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GRO J1008-57 Brightening

ATel #413; Jean Swank (GSFC) for the RXTE team
on 19 Feb 2005; 00:06 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Jean Swank (swank@milkyway.gsfc.nasa.gov)

Subjects: X-ray, Binary, Transient, Pulsar

Referred to by ATel #: 4759, 7490

The transient pulsar GRO J1008-57 may be starting an outburst. On Feb 18.00, the ASM on the Rossi X-Ray timing Explorer (RXTE) detected a flux of 36(3) mCrab. The source first spent a week, starting on Feb 6, at a level of 5 mcrab; it then rose to 20 mcrab on Feb 15. The ASM hardness ratio HR2 is 2.0(0.3), consistent with a pulsar spectrum, in comparison to the Crab at 1, though soft compared to the still active V0332+53. The Gamma-Ray Observatory discovered 93.5 s pulsations in the discovery outburst of July 1993, which reached a peak of 1.4 Crab (Bildsten et al. 1997, ApJS. 113, 367; Shrader et al. 1999, ApJ, 512,920). A probable Be star companion was found at that time (Coe et al. 1994, MNRAS, 270, L57).