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Fermi LAT and GASP detections of a concurrent GeV and optical flare from the blazar OJ 287

ATEL # 2256; S. Ciprini (Perugia Univ. / ASI-INAF, Italy), D. Gasparrini (ASDC, Italy), L. C. Reyes (Univ. Chicago / KICP, USA), Y.T. Tanaka (ISAS / JAXA, Japan), G. Tosti (Univ. Perugia / INFN, Italy) on behalf of the Fermi Large Area Telescope Collaboration, M. Villata and C. M. Raiteri (INAF, Osservatorio Astronomico di Torino, Italy), and L. O. Takalo (Tuorla Observatory, University of Turku, Finland), for the GASP-WEBT Collaboration
on 24 Oct 2009; 2:28 UT
Distributed as an Instant Email Notice (Request for Observations)
Password Certification: Stefano Ciprini (

Subjects: Optical, Gamma Ray, >GeV, AGN, Quasars

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope discovered a rapid gamma-ray flare from a source positionally consistent with the optically bright BL Lac object OJ 287 (RA: 08h 54m 48.874s , Dec: +20d 06m 30.64s, J2000.0, Johnston et al. 1995, AJ, 110, 880, -- redshift z=0.306, Falomo, Scarpa, & Bersanelli 1994, ApJS, 93, 125; Sitko & Junkkarinen 1985, PASP, 97, 1158).

Preliminary analysis indicates that on October 22, 2009 (UT), this source showed a rapid gamma-ray flare with daily bin flux (E>100MeV) of (0.98 + / - 0.23 ) x 10^-6 photons cm^-2 s^-1 (statistical only) . This is about one order of magnitude higher than the average flux during the first 11 months of Fermi LAT all-sky survey. The flare occurred likely during the first 6 hours (UT) of this day (exceeding the level of 2 x 10^-6 photons cm^-2 s^-1 in this time bin).

The GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT) reports that the source has been optically bright since the start of this optical season (early October), oscillating in the range R = 13.9-14.2 (data from Crimean, KVA, and St. Petersburg observatories). Last night, on October 22.25 (i.e. in the 6h interval candidate for the rapid gamma-ray flare), OJ 287 was observed at optical R-band magnitude = 13.45 0.02, close to the optical maxima of the last years.

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue, joined with regular optical-to-radio monitoring by ground-based GASP observatories. In consideration of the ongoing optical and gamma-ray activity of this source, we strongly encourage multiwavelength observations. For this source the Fermi LAT contact persons are S. Ciprini (, E. Ferrara ( and K. Sokolovsky ( and the GASP contact person is M. Villata (

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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