Soft X-ray precursors of the non-thermal flares in blazars - theoretical predictions.pdf

a r X i v : a s t r o - p h / 0 4 0 5 2 2 9 v 1 1 2 M a y 2 0 0 4 Soft X-ray precursors of the non-thermal flares in blazars - theoretical predictions Rafa l Moderski1, Marek Sikora1,2, Greg M. Madejski2, and Tuneyoshi Kamae2 ABSTRACT Popular internal shock models, developed to explain production of high en- ergy flares in blazar jets, involve collisions between local overdensities of matter being ejected by a central engine and moving along the jet with different veloci- ties. Prior to such collisions, the matter is relatively cold and therefore does not produce intrinsic non-thermal radiation. However, due to Comptonization of ex- ternal radiation by cold electrons, the presence of such matter should be apparent by prominent precursor soft X-ray flares, visible prior to non-thermal γ-ray flares. In this paper we discuss the predicted properties of such precursors and study the dependence of their properties (luminosities and light curves) on kinematic parameters of relativistic ejecta and on an angle of view. We demonstrate that the lack of evidence for luminous soft X-ray precursors can be reconciled with our predictions for their properties if acceleration and collimation of a jet takes about three distance decades. We briefly discuss the severe constraints on the internal shock models that would be imposed by a non-detection of such precursors. Subject headings: galaxies: quasars: general — galaxies: jets — radiation mech- anisms: non-thermal — gamma rays: theory — X-rays: general 1. INTRODUCTION Strong jets in radio loud quasars must be launched very deeply in the gravitational potential well, and most likely are powered by rotating black hole and/or innermost parts of an accretion disk. Their formation is very likely mediated by magnetic fields, but the detailed model is not yet established (compare, e.g., scenarios suggested by Contopoulos 1995; Lovelace et al. 1997; Vlahakis Ko?nigl 2003). In magnetic models, acceleration and 1Nicolaus Copernicus Astr