V4641 Sgr entering new period of activity
ATel #540; I. Khamitov, M. Parmaksizoglu, Z. Tunca, Z. Aslan (TUG),R. Burenin, M. Revnivtsev, M. Pavlinksy, R. Sunyaev (IKI),I. Bikmaev, N. Sakhibullin (KGU)
on 29 Jun 2005; 17:09 UT
Credential Certification: M. Revnivtsev (mikej@mpa-garching.mpg.de)
Subjects: Optical, Request for Observations, Binary, Black Hole
We observed V4641 Sgr with 1.5-m Russian-Turkish telescope (RTT150) on June
27 from 00:08 till 00:53(UT) in response to HETE alert distributed through
Bacodine. The observations were continued during the following two nights on
June 27 from 21:24 till June 28 00:53 (UT) and on June 28 from 22:02 till
23:41 (UT).
The source was variable during the first night in Rc filter in a time scale
of approximately 30 minutes and was brighter by 0.1 mag than the
corresponding phase in its light curve in quiescence, showing that source is
now entering a new period of activity. The variability is growing, reaching
a level about 1 mag above the light curve in the third night of
observations. Similar brightening above the phased light curve was observed
during the period of activity in 2004 between the optical flares (Revnivtsev
et al., ATEL 297; Bikmaev et al., ATEL 309). The phased light curve with
June 26, 27 and 28 data points can be found at: http://www.tug.tubitak.gov.tr/~irekk/V4641Sgr/2005/phase_2005June.jpg
The light curve with the June 28 data points where we see strong variability
can be found at: http://www.tug.tubitak.gov.tr/~irekk/V4641Sgr/2005/lc20050628.jpg
We therefore confirm RXTE findings in X-rays (Swank et al., ATEL 536) and
earlier VSNET alert.
Further observations at all wavelengths are encouraged.
