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Detection of a simultaneous optical and gamma-ray flare from blazar PMN J2345-1555

ATEL # 2972; D. Donato (NASA/GSFC) on behalf of the Fermi LAT Collaboration, M. Hauser, S. Wagner (LSW Heidelberg), H. Hagen (Sternwarte Hamburg) on behalf of the ATOM team
on 26 Oct 2010; 19:30 UT
Password Certification: Davide Donato (

Subjects: Optical, Gamma Ray, >GeV, Transients
Referred to by ATEL #: 2977, 2986, 2989, 3004

On October 24, 2010 the Automatic Telescope for Optical Monitoring (ATOM), operated by the H.E.S.S. collaboration and located next to the H.E.S.S. IACT array in Namibia, showed significant optical flaring activity of the intermediate redshift flat spectrum radio quasar PMN J2345-1555 (RA=23:45:12.5, Dec=-15:55:07.8 (J2000); Petrov et al. 2006, AJ, 131, 1872; z=0.621, Healey et al. 2008, ApJS, 175, 97). The optical source was observed to have brightened by 2 mag in the last week (Oct 17th: R=16.1mag, Oct 24: R=14.6mag, Oct 25: R=14.0mag) and by 4 mag with respect to its faint state in July 2010. The R-band brightness of this source monitored by ATOM during the last year varied between R=15.9mag in January 2010 and a faint state of R=18.4mag in July 2010.

Also the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope, has observed a flare from a source positionally consistent with this blazar. Preliminary analysis indicates that the source showed a bright gamma-ray outburst with a daily flux (E>100MeV) of (0.6 +/- 0.2) x 10^-6 ph cm^-2 s^-1 (errors are statistical only), a factor of 15 greater than that reported in the Fermi-LAT 1st year catalog (1FGL J2344.6-1554; Abdo et al. 2010, ApJS 188, 405).

Because Fermi operates in all-sky survey mode, gamma-ray monitoring of this source will continue. In consideration of the activity of this source we strongly encourage multiwavelength observations. The Fermi LAT contact person for this source is D. Donato (

The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.

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R. E. Rutledge , Editor
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