Measurement of the Multi‐TeV Gamma‐Ray Flare Spectra of Markarian 421 and Markarian 501

Abstract

The energy spectrum of Markarian~421 in flaring states has been measured from 0.3 to 10 TeV using both small zenith angle and large zenith angle observations with the Whipple Observatory 10 m imaging telescope. The large zenith angle technique is useful for extending spectra to high energies, and the extraction of spectra with this technique is discussed. The resulting spectrum of Markarian~421 is fit reasonably well by a simple power-law. This is in contrast to our recently reported spectrum of Markarian 501 which, over a similar energy range, has substantial curvature. The differences in TeV energy spectra of gamma-ray blazars reflect both the physics of the gamma-ray production mechanism and possibly differential absorption effects at the source or in the intergalactic medium. Since Markarian~421 and Markarian~501 have almost the same redshift (0.031 and 0.033 respectively), the difference in their energy spectra must be intrinsic to the sources and not due to intergalactic absorption, assuming the intergalactic infrared background is uniform.