The Energy Spectrum of the Blazar Markarian 421 above 130 GeV
Abstract
Markarian 421 (Mrk 421) was the first blazar detected at gamma-ray energies above 300 GeV, and it remains one of only twelve TeV blazars detected to date. TeV gamma-ray measurements of its flaring activity and spectral variability have placed constraints on models of the high-energy emission from blazars. However, observations between 50 and 300 GeV are rare, and the high-energy peak of the spectral energy distribution (SED), predicted to be in this range, has never been directly detected. We present a detection of Mrk 421 above 100 GeV as made by the Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE) during a multiwavelength campaign in early 2004. STACEE is a ground-based atmospheric Cherenkov telescope using the wave-front sampling technique to detect gamma rays at lower energies than achieved by most imaging Cherenkov telescopes. We also outline a method for reconstructing gamma-ray energies using a solar heliostat telescope. This technique was applied to the 2004 data, and we present the differential energy spectrum of Mrk 421 above 130 GeV. Assuming a differential photon flux dN/dE~E-α, we measure a spectral index α=2.1+/-0.2stat +0.2-0.1sys. Finally, we discuss the STACEE spectrum in the context of the multiwavelength results from the same epoch.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 2007
- DOI:
- 10.1086/516818
- arXiv:
- arXiv:astro-ph/0612562
- Bibcode:
- 2007ApJ...662..199C
- Keywords:
-
- Galaxies: BL Lacertae Objects: Individual: Name: Markarian 421;
- Galaxies: Active;
- Gamma Rays: Observations;
- Astrophysics
- E-Print:
- 16 pages, 4 figures, submitted to ApJ