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INTEGRAL detects the BeXRB GS 0834-43 returning to an active state

ATel #4218; S. P. Drave (Univ. of Southampton), V. Sguera (INAF/IASF Bologna), A. J. Bird, M. Goossens (Univ. of Southampton), L. Sidoli (INAF/IASF Milano), A. Bazzano, M. Fiocchi (INAF/IASF Roma) on behalf of the INTEGRAL/GPS team
on 27 Jun 2012; 15:08 UT
Credential Certification: Sebastian Drave (sd805@soton.ac.uk)

Subjects: X-ray, Binary, Neutron Star, Transient

Referred to by ATel #: 4235, 8175

During INTEGRAL Galactic Plane Scan (GPS) observations between 2012-06-26 06:44:07 and 2012-06-26 15:27:19 (UTC) the BeXRB GS 0834-43 was detected at a high level of significance of 47 sigma by IBIS/ISGRI (net exposure time of 15.8 ks). The source had a count rate of 20.1 ± 0.4 in the 18-60 keV energy band, corresponding to a flux of 109 ± 2 mCrab. GS 0834-43 was also in the field of view of the JEM-X soft X-ray instrument for an exposure time of 1.7 ks during these observations where it was detected at a significance of 19 sigma. The count rate in the 3-10 keV energy band was 1.41 ± 0.08 counts per second, corresponding to a flux of 64 ± 4 mCrab in this band.

A light curve with 200 second bin times was extracted from the IBIS data and it was seen that the source flux remained constant, within errors, with no evident sign of flaring activity throughout the duration of the observations. A spectrum was also extracted and fit in the energy range with the best signal-to-noise (53 sigma), namely 18-40 keV. A simple powerlaw model was used and an acceptable fit (red. χ2 of 1.4 for 9 d.o.f.) was achieved with Γ = 2.98 ± 0.21. The corresponding 18-60 keV flux was 1.8 × 10-9 erg/cm2/s.

GS 0834-43 was first detected in outburst by Granat/WATCH in February 1990 (Lapshov et al. 1992) displaying an outburst with a peak flux of ~ 500 mCrab. Subsequently CGRO/BATSE detected GS 0834-43 at regular intervals until June 1993 (Wilson et al. 1997). No outbursts were detected with BATSE after this date and the source has not been detected by monitoring instruments such as Swift/BAT (Cusumano et al. 2010) or INTEGRAL/IBIS (Bird et al. 2010) between that date and now. This new, strong detection may therefore be signalling a renewed period of activity of GS 0834-43 after a long period of inactivity in the system.

We encourage multi-waveband follow up of this system to investigate the cause of the renewed activity in GS 0843-34. INTEGRAL will continue to provide hard X-ray coverage of the source until approximately mid-July through the GPS program, the results of which can be found here:
http://gpsiasf.iasf-roma.inaf.it/