BeppoSAX Observation of NGC 7582: Constraints on
the X-Ray Absorber
Authors:
Turner, T.J. 1,2 ,
Perola, G.C. 3 ,
Fiore, F. 4,5 ,
Matt, G. 3 ,
George, I.M. 1,6 ,
Piro, L. 7 ,
Bassani, L. 8
Affiltns:
1 LHEA,
NASA/GSFC,
2 UMBC,
3 Univ Roma Tre,
4 SAX/SDC,
5 Oss. Roma,
6 USRA,
7 ITeSRE, Bologna,
8 IAS, Roma.
Journal: ApJ
Publication Date: 2000 Mar 01
Abstract
This paper presents a BeppoSAX observation of NGC 7582 made during
1998 November and an optical spectrum taken in 1998 October. The new
X-ray data reveal a previously unknown hard X-ray component in
NGC 7582, peaking close to 20 keV. Rapid variability is observed
with correlated changes in the 5-10 and 13-60 keV bands, indicating
that a single-continuum component, produced by the
active nucleus, provides the dominant flux across both bands.
Comparison between RXTE and BeppoSAX data reveals changes in the
2-10 keV flux on timescales of months. Changes in the nuclear X-ray
flux appear unrelated to the gradual decline in optical flux noted
since the high state in 1998 July. The 0.52 keV flux of NGC 7582 is
not significantly variable within the BeppoSAX observation but has
brightened by a factor of approx 2 since the ASCA observation of
1994. While there is some concern about contamination from spatially
unresolved sources, the long-term variability in soft X-ray flux
seems most likely associated with the nucleus or an event within the
host galaxy of NGC 7582. The 2-100 keV spectrum is well fit by a
power law of photon index Gamma = 1.95, steeper by
DeltaGamma approxeq 0.40 than the index during the 1994 ASCA
observation. The X-ray continuum is attenuated by a thick absorber
of NH approx 1.6x10^{24} cm^{-2} covering approx 60% (+10%, -14%)
of the nucleus plus a screen with NH approx 1.4x10^{23} cm^{-2}
covering the entire nucleus.
Comparison of the BeppoSAX and ASCA spectra shows an increase in the
full screen by Delta NH approx 7x10^{22} cm^{-2} since 1994,
confirming the absorption variability found by Xue et al.
The increase in soft X-ray flux between 1994 and 1998 is
consistent with the appearance of holes in the full screen,
allowing {< or approx =} 1% of the nuclear flux to escape and
producing some clear lines of sight to the broad-line region.
The data are also consistent with the scenario suggested by
Aretxaga et al. of the radiative onset of a Type IIn supernova
causing the observed optical change in NGC 7582.
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