Constraining the soft X-ray spectrum of 3C 273 with ROSAT
Open Access
- 1 January 1995
- journal article
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 272 (1) , 221-230
- https://doi.org/10.1093/mnras/272.1.221
Abstract
We present below a study of the soft X-ray emission (0.1-2.4 keV) of the quasar 3C 273 with the Position Sensitive Proportional Counter (PSPC) instrument on the ROSAT satellite. The overall count rate shows variations of ∼20 per cent in ∼2d, a considerably higher degree of short-term X-ray variability than had been expected from previous studies. The count rates, when split into hard (1.5-2.4 keV) and soft (0.1-0.3 keV) energy bands, are not correlated, showing that two physically distinct emission components are present. The spectra are modelled best by a combination of two power laws with absorption at the galactic value. The photon number spectral index, Γhard, of the harder power law is fixed at 1.5, the value determined by observations in the 2-10 keV band. The spectral index of the softer power law, Γsoft, is then determined to be ∼2.7. There are small but significant variations in Γsoft which are not correlated with the soft count rate. We discuss the nature of this variable soft component in the light of present theories.Keywords
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