Radio Observations of V4641 Sgr

VLA data: Michael Rupen, Amy Mioduszewski, & Vivek Dhawan

maintained by
Michael Rupen

Last update: 24 August 2004

This reflects my best current understanding of on-going observations of V4641 Sgr (= SAX J1819.3-2525). If you know of any not listed here, or know this to be out of date, or simply want further information, please send me e-mail at .

This page is intended to help observers schedule simultaneous observations at different wavelengths. Given the ridiculously fast and strong variability of this source, one needs truly simultaneous observations to figure out what's going on. Multi-wavelength studies are essential to understand physics as basic as the emission mechanisms. Please help by telling me when you have been or will be observing!

Helpful Information for the Observer


The best radio position so far is (ATel #172)

18 19 21.634    -25 24 25.845 (J2000)
with an uncertainty of +/-30 milliarcseconds. There is a nice radio calibrator (ICRF source), J1820-2528, about 27 arcminutes away.

Finding Chart and Reference Stars

This is taken directly from the old VSNet web page, which alas has vanished. It is reproduced here purely for your convenience.

(Peter Nelson's V-band CCD image; suggested comparison stars are marked).

Radio light curve

Our most recent data are reported in ATel #305: no radio detections since 20 July 2004, with the most recent radio data taken on 22 August 2004 (rms 0.10 mJy/beam at 8.5 GHz).

This includes both VLA data (our program) and ATCA data (from Bob Sault's Web page). The colors represent different frequencies, as indicated (labels are in GHz); the error bars are intended to be 1sigma, while the upper limits represent 3sigma plus the nominal value at the location of the source. The latest data shown here were taken on 28 July 2004, giving no detection with a nominal flux density at the position of the source of 0.05 +/- 0.04 mJy/beam at 8.46 GHz. The variations seen on individual days (e.g., 7 July 2004= MJD 53193) are real; see the ATCA Web page for a lovely example.

Radio light curve as of 29jul04

Schedule of Upcoming Observations

Sources and last updates

VLA -- M.Rupen, 6aug04
RXTE -- short-term schedule, 6aug04
Chandra -- P. Jonker, 4aug04

Misc. information

The Schedule

Green listings represent radio observations
Black telescopes are X-ray satellites
Red listings represent optical/infrared observations

Note that the VLA schedule does not appear until the end of the month -- we expect further observations in September, probably every week or two.

Telescope UT start & stop comments
VLA 15 Aug. 2004: 0305-0435 UT short observations
VLA 22 Aug. 2004: 0237-0407 UT short observations
VLA 29 Aug. 2004: 0310-0440 UT short observations

Other V4641 Sgr Links


Please send any questions, comments, or suggestions to Michael Rupen at the e-mail address given below.

Last modified 24 August 2004