Suzaku Confirms NGC~3660 is an Unabsorbed Seyfert 2

TL;DR

Suzaku observations confirm that NGC 3660 is an unabsorbed Seyfert 2 galaxy with a typical X-ray continuum, resolving previous ambiguities about its obscuration status and clarifying earlier conflicting measurements.

Contribution

This study provides the first clear Suzaku-based confirmation that NGC 3660 lacks significant obscuration, clarifying its classification among Seyfert 2 galaxies.

Findings

NGC 3660 has a typical power law X-ray spectrum.

Previous Beppo-SAX detection was likely due to source confusion.

No evidence of obscuration in Suzaku, Swift-BAT, or RXTE data.

Abstract

An enigmatic group of objects, unabsorbed Seyfert 2s may have intrinsically weak broad line regions, obscuration in the line of sight to the BLR but not to the X-ray corona, or so much obscuration that the X-ray continuum is completely suppressed and the observed spectrum is actually scattered into the line of sight from nearby material. NGC 3660 has been shown to have weak broad optical/near infrared lines, no obscuration in the soft X-ray band, and no indication of "changing look" behavior. The only previous hard X-ray detection of this source by Beppo-SAX seemed to indicate that the source might harbor a heavily obscured nucleus. However, our analysis of a long-look Suzaku observation of this source shows that this is not the case, and that this source has a typical power law X-ray continuum with normal reflection and no obscuration. We conclude that NGC 3660 is confirmed to have no unidentified obscuration and that the anomolously high Beppo-SAX measurement must be due to source confusion or similar, being inconsistent with our Suzaku measurements as well as non-detections from Swift-BAT and RXTE.