Spectro-polarimetric view of the gamma-ray emitting NLS1 1H0323+342

TL;DR

This study uses spectro-polarimetric observations of the gamma-ray emitting NLS1 galaxy 1H0323+342 to analyze the broad-line region and estimate the viewing angle, providing insights into the central engine and jet launching mechanisms.

Contribution

It presents the first spectro-polarimetric analysis of this galaxy, revealing the geometry of the broad-line region and constraining the viewing angle with radiative transfer modeling.

Findings

Polarization degree is 0.122% with a polarization angle of 142 degrees.

Broad Hα line has a FWHM of 1015 km/s, with a similar broadening in polarized flux.

A thick BLR with a small viewing angle explains the observed spectra.

Abstract

The gamma-ray emitting narrow-line Seyfert 1 galaxies are a unique class of objects that launch powerful jets from relatively lower-mass black hole systems compared to the Blazars. However, the black hole masses estimated from the total flux spectrum suffer from the projection effect, making the mass measurement highly uncertain. The polarized spectrum provides a unique view of the central engine through scattered light. We performed spectro-polarimetric observations of the gamma-ray emitting narrow-line Seyfert 1 galaxy 1H0323+342 using SPOL/MMT. The degree of polarization and polarization angle is 0.122 $\pm$ 0.040 % and 142 $\pm$ 9 degrees, while the H$\alpha$ line is polarized at 0.265 $\pm$ 0.280 %. We decomposed the total flux spectrum and estimated broad H$\alpha$ FWHM of 1015 km/s. The polarized flux spectrum shows a broadening similar to the total flux spectrum, with a broadening ratio of 1.22. The Monte Carlo radiative transfer code `STOKES' applied to the data provides the best fit for a small viewing angle of 9-24 degrees and a small optical depth ratio between the polar and the equatorial scatters. A thick BLR with significant scale height can explain a similar broadening of the polarized spectrum compared to the total flux spectrum with a small viewing angle.