Observations of a large flare in GX 1+4 with the Compton gamma ray observatory

Details Observations of a large flare in GX 1+4 with the Compton gamma ray observatory Observations of a large flare in GX 1+4 with the Compton gamma ray observatory

May 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995adspr..15..119s&link_type=abstract

Advances in Space Research (ISSN 0273-1177), vol. 15, no. 5, p. (5)119-(5)122

Astronomy and Astrophysics

Astronomy

5

Gamma Ray Astronomy, Light Curve, Periodic Variations, Pulse Rate, Stellar Flares, X Ray Astronomy, X Ray Binaries, X Ray Spectra, Astronomical Spectroscopy, Gamma Ray Observatory, Rosat Mission, Scintillation, X Ray Telescopes

Scientific paper

The pulsating X-ray binary GX 1+4 (4U 1728-24) was observed by Oriented Scintillation Spectrometer Experiment (OSSE) onboard the Compton Gamma Ray Observatory (CGRO) from 9 to 21 September 1993 as a target of oppurtunity after Burst and Transient Source Experiment (BATSE) had detected the onset of a large flare by the greatly increased pulsed flux at the period of approximately 2 min. The total flux in the 40-100 keV range as observed by the OSSE reached its maximum of 83 mCrab on 14/15 September, after which it fell sharply to about 31 mCrab within 2 days. The spectrum is well described by thermal type spectra. The characteristic temperature of the average OSSE spectrum for a thermal Bremsstrahlung model is kT = (35.5 +/- 0.5) keV. A single power law can be ruled out. There is evidence for a hardening of the spectrum with decreasing intensity at the end of the flare. The barycentric pulse period was (120.567 +/- 0.005) s on 5 September. The average spin-down rate as taken from the standard BATSE analysis was dP/dt = 0.0105 s/day, and constant over the time of the flare. A further target of oppurtunity (TOO) observation with the ROSAT Position Sensitive Proportional Counter (PSPC) on 18 September led to the first detection of the source with a reflecting X-ray telescope and to a signifcantly improved position: RA(2000) = 17h 32m 2.1s and DEC(2000) = -24 deg 44 min 44 sec. This position 3.5 sec from V2116 Oph, with a 90% error radius of 8 sec is the most accurate so far obtained with an X-ray instrument, thus confirming the identification with the suspected stellar counterpart.

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