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Multiwavelength study of quiescent states of Mrk 421 with unprecedented hard X-ray coverage provided by NuSTAR in 2013.

Baloković, M. and Paneque, D. and Madejski, G. and Furniss, A. and Chiang, J. and The NuSTAR team, 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. and Mao, P.H. and Miyasaka, H. and Mori, K. and Perri, M. and Pivovaroff, M.J. and Puccetti, S. and Rana, V. and Stern, D. and Tagliaferri, G. and Urry, C.M. and Westergaard, N.J. and Zhang, W.W. and Zoglauer, A. and The VERITAS collaboration, and Archambault, S. and Archer, A.A. and Barnacka, A. and Benbow, W. and Bird, R. and Buckley, J. and Bugaev, V. and Cerruti, M. and Chen, X. and Ciupik, L. and Connolly, M.P. and Cui, W. and Dickinson, H.J. and Dumm, J. and Eisch, J.D. and Falcone, A. and Feng, Q. and Finley, J.P. and Fleischhack, H. and Fortson, L. and Griffin, S. and Griffiths, S.T. and Grube, J. and Gyuk, G. and Huetten, M. and Haakansson, N. and Holder, J. and Humensky, T.B. and Johnson, C.A. and Kaaret, P. and Kertzman, M. and Khassen, Y. and Kieda, D. and Krause, M. and Krennrich, F. and Lang, M.J. and Maier, G. and McArthur, S. and Meagher, K. and Moriarty, P. and Nelson, T. and Nieto, D. and Ong, R.A. and Park, N. and Pohl, M. and Popkow, A. and Pueschel, E. and Reynolds, P.T. and Richards, G.T. and Roache, E. and Santander, M. and Sembroski, G.H. and Shahinyan, K. and Smith, A.W. and Staszak, D. and Telezhinsky, I. and Todd, N.W. and Tucci, J.V. and Tyler, J. and Vincent, S. and Weinstein, A. and Wilhelm, A. and Williams, D.A. and Zitzer, B. and The MAGIC collaboration, and Ahnen, M.L. and Ansoldi, S. and Antonelli, L.A. and Antoranz, P. and Babic, A. and Banerjee, B. and Bangale, P. and Barres de Almeida, U. and Barrio, J. and Becerra González, J. and Bednarek, W. and Bernardini, E. and Biasuzzi, B. and Biland, A. and Blanch, O. and Bonnefoy, S. and Bonnoli, G. and Borracci, F. and Bretz, T. and Carmona, E. and Carosi, A. and Chatterjee, A. and Clavero, R. and Colin, P. and Colombo, E. and Contreras, J.L. and Cortina, J. and Covino, S. and Da Vela, P. and Dazzi, F. and de Angelis, A. and De Lotto, B. and de Oña Wilhelmi, E.D. and Delgado Mendez, C. and Di Pierro, F. and Dominis Prester, D. and Dorner, D. and Doro, M. and Einecke, S. and Elsaesser, D. and Fernández-Barral, A. and Fidalgo, D. and Fonseca, M.V. and Font, L. and Frantzen, K. and Fruck, C. and Galindo, D. and García López, R.J. and Garczarczyk, M. and Garrido Terrats, D. and Gaug, M. and Giammaria, P. and Eisenacher, D. and Godinović, N. and González Muñoz, A. and Guberman, D. and Hahn, A. and Hanabata, Y. and Hayashida, M. and Herrera, J. and Hose, J. and Hrupec, D. and Hughes, G. and Idec, W. and Kodani, K. and Konno, Y. and Kubo, H. and Kushida, J. and La Barbera, A. and Lelas, D. and Lindfors, E. and Lombardi, S. and Longo, F. and López, M. and López-Coto, R. and López-Oramas, A. and Lorenz, E. and Majumdar, P. and Makariev, M. and Mallot, K. and Maneva, G. and Manganaro, M. and Mannheim, K. and Maraschi, L. and Marcote, B. and Mariotti, M. and Martínez, M. and Mazin, D. and Menzel, U. and Miranda, J.M. and Mirzoyan, R. and Moralejo, A. and Moretti, E. and Nakajima, D. and Neustroev, V. and Niedzwiecki, A. and Nievas-Rosillo, M. and Nilsson, K. and Nishijima, K. and Noda, K. and Orito, R. and Overkemping, A. and Paiano, S. and Palacio, S. and Palatiello, M. and Paoletti, R. and Paredes, J.M. and Paredes-Fortuny, X. and Persic, M. and Poutanen, J. and Prada Moroni, P.G. and Prandini, E. and Puljak, I. and Rhode, W. and Ribó, M. and Rico, J. and Rodriguez Garcia, J. and Saito, T. and Satalecka, K. and Scapin, V. and Schultz, C. and Schweizer, T. and Shore, S.N. and Sillanpää, A. and Sitarek, J. and Snidaric, I. and Sobczynska, D. and Stamerra, A. and Steinbring, T. and Strzys, M. and Takalo, L.O. and Takami, H. and Tavecchio, F. and Temnikov, P. and Terzić, T. and Tescaro, D. and Teshima, M. and Thaele, J. and Torres, D.F. and Toyama, T. and Treves, A. and Verguilov, V. and Vovk, I. and Ward, J.E. and Will, M. and Wu, M.H. and Zanin, R. and External collaborators, and Perkins, J. and Verrecchia, F. and Leto, C. and Böttcher, M. and Villata, M. and Raiteri, C.M. and Acosta-Pulido, J.A. and Bachev, R. and Berdyugin, A. and Blinov, D.A. and Carnerero, M.I. and Chen, W.P. and Chinchilla, P. and Damljanovic, G. and Eswaraiah, C. and Grishina, T.S. and Ibryamov, S. and Jordan, B. and Jorstad, S.G. and Joshi, M. and Kopatskaya, E.N. and Kurtanidze, O.M. and Kurtanidze, S.O. and Larionova, E.G. and Larionova, L.V. and Larionov, V.M. and Latev, G. and Lin, H.C. and Marscher, A.P. and Mokrushina, A.A. and Morozova, D.A. and Nikolashvili, M.G. and Semkov, E. and Strigachev, A. and Troitskaya, Yu V. and Troitsky, I.S. and Vince, O. and Barnes, J. and Güver, T. and Moody, J.W. and Sadun, A.C. and Sun, S. and Hovatta, T. and Richards, J.L. and Max-Moerbeck, W. and Readhead, A.C. and Lähteenmäki, A. and Tornikoski, M. and Tammi, J. and Ramakrishnan, V. and Reinthal, R. and Angelakis, E. and Fuhrmann, L. and Myserlis, I. and Karamanavis, V. and Sievers, A. and Ungerechts, H. and Zensus, J.A. (2016) 'Multiwavelength study of quiescent states of Mrk 421 with unprecedented hard X-ray coverage provided by NuSTAR in 2013.', Astrophysical journal., 819 (2). p. 156.


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 G » 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-toVHE 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.

Item Type:Article
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Publisher statement:© 2016. The American Astronomical Society. All rights reserved.
Date accepted:05 December 2015
Date deposited:28 July 2016
Date of first online publication:09 March 2016
Date first made open access:28 July 2016

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