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New X-ray Constraints on Starburst and Seyfert Activity in the Barred Spiral Galaxy NGC 1672
Astrophysics · Submitted 20 Oct 1999
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim 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 > 2 x 10^{24} cm^{-2}.
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The abstract, sentence by sentence
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 long-term variability of the known X-ray sources and to search for new sources of X-ray emission. We find large-amplitude (about 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 about 2.5 x 10^{39} erg/s, 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 about 6 x 10^{39} erg/s. 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 > 2 x 10^{24} cm^{-2}.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | The nearby barred spiral galaxy NGC 1672 shows dramatic starburst activity and may also host a Seyfert 2 nucleus. | background 1.00 | 0.09 | 0.05 | hedged possibility 0.71 |
| s1 | We present new X-ray observations that set constraints on starburst and Seyfert activity in NGC 1672. | contribution 1.00 | 0.92 | 0.09 | asserted 1.00 |
| s2 | Two ROSAT HRI exposures, taken in 1992 and 1997, are used to investigate long-term variability of the known X-ray sources and to search for new sources of X-ray emission. | method 0.99 | 0.86 | 0.02 | asserted 0.98 |
| s3 | We find large-amplitude (about 69%) variability from X-3, one of the off-nuclear sources located near an end of the galactic bar. | result 1.00 | 0.97 | 0.11 | asserted 1.00 |
| s4 | X-3 has a peak observed 0.2-2.0 keV luminosity of about 2.5 x 10^{39} erg/s, and it is probably a luminous X-ray binary or young supernova remnant. | result 0.74 | 0.93 | 0.09 | hedged possibility 0.78 |
| s5 | We do not observe variability of the nuclear source X-1 or the strong off-nuclear source X-2. | result 1.00 | 0.97 | 0.06 | asserted 1.00 |
| s6 | 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. | result 1.00 | 0.97 | 0.09 | asserted 0.99 |
| s7 | Furthermore, we use ASCA data taken in 1995 to constrain the hard X-ray properties of NGC 1672. | method 0.93 | 0.94 | 0.03 | asserted 0.98 |
| s8 | 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 about 6 x 10^{39} erg/s. | result 1.00 | 0.97 | 0.28 | asserted 1.00 |
| s9 | A power-law plus Raymond-Smith model provides an acceptable fit to the full-band ASCA spectra. | method 0.57 | 0.93 | 0.06 | asserted 0.84 |
| s10 | We do not find any evidence for a luminous but absorbed nuclear X-ray source. | result 0.99 | 0.97 | 0.22 | asserted 1.00 |
| s11 | 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 > 2 x 10^{24} cm^{-2}. | interpretation 0.93 | 0.75 | 0.40 | hedged possibility 0.73 |
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The paper
Original abstract
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 long-term variability of the known X-ray sources and to search for new sources of X-ray emission. We find large-amplitude (about 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 about 2.5 x 10^{39} erg/s, 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 about 6 x 10^{39} erg/s. 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 > 2 x 10^{24} cm^{-2}.
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