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Underlying particle spectrum of Mkn 421 during the huge X-ray flare in April 2013

Sinha, A. and Shukla, A. and Misra, R. and Chitnis, V. R. and Rao, A. R. and Acharya, B. S. (2015) Underlying particle spectrum of Mkn 421 during the huge X-ray flare in April 2013. Astronomy and Astrophysics, 580 . Art No.100. ISSN 0004-6361. doi:10.1051/0004-6361/201526264.

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Context. In April 2013, the nearby TeV blazar, Mkn 421, showed one of the largest flares in X-rays in the past decade. Aims. We study all multiwavelength data available during MJD 56 392 to 56 403, with special emphasis on X-ray data to understand the underlying particle energy distribution. Methods. We studied the correlations between the UV and gamma-ray bands with the X-ray band using the z-transformed discrete correlation function. We modelled the underlying particle energy spectrum with a single population of electrons emitting synchrotron radiation, and statistically fitted the simultaneous time-resolved data from Swift-XRT and NuSTAR. Results. The flux varied rapidly in the X-ray band, with a minimum doubling timescale of 1.69 ± 0.13 h. There were no corresponding flares in UV and gamma-ray bands. The variability in UV and gamma rays was relatively modest with ~8% and ~16%, respectively, and no significant correlation was found with the X-ray light curve. The observed X-ray spectrum shows a clear curvature that can be fit by a log parabolic spectral form. This is best explained as originating from a log parabolic electron spectrum. However, a broken power law or a power law with an exponentially falling electron distribution cannot be ruled out either. Moreover, the excellent broadband spectrum from 0.3–79 keV allows us to make predictions of the UV flux. We find that this prediction is compatible with the observed flux during the low state in X-rays. However, during the X-ray flares, depending on the adopted model, the predicted flux is a factor of 2–50 lower than the observed one. This suggests that the X-ray flares are probably caused by a separate population that does not contribute significantly to the radiation at lower energies. Alternatively, the underlying particle spectrum can be much more complex than those explored in this work.

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Sinha, A.0000-0002-7122-3549
Additional Information:© ESO, 2015. Received: 6 April 2015. Accepted: 9 June 2015. Published: 7 Aug 2015. A. Sinha would like to thank Sunder Sahayanathan from the Bhabha Atomic Research Center, Mumbai, for helpful discussions and comments. This research has made use of data, software and/or web tools obtained from NASAs High Energy Astrophysics Science Archive Research Center (HEASARC), a service of Goddard Space Flight Center and the Smithsonian Astrophysical Observatory. Part of this work is based on archival data, software, or online services provided by the ASI Science Data Center (ASDC). This research has made use of the XRT Data Analysis Software (XRTDAS) developed under the responsibility the ASI Science Data Center (ASDC), Italy, and the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (Caltech, USA). Data from the Steward Observatory spectropolarimetric monitoring project were used. This program is supported by Fermi Guest Investigator grants NNX08AW56G, NNX09AU10G, and NNX12AO93G.
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ID Code:64074
Deposited By: Joy Painter
Deposited On:03 Feb 2016 00:52
Last Modified:10 Nov 2021 23:25

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