Repost form the AAVSO list: Message: 1 Date: Fri, 21 Aug 2009 22:30:50 +0400 (MSD) From: Kirill Sokolovsky <ksokolov@mpifr-bonn.mpg.de> Subject: [Aavso-photometry] Request for observations: multicolor photometry of 3C 273 is needed urgently To: aavso-discussion@mira.aavso.org, aavso-photometry@aavso.org, aavso-hen@aavso.org Message-ID: <Pine.LNX.4.64.0908212216540.10950@tau.asc.rssi.ru> Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Dear observers, quasar 3C 273 (12:29:06.7 +02:03:08, J2000, V~12.5-13.0 mag.) is currently undergoing a major gamma-ray flare as indicated by Fermi space telescope observations, see ATel #2168 http://www.astronomerstelegram.org/?read=2168 and Fermi gamma-ray lightcurve http://fermi.gsfc.nasa.gov/FTP/glast/data/lat/catalogs/asp/current/lightcurv... Me and my colleagues are planning to conduct radio VLBI observations of this event with the VLBA and X-ray observations with the RXTE satellite. It is very desirable to have multicolor optical photometry of this object around the time of radio and X-ray observation which will take place some time next week. This observations will allow to reconstruct the Spectral Energy Distribution (SED) from radio to gamma-rays of this object during the flare. If multi-epoch observations are possible, an interesting comparison of optical and gamma-ray lightcurves could be made. Unfortunately, 3C 273 is currently situated very close to the Sun which makes it a very challenging target for observations. The object could be seen at low altitude after the sunset, observers at the southern hemisphere are in more favorable conditions then thouse in the north. Photometry in (at least any subset of) Johnson-Cousins UBVRI filters is needed starting from now to (approximately) end of next week. Please submit your observations to the AAVSO International Database or send them directly to me by e-mail: ksokolov@mpifr-bonn.mpg.de The finding chart and list of comparison stars may be obtained here: http://www.lsw.uni-heidelberg.de/projects/extragalactic/charts/1226+023.html or using the VSP http://www.aavso.org/observing/charts/vsp/index.html?pickname=3C%20273 Use of many comparison stars simultaneously (ensemble photometry) is recommended, if possible. Of course, everybody who will be able to contribute observations will be properly acknowledged when it comes to publication of the results. Best wishes, Kirill Sokolovsky graduate student at the Max Planck Institute for Radio Astronomy (Bonn, Germany)