Swift/BAT reports renewed activity from Cir X-1
ATel #3505; H. A. Krimm (CRESST/GSFC/USRA), S. D. Barthelmy (GSFC), W. Baumgartner (CRESST/GSFC/UMBC), J. Cummings (CRESST/GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), C. B. Markwardt (GSFC), D. Palmer (LANL), T. Sakamoto (CRESTT/GSFC/UMBC), G. Skinner (CRESST/GSFC/UMD), M. Stamatikos (OSU/GSFC), J. Tueller (GSFC), T. Ukwatta (GSFC/MSU)
on 21 Jul 2011; 20:32 UT
Credential Certification: Hans A. Krimm (Hans.Krimm@nasa.gov)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
The Swift/BAT hard X-ray transient monitor reports renewed activity in the 15-50 keV band from the LMXB accreting neutron star system Cir X-1. The source has increased in intensity from non-detection on 2011 July 12 (1-sigma upper limit of 0.002 cts/cm2/s) to 0.020 +/- 0.0012 cts/cm2/sec (~90 mcrab) on 2011 July 18 (MJD 55760) with emission remaining roughly constant or possibly rising since then. This is the fourth episode of increased activity detected by the BAT over multiple days since the outburst of Cir X-1 reported beginning 2010 May 7 (Nakajima et al, ATel #2608). The earlier episodes were 2010 June 25 to July 6 (MJD 55372-55383; peak 85 mCrab), 2011 Jan. 27 to Feb. 16 (MJD 55588-55608; peak 55 mCrab) and 2011 April 28 to May 3 (MJD 55679-55684; peak 110 mCrab). We note that the rebrightening of Cir X-1 reported in June 2011 in the 4-10 keV band by Isobe et al (ATel #2674) preceded the increase in BAT flux by about 10 days. This suggests that the hard and soft X-ray emission from Cir X-1 are not correlated.
BAT hard X-ray transient monitor light curve for Cir X-1
