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Discovery of High-Energy Gamma-Ray Emission from the BL Lac Object RBS 0413

ATEL # 2272; Rene A. Ong (UCLA), on behalf of the VERITAS Collaboration; Pascal Fortin (LLR), on behalf of the Fermi Large Area Telescope Collaboration
on 29 Oct 2009; 18:42 UT
Password Certification: Rene Ong (

Subjects: Gamma Ray, >GeV, Request for Observations, AGN

The VERITAS and Fermi-LAT Collaborations report the discovery of gamma-ray emission from the high-frequency-peaked BL Lac object RBS 0413 (RA: 03h19m51.8s, Dec: +18d45m34s). The redshift of this blazar is 0.19 (Stocke, J. et al. 1991, ApJS, 76, 813). Very-high-energy (VHE; >100 GeV) gamma rays were detected in ~16 hours of good-quality observations obtained between 23 September 2008 and 26 October 2009 with the VERITAS atmospheric-Cherenkov telescope array. Analysis of the VERITAS data yields a detection of ~270 gamma rays from a source position that is consistent with RBS 0413, corresponding to a statistical significance of ~6 standard deviations. The observed VHE flux is ~2% of the Crab flux above 200 GeV.

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, detected high-energy (HE; > 100 MeV) gamma rays from a source positionally consistent with RBS 0413 with a statistical significance of ~10 standard deviations. Preliminary analysis of the data taken during the first 12 months of the mission (4 August 2008 to 4 August 2009) indicates an average flux above 100 MeV of (2.4 +/- 1.0) x 10 -9 photons cm -2 s -1, and a very hard spectral index of (1.42 +/- 0.15). Errors are statistical only.

Multi-wavelength observations of this blazar are encouraged. The LAT contact person for this blazar is Pascal Fortin ( Questions regarding the VERITAS observations should be directed to Rene Ong (

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