First NuSTAR Observations of the BL Lac-type Blazar PKS 2155-304: Constraints on the Jet Content and Distribution of Radiating Particles
Journal
Date Issued
2016
Author(s)
Madejski, G. M.
•
Nalewajko, K.
•
Madsen, K. K.
•
Chiang, J.
•
Baloković, M.
•
Paneque, D.
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Furniss, A. K.
•
Hayashida, M.
•
Urry, C. M.
•
Sikora, M.
•
Ajello, M.
•
Blandford, R. D.
•
Harrison, F. A.
•
Sanchez, D.
•
Giebels, B.
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Stern, D.
•
Alexander, D. M.
•
Barret, D.
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Boggs, S. E.
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Christensen, F. E.
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Craig, W. W.
•
Forster, K.
•
Giommi, P.
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Grefenstette, B.
•
Hailey, C.
•
Hornstrup, A.
•
Kitaguchi, T.
•
Koglin, J. E.
•
Mao, P. H.
•
Miyasaka, H.
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Mori, K.
•
•
Pivovaroff, M. J.
•
Puccetti, S.
•
Rana, V.
•
Westergaard, N. J.
•
Zhang, W. W.
•
Zoglauer, A.
Abstract
We report the first hard X-ray observations with NuSTAR of the BL Lac-type blazar PKS 2155-304, augmented with soft X-ray data from XMM-Newton and γ-ray data from the Fermi Large Area Telescope, obtained in 2013 April when the source was in a very low flux state. A joint NuSTAR and XMM spectrum, covering the energy range 0.5-60 keV, is best described by a model consisting of a log-parabola component with curvature β = 0.3(-0.1,+0.2) and a (local) photon index 3.04 ± 0.15 at photon energy of 2 keV, and a hard power-law tail with photon index 2.2 ± 0.4. The hard X-ray tail can be smoothly joined to the quasi-simultaneous γ-ray spectrum by a synchrotron self-Compton component produced by an electron distribution with index p = 2.2. Assuming that the power-law electron distribution extends down to γ_min = 1 and that there is one proton per electron, an unrealistically high total jet power of L_p ∼ 10^47 erg s^-1 is inferred. This can be reduced by two orders of magnitude either by considering a significant presence of electron-positron pairs with lepton-to-proton ratio n_e+_e-/n_p ∼ 30, or by introducing an additional, low-energy break in the electron energy distribution at the electron Lorentz factor γ_br1 ∼ 100. In either case, the jet composition is expected to be strongly matter-dominated.
Volume
831
Issue
2
Start page
142
Issn Identifier
0004-637X
Ads BibCode
2016ApJ...831..142M
Rights
open.access
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