A SEARCH FOR SPECTRAL HYSTERESIS AND ENERGY-DEPENDENT TIME LAGS FROM X-RAY AND TeV GAMMA-RAY OBSERVATIONS OF Mrk 421
- Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112 (United States)
- Physics Department, McGill University, Montreal, QC H3A 2T8 (Canada)
- Department of Physics, Washington University, St. Louis, MO 63130 (United States)
- Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645 (United States)
- Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States)
- Department of Physics and Astronomy, Iowa State University, Ames, IA 50011 (United States)
- Institute of Physics and Astronomy, University of Potsdam, D-14476 Potsdam-Golm (Germany)
- Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605 (United States)
- School of Physics, National University of Ireland Galway, University Road, Galway (Ireland)
- Department of Physics and Astronomy, Purdue University, West Lafayette, IN 47907 (United States)
- Department of Astronomy and Astrophysics, 525 Davey Lab, Pennsylvania State University, University Park, PA 16802 (United States)
- DESY, Platanenallee 6, D-15738 Zeuthen (Germany)
Blazars are variable emitters across all wavelengths over a wide range of timescales, from months down to minutes. It is therefore essential to observe blazars simultaneously at different wavelengths, especially in the X-ray and gamma-ray bands, where the broadband spectral energy distributions usually peak. In this work, we report on three “target-of-opportunity” observations of Mrk 421, one of the brightest TeV blazars, triggered by a strong flaring event at TeV energies in 2014. These observations feature long, continuous, and simultaneous exposures with XMM-Newton (covering the X-ray and optical/ultraviolet bands) and VERITAS (covering the TeV gamma-ray band), along with contemporaneous observations from other gamma-ray facilities (MAGIC and Fermi -Large Area Telescope) and a number of radio and optical facilities. Although neither rapid flares nor significant X-ray/TeV correlation are detected, these observations reveal subtle changes in the X-ray spectrum of the source over the course of a few days. We search the simultaneous X-ray and TeV data for spectral hysteresis patterns and time delays, which could provide insight into the emission mechanisms and the source properties (e.g., the radius of the emitting region, the strength of the magnetic field, and related timescales). The observed broadband spectra are consistent with a one-zone synchrotron self-Compton model. We find that the power spectral density distribution at ≳4 × 10{sup −4} Hz from the X-ray data can be described by a power-law model with an index value between 1.2 and 1.8, and do not find evidence for a steepening of the power spectral index (often associated with a characteristic length scale) compared to the previously reported values at lower frequencies.
- OSTI ID:
- 22661106
- Journal Information:
- Astrophysical Journal, Vol. 834, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COSMOLOGY AND ASTRONOMY
BL LACERTAE OBJECTS
BLACK HOLES
COMPARATIVE EVALUATIONS
CORRELATIONS
ENERGY DEPENDENCE
ENERGY SPECTRA
GALAXIES
GAMMA RADIATION
INDEXES
MAGNETIC FIELDS
QUASARS
SPECTRAL DENSITY
STELLAR FLARES
TELESCOPES
TEV RANGE
TIME DELAY
ULTRAVIOLET RADIATION
WAVELENGTHS
X RADIATION
X-RAY SPECTRA