On the origin of the FeK alpha line in the Seyfert 2 galaxy NGC 7172

Citation
M. Dadina et al., On the origin of the FeK alpha line in the Seyfert 2 galaxy NGC 7172, ASTRON ASTR, 370(1), 2001, pp. 70-77
Citations number
38
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Space Sciences
Journal title
ASTRONOMY AND ASTROPHYSICS
ISSN journal
0004-6361 → ACNP
Volume
370
Issue
1
Year of publication
2001
Pages
70 - 77
Database
ISI
SICI code
0004-6361(200104)370:1<70:OTOOTF>2.0.ZU;2-4
Abstract
The Seyfert 2 Galaxy NGC 7172 was observed twice by BeppoSAX narrow held in struments approximately one year apart. As found in previous observations, the source is variable on short time scales (hours) by a factor of similar to 30%, confirming the presence of a type 1 nucleus at the center. A strong flux variability (by a factor of 2) on a longer time scale was observed be tween the two observations. Indeed, in November 1997, the lowest flux ever recorded was detected by BeppoSAX. The broad band spectra obtained with the BeppoSAX narrow field instruments show marginal evidence of a reflection c omponent. This structure could explain the very flat spectra previously obs erved in the 2-10 keV band. An FeK alpha: line was also detected in both ob servations. The line intensity appears to remain almost constant between th e two observations even if the associated large errors cannot exclude some variability. In order to understand the problem of the origin of the line, data from previous observations, performed with other satellites, were also used. The scenario favored is one where the line is produced at a distance of approximatively 8 light years from the continuum source region, rather than having its origin in the accretion disk. In the framework of the stand ard unified models for AGN, this suggests that its origin is located in the molecular torus.