BATSE Soft Gamma-Ray Observations of GROJ0422+32

Details BATSE Soft Gamma-Ray Observations of GROJ0422+32 BATSE Soft Gamma-Ray Observations of GROJ0422+32

Apr 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002aps..aprn17091l&link_type=abstract

American Physical Society, April Meeting, Jointly Sponsored with the High Energy Astrophysics Division (HEAD) of the American As

Astronomy and Astrophysics

Astrophysics

Scientific paper

We report results of a comprehensive study of the soft gamma-ray (30 keV to 1.7 MeV) emission of GROJ0422+32 during its first known outburst in1992. These results were derived from CGRO BATSE data made available by the BATSE team at MSFC, and analyzed using the analysis package (EBOP) developed at JPL. Our analyses focus on the long-term temporal and spectral variability of the source emission associated with the outburst, and complement those reported earlier by BATSE (Harmon et al. 1993), OSSE (Grove et al. 1998), COMPTEL (Van Dijk et al. 1995) and SIGMA(Sunyaev et al. 1993; Roques et al. 1994). The light curves show marked differences between low (30-200 keV) and high (200-700 keV) energy, with corresponding spectral variability over the course of the 200-day event. After the onset of the outburst on 5 August 1992 (TJD 8839), the 200-700 keV flux reached the first of two sub-maxima during the peak-phase of the event on 9 August (TJD 8843). The lower-energy (30-200 keV) flux lagged by approximately 5 days, reaching its first sub-maximum on 14 August (TJD 8848). After the first sub-maximum, the high-energy flux declined for the about nine days before rising again to a second sub-maximum on 28 August (TJD 8862). However the 30-200 keV flux, after the first peak, reached its second sub-maximum a week earlier, on 21 August (TJD 8855), and was well into decline by the second peak of the >200 keV flux. The so-called “secondary maximum” of the 30-200 keV flux at TJD 8970-8981 reported earlier (Harmon et al. 1993) was also prominently observed in the 200-300 keV bin, but became less pronounced at higher energies. During this period the spectrum evolved from a power-law with photon index of 1.75 on TJD 8839, to a shape that can be described by either a Comptonized model or a power law with an exponential cut-off. The spectrum measured around TJD 8862, during the second sub-maximum of the >200 keV flux, shows a high-energy power-law tail from 400 keV to 1 MeV, superposed on the Compton-like spectrum at lower energy. The spectral shape then remained roughly the same until 9 November (TJD 8935), when it evolved back to the power law form. During this period the 35-500 keV flux gradually decreased by a factor of ten from the peak value to approximately the same level as seen on TJD 8839. The correlation of the two spectral shapes (e.g. Compton/power law tail vs. power law) with the high and low luminosities of the soft gamma-ray (35-500 keV) emission is strongly reminiscent of that seen in Cygnus X-1; the similarity supports the belief that both systems contain black-holes.

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