Weak emission line quasar SDSS J101353.45+492758.1 I. Continuum fitting

TL;DR

This study models the broadband spectrum of the weak emission line quasar SDSS J101353.45+492758.1, revealing a luminous accretion disk with an unusually weak hot corona, explaining its X-ray faintness and spectral peculiarities.

Contribution

It provides the first detailed physical modeling of a WLQ's spectral energy distribution, highlighting the role of a highly inefficient inner corona in its extreme spectral features.

Findings

Black hole mass approximately 2 billion solar masses

Extremely weak hot corona with suppressed X-ray emission

Presence of a warm corona extending to ~34 gravitational radii

Abstract

We present a broadband study of the WLQ SDSS J101353.45+492758.1, which displays a nearly featureless UV-optical spectrum with only a weak Mg II line alongside an exceptionally low X-ray flux. We model its spectral energy distribution using the relativistic thin-disk model kerrbb with a power law, and the multicomponent AGN model relagn, a physically motivated extension of agnsed incorporating warm and hot Comptonizing regions. Our fits constrain the black hole mass, accretion rate, X-ray loudness, and coronal energetics. Both approaches yield consistent BH masses of M_{BH} \approx 2 \times 10^{9} M_\odot and an Eddington accretion rate of \dot m \approx 0.1. The relagn fit including a warm Comptonizing region provides a significantly improved representation of the UV-soft X-ray continuum. The warm corona, characterized by kTe \simeq 0.20 keV, {\Gamma} \simeq 3.8, and an optical depth {\tau} \simeq 7.26, extends to \sim 34 R_g. The hot corona appears compact and energetically suppressed, leading to an intrinsically weak X ray output with log(L_{X}/L_{bol}) \simeq -4.29, among the lowest reported for WLQs. The {\alpha}_{ox} \sim 2.06 indicates the source to be in high/soft AGN spectral state. The combination of a luminous, standard disk and extremely weak hot corona suggests that this quasar hosts a highly inefficient inner coronal region. This explains its X-ray faintness and extreme deficit of high-ionization emission lines. The source may represent an AGN analog in "ultrasoft" accretion state, or a system in which the ionizing continuum is suppressed by a compact or quenched corona. Our study suggests that the source is not accreting at high Eddington ratio, highlighting the physical diversity of WLQs, and supports the view that geometric and radiative effects jointly shape their extreme spectral properties.