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2000MNRAS.311..755G - Mon. Not. R. Astron. Soc., 311, 755-761 (2000/February-1)
Spectral variation in the X-ray pulsar GX 1+4 during a low-flux episode.
GALLOWAY D.K., GILES A.B., GREENHILL J.G. and STOREY M.C.
Abstract (from CDS):
BATSE pulse timing measurements indicate that a torque reversal took place approximately 10d after this observation. Both the mean pulse profile and the photon spectrum varied significantly. The observed variation in the source may provide important clues as to the mechanism of torque reversals.
The single best-fitting spectral model was based on a component originating from thermal photons with kT0~1keV Comptonized by a plasma of temperature kT~7keV. Both the flux modulation with phase during the brightest interval and the evolution of the mean spectra over the course of the observation are consistent with variations in this model component; with, in addition, a doubling of the column density nH contributing to the mean spectral change.
A strong flare of duration ≲50s was observed during the interval of minimum flux, with the peak flux ~20 times the mean level. Although beaming effects are likely to mask the true variation in M{dot} thought to give rise to the flare, the timing of a modest increase in flux prior to the flare is consistent with dual episodes of accretion resulting from successive orbits of a locally dense patch of matter in the accretion disc.
Abstract Copyright: 2000, Royal Astronomical Society
Journal keyword(s): binaries: symbiotic - pulsars: individual: GX 1+4 - X-rays: stars
Simbad objects: 3
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