A Comparison of X-Ray Photon Indices among the Narrow- and Broad-line Seyfert 1 Galaxies

Abstract

We present a detailed comparative systematic study using a sample of 221 narrow-line Seyfert 1 (NLSy1) galaxies in comparison to a redshift-matched sample of 154 broad-line Seyfert 1 (BLSy1) galaxies based on their observations using ROSAT and/or XMM-Newton in soft X-ray band (0.1–2.0 keV). A homogeneous analysis is carried out to estimate their soft X-ray photon indices ( ) and its correlations with other parameters of nuclear activities such as Eddington ratios (R Edd), bolometric luminosities (L bol), black hole masses (M BH), and the widths of the broad component of Hβ lines (FWHM(Hβ)). In our analysis, we found clear evidence of the difference in the and R Edd distributions among NLSy1 and BLSy1 galaxies, with steeper and higher R Edd for the former. Such a difference also exists in the spectral index distribution in hard X-ray ( ), based on the analysis of 53 NLSy1 and 46 BLSy1 galaxies in the 2–10 keV energy band. The difference in R Edd distributions does exist even after applying the average correction for the difference in the inclination angle of NLSy1 and BLSy1 galaxies. We also estimated R Edd, based on SED fitting of 34 NLSy1 and 30 BLSy1 galaxies over the 0.3–10 keV energy band, and found that results are still consistent with R Edd estimates based on the optical bolometric luminosity. Our analysis suggests that the higher R Edd in NLSy1 is responsible for its steeper X-ray spectral slope compared to the BLSy1, consistent with the disk-corona model as proposed for the luminous AGNs.

High-redshift Narrow-line Seyfert 1 Galaxies: A Candidate Sample

“…We find a general trend of decreasing photon index with increasing line width, both for Hβ and Mg II line with r s = −0.30 and r s = −0.31 ‡ ‡ , respectively. This is consistent with the fact of low-z NLS1s having a higher photon index compared to the BLS1s found in previous studies (e.g., Boller et al 1996;Ojha et al 2020). The anti-correlation of photon index with FWHM(Mg II) suggests that the latter is a good proxy for FWHM(Hβ) for selecting high-z NLS1s.…”

Properties of Broad and Narrow Line Seyfert galaxies selected from SDSS

“…We estimated the Eddington ratio using optical spectra itself. In Ojha et al (2020b), R Edd was calculated using X-ray observations which was consistent with the estimation from that obtained from optical parameters hence we did not attempt to estimate R Edd using other methods.…”

“…Naturally with the NlSy1 galaxies occupying extreme ends in some parameters space, it becomes imperative to understand the properties of these galaxies. In Grupe (2004), and more recently Ojha et al (2020b) and Waddell & Gallo (2020) the properties of NlSy1 galaxies have been studied comparatively with BlSy1 galaxies. In Grupe (2004), a sample of 110 X-ray selected galaxies was available, which is around 250 in our case, owing to the availability of SDSS sepctrum.…”

“…We also obtained the soft X-ray photon index as it is one of the fundamental components in the 4DE1 formalism. The X-ray photon indices were obtained from (Ojha et al, 2020b). The comparison between X-ray photon indices and the BLR asymmetry provides clues to the connection of the corona in the accretion disk with the BLR.…”

“…A sample comprising of both BlSy1 and NlSy1 galaxies with almost similar luminosity and matching in the redshift domain has been assembled in order to study the properties of these two seemingly different classes of galaxies. More information about this sample is available in Ojha et al (2020b). The single epoch optical spectrum for all the sources was obtained from the SDSS archives (see , Shen et al, 2011, York et al, 2000) using the SDSS-SAS DR16 server 1 .…”