New X-ray constraints on starburst and Seyfert activity in the barred spiral galaxy NGC 1672

摘要

The nearby barred spiral galaxy NGC 1672 shows dramatic starburst activity and may also host a Seyfert 2 nucleus. We present new X-ray observations that set constraints on starburst and Seyfert activity in NGC 1672. Two ROSAT HRI exposures, taken in 1992 and 1997, are used to investigate longterm variability of the known X-ray sources and to search for new sources of X-ray emission. We find large-amplitude (approximate to 69) variability from X-3, one of the off-nuclear sources located near an end of the galactic bar. X-3 has a peak observed 0.2-2.0 keV luminosity of approximate to 2.5 x 10(39) ergs s(-1), and it is probably a luminous X-ray binary or young supernova remnant. We do not observe variability of the nuclear source X-1 or the strong off-nuclear source X-2. Our analyses also reveal two new off-nuclear sources, one of which is associated with a bright region along a spiral arm, and we find evidence for large-scale diffuse X-ray emission throughout part of the disk of NGC 1672. Furthermore, we use ASCA data taken in 1995 to constrain the hard X-ray properties of NGC 1672. While the nuclear source X-1 is the dominant soft X-ray source in NGC 1672, we find that the bulk of the 2-10 keV and 5-10 keV emission is spatially coincident with the off-nuclear source X-3, giving it an apparent 0.2-8 keV luminosity of greater than or similar to 6 x 10(39) ergs s(-1). A power-law-plus-Raymond-Smith model provides an acceptable fit to the full-band ASCA spectra. We do not find any evidence for a luminous but absorbed nuclear X-ray source. If there is a luminous Seyfert 2 nucleus in NGC 1672, it must be obscured by a "Compton-thick" torus with a column density of greater than or similar to 2 x 10(24) cm(-2). References: 36