The Highly Relativistic Kiloparsec‐Scale Jet of the Gamma‐Ray Quasar 0827+243

Abstract

We present Chandra X-ray (0.2-8 keV) and Very Large Array radio (15 and 5 GHz) images of the γ-ray-bright, superluminal quasar 0827+243. The X-ray jet bends sharply—by ~90°, presumably amplified by projection effects—5'' from the core. Only extremely weak radio emission is detected between the nuclear region and the bend. The X-ray continuum spectrum of the combined emission of the knots is rather flat, with a slope of -0.4 ± 0.2, while the 5-15 GHz spectra are steeper for knots detected in the radio. These characteristics, as well as nondetection of the jet in the optical band by the Hubble Space Telescope, pose challenges to models for the spectral energy distributions (SEDs) of the jet features. The SEDs could arise from pure synchrotron emission from either a single or dual population of relativistic electrons only if the minimum electron energy per unit mass γmin 1000. In the case of a single population, the radiative energy losses of the X-ray-emitting electrons must be suppressed owing to inverse Compton scattering in the Klein-Nishina regime, as proposed by Dermer & Atoyan. Alternatively, the X-ray emission could result from inverse Compton scattering of the cosmic microwave background photons by electrons with Lorentz factors as low as γ ~ 15. In all models, the bulk Lorentz factor of the jet flow Γ 20 found on parsec scales must continue without substantial deceleration out to 800 kpc (deprojected) from the nucleus, and the magnetic field is very low, 2 μG, until the bend. Deceleration does appear to occur at and beyond the sharp bend, such that the flow could be only mildly relativistic at the end of the jet. Significant intensification of the magnetic field occurs downstream of the bend, where there is an offset between the projected positions of the X-ray and radio features.