Abstract
A sample of 45 quasars observed by the IPC on the Einstein satellite is used to reexamine the relationship of the soft X-ray energy index with radio properties and the optical Fe II emission. The tendency for radio-loud quasars to have systematically flatter X-ray energy indices than radio-quiet quasars is confirmed with the soft X-ray excess having negligible effect. There is a tendency for the flatness of the X-ray slope to correlate with radio core dominance for radio-loud quasars, suggesting that a component of the X-ray emission is relativistically beamed. For the radio-quiet quasars, the soft X-ray energy indices with a mean of about 1.0 are consistent with the indices found at higher energies, although steeper than those observed for Seyfert 1 galaxies where the reflection model gives a good fit to the data. The correlation of Fe II emission line strength with X-ray energy index is confirmed for radio-quiet quasars using a subset of 18 objects. The radio-loud quasars show no evidence for a correlation. This relation suggests a connection between the ionizing continuum and line emission from the broad emission-line region (BELR) of radio-quiet quasars, but in the opposite sense to that predicted by current photoionization models. The correlations of X-ray slope with radio core dominance and Fe II equivalent width within the radio-loud and radio-quiet subclasses, respectively, imply that the observed wide range of X-ray energy indices is real rather than due to the large measuring uncertainties for individual objects.
Highlights
The powerful X-ray emission that is commonly seen from quasars and other active galactic nuclei is widely believed to originate close to the "central engine" in these objects
Recent studies have made it clear that there is a wide range in the energy indices of the X-ray emission, both in the soft (_0.3-2keV: Wilkes and Elvis 1987) and hard (2-10keV: Comastri et al 1992; Williams et al 1992) energy ranges, laying to rest the older view that Xray slopes of all broad-line active galactic nuclei can be adequately described by a single power law of energy slope --.0.7 (e.g. Mushotzky 1984)
Wilkes and Elvis (1987) derived X-ray energy indices, dE(f,. " v-"'), in the soft X-ray region (0.2-3.5 keV) for a sample of 33 quasars that were observed with sufficient signal-tonoise with the Einstein !PC. They reported that the best-fit power-law energy slopes have a wide range (-0.2 to 1.8), and that radio-loudness correlated with the soft X-ray energy index in the sense that radio-loud quasars (RLQs) had flatter X-ray slopes than radio-quiet quasars (RQQs)
Summary
The powerful X-ray emission that is commonly seen from quasars and other active galactic nuclei is widely believed to originate close to the "central engine" in these objects. " v-"'), in the soft X-ray region (0.2-3.5 keV) for a sample of 33 quasars that were observed with sufficient signal-tonoise with the Einstein !PC They reported that the best-fit power-law energy slopes have a wide range (-0.2 to 1.8), and that radio-loudness correlated with the soft X-ray energy index in the sense that radio-loud quasars (RLQs) had flatter X-ray slopes than radio-quiet quasars (RQQs). Wilkes and Elvis (1987) explain the difference between these soft slopes and the mean slope of _0.7 observed at higher energies in terms of a mixing of the two components They found evidence for an upturn in the X-ray spectrum at lower energies (
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
