V4641 Sgr X-Ray Activity
ATel #536; J. H. Swank (NASA/GSFC), E. A. Smith (NASA/GSFC & L-3), & C. B. Markwardt (Univ. MD and NASA/GSFC)
on 25 Jun 2005; 22:05 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: Jean Swank (swank@milkyway.gsfc.nasa.gov)
Subjects: X-ray, Request for Observations, Black Hole, Transient
In response to reports on vsnet-alert (by Stubbings, Uemura, Kubota,
Akira, and Monard) that V4641 Sgr was exhibiting significant optical
activity, RXTE carried out a short
pointing (16 minutes) to check whether the source is also X-ray
active. We observed June 25.338-25.370, slightly overlapping an
optical observation by Stubbings. We observed an average of 8.6e-11
ergs/cm2/s 2-10 keV and 6.4e-10 ergs/cm2/s 10-60 keV. The spectrum
was hard (photon spectral index 0.80) with strong (1.6 keV equivalent
width) fluorescent Fe line emission. The source was variable by a
factor of 5 in flares with a time scale of 100s, similar to the
activity shown in low level outbursts in 2002, 2003, and
2004. Additional RXTE observations are being planned.
