ROSAT PSPC observations of the infrared quasar IRAS 13349+2438: evidence for a warm absorber with internal dust

TL;DR

This study analyzes ROSAT X-ray data of the infrared quasar IRAS 13349+2438, revealing variability and evidence for a warm, dusty absorber, challenging existing scattering models and suggesting complex internal structures.

Contribution

It provides the first detailed X-ray spectral and temporal analysis of IRAS 13349+2438, highlighting the presence of a warm absorber with internal dust and its implications.

Findings

Detected significant X-ray variability within a year and a week.

Found no evidence of large cold X-ray absorption.

Identified an ionized oxygen edge in the spectrum.

Abstract

We present spatial, temporal and spectral analyses of ROSAT Position Sensitive Proportional Counter (PSPC) observations of the infrared loud quasar IRAS 13349+2438. IRAS 13349+2438 is the archetypal highly-polarized radio-quiet QSO and has an optical/infrared luminosity of about 2E46 erg/s. We detect variability in the ROSAT count rate by a factor of 4.1 in about one year, and there is also evidence for about 25 per cent variability within one week. We find no evidence for large intrinsic cold absorption of soft X-rays. These two facts have important consequences for the scattering-plus-transmission model of this object which was developed to explain its high wavelength-dependent polarization and other properties. The soft X-ray variability makes electron scattering of most of the soft X-rays difficult without a very peculiar scattering mirror. The lack of significant intrinsic cold X-ray absorption together with the large observed E(B-V) suggests either a very peculiar system geometry or, more probably, absorption by warm ionized gas with internal dust. There is evidence for an ionized oxygen edge in the X-ray spectrum. IRAS 13349+2438 has many properties that are similar to those of the Osterbrockian `narrow-line' Seyfert 1s.