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Title: Multiwavelength Study of Quiescent States of Mrk 421 with Unprecedented Hard X-Ray Coverage Provided by NuSTAR in 2013

Authors:
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Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC); National Aeronautics and Space Administration (NASA)
OSTI Identifier:
1313954
Report Number(s):
SLAC-PUB-16788
Journal ID: ISSN 1538-4357; arXiv:1512.02235
DOE Contract Number:
AC02-76SF00515
Resource Type:
Journal Article
Resource Relation:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 819; Journal Issue: 2
Country of Publication:
United States
Language:
English
Subject:
Astrophysics,ASTRO, GRQC

Citation Formats

Balokovic, M., Paneque, D., Madejski, G., Furniss, A., Chiang, J., Ajello, M., Alexander, D.M., Barret, D., Blandford, R., Boggs, S.E., Christensen, F.E., Craig, W.W., Forster, K., Giommi, P., Grefenstette, B.W., Hailey, C.J., Harrison, F.A., Hornstrup, A., Kitaguchi, T., Koglin, J.E., and Madsen, K.K. Multiwavelength Study of Quiescent States of Mrk 421 with Unprecedented Hard X-Ray Coverage Provided by NuSTAR in 2013. United States: N. p., 2016. Web. doi:10.3847/0004-637X/819/2/156.
Balokovic, M., Paneque, D., Madejski, G., Furniss, A., Chiang, J., Ajello, M., Alexander, D.M., Barret, D., Blandford, R., Boggs, S.E., Christensen, F.E., Craig, W.W., Forster, K., Giommi, P., Grefenstette, B.W., Hailey, C.J., Harrison, F.A., Hornstrup, A., Kitaguchi, T., Koglin, J.E., & Madsen, K.K. Multiwavelength Study of Quiescent States of Mrk 421 with Unprecedented Hard X-Ray Coverage Provided by NuSTAR in 2013. United States. doi:10.3847/0004-637X/819/2/156.
Balokovic, M., Paneque, D., Madejski, G., Furniss, A., Chiang, J., Ajello, M., Alexander, D.M., Barret, D., Blandford, R., Boggs, S.E., Christensen, F.E., Craig, W.W., Forster, K., Giommi, P., Grefenstette, B.W., Hailey, C.J., Harrison, F.A., Hornstrup, A., Kitaguchi, T., Koglin, J.E., and Madsen, K.K. Fri . "Multiwavelength Study of Quiescent States of Mrk 421 with Unprecedented Hard X-Ray Coverage Provided by NuSTAR in 2013". United States. doi:10.3847/0004-637X/819/2/156. https://www.osti.gov/servlets/purl/1313954.
@article{osti_1313954,
title = {Multiwavelength Study of Quiescent States of Mrk 421 with Unprecedented Hard X-Ray Coverage Provided by NuSTAR in 2013},
author = {Balokovic, M. and Paneque, D. and Madejski, G. and Furniss, A. and Chiang, J. and Ajello, M. and Alexander, D.M. and Barret, D. and Blandford, R. and Boggs, S.E. and Christensen, F.E. and Craig, W.W. and Forster, K. and Giommi, P. and Grefenstette, B.W. and Hailey, C.J. and Harrison, F.A. and Hornstrup, A. and Kitaguchi, T. and Koglin, J.E. and Madsen, K.K.},
abstractNote = {},
doi = {10.3847/0004-637X/819/2/156},
journal = {The Astrophysical Journal (Online)},
number = 2,
volume = 819,
place = {United States},
year = {Fri Aug 19 00:00:00 EDT 2016},
month = {Fri Aug 19 00:00:00 EDT 2016}
}
  • 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 Γmore » ≃ 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 4 σ 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.« less
  • We present the results of the Swift and NuSTAR observations of the nearby BL Lac object Mrk 421 during 2013 January–June. The source exhibited a strong long-term variability in the 0.3–10 keV and 3–79 keV bands with the maximum-to-minimum daily-binned flux ratios of 22 and 95, respectively, in about 3 months, mainly due to unprecedented strong X-ray outbursts by more than an order of magnitude in both bands within 2 weeks in 2013 April when the 0.3–10 keV count rate exceeded the level of 200 cts s{sup −1} for the first time, and Mrk 421 became one of the brightestmore » sources in the X-ray sky. The source was also very active on intra-day timescales, and it showed flux doubling and halving timescales of 1.16–7.20 hr and 1.04–3.54 hr, respectively. On some occasions, the flux varied by 4%–23% within 300–840 s. During this period, the source also exhibited some of the most extreme X-ray spectral variability ever reported for BL Lacs—the location of the synchrotron spectral energy distribution peak shifted from a few eV to ∼10 keV, and the photon index at 1 keV and curvature parameter varied on timescales from a few weeks down to intervals shorter than 1 ks. MAGIC and First G-APD Cherenkov Telescope observations also revealed a very strong very high energy (VHE) flare during April 11–17. The UV and HE γ -ray flares were much weaker compared to their X-ray counterparts, and they generally showed significantly stronger correlation with each other than with the X-ray fluxes.« less
