Swift observations of the highly X-ray variable narrow-line Seyfert 1 galaxy RX J0148.3-2758

Dirk Grupe, Karen M. Leighly, Stefanie Komossa, Patricia Schady, Paul T. O'Brien, David N. Burrows, John A. Nousek

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We report on Swift observations of the narrow-line Seyfert 1 galaxy RX J0148.3-2758. It was observed for 41.6 ks in 2005 May and for 15.8 ks in 2005 December. On short as well as on long timescales, RX J0148.3-2758 is a highly variable source. It doubles its X-ray flux within 18-25 ks. The observation of 2005 December 9, which had a flux 4 times lower than during the 2005 May observations, shows a significant hardening of the X-ray hardness ratio compared with the 2005 May and December 20 and 21 observations. A detailed analysis of the X-ray spectra shows that we actually observe two spectral changes in RX J0148.3-2758: first, a decrease of the soft X-ray component between 2005 May and December 9, which is most likely due to an increase of the intrinsic absorber column, and second, a decrease of the hard X-ray flux in the December 20 and 21 observations. The soft X-ray spectral slope α X,soft = 2.58 -0.12 +0.15 during the high state in 2005 May agrees well with that measured by ROSAT (α X,soft = 2.54 ± 0.82). This soft X-ray spectrum is superposed on a hard X-ray component with α X,hard = 0.96 -0.14 +0.16, which is consistent with the hard X-ray spectral slope α X,hard = 1-11 -0.19 +0.16 found by ASCA. The soft X-ray slope α X,soft = 1.93 -0.42 +0.58 measured during the December 9 observation agrees well with α X,soft = 2.03 -0.20 +0.23 measured from the ASCA observation when RX J0148.3-2758 was also in a low state. In contrast to the strong X-ray variability, the analysis of the Swift UV-Optical Telescope (UVOT) photometry from 2005 December of RX J0148.3-2758 shows no significant variability in any of the six UVOT filters. From the simultaneous X-ray and UV observations in 2005 December we measured the X-ray loudness α ox and found it to vary between α ox = 1.5 and 1.8. Our Swift observations of RX J0148.3-2758 demonstrate the great potential that the multiwavelength observatory Swift has for active galactic nucleus science.

Original languageEnglish (US)
Pages (from-to)1189-1201
Number of pages13
JournalAstronomical Journal
Issue number3
StatePublished - Sep 2006

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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