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Astron. Astrophys. 337, 685-690 (1998)

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Quasi-simultaneous observations of 3C 273 by BeppoSAX and ASCA

Astrid Orr 1, T. Yaqoob * 2, A.N. Parmar 1, L. Piro 3, N.E. White 2 and P. Grandi 4

1 Astrophysics Division, Space Science Department of ESA, ESTEC, P.O. Box 299, 2200 AG Noordwijk, The Netherlands
2 Laboratory for High Energy Astrophysics, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
3 Istituto di Astrofisica Spaziale, CNR, Via Fosso del Cavaliere, I-00133 Roma, Italy
4 Istituto di Astrofisica Spaziale, C.N.R., Via Enrico Fermi, I-00044 Frascati, Italy

Received 10 March 1998 / Accepted 20 May 1998


We report the results of quasi-simultaneous observations of the bright quasar 3C 273 using the BeppoSAX Low-Energy Concentrator Spectrometer (LECS) and the ASCA Solid-State Imaging Spectrometer (SIS). These observations are part of an intercalibration programme and demonstrate good agreement between both instruments in the common energy range 0.5-10 keV. In particular, the absorption feature discovered by BeppoSAX/LECS at [FORMULA]0.5 keV is consistently seen by ASCA/SIS. We present the most accurate measurement yet of the spectral shape of this absorption feature and provide constraints on its physical interpretation. A self-consistent warm absorber model in photoionization equilibrium only gives an adequate spectral fit if a very high velocity inflow is allowed for the warm absorber (v[FORMULA]0.36 c). The ionization parameter and the column density of the warm absorber are then [FORMULA]1 and [FORMULA]1.3 [FORMULA] cm-2, respectively. If the differences in best-fit neutral absorption column density between the LECS and each SIS are taken as estimates of the systematic spectral uncertainties, then these are [FORMULA]0.8[FORMULA] and [FORMULA]2.0[FORMULA] cm-2 (at 90% confidence) for SIS0 and SIS1, respectively.

Key words: instrumentation: miscellaneous – quasars: individual: 3C 273  – quasars: absorption lines – X-rays: galaxies

* Universities Space Research Association

Send offprint requests to: A. Orr, (aorr@astro.estec.esa.nl)

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© European Southern Observatory (ESO) 1998

Online publication: August 27, 1998