
Pages (from-to)823-831
Number of pages9
JournalMonthly Notices of the Royal Astronomical Society
Volume341
Publication statusPublished - 21 May 2003

Keywords

  • stars : individual
  • RX J170930.2-263927
  • stars : neutron
  • X-rays : stars
  • BLACK-HOLE CANDIDATE
  • MILLISECOND PULSAR
  • ROSAT OBSERVATIONS
  • GLOBULAR-CLUSTERS
  • ACCRETING PULSAR
  • SAX J1808.4-3658
  • GALACTIC BULGE
  • DWARF NOVAE
  • AQUILA X-1
  • XMM-NEWTON

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