Constraining black hole spin in PG 1535+547 amid complex multi-layered absorption

ABSTRACT We present a spectroscopic analysis of XMM–Newton and NuSTAR observations of the ‘complex’ narrow-line Seyfert 1 PG 1535+547 at redshift $z=0.038$. These observations span three epochs: 2002 and 2006 with XMM–Newton alone, covering the $0.3 \mathrm{ -} 10$ keV energy range, and a coordinated XMM–Newton and NuSTAR observation in 2016, covering the $0.3\mathrm{ -}60$ keV energy range. The X-ray spectra across all epochs exhibit both neutral and ionized absorption, along with reflection features from the accretion disc, including a prominent Compton hump in the broadband data. Notably, the spectral shape varies across epochs. Our analysis suggests this variability is attributed to changes in both line-of-sight absorption and the intrinsic emission from PG 1535+547. The source is obscured by multiple layers of partially and/or fully covering neutral and ionized absorbers, with neutral column densities ranging from undetectable levels in the least obscured phase to $\sim 0.3\mathrm{ -}5\times 10^{23} ~ \rm cm^{-2}$ in the most obscured phase. A clear warm absorber is revealed during the least obscured phase. The continuum remains fairly consistent ($\Gamma \approx 2.2\pm 0.1$) during the first two observations, followed by a substantial flux decrease (by a factor of $\sim 7$ in the $2\mathrm{ -}10$ keV band) in 2016 compared to 2006. The 2016 data indicate the source is in a reflection-dominated state during this epoch, with a reflection fraction of $R > 7$ and an X-ray source located at a height $\le 1.72r_g$. Simultaneous fitting of the multi-epoch data suggests a rapidly rotating black hole with a spin parameter, $a > 0.99$. These findings imply that strong light-bending effects may account for the observed continuum flux reduction.