Search for TeV gamma-ray emission from blazar 1ES1218+304 with TACTIC telescope during March–April 2013

Abstract

In this paper, we present results of TeV ƴ-ray observations of the high synchrotron peaked BL Lac object 1ES 1218+304 (z = 0.182) with the TACTIC (TeV Atmospheric Cherenkov Telescope with Imaging Camera). The observations are primarily motivated by the unusually hard GeV–TeV spectrum of the source despite its relatively large redshift. The source is observed in the TeV energy range with the TACTIC from March 1, 2013 to April 15, 2013 (MJD 56352–56397) for a total observation time of 39.62 h and no evidence of TeV ƴ-ray activity is found from the source. The corresponding 99% confidence level upper limit on the inte- gral flux above a threshold energy of 1.1 TeV is estimated to be 3.41 Ⅹ 10⁻¹² photons cm⁻² s⁻¹ (i.e. <23% Crab Nebula flux) assuming a power law differential energy spectrum with photon index 3.0, as previ- ously observed by the MAGIC and VERITAS telescopes. For the study of multi-wavelength emission from the source, we use nearly simultaneous optical, UV and X-ray data collected by the UVOT and XRT instru- ments on board the Swift satellite and high energy ƴ-ray data collected by the Large Area Telescope on board the Fermi satellite. We also use radio data at 15 GHz from OVRO 40 m telescope in the same period. No significant increase of activity is detected from radio to TeV ƴ-rays from 1ES1218+304 during the per- iod from March 1, 2013 to April 15, 2013.