The variable ROSAT X-ray spectrum of the BL Lac 0716+714.
Abstract
The BLLac object 0716+714 is a powerful flat-spectrum radio source detected by CGRO EGRET at gamma ray energies. It has been observed for about 21 000 s over 2 d by the X-ray telescope on board the ROSAT satellite, and strong flux and spectral variations have been detected. In the time-scale of 2 d, the source varied by a factor of 7; during a sudden ( 1000 s) flux increase, the variation was 70 per cent. Spectral analysis was performed first, using the model-independent hardness ratio, and then the data were fitted using several standard spectral shapes. Both analyses agree on the conclusion that 0716+714 exhibits spectral variations related to source flux variability, which may be attributed to a `soft excess' component which is most prominent when the source is in a low state. The spectrum of 0716+714 steepens in the soft X-ray band when the flux decreases, while in the hard X-ray band it remains constant. A double power-law model, representing steep synchrotron radiation at low energies and flat inverse Compton radiation above 1 keV gives the best fit to both the low and high states. Key words: galaxies: active - BL Lacertae objects: individual: 0716+714 - X-rays: galaxies.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- November 1994
- DOI:
- 10.1093/mnras/271.2.438
- arXiv:
- arXiv:astro-ph/9409068
- Bibcode:
- 1994MNRAS.271..438C
- Keywords:
-
- BL Lacertae Objects: X-Ray Spectra;
- BL Lacertae Objects: X-Ray Light Curves;
- BL Lacertae Objects: Radiation Mechanisms;
- Astrophysics
- E-Print:
- Standard LateX file, for hardcopy of figures and tables please contact: comastri@astbo1.bo.cnr.it