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Durham University

Department of Physics

Staff profile

Publication details for Prof David Alexander

Hayashida, M., Nalewajko, K., Madejski, G.M., Sikora, M., Itoh, R., Ajello, M., Blandford, R.D., Buson, S., Chiang, J., Fukazawa, Y., Furniss, A.K., Urry, C.M., Hasan, I., Harrison, F.A., Alexander, D.M., Baloković, 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., Madsen, K.K., Mao, P.H., Miyasaka, H., Mori, K., Perri, M., Pivovaroff, M.J., Puccetti, S., Rana, V., Stern, D., Tagliaferri, G., Westergaard, N.J., Zhang, W.W., Zoglauer, A., Gurwell, M.A., Uemura, M., Akitaya, H., Kawabata, K.S., Kawaguchi, K., Kanda, Y., Moritani, Y., Takaki, K., Ui, T., Yoshida, M., Agarwal, A. & Gupta, A.C. (2015). Rapid Variability of Blazar 3C 279 during Flaring States in 2013-2014 with Joint Fermi-LAT, NuSTAR, Swift, and Ground-Based Multiwavelength Observations. The Astrophysical Journal 807(1): 79.

Author(s) from Durham


We report the results of a multiband observing campaign on the famous blazar 3C 279 conducted during a phase of
increased activity from 2013 December to 2014 April, including first observations of it with NuSTAR. The γ-ray
emission of the source measured by Fermi-LAT showed multiple distinct flares reaching the highest flux level
measured in this object since the beginning of the Fermi mission, with F E( 100 MeV) > of 10−5 photons cm−2 s
and with a flux-doubling time scale as short as 2 hr. The γ-ray spectrum during one of the flares was very hard, with
an index of Γ= ± γ 1.7 0.1, which is rarely seen in flat-spectrum radio quasars. The lack of concurrent optical
variability implies a very high Compton dominance parameter Lγ Lsyn > 300. Two 1 day NuSTAR observations with
accompanying Swift pointings were separated by 2 weeks, probing different levels of source activity. While the 0.5
−70 keV X-ray spectrum obtained during the first pointing, and fitted jointly with Swift-XRT is well-described by a
simple power law, the second joint observation showed an unusual spectral structure: the spectrum softens by
ΔΓ ≃ X 0.4 at ∼4 keV. Modeling the broadband spectral energy distribution during this flare with the standard
synchrotron plus inverse-Compton model requires: (1) the location of the γ-ray emitting region is comparable with
the broad-line region radius, (2) a very hard electron energy distribution index p ≃ 1, (3) total jet power significantly
exceeding the accretion-disk luminosity L j d L ≳ 10, and (4) extremely low jet magnetization with ≲ − LB j L 10 4.
We also find that single-zone models that match the observed γ-ray and optical spectra cannot satisfactorily explain
the production of X-ray emission.