Swift XRT observations of the black hole binary V4641 Sgr
ATel #1796; Kazutaka Yamaoka (Aoyama Gakuin Univ.), Jeroen Homan (MIT), and Makoto Uemura (Hiroshima Univ.)
on 21 Oct 2008; 20:29 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: Kazutaka Yamaoka (yamaoka@phys.aoyama.ac.jp)
Subjects: X-ray, Request for Observations, Binary, Black Hole, Transient
In response to the recent X-ray and optical activity reported in VSNET
alerts, we have performed a Swift ToO observation of V4641 Sgr on
October 17 2008, for a total exposure of 2.1 ks.
The source was clearly detected in the Swift XRT image. The energy
spectrum was could be fit reasonably well by an absorbed power law with
a photon index of 2.1+-0.2 and a hydrogen column density of
(2.9+-0.6)x10^21 cm^-2. The absorbed fluxes in 0.3-10 keV and 2-10 keV
bands were 2.16e-11 erg/cm^2/s and 1.43e-11 erg/cm^2/s,
respectively, corresponding to ~0.6-0.7 mCrab. Variability up to a
factor of ~4 was seen on a time scale of a few hours.
The source has been active for two weeks now, but at a very low level in
both X-rays and optical. Further multiwavelength observations are
encouraged.
