NuSTAR Detection of the Blazar B2 1023+25 at Redshift 5.3

T. Sbarrato, G. Tagliaferri, G. Ghisellini, M. Perri, S. Puccetti, M. Balokovi, M. Nardini, D. Stern, S.~E. Boggs, W.~N. Brandt, F.~E. 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 (5-10 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
Pages (from-to)147
Number of pages1
JournalAstrophysical Journal
Issue number2
Publication statusPublished - 23 Oct 2013


  • galaxies: active, quasars: general, quasars: individual: B2 1023+25, X-rays: general, Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - High Energy Astrophysical Phenomena

Cite this

Sbarrato, T., Tagliaferri, G., Ghisellini, G., Perri, M., Puccetti, S., Balokovi, M., Nardini, M., Stern, D., Boggs, S. E., Brandt, W. N., Christensen, F. E., Giommi, P., Greiner, J., Hailey, C. J., Harrison, F. A., Hovatta, T., Madejski, G. M., Rau, A., Schady, P., ... Zhang, W. W. (2013). NuSTAR Detection of the Blazar B2 1023+25 at Redshift 5.3. Astrophysical Journal, 777(2), 147.