[AAVSO-HEN] Request for observations: multicolor photometry of 3C 273 is needed urgently

[Kirill Sokolovsky]

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/lightcurves/3C273_86400.png

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 at 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)