Since the discovery of nonthermal X-rays in the shell-type supernova remnant SN1006 almost 20 years ago, the field has developed considerably, owing significant progress to our understanding of particle acceleration. Key to the characterization of the nonthermal emission is the ability of current satellites, XMM-Newton and Chandra, to perform spatially resolved spectroscopy at a relatively small spatial scale.

In this review, I intend to present the main contributions of the study of nonthermal X-rays from supernova remnants to the understanding of particle acceleration.

Recent observational evidence suggests the existence of two tracks in the radio-X-ray relation for X-ray binaries. Claims have also been made for deviations from the so-called fundamental plane of black hole activity due to the influence of radiative cooling on synchrotron emission from jets and the relative importance of disk and jet emission. In addition, cases of strongly boosted classes of objects, such as BL Lacs, show evidence for jet emission in their location relative to the fundamental plane. In light of the recent literature activity discussing these issues, we revisit the scaling relations expected for synchrotron emission from jet cores. We review the set of scaling laws expected for different types of emission and discuss their relevance to the new observational data, and the conditions under which breaks in the observed scaling relations should be expected. None of the canonical cases offer a satisfactory explanation for the best fit slope of the steep branch of the radio-X-ray relation in hard-state X-ray binaries.