2015/04/02 by Eileen T. Meyer, Markos Georganopoulos, William B. Sparks +3 · 3 citations
Earth and Planetary Sciences · Physics and Astronomy · #Active galactic nucleus #Astrophysical Phenomena and Observations #Astrophysical jet #Astrophysics and Cosmic Phenomena #Blazar #Cosmic microwave background #Doppler effect #Earth Systems and Cosmic Evolution #Jet (fluid) #Observatory #Quasar #Synchrotron #astro-ph.HE
paper · pdf · doi:10.1088/0004-637x/805/2/154
8 pages, 7 figures, accepted for publication in ApJ
arxiv created 2015/04/02 · openalex publication_date 2015/05/28 · arxiv updated 2015/06/03 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The Chandra X-ray observatory has discovered dozens of resolved, kiloparsec-scale jets associated with powerful quasars in which the X-ray fluxes are observed to be much higher than the expected level based on the radio-optical synchrotron spectrum. The most popular explanation for the anomalously high and hard X-ray fluxes is that these jets do not decelerate significantly by the kiloparsec scale, but rather remain highly relativistic (Lorentz factors ). By adopting a small angle to the line of sight, the X-rays can thus be explained by inverse Compton upscattering of cosmic microwave background (CMB) photons (IC/CMB), where the observed emission is strongly Doppler boosted. Using over six years of Fermi monitoring data, we show that the expected hard, steady gamma-ray emission implied by the IC/CMB model is not seen in PKS 0637-752, the prototype jet for which this model was first proposed. IC/CMB emission is thus ruled out as the source of the X-rays, joining recent results for the jets in 3C 273 (using the same method) and PKS 1136-135 (using UV polarization). We further show that the Fermi observations give an upper limit of for the four brightest X-ray knots of PKS 0637-752, and derive an updated limit of for knots A and B1 of 3C 273 (assuming equipartition). Finally, we discuss the fact that high levels of synchrotron X-ray emission in a slow jet will unavoidably lead to a level of angle-integrated TeV emission which exceeds that of the TeV BL Lac class.