HEXE/Mir-Kvant observations of the bursting X-ray pulsar GRO J1744-28

Details HEXE/Mir-Kvant observations of the bursting X-ray pulsar GRO J1744-28 HEXE/Mir-Kvant observations of the bursting X-ray pulsar GRO J1744-28

Jul 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997astl...23..421b&link_type=abstract

Astronomy Letters, Volume 23, Issue 4, July 1997, pp.421-432; Pis'ma v Astronomicheskii Zhurnal, Vol. 23, p. 483

Astronomy and Astrophysics

Astronomy

1

Scientific paper

We present the results of a timing and spectral analysis of the bursting X-ray pulsar GRO J1744-28 performed by the HEXE instrument of the Mir-Kvant Observatory. In early 1996, we carried out two series of observations separated by a month and detected no significant prolonged luminosity variations. The mean luminosity in the energy range 20-100 keV was ~ 2 x 10^36d^2 erg s^-1 and ~ 1.5 x 10^36d^2 erg s^-1 during the first and second series of observations, respectively (assuming that a point source is located at distance d kpc). The period of the pulsar, ~0.46706 s, and the rate of its evolution match the BATSE values. The constructed pulse profile is nearly sinusoidal in shape, and the pulse fraction changes from ~20% (rms ~ 13.8 +/- 0.6% at energies up to 30 keV to ~25% (rms ~ 17.5 +/- 1.2%) in harder energy channels. During the observations, four strong bursts of duration 8-10 s were detected. The burst luminosity at maximum was a factor of 5-10 higher than the mean value for the source. After each of the bursts, the flux from the source rapidly decreased to ~80% of the normal level and then began to slowly rise. However, the temporal properties of these processes differ for different bursts. Within the limits of the available statistics, the 20-80-keV burst spectra are similar to the spectrum of the primary component. The averaged spectrum of the source turned out to be harder than the spectrum pre dicted by the `canonical' model and exhibits a considerable excess of photons in the band 60-120-keV, which can be offset either by introducing an additional power-law component or (in part) by introducing an absorption gyroline at energy E_1 ~ 45 keV. However, because of the high density of sources in the region of the Galactic center, the additional component cannot be uniquely attributed to GRO J1744-28.

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