Swift/BAT detection of IGR J19294+1816

ATel #1999; 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 (CRESST/GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (CRESTT/GSFC/UMBC), G. Skinner (CRESST/GSFC/UMBC), J. Tueller (GSFC), T. Ukwatta (GSFC/GWU)
on 31 Mar 2009; 22:24 UT
Credential Certification: Hans A. Krimm (Hans.Krimm@nasa.gov)

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Examination of archival data from the Swift/BAT hard X-ray transient monitor reveals that Swift/BAT has detected the newly discovered source IGR J19294+1816 (Turler et al, ATel #1997) several times during the past three years. The detections were

2006-01-13 = MJD 53748: 0.002 ± 0.0003 ct/s/cm^2 (7 mCrab)
2006-11-13 = MJD 54052: 0.001 ± 0.0004 ct/s/cm^2 (6 mCrab)
2007-04-27 = MJD 54217: 0.003 ± 0.0006 ct/s/cm^2 (11 mCrab)
2007-12-15 = MJD 54449: 0.002 ± 0.0004 ct/s/cm^2 (8 mCrab)
2008-08-03 = MJD 54681: 0.002 ± 0.0003 ct/s/cm^2 (7 mCrab)
2008-09-28 = MJD 54737: 0.001 ± 0.0006 ct/s/cm^2 (6 mCrab)
2008-12-01 = MJD 54801: 0.002 ± 0.0006 ct/s/cm^2 (9 mCrab)

All results are for 8-day averages starting on the day listed and are for the 15-50 keV band. The archive used for this search starts on 2006-01-01.

Most recently, the source rose to 0.006 ± 0.001 ct/s/cm^2 (25 mCrab) in the daily average for 2008-03-23 (MJD 54913). It remained above 10 mCrab until 2008-03-28, but has now faded below detectability.

We associate these detections with episodic increased source activity. We also note that the average time between the 2008 detections is 60 ± 4 days and that the times between the more temporally dispersed detections are multiples of 56 ± 4 days. The 3-sigma upper limit for the "missing" detection at around 2009-01-26 is .003 ct/s/cm^2 (12 mCrab). Although it will require further observations and analysis to confirm, this regularity is suggestive of some sort of periodicity in the system.