Nustar detection of the blazar B2 1023+25 at redshift 5.3

T. Sbarrato, G. Tagliaferri, G. Ghisellini, M. Perri, S. Puccetti, M. Balokovic´, M. Nardini, D. Stern, S. E. Boggs, W. N. Brandt, Finn Erland Christensen, P. Giommi, J. Greiner, C. J. Hailey, F. A. Harrison, T. Hovatta, G. M. Madejski, A. Rau, P. Schady, V. SudilovskyC. M. Urry, W. W. Zhang

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B2 1023+25 is an extremely radio-loud quasar at z = 5.3 that was first identified as a likely high-redshift blazar candidate in the SDSS+FIRST quasar catalog. Here, we use the Nuclear Spectroscopic Telescope Array (NuSTAR) to investigate its non-thermal jet emission, whose high-energy component we detected in the hard X-ray energy band. The X-ray flux is ~5.5 × 10-14 erg cm-2 s-1 (5-10 keV) and the photon spectral index is ΓX ≃ 1.3-1.6. Modeling the full spectral energy distribution, we find that the jet is oriented close to the line of sight, with a viewing angle of ~3°, and has significant Doppler boosting, with a large bulk Lorentz factor ~13, which confirms the identification of B2 1023+25 as a blazar. B2 1023+25 is the first object at redshift larger than 5 detected by NuSTAR, demonstrating the ability of NuSTAR to investigate the early X-ray universe and to study extremely active supermassive black holes located at very high redshift.
Original languageEnglish
Article number147
JournalAstrophysical Journal
Issue number2
Number of pages8
Publication statusPublished - 2013

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