2003/12/12 by G. C. Dewangan, Dewangan, G. C., R. E. Griffiths +1
Physics and Astronomy · #Astrophysics (astro-ph) #FOS: Physical sciences #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/0312342
14 pages, uses emulateapj5, submitted to ApJ
arxiv created 2003/12/12 · arxiv updated 2009/12/01
We present results based on an XMM-Newton observation of the prototype narrow-line Seyfert 1 galaxy I Zw 1 performed in June 2002. The 0.6-12 keV spectrum is well described by a steep power-law (Gamma∼ 2.3) and a weak soft blackbody component (kT ∼ 200 eV) below 2 kev. The soft X-ray excess emission is featureless and contributes only about 10% to the total X-ray emission in the 0.6-2\kev band. There are tentative evidences for an iron iron Kalpha line and an iron K edge, both from high ionized He-like iron. The 0.6-12kev continuum of I Zw 1 can be explained in terms of a blackbody (kT ∼ 40eV), thermal comptonization and its reflection off the surface of an ionized accretion disk. We note that characterizing the soft excess copmonent `above a power law continuum' may not be appropriate due to the low energy curvature of a comptonized spectrum. X-ray emission from I Zw 1 was highly variabile during the observation. I Zw 1 showed a large, symmetric X-ray flare during which the X-ray luminosity increased by about 6e43 erg/s in an interval of 2800s only. The X-ray spectral variability was unusual during the flare. In contrast to the general observation of spectral steepening with flux from Seyfert galaxies, there is a clear evidence for hardening of the 0.6-10kev spectrum of I Zw 1 with increasing flux. This hardening is due to a stronger and slightly flatter power-law component at higher flux without any change in the soft X-ray excess component. The large flare, the accompanying spectral flattening, and the steady nature of the soft excess component may be due to an additional flatter power-law component during the flare possibly arising as a result of ejection of electron plasma and the SSC process.