Discovery of VHE gamma-ray emission from 4C +21.35 with Fermi

ATel #2617; A. Neronov (ISDC) D. Semikoz (APC), Ie. Vovk (ISDC)
on 13 May 2010; 11:27 UT
Credential Certification: Andrii Neronov (andrii.neronov@obs.unige.ch)

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We report the discovery of VHE (E>100 GeV) emission from the blazar 4C +21.35 (z=0.432, RA: 12h24m54.4s DEC: +21d22m46s, J2000). Evidence for the VHE gamma-ray emission from this source was previously found in the 100-300 GeV band data of Fermi telescope (Neronov et al. arXiv:1004.3767). The source has recently experienced a bright flare in the energy band above 100 MeV detected by Fermi telescope (Donato D., ATEL #2584). We have analyzed the Fermi data collected during the last 40 days of the flaring period in April-May 2010 and found that the flaring activity of the source was accompanied by gamma-ray emission in the VHE band with the source flux reaching the level of ~1 Crab level above 100 GeV. Significance of the source detection above 100 GeV for the entire Fermi exposure from August 2008 to May 2010 is 5.6 sigma (the Test Statistics value TS=32.4 found in the likelihood analysis of Fermi data). Restricting the exposure time to the 40 day flaring period in April-May 2010 one finds the detection significance 6.5 sigma above 100 GeV (TS=42.8). Additional information about the source properties (the lightcurve and spectrum) could be found at the URL http://www.isdc.unige.ch/vhe/Objects/1FGL_J1224.7+2121/page.html