[vsnet-alert 8476] V4641 Sgr: X-ray flare (fwd: ATEL #536)

[Taichi Kato]

V4641 Sgr: X-ray flare (fwd: ATEL #536)

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)
Password Certification: Jean Swank (swank at milkyway.gsfc.nasa.gov)

Subjects: X-ray, Request for Observations, Black Holes, Transients

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.