Open AccessASCA spectroscopy of the luminous infrared galaxy NGC 6240: X‐ray emission from a starburst and a buried active nucleus
Author(s) -
Iwasawa K.,
Comastri A.
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.1365-8711.1998.01588.x
Subject(s) - physics , astrophysics , active galactic nucleus , luminosity , galaxy , luminous infrared galaxy , infrared , astronomy , emission spectrum , quasar , spectroscopy , spectral line
We present an X‐ray spectroscopic study of the prototype far‐infrared galaxy NGC 6240 from ASCA . The soft X‐ray spectrum (below 2 keV) shows clear signatures of thermal emission well described by a multitemperature optically thin plasma, which probably originates in a powerful starburst. Strong hard X‐ray emission is also detected with ASCA and its spectrum above 3 keV is extremely flat with a prominent iron K line complex, very similar to that seen in the Seyfert 2 galaxy NGC 1068 but about an order of magnitude more luminous ( L 3−10keV ≈ 1.4 × 10 42 erg s −1 ). The hard X‐ray spectrum indicates that only reflected X‐rays of an active galactic nucleus (AGN) buried in a heavy obscuration ( N H > 2 × 10 24 cm −2 ) are visible. This is evidence for an AGN in NGC 6240, emitting possibly at a quasar luminosity (∼ 10 45 erg s −1 ), and suggests its significant contribution to the far‐infrared luminosity.