First NuSTAR observations of the BL Lac-type blazar PKS 2155-304: constraints on the jet content and distribution of radiating particles

Madejski, G.M.; Nalewajko, K.; Madsen, K.K.; Chiang, J.; Baloković, M.; Paneque, D.; Furniss, A.K.; Hayashida, M.; Urry, C.M.; Sikora, M.; Ajello, M.; Blandford, R.D.; Harrison, F.A.; Sanchez, D.; Giebels, B.; Stern, D.; Alexander, D.M.; Barret, D.; Boggs, S.E.; Christensen, F.E.; Craig, W.W.; Forster, K.; Giommi, P.; Grefenstette, B.; Hailey, C.; Hornstrup, A.; Kitaguchi, T.; Koglin, J.E.; Mao, P.H.; Miyasaka, H.; Mori, K.; Perri, M.; 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 $\beta ={0.3}_{-0.1}^{+0.2}$ 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 ~ 1047 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 ${n}_{{\rm{e}}+{\rm{e}}-}/{n}_{{\rm{p}}}\sim 30$, 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.

Citation

Madejski, G., Nalewajko, K., Madsen, K., Chiang, J., Baloković, M., Paneque, D., …Zoglauer, A. (2016). First NuSTAR observations of the BL Lac-type blazar PKS 2155-304: constraints on the jet content and distribution of radiating particles. Astrophysical Journal, 831(2), Article 142. https://doi.org/10.3847/0004-637x/831/2/142

• Journal Article Type: Article
• Acceptance Date: Aug 29, 2016
• Online Publication Date: Nov 3, 2016
• Publication Date: Nov 3, 2016
• Deposit Date: Jun 21, 2017
• Publicly Available Date: Jul 3, 2017
• Journal: Astrophysical Journal
• Print ISSN: 0004-637X
• Electronic ISSN: 1538-4357
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 831
• Issue: 2
• Article Number: 142
• DOI: https://doi.org/10.3847/0004-637x/831/2/142
• Public URL: https://durham-repository.worktribe.com/output/1384377