Journal
ASTROPHYSICAL JOURNAL
Volume 738, Issue 1, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/738/1/25
Keywords
BL Lacertae objects: individual (Mrk 421); galaxies: jets; galaxies: nuclei; gamma rays: galaxies; X-rays: galaxies
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Funding
- U.S. Department of Energy
- U.S. National Science Foundation
- Smithsonian Institution
- NSERC in Canada
- Science Foundation Ireland
- STFC in the U.K
- Academy of Finland
- NSF
- University of Michigan
- NASA [NNX08AV77G, NNX08AT31G, NNX08AZ76G]
- Direct For Mathematical & Physical Scien
- Division Of Physics [900928] Funding Source: National Science Foundation
- Division Of Physics
- Direct For Mathematical & Physical Scien [0970134] Funding Source: National Science Foundation
- NASA [95223, NNX08AT31G, NNX08AV77G, 94453, NNX08AZ76G, 92110] Funding Source: Federal RePORTER
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We report on TeV gamma-ray observations of the blazar Mrk 421 (redshift of 0.031) with the VERITAS observatory and the Whipple 10m Cherenkov telescope. The excellent sensitivity of VERITAS allowed us to sample the TeV gamma-ray fluxes and energy spectra with unprecedented accuracy where Mrk 421 was detected in each of the pointings. A total of 47.3 hr of VERITAS and 96 hr of Whipple 10m data were acquired between 2006 January and 2008 June. We present the results of a study of the TeV gamma-ray energy spectra as a function of time and for different flux levels. On 2008 May 2 and 3, bright TeV gamma-ray flares were detected with fluxes reaching the level of 10 Crab. The TeV gamma-ray data were complemented with radio, optical, and X-ray observations, with flux variability found in all bands except for the radio wave band. The combination of the Rossi X-ray Timing Explorer and Swift X-ray data reveal spectral hardening with increasing flux levels, often correlated with an increase of the source activity in TeV gamma-rays. Contemporaneous spectral energy distributions were generated for 18 nights, each of which are reasonably described by a one-zone synchrotron self-Compton model.
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