Multi-wavelength study of Mrk 421 TeV flare observed with TACTIC telescope in February 2010

Abstract

We present results from multi-wavelength study of intense flaring activity from a high frequency peaked BL Lac object Mrk 421. The source was observed in its flaring state on February 16, 2010 with the TACTIC at energies above 1.5TeV. Near simultaneous multi-wavelength data were obtained from high energy (MeV–GeV) γ-ray observations with Fermi–LAT, X-ray observations by the Swift and MAXI satellites, optical V-band observation by SPOL at Steward Observatory and radio 15GHz observation at OVRO 40 meter-telescope. We have performed a detailed spectral and temporal analysis of TACTIC, Fermi–LAT and Swift–XRT observations of Mrk 421 during February 10–23, 2010 (MJD 55237–55250). The flaring activity of the source is studied by investigating the properties of daily light curves from radio to TeV energy range and we present the correlation and variability analysis in each energy band. The TeV flare detected by TACTIC on February 16, 2010 is well correlated with the activity in lower energy bands. The differential energy spectrum of the source, in the energy range 1.5–11TeV, as measured by TACTIC on this night is described by a power law (dN/dE∝E-Γ) with spectral index Γ=2.6±0.3. After accounting for absorption of TeV photons by low energy extragalactic background light photons via pair production, the intrinsic TeV spectrum reveals a power law index of 2.3±0.3. Finally the broad band spectral energy distribution of the source in flaring state is reproduced using a simple emission model involving synchrotron and synchrotron self Compton processes. The obtained parameters are then used to understand the energetics of the source during the flaring episode.