Swift/BAT detects an outburst from EXO 2030+375
ATel #861; H. Krimm (GFSC/USRA), S. Barthelmy (GSFC), N. Gehrels (GSFC), C. Markwardt (GSFC/UMD), D. Palmer (LANL), D. Sanwal (GSFC/JHU), J. Tueller (GSFC)
on 20 Jul 2006; 21:02 UT
Credential Certification: Hans A. Krimm (krimm@milkyway.gsfc.nasa.gov)
Subjects: X-ray, Binary, Neutron Star
Referred to by ATel #: 868, 877
Observations with the Burst Alert Telescope (BAT) on Swift show that the Be/neutron star binary EXO 2030+375 is currently in outburst in the 15-50 keV energy range. The high energy outburst started about June 21, 2006 (MJD 53906) four days after the outburst was first detected by the RXTE All-Sky Monitor (ATel #843, Corbet & Levine). The count rate rose steadily from 0.04 +/- 0.007 cts/sec/cm^2 on June 21 to a peak of 0.17 +/- 0.017 cts/s/cm^2 on July 9. The count rate has been roughly constant since that time. The peak count rate corresponds to approximately 750 mCrab.
We note that prior to the current outburst, EXO 2030+375 showed periodicity in the BAT light curve on the known 46-day orbital period, with a pre-outburst peak of 0.035 cts/s/cm^2. In the discovery observations (Parmar et al, ApJ 338, 359, 1989), no modulation at the orbital period was seen. The current outburst began at approximately the same point in orbital phase as the rises seen in the periodic bursts, however the count rate from this outburst continued to rise after the point in phase when periodic bursts have begun to decline.
