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

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 <sup>4

1</sup> 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

Abstract

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 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 (v0.36 c). The ionization parameter and the column density of the warm absorber are then 1 and 1.3 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 0.8 and 2.0 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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Contents

• 1. Introduction
• 2. The instruments
• 3. Observations and data reduction
• 4. Spectral fits
  • 4.1. SIS-only fits
  • 4.2. LECS-only fits
  • 4.3. Estimates of the relative SIS/LECS systematic deviation
  • 4.4. Fitting the absorption feature: 0.1-10 keV fits
  • 4.5. Fitting the absorption feature: photoionization models
• 5. Discussion
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: August 27, 1998
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