B2 1023+25 is an extremely radio-loud quasar at z=5.3 which 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 ~5.5x10^(-14) erg cm^(-2)s^(-1) (5-10keV) and the photon spectral index is Gamma_X=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 ~3deg, 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.
@article{arxiv.1309.3280,
title = {NuSTAR detection of the blazar B2 1023+25 at redshift 5.3},
author = {T. Sbarrato and G. Tagliaferri and G. Ghisellini and M. Perri and S. Puccetti and M. Balokovic and M. Nardini and D. Stern and S. E. Boggs and W. N. Brandt and F. E. Chirstensen and P. Giommi and J. Greiner and C. J. Hailey and F. Harrison and T. Hovatta and G. M. Madejski and A. Rau and P. Schady and V. Sudilovsky and C. M. Urry and W. W. Zhang},
journal= {arXiv preprint arXiv:1309.3280},
year = {2015}
}
Comments
10 pages, 3 figures, 3 tables. Accepted for publication in ApJ