Very-high-energy (VHE; > 100 GeV) gamma-ray emission from the blazar RGB J2243+203 was discovered with the VERITAS Cherenkov telescope array, during the period between 2014 December 21 and 24. The VERITAS energy spectrum from this source can be fitted by a power law with a photon index of 4.6±0.5, and a flux normalization at 0.15 TeV of (6.3 ±1.1 10-10 cm-2 s-1 TeV-1 )10-2 1 1. The integrated Fermi-LAT flux from 1 to 100 GeV during the VERITAS detection is (4.1 ±0.8× 10 cm-2 s-1 ), which is an order of magnitude larger than the four-year-averaged flux in the same energy range reported in the 3FGL catalog, (4.0± 0.1× 10-9 cm-2s -1). The detection with VERITAS triggered observations in the X-ray band with the Swift-XRT. However, due to scheduling constraints Swift-XRT observations were performed 67 hr after the VERITAS detection, rather than simultaneously with the VERITAS observations. The observed X-ray energy spectrum between 2 and 10 keV can be fitted with a power law with a spectral index of 2.7±0.2, and the integrated photon flux in the same energy band is (3.6 ±0.6 10-13 cm-2 s-1 ). EBL-model-dependent upper limits of the blazar redshift have been derived. Depending on the EBL model used, the upper limit varies in the range from z < 0.9 to z < 1.1.
Bibliographical noteFunding Information:
VERITAS is supported by grants from the U.S. Department of Energy Office of Science, the U.S. National Science Foundation and the Smithsonian Institution, and by NSERC in Canada. We acknowledge the excellent work of the technical support staff at the Fred Lawrence Whipple Observatory and at the collaborating institutions in the construction and operation of the instrument. The VERITAS Collaboration is grateful to Trevor Weekes for his seminal contributions and leadership in the field of VHE gamma-ray astrophysics, and for his interest in the wider applications of IACTs, which made this study possible.
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- Galaxies: individual (RGB J2243+203)