Multiwavelength study of the TeV blazar Mrk 421 during a giant flare

Aims. The nearby (z = 0.031) TeV blazar Mrk 421 was reported to be in a high state of flux activity since November, 2009. We aim to investigate possible changes in the physical parameters of Mrk 421 during its high state of activity using multiwavelength data. Methods. We have observed this source in the bright state using the High Altitude GAmma Ray (HAGAR) telescope array at energies above 250 GeV during February 13-19, 2010. Optical, X-ray and gamma-ray archival data were also used to obtain the spectral energy distribution and light curves. Results. Mrk 421 was found to undergo one of its brightest flaring episodes on February 17, 2010 by various observations in X-rays and gamma-rays. HAGAR observations during February 13-19, 2010 at energies above 250 GeV show an enhancement in the flux level, with a maximum flux of similar to 7 Crab units being detected on February 17, 2010. We present the spectral energy distributions during this flaring episode and investigate the correlation of the variability in X-ray and gamma-ray bands. Conclusions. Our multiwavelength study suggests that the flare detected during February 16 and 17, 2010 may have been caused by a passing shock in the jet.