Multiwavelength study of the radio galaxy NGC 1275 with TACTIC, [formula omitted] and [formula omitted] during December, 2016 – February, 2017

Abstract

Located in the Perseus galaxy cluster, NGC 1275 (z=0.0179), is the brightest radio galaxy detected in both high energy (HE ; E > 100 MeV) and very high energy (VHE ; E > 100 GeV) regimes. Here we present the results from the observations of NGC 1275 with TACTIC for 37.1 h between December, 2016 and February, 2017. In the absence of a statistically significant VHE γ-ray detection from the TACTIC observations, we estimate the 3σ upper limit on the integral flux above 0.85 TeV to be ∼2.85×10−11ergcm−2s−1. We also report the results of near simultaneous multiwavelength observations of the source from the Fermi-LAT, Swift-XRT/UVOT and OVRO. We find the source to be in flaring state on the night of 31 December, 2016 – 1 January, 2017 when the HE γ-ray flux above 0.1 GeV went up to ∼2.0×10−6phcm−2s−1 which is approximately 4 times the flux level during its low state. We present the broad-band spectral energy distributions (SED) of the source during its flaring and low states. It is evident from the SED that the VHE upper limit obtained from the TACTIC observations is consistent with the low emission state of the source.