  • We present the results of the Swift observations of the nearby BL Lac object Mrk 421 during 2013 November–2015 June. The source exhibited a strong long-term variability in the 0.3–10 keV band, with a maximum-to-minimum flux ratio of 13, and underwent X-ray flares by a factor of 1.8–5.2 on timescales of a few weeks or shorter. The source showed 48 instances of intraday flux variability in this period, which sometimes was observed within the 1 ks observational run. It was characterized by fractional amplitudes of 1.5(0.3)%–38.6(0.4)% and flux doubling/halving times of 2.6–20.1 hr. The X-ray flux showed a lack ofmore » correlation with the TeV flux on some occasions (strong TeV flares were not accompanied by comparable X-ray activity and vice versa), indicating that the high-energy emission in Mrk 421 was generated from an emission region more complex than a single zone. The best fits of the 0.3–10 keV spectra were mainly obtained using the log-parabola model, showing a strong spectral variability that generally followed a “harder-when-brighter” trend. The position of the synchrotron spectral energy distribution peak showed an extreme range from a few eV to ∼10 keV that happens rarely in blazars.« less
  • Because of its proximity, Mrk 421 is one of the best sources on which to study the nature of BL Lac objects. Its proximity allows us to characterize its broadband spectral energy distribution (SED). Here, the goal is to better understand the mechanisms responsible for the broadband emission and the temporal evolution of Mrk 421. These mechanisms may also apply to more distant blazars that cannot be studied with the same level of detail. A flare occurring in March 2010 was observed for 13 consecutive days (from MJD 55 265 to MJD 55 277) with unprecedented wavelength coverage from radiomore » to very high energy (VHE; E> 100 GeV) γ-rays with MAGIC, VERITAS, Whipple, Fermi-LAT, MAXI, RXTE, Swift, GASP-WEBT, and several optical and radio telescopes. We modeled the day-scale SEDs with one-zone and two-zone synchrotron self-Compton (SSC) models, investigated the physical parameters, and evaluated whether the observed broadband SED variability can be associated with variations in the relativistic particle population. As a result, the activity of Mrk 421 initially was high and then slowly decreased during the 13-day period. The flux variability was remarkable at the X-ray and VHE bands, but it was minor or not significant at the other bands. The variability in optical polarization was also minor. These observations revealed an almost linear correlation between the X-ray flux at the 2–10 keV band and the VHE γ-ray flux above 200 GeV, consistent with the γ-rays being produced by inverse-Compton scattering in the Klein-Nishina regime in the framework of SSC models. The one-zone SSC model can describe the SED of each day for the 13 consecutive days reasonably well, which once more shows the success of this standard theoretical scenario to describe the SEDs of VHE BL Lacs such as Mrk 421. This flaring activity is also very well described by a two-zone SSC model, where one zone is responsible for the quiescent emission, while the other smaller zone, which is spatially separated from the first, contributes to the daily variable emission occurring at X-rays and VHE γ-rays. The second blob is assumed to have a smaller volume and a narrow electron energy distribution with 3 × 104« less
  • We report on the findings of a 364 ks observation of the BL LAC object Mrk 421 with the X-ray observatory Suzaku. The analysis in this paper uses fluxes and hardness ratios (HRs) in the broad energy range from 0.5 keV to 30 keV. During the course of the observation, the 0.5-30 keV flux decreased by a factor of {approx}2 and was accompanied by several large flares occurring on timescales of a few hours. We find that fitting a broken power model to spectra from isolated epochs during the observation describes the data well. Different flares exhibit different spectral andmore » HR evolutions. The cumulative observational evidence indicates that the particle acceleration mechanism in the Mrk 421 jet produces electron energy distributions with a modest range of spectral indices and maximum energies. We argue that the short-timescale X-ray spectral variability in the flares can be attributed mostly to intrinsic changes in the acceleration process, dominating other influences such as fluctuations in the Doppler beaming factor, or radiative cooling in or outside the acceleration zone.« less