ROSAT PSPC observations of six PG quasars and PHL 1657
| dc.creator | Rachen, Joerg P. | |
| dc.creator | Mannheim, Karl | |
| dc.creator | Biermann, Peter L. | |
| dc.date | 1995-12-08 | |
| dc.date.accessioned | 2026-07-07T02:20:34Z | |
| dc.date.available | 2026-07-07T02:20:34Z | |
| dc.description | We report results from the spectral analysis of pointed ROSAT PSPC observations of six PG quasars and the weak-bump quasar PHL 1657. Disregarding other frequency bands, the PSPC data are represented best by simple power-law source spectra ($dN/dE \propto E^Γ$) with a slope $Γ= -2.5\pm 0.4$ and do not show evidence for a more complex structure. However, within the limits given by statistics and systematical errors, a superposition of two power-law spectra, which allows a connection to the observed UV fluxes and to the generally flatter hard-X-ray spectra observed by EXOSAT and GINGA, is found to be indistinguishable from a simple power-law in the PSPC energy band. For the PG quasars, a direct connection to the observed UV flux is obtained with a steep soft-X-ray slope $Γ_{sx}= -3.1\pm 0.3$, fixing the hard-X-ray slope. For PHL 1657, the soft-X-ray spectrum seen by ROSAT is much steeper than the GINGA spectrum, rising towards the EUV in $νF_ν$, and it can not be extrapolated down to meet the exceptionally weak UV flux. A Wien-shaped thermal UV/soft-X-ray bump with a temperature of $\sim $50\,eV connects the UV and soft-X-ray spectra in all cases, but gives only a poor representation of the high signal-to-noise PSPC spectra. We discuss implications of our results for models of the X-ray emission in quasars. | |
| dc.description | 10 pages, 4 figures, uuencoded compressed PostScript file, accepted by Astronomy and Astrophysics | |
| dc.identifier | https://arxiv.org/abs/astro-ph/9512048 | |
| dc.identifier | http://arxiv.org/abs/astro-ph/9512048 | |
| dc.identifier | Astron.Astrophys. 310 (1996) 371-380 | |
| dc.identifier.uri | http://salesiana.dossiersoluciones.com/handle/123456789/10250 | |
| dc.subject | Astrophysics | |
| dc.title | ROSAT PSPC observations of six PG quasars and PHL 1657 | |
| dc.type | text |