The violent hard X-ray variability of MRK 421 observed by NuSTAR in 2013 April
- Indian Institute of Astrophysics, Block II, Koramangala, Bangalore-560034 (India)
- Centre for Space Research, North-West University, Potchefstroom, 2520 (South Africa)
- Astrophysical Institute, Department of Physics and Astronomy, Ohio University, Athens, OH 45701 (United States)
- Astrophysical Sciences Division, Bhabha Atomic Research Centre, Mumbai-400085 (India)
The well-studied blazar Markarian 421 (Mrk 421, z = 0.031) was the subject of an intensive multi-wavelength campaign when it flared in 2013 April. The recorded X-ray and very high-energy (E > 100 GeV) γ-ray fluxes are the highest ever measured from this object. At the peak of the activity, it was monitored by the hard X-ray focusing telescope Nuclear Spectroscopic Telescope Array (NuSTAR) and the Swift X-Ray Telescope (XRT). In this work, we present a detailed variability analysis of NuSTAR and Swift-XRT observations of Mrk 421 during this flaring episode. We obtained the shortest flux doubling time of 14.01 ± 5.03 minutes, which is the shortest hard X-ray (3–79 keV) variability ever recorded from Mrk 421, and is on the order of the light-crossing time of the black hole's event horizon. A pattern of extremely fast variability events superposed on slowly varying flares is found in most of the NuSTAR observations. We suggest that these peculiar variability patterns may be explained by magnetic energy dissipation and reconnection in a fast-moving compact emission region within the jet. Based on the fast variability, we derive a lower limit on the magnetic field strength of B⩾0.73δ{sub 1}{sup −2/3} ν{sub 19}{sup 1/3} G, where δ{sub 1} is the Doppler factor in units of 10, and ν{sub 19} is the characteristic X-ray synchrotron frequency in units of 10{sup 19} Hz.
- OSTI ID:
- 22882519
- Journal Information:
- Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 811; ISSN ASJOAB; ISSN 0004-637X
- Country of Publication:
- United Kingdom
- Language:
- English
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