ASCA PV observations of the Seyfert 2 galaxy NGC 4388: the obscured nucleus and its X-ray emission
Abstract
We present results on the Seyfert 2 galaxy NGC 4388 in the Virgo cluster observed with ASCA during its performance verification (PV) phase. The 0.5-10 keV X-ray spectrum consists of multiple components: (1) a continuum component heavily absorbed by a column density N_H~4x10^23cm^-2 above 3 keV; (2) a strong 6.4-keV line (equivalent width EW~500eV) (3) a weak flat continuum between 1 and 3 keV; and (4) excess soft X-ray emission below 1 keV. The detection of strong absorption for the hard X-ray component is firm evidence for an obscured active nucleus in this Seyfert 2 galaxy. The absorption-corrected X-ray luminosity is about 2x10^42erg s^-1. This is the first time that the fluorescent iron K line has been detected in this object; the large EW is a common property of classical Seyfert 2 nuclei. The flat spectrum in the intermediate energy range may be a scattered continuum from the central source. The soft X-ray emission below 1 keV can be thermal emission from a temperature kT~=0.5keV, consistent with the spatially extended emission observed by ROSAT HRI. However, the low abundance (Z~0.05Z_solar) and high mass flow rate required for the thermal model and an iron K line stronger than expected from the obscuring torus model are puzzling. An alternative consistent solution can be obtained if the central source was a hundred times more luminous over a thousand years ago. All the X-ray emission below 3 keV is then scattered radiation.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- March 1997
- DOI:
- 10.1093/mnras/285.4.683
- arXiv:
- arXiv:astro-ph/9609191
- Bibcode:
- 1997MNRAS.285..683I
- Keywords:
-
- GALAXIES: ACTIVE;
- GALAXIES: INDIVIDUAL: NGC 4388;
- GALAXIES: SEYFERT;
- X-RAYS: GALAXIES;
- Astrophysics
- E-Print:
- 9 pages, 5 Postscript figures, to be published in MNRAS