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

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Multiwavelength Study of Quiescent States of Mrk 421 with Unprecedented Hard X-Ray Coverage Provided by NuSTAR in 2013. / NuSTAR Team; VERITAS Collaboration; MAGIC Collaboration.

In: Astrophysical Journal, Vol. 819, No. 2, 156, 03.2016.

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@article{18a0e3d935e141948461497f91e31214,
title = "Multiwavelength Study of Quiescent States of Mrk 421 with Unprecedented Hard X-Ray Coverage Provided by NuSTAR in 2013",
abstract = "We present coordinated multiwavelength observations of the bright, nearby BL Lacertae object 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) γ-ray bands. NuSTAR yielded previously unattainable sensitivity in the 3–79 keV range, revealing that the spectrum softens when the source is dimmer until the X-ray spectral shape saturates into a steep {{Γ }}≈ 3 power law, with no evidence for an exponential cutoff or additional hard components up to ∼80 keV. 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.",
keywords = "BL Lacertae objects: individual: Markarian 421, galaxies: active, gamma rays: general, radiation mechanisms: nonthermal, X-rays: galaxies",
author = "M. Baloković and D. Paneque and G. Madejski and A. Furniss and J. Chiang and M. Ajello and Alexander, {D. M.} and D. Barret and Blandford, {R. D.} and Boggs, {S. E.} and Christensen, {F. E.} and Craig, {W. W.} and K. Forster and P. Giommi and B. Grefenstette and C. Hailey and Harrison, {F. A.} and A. Hornstrup and T. Kitaguchi and Koglin, {J. E.} and Madsen, {K. K.} and Mao, {P. H.} and H. Miyasaka and K. Mori and M. Perri and Pivovaroff, {M. J.} and S. Puccetti and V. Rana and D. Stern and G. Tagliaferri and Urry, {C. M.} and Westergaard, {N. J.} and Zhang, {W. W.} and A. Zoglauer and S. Archambault and A. Archer and A. Barnacka and W. Benbow and R. Bird and Buckley, {J. H.} and V. Bugaev and M. Cerruti and A. Chatterjee and J. Poutanen and Lin, {H. C.} and T. Hovatta and A. L{\"a}hteenm{\"a}ki and M. Tornikoski and J. Tammi and V. Ramakrishnan and {NuSTAR Team} and {VERITAS Collaboration} and {MAGIC Collaboration}",
year = "2016",
month = "3",
doi = "10.3847/0004-637X/819/2/156",
language = "English",
volume = "819",
journal = "Astrophysical Journal",
issn = "0004-637X",
number = "2",

}

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TY - JOUR

T1 - Multiwavelength Study of Quiescent States of Mrk 421 with Unprecedented Hard X-Ray Coverage Provided by NuSTAR in 2013

AU - Baloković, M.

AU - Paneque, D.

AU - Madejski, G.

AU - Furniss, A.

AU - Chiang, J.

AU - Ajello, M.

AU - Alexander, D. M.

AU - Barret, D.

AU - Blandford, R. D.

AU - Boggs, S. E.

AU - Christensen, F. E.

AU - Craig, W. W.

AU - Forster, K.

AU - Giommi, P.

AU - Grefenstette, B.

AU - Hailey, C.

AU - Harrison, F. A.

AU - Hornstrup, A.

AU - Kitaguchi, T.

AU - Koglin, J. E.

AU - Madsen, K. K.

AU - Mao, P. H.

AU - Miyasaka, H.

AU - Mori, K.

AU - Perri, M.

AU - Pivovaroff, M. J.

AU - Puccetti, S.

AU - Rana, V.

AU - Stern, D.

AU - Tagliaferri, G.

AU - Urry, C. M.

AU - Westergaard, N. J.

AU - Zhang, W. W.

AU - Zoglauer, A.

AU - Archambault, S.

AU - Archer, A.

AU - Barnacka, A.

AU - Benbow, W.

AU - Bird, R.

AU - Buckley, J. H.

AU - Bugaev, V.

AU - Cerruti, M.

AU - Chatterjee, A.

AU - Poutanen, J.

AU - Lin, H. C.

AU - Hovatta, T.

AU - Lähteenmäki, A.

AU - Tornikoski, M.

AU - Tammi, J.

AU - Ramakrishnan, V.

AU - NuSTAR Team

AU - VERITAS Collaboration

AU - MAGIC Collaboration

PY - 2016/3

Y1 - 2016/3

N2 - We present coordinated multiwavelength observations of the bright, nearby BL Lacertae object 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) γ-ray bands. NuSTAR yielded previously unattainable sensitivity in the 3–79 keV range, revealing that the spectrum softens when the source is dimmer until the X-ray spectral shape saturates into a steep {{Γ }}≈ 3 power law, with no evidence for an exponential cutoff or additional hard components up to ∼80 keV. 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.

AB - We present coordinated multiwavelength observations of the bright, nearby BL Lacertae object 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) γ-ray bands. NuSTAR yielded previously unattainable sensitivity in the 3–79 keV range, revealing that the spectrum softens when the source is dimmer until the X-ray spectral shape saturates into a steep {{Γ }}≈ 3 power law, with no evidence for an exponential cutoff or additional hard components up to ∼80 keV. 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.

KW - BL Lacertae objects: individual: Markarian 421

KW - galaxies: active

KW - gamma rays: general

KW - radiation mechanisms: nonthermal

KW - X-rays: galaxies

U2 - 10.3847/0004-637X/819/2/156

DO - 10.3847/0004-637X/819/2/156

M3 - Article

VL - 819

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2

M1 - 156

ER -

ID: 1757898