Journal article
Multiwavelength Study of Quiescent States of Mrk 421 with Unprecedented Hard X-Ray Coverage Provided by NuSTAR in 2013
Astrophysical journal. Letters, Vol.819(2)
03/09/2016
Abstract
We present coordinated multiwavelength observations of the bright, nearby BL Lacertae object Markarian 421 (Mrk 421) taken in 2013 January-March, involving GASP-WEBT, Swift, NuSTAR, Fermi-LAT, MAGIC, VERITAS, and other collaborations and instruments, providing data from radio to very high energy„ (VHE) gamma-ray bands. NuSTAR yielded previously unattainable sensitivity in the 3-79 kiloelectronvolt range, revealing that the spectrum softens when the source is dimmer until the X-ray spectral shape saturates into a steep Gamma approximating 3 power law, with no evidence for an exponential cutoff or additional hard components up to 80 kiloelectronvolts. For the first time, we observed both the synchrotron and the inverse-Compton peaks of the spectral energy distribution (SED) simultaneously shifted to frequencies below the typical quiescent state by an order of magnitude. The fractional variability as a function of photon energy shows a double-bump structure that relates to the two bumps of the broadband SED. In each bump, the variability increases with energy, which, in the framework of the synchrotron self-Compton model, implies that the electrons with higher energies are more variable. The measured multi band variability, the significant X-ray-to-VHE correlation down to some of the lowest fluxes ever observed in both bands, the lack of correlation between optical/UV and X-ray flux, the low degree of polarization and its significant (random) variations, the short estimated electron cooling time, and the significantly longer variability timescale observed in the NuSTAR light curves point toward in situ electron acceleration and suggest that there are multiple compact regions contributing to the broadband emission of Mrk 421 during low-activity states.
Details
- Title: Subtitle
- Multiwavelength Study of Quiescent States of Mrk 421 with Unprecedented Hard X-Ray Coverage Provided by NuSTAR in 2013
- Creators
- M. Balokovic - California Institute of TechnologyD. Paneque - Max Planck SocietyG. Madejski - Stanford UniversityJ. Chiang - Kavli Institute for Particle Astrophysics and CosmologyA Furniss - California State University, East BayM. Ajello - Stanford UniversityD. M. Alexander - Durham UnivD. Barret - Université de ToulouseR. D. Blandford - Kavli Institute for Particle Astrophysics and CosmologyS. E. Boggs - University of California, BerkeleyF. E. Christensen - Technical University of DenmarkW. W. Zhang - Goddard Space Flight CenterD. Stern - California Institute of TechnologyJ. Perkins - NASA Goddard Space Flight CenterA. W. Smith - Goddard Space Flight CenterJ. Becerra Gonzalez - NASA Goddard Space Flight Center
- Resource Type
- Journal article
- Publication Details
- Astrophysical journal. Letters, Vol.819(2)
- Publisher
- The American Astronomical Society
- ISSN
- 2041-8205
- eISSN
- 2041-8213
- Language
- English
- Date published
- 03/09/2016
- Description audience
- PUBLIC
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984199822502771
Metrics
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83 Times Cited - Web of Science