Observations of short-duration X-ray transients by WATCH on Granat

A.J. Castro-Tirado, Søren Kristian Brandt, Niels Lund, R. Sunyaev

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    Abstract

    During 1990-92, the WATCH all-sky X-ray monitor on Granat discovered six short-duration X-ray transients. In this paper we discuss their possible relationship to peculiar stars. Only one of the fast (few hours) X-ray transients (GRS 1100-771) might be tentatively ascribed to a superflare arising from a young stellar object in the Chamaeleon I star-forming cloud. At the distance of similar to 150 pc, L-x = 1.35 x 10(34) erg s(-1). (8-15 keV), or 2.6 x 10(34) erg s(-1) (0.1-2.4 keV) assuming a thermal spectrum with kT similar to 10 keV, a temperature higher than those previously seen in T Tauri stars (Tsuboi et al. 1998). The peak X-ray luminosity is at least 2 times higher than that derived for the protostar IRS 43 (Grosso et al. 1997) which would make - to our knowledge- the strongest flare ever seen in a YSO. However, the possibility of GRS 1100-771 being an isolated neutron star unrelated to the cloud cannot be excluded, given the relatively large error box provided by WATCH. Regarding the longer duration (similar to 1 day) X-ray transients, none of them seem to be related to known objects. We suggest that the latter are likely to have originated from compact objects in low-mass or high-mass X-ray binaries, similarly to XTE J0421+560.
    Original languageEnglish
    JournalAstronomy and Astrophysics
    Volume347
    Issue number3
    Pages (from-to)927-931
    ISSN0004-6361
    Publication statusPublished - 1999

    Keywords

    • X-rays : bursts
    • ISM : individual objects : Chamaeleon I cloud
    • stars : pre-main sequence
    • stars : flare
    • X-rays : stars

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