Discovery of Gamma‐Ray Emission above 350 GeV from the BL Lacertae Object 1ES 2344+514

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Abstract

We present the discovery of gamma-ray emission greater than 350 GeV from the BL Lacertae (BL Lac) object 1ES 2344]514 with the Whipple Observatory 10 m gamma-ray telescope. This is the third BL Lac object detected at very high energies (VHE, E [ 300 GeV), the other two being Markarian 421 (Mrk 421) and Mrk 501. These three active galactic nuclei are all X-ray selected and have the lowest known redshifts of any BL Lac objects currently identied with declination greater than 0. The evidence for emission from 1ES 2344]514 comes mostly from an apparent are on 1995 December 20 (UT) during which a 6 p excess was detected with an average ux of I([350 GeV) \ 6.6 ^1.9 ] 10~11 photons cm~2 s~1. This is approximately 63% of the VHE emission from the Crab Nebula, the standard candle in this eld. Observations taken between 1995 October and 1996 January, excluding the night of the are, yield a 4 p detection indicating a ux level of I([350 GeV) \ 1.1 ^0.4 ] 10~11 photons cm~2 s~1, or about 11% of the VHE Crab Nebula ux. Observations taken between 1996 September and 1997 January on this object did not yield a signicant detection of a steady ux or any evidence of aring activity. The 99.9% condence level upper limit from these observations is I([350 GeV) \ 8.2 ] 10~12 photons cm~2 s~1, of the Crab Nebula ux. The low baseline emission level and variation in the [8% nightly and yearly ux of 1ES 2344]514 are the same as the VHE emission characteristics of Mrk 421 and Mrk 501.

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