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Detection of Persistent VHE emission from PKS 1222+216 (4C +21.35) with VERITAS

ATel #5981; J. Holder for the VERITAS Collaboration
on 14 Mar 2014; 18:34 UT
Credential Certification: Jamie Holder (jholder@physics.udel.edu)

Subjects: X-ray, Gamma Ray, >GeV, TeV, VHE, AGN

Referred to by ATel #: 6194, 6207

The VERITAS collaboration reports the detection of very-high-energy (VHE, E>100GeV) gamma-ray emission from the flat spectrum radio quasar PKS 1222+216 (z=0.432). This source has previously shown intense and rapid flaring episodes in the gamma-ray band (ATel #2584, ATel #2684, ATel #2687).

VERITAS observations of PKS 1222+216 started 11 days after a bright GeV flare reported by the Fermi-LAT Collaboration. An enhanced flux in the optical band was also reported (Larionov et al, ATel #5921). The VERITAS dataset consists of 5.9 hours of quality-selected exposure spread over 10 nights between Feb 26 and Mar 10 2014 (MJD 56714 - 56726). A preliminary analysis of these data reveals a gamma-ray excess with statistical significance of ~6 standard deviations. The integral flux above 100 GeV corresponds to (1.4 +/- 0.3) x 10^-11 ph cm^-2 s^-1 (equivalent to ~3% of the Crab Nebula flux). The excess is consistent with a constant flux over the ten nights of observation, although we note that there are limited statistics. This is the first VHE detection of this source since the brief VHE flare detected by MAGIC on June 17th 2010 (Aleksic et al. 2011, ApJL, 730, 8).

The Swift-XRT monitoring of Fermi-LAT Sources of Interest shows an enhanced flux for PKS 1222+216 in the 0.3 - 10 keV band, 2-3 times above the non-flaring average ( http://www.swift.psu.edu/monitoring/source.php?source=PKS1222+216 ).

VERITAS observations of PKS 1222+216 are currently precluded by the bright Moon. Observations will resume after the full Moon period, starting March 22nd. Multi-wavelength observations are strongly encouraged.