# Compton thick absorber in type 1 quasar 3C 345 revealed by Suzaku and Swift/BAT

## TL;DR

This study analyzes Suzaku and Swift/BAT data of quasar 3C 345, revealing a heavily obscured nucleus with a Compton thick absorber, and compares different models to determine the best fit for its properties.

## Contribution

It introduces a partial covering ionized absorber model as the most consistent explanation for 3C 345's X-ray spectrum, challenging previous torus model interpretations.

## Key findings

- Detection of a Compton thick absorber with N_H ≈ 10^25 cm^-2
- Partial covering ionized absorber model fits the data best
- 3C 345 is the most distant and obscured hard excess AGN known

## Abstract

The archival data of 3C 345, a type 1 quasar at $z = 0.5928$, obtained with Suzaku and Swift/BAT are analysed. Though previous studies of this source applied only a simple broken power law model, a heavily obscuring material is found to be required by considering Akaike information criteria. The application of the numerical torus model by Murphy & Yaqoob (2009) surprisingly reveals the existence of Compton thick type 2 nucleus with the line-of-sight hydrogen column density of the torus of $N_{\rm H} = 10^{24.5}$ cm$^{-2}$ and the inclination angle of $\theta_{\rm inc} = 90^{\circ}$. However, this model fails to account for the Eddington ratio obtained with the optical observations by Gu et al. (2001) and Shen et al. (2011), or requires the existence of a supermassive black hole binary, which was suggested by Lobanov & Roland (2005), thus this model is likely to be inappropriate for 3C 345. A partial covering ionized absorber model which accounts for absorption in "hard excess" type 1 AGNs is also applied, and finds a Compton thick absorber with the column density of $N_{\rm H} \simeq 10^{25}$ cm$^{-2}$, the ionization parameter of $\log \xi \gtrsim 2$, and the covering fraction of $75\% \lesssim f_{c} \lesssim 85\%$. Since this model obtains a black hole mass of $\log ( M_{\rm BH} / M_{\odot} ) = 9.8$, which is consistent with the optical observation by Gu et al. (2001), this model is likely to be the best-fitting model of this source. The results suggest that 3C 345 is the most distant and most obscured hard excess AGN at this time.