NGC3147: a "true" Seyfert 2 without the broad-line region

TL;DR

This study presents simultaneous optical and X-ray observations of NGC3147, demonstrating it is an intrinsically BLR-lacking Seyfert 2 galaxy, challenging the traditional unification model of active galactic nuclei.

Contribution

First direct evidence of a Seyfert 2 galaxy intrinsically lacking a broad-line region, not due to obscuration or variability, but as an inherent property.

Findings

NGC3147 is unabsorbed in X-rays with low column density.

Optical spectrum shows no broad emission lines.

X-ray and optical data are simultaneous, ruling out variability effects.

Abstract

We report on simultaneous optical and X-ray observations of the Seyfert galaxy, NGC3147. The XMM-Newton spectrum shows that the source is unabsorbed in the X-rays ($N_H<5\times10^{20}$ cm$^{-2}$). On the other hand, no broad lines are present in the optical spectrum. The origin of this optical/X-rays misclassification (with respect to the Unification Model) cannot be attributed to variability, since the observations in the two bands are simultaneous. Moreover, a Compton-thick nature of the object can be rejected on the basis of the low equivalent width of the iron K$\alpha$ line ($\simeq130$ eV) and the large ratio between the 2-10 keV and the [OIII] fluxes. It seems therefore inescapable to conclude that NGC3147 intrinsically lacks the Broad Line Region (BLR), making it the first "true" Seyfert 2.