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 0.5-2 keV flux of NGC 7582 is not significantly variable within the BeppoSAX observation but has brightened by a factor of similar to 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(-0.18)(+0.09), steeper by Delta Gamma similar or equal to 0.40 than the index during the 1994 ASCA observation. The X-ray continuum is attenuated by a thick absorber of N-H similar to 1.6 x 10(24) cm(-2) covering similar to 60(-14)(+10) % of the nucleus plus a screen with N-H similar to 1.4 x 10(23) cm(-2) covering the entire nucleus. Comparison of the BeppoSAX and ASCA spectra shows an increase in the full screen by Delta N-H similar or equal to 7 x 10(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 less than or similar to 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.

Turner, T.j., Perola, G.c., Fiore, F., Matt, G., George, I.m., Piro, L., et al. (2000). Bepposax observation of NGC 7582: Constraints on the X-ray absorber. THE ASTROPHYSICAL JOURNAL, 531(1), 245-256 [10.1086/308459].

Bepposax observation of NGC 7582: Constraints on the X-ray absorber

MATT, Giorgio;
2000-01-01

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 0.5-2 keV flux of NGC 7582 is not significantly variable within the BeppoSAX observation but has brightened by a factor of similar to 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(-0.18)(+0.09), steeper by Delta Gamma similar or equal to 0.40 than the index during the 1994 ASCA observation. The X-ray continuum is attenuated by a thick absorber of N-H similar to 1.6 x 10(24) cm(-2) covering similar to 60(-14)(+10) % of the nucleus plus a screen with N-H similar to 1.4 x 10(23) cm(-2) covering the entire nucleus. Comparison of the BeppoSAX and ASCA spectra shows an increase in the full screen by Delta N-H similar or equal to 7 x 10(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 less than or similar to 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.
2000
Turner, T.j., Perola, G.c., Fiore, F., Matt, G., George, I.m., Piro, L., et al. (2000). Bepposax observation of NGC 7582: Constraints on the X-ray absorber. THE ASTROPHYSICAL JOURNAL, 531(1), 245-256 [10.1086/308459].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11590/122016
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