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ATEL # 1061; H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), L. Barbier (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC) on behalf of the Swift-BAT team
on 24 Apr 2007; 21:29 UT
Password Certification: Hans A. Krimm (email@example.com)
Subjects: X-ray, Gamma Ray, Binaries, Transients
Swift-BAT reports that the microquasar Cygnus X-3 appears to be re-entering the high-soft state that it left in early March 2007 (ATEL #1028). The BAT count rate in the 15-50 keV energy band has fallen from a high of 0.05 +/- 0.0025 counts/sec/cm^2 (220 +/- 11 mCrab) on March 15, 2007 to its current level of 0.01 +/- 0.004 counts/sec/cm^2 (50 mCrab +/- 20 mCrab) on April 24, 2007. At the current rate of decline we expect the flux to fall below 10 mCrab within a week. We note that the decline in the BAT count rate mirrors a rise in the count rate seen in the All-Sky Monitor (ASM) on RXTE from 5 counts/sec in mid-March, 2007 to 21 counts/sec on April 17.
We believe that Cygnus X-3 was indeed in the low-hard state from mid-February to late March, 2007 and not in an extended flare because (1) the BAT rate averaged 180 mCrab during this period, above the peak of any of the flares reported in ATEL #1028, (2) the ASM count rate fell below 5 counts/sec which it did not do during the previous high-soft state, and (3) the duration of the high BAT emission lasted more than 50 days compared to between 12 and 23 days for the flares.
The BAT rates are based on values from the Swift/BAT Hard X-ray Transient Monitor (ATEL #904), http://swift.gsfc.nasa.gov/docs/swift/results/transients/CygX-3/. The ASM results are quick-look results provided by the ASM/RXTE team: http://xte.mit.edu/asmlc/srcs/cygx3.html
Cyg X-3 Observations With Swift/BAT