Cygnus X-3 re-enters the low-hard state

ATel #1028; 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 12 Mar 2007; 22:34 UT
Credential Certification: Hans A. Krimm (krimm@milkyway.gsfc.nasa.gov)

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Swift-BAT reports that the microquasar Cygnus X-3 has apparently left the high-soft state that it entered in December, 2005. Since Feb. 6, 2007 (MJD 54138), Cygnus X-3 has been detected in the Burst Alert Telescope (BAT) on Swift at above 130 mCrab and since March 3 (MJD 54162) it has been consistently above 170 mCrab. This is comparable to its mean rate in the BAT before December 2005 when it was found to vary between 120 and 270 mCrab. This rise in 15-50 keV X rays is mirrored by a similar decline in counts seen in the the All-Sky Monitor (ASM) on RXTE which has averaged 10 counts/sec since Feb 11, 2007 and 5 counts/sec since March 7, compared to an average of 20 counts/sec during the quenched state.

From late December 2005 until early February, 2007, Cygnus X-3 had been simultaneously in a low state in the 15-50 keV X rays observed by BAT and in a high state in the 2-10 keV range as observed by the ASM. During this high-soft state there were five episodes of hard X-ray flaring (considered as daily average flux above 100 mCrab), each lasting for between 12 and 23 days:

May 10-24, 2006: peak 130 +/- 5 mCrab
June 7-28, 2006: peak 135 +/- 19 mCrab
July 26-Aug. 15, 2006: peak 138 +/- 7 mCrab
Oct 7-19, 2006: peak 138 +/- 8 mCrab
Nov 22-Dec 15, 2006: peak 140 +/- 10 mCrab

The May episode (ATEL #807) was temporally consistent with reported radio flares (ATEL #806, #809), the June episode started two days after another radio flare (ATEL #828) and the November episode also coincided with radio flares (ATEL #952).

A figure showing both the BAT and ASM rates for this period can be found at http://swift.gsfc.nasa.gov/docs/swift/results/transients/CygX-3/ATEL/

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/. The ASM results are quick-look results provided by the ASM/RXTE team: http://xte.mit.edu/ASM_lc.html

Cyg X-3 Observations With Swift/BAT and RXTE/ASM