Open AccessX‐ray absorption in the strong Fe ii narrow‐line Seyfert 1 galaxy Markarian 507
Author(s) -
K. Iwasawa,
W. N. Brandt,
A. C. Fabian
Publication year - 1998
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1998.01085.x
Subject(s) - physics , rosat , astrophysics , galaxy , ionization , spectral line , absorption (acoustics) , extrapolation , absorption edge , absorption spectroscopy , line (geometry) , astronomy , optics , ion , mathematical analysis , quantum mechanics , band gap , geometry , mathematics
We present results from spectral analysis of ASCA data on the strong Fe ii narrow‐line Seyfert 1 galaxy Mrk 507. This galaxy was found to have an exceptionally flat ROSAT spectrum among the narrow‐line Seyfert 1 galaxies (NLS1s) studied by Boller, Brandt & Fink. The ASCA spectrum, however, shows a clear absorption feature in the energy band below 2 keV, which partly accounts for the flat spectrum observed with the ROSAT Position Sensitive Proportional Counter (PSPC). Such absorption is rarely observed in other NLS1s. The absorption is mainly the result of cold (neutral or slightly ionized) gas with a column density of (2–3) × 10 21 cm −2 . A reanalysis of the PSPC data shows that an extrapolation of the best‐fitting model for the ASCA spectrum underpredicts the X‐ray emission observed with the PSPC below 0.4 keV if the absorber is neutral (which indicates that the absorber is slightly ionized), covers only part of the central source, or there is extra soft thermal emission from an extended region. There is also evidence that the X‐ray absorption is complex; an additional edge feature marginally detected at 0.84 keV suggests the presence of an additional high‐ionization absorber, which imposes a strong O viii edge on the spectrum. After correction for the absorption, the photon index of the intrinsic continuum, Γ ≃ 1.8, obtained from the ASCA data is quite similar to that of ordinary Seyfert 1 galaxies. Mrk 507 still has one of the flattest continuum slopes among the NLS1s, but is no longer exceptional. The strong optical Fe ii emission remains unusual in the light of the correlation between Fe ii strengths and steepness of soft X‐ray slope.