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Discovery of the 198 Second X‐Ray Pulsar GRO J2058+42

1998; IOP Publishing; Volume: 499; Issue: 2 Linguagem: Inglês

10.1086/305677

1538-4357

C. A. Wilson, Mark H. Finger, B. Alan Harmon, Deepto Chakrabarty, Tod E. Strohmayer,

Gamma-ray bursts and supernovae

GRO J2058+42, a transient 198 s X-ray pulsar, was discovered by the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (CGRO) during a "giant" outburst in 1995 September-October. The total flux peaked at about 300 mcrab (20-50 keV) as measured by Earth occultation. The pulse period decreased from 198 to 196 s during the 46 day outburst. The pulse shape evolved over the course of the outburst and exhibited energy-dependent variations. BATSE observed five additional weak outbursts from GRO J2058+42, each with a 2 week duration and a peak-pulsed flux of about 15 mcrab (20-50 keV), that were spaced by about 110 days. An observation of the 1996 November outburst by the Rossi X-Ray Timing Explorer (RXTE) proportional counter array (PCA) localized the source to within a 4' radius error circle (90% confidence) centered on R.A. = 20h590, decl. = 41°43' (J2000). Additional shorter outbursts with peak-pulsed fluxes of about 8 mcrab were detected by BATSE halfway between the first four 15 mcrab outbursts. The RXTE All-Sky Monitor detected all eight weak outbursts with approximately equal durations and intensities. GRO J2058+42 is most likely a Be/X-ray binary that appears to outburst at periastron and apastron. No optical counterpart has been identified to date, and no X-ray source was present in the error circle in archival ROSAT observations.