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Inverse Compton X-Ray Emission from TeV Blazar Mrk 421 During a Historical Low-flux State Observed with NuSTAR

Kataoka, Jun and Stawarz, Łukasz (2016) Inverse Compton X-Ray Emission from TeV Blazar Mrk 421 During a Historical Low-flux State Observed with NuSTAR. Astrophysical Journal, 827 (1). Art. No. 55. ISSN 0004-637X. doi:10.3847/0004-637X/827/1/55.

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We report on the detection of excess hard X-ray emission from the TeV BL Lac object Mrk 421 during the historical low-flux state of the source in 2013 January. Nuclear Spectroscopic Telescope Array observations were conducted four times between MJD 56294 and MJD 56312 with a total exposure of 80.9 ks. The source flux in the 3–40 keV range was nearly constant, except for MJD 56307 when the average flux level increased by a factor of three. Throughout the exposure, the X-ray spectra of Mrk 421 were well represented by a steep power-law model with a photon index of Γ ≃ 3.1, although a significant excess was noted above 20 keV in the MJD 56302 data when the source was in its faintest state. Moreover, Mrk 421 was detected at more than the 4σ level in the 40–79 keV count maps for both MJD 56307 and MJD 56302 but not during the remaining two observations. The detected excess hard X-ray emission connects smoothly with the extrapolation of the high-energy γ-ray continuum of the blazar constrained by Fermi-LAT during source quiescence. These findings indicate that while the overall X-ray spectrum of Mrk 421 is dominated by the highest-energy tail of the synchrotron continuum, the variable excess hard X-ray emission above 20 keV (on the timescale of a week) is related to the inverse Compton emission component. We discuss the resulting constraints on the variability and spectral properties of the low-energy segment of the electron energy distribution in the source.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Kataoka, Jun0000-0003-2819-6415
Additional Information:© 2016 The American Astronomical Society. Received 2016 May 12; revised 2016 June 7; accepted 2016 June 10; published 2016 August 8. Ł.S. was supported by Polish NSC grant DEC-2012/04/A/ST9/00083.
Funding AgencyGrant Number
National Science Centre (Poland)DEC-2012/04/A/ST9/00083
Subject Keywords:acceleration of particles – BL Lacertae objects: individual (Mrk 421) – galaxies: active – galaxies: jets – radiation mechanisms: non-thermal
Issue or Number:1
Record Number:CaltechAUTHORS:20160615-154451842
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Official Citation:Jun Kataoka and Łukasz Stawarz 2016 ApJ 827 55
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:67950
Deposited By: Joy Painter
Deposited On:15 Jun 2016 23:16
Last Modified:11 Nov 2021 03:57

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