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

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, Γ \simeq 3.8, and an optical depth τ \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 α_{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.

Figures (13)

• Figure 1: Data points (black) and spectrum (blue -- extracted from the SDSS data release 17) of SDSS J101353 in observed-frame. The light gray box represents the typical X-ray flux measured in the 2--10 keV energy band of classical quasars (e.g., young2009).
• Figure 2: Rest-frame spectrum of SDSS J101353 (blue) shown with the fitted continuum (orange) and the broadened iron emission (green). For comparison, the composite quasar spectrum 2 from richards2003 is also displayed (red).
• Figure 3: Mg II emission line fitting. The rebinned rest-frame spectrum of SDSS J101353 after iron subtraction is displayed in orange. The signal from which the continuum has been subtracted, underlying the emission line is shown in blue. The green line materializes the best fit with a single Gaussian.
• Figure 4: Schematic geometry used in the fitting process for Models 1a. The BH is in black, the standard geometrically thin accretion disk in blue-gray, and the hot corona in yellow.
• Figure 5: $\chi^{2}$ confidence contours in the spin-inclination ($a$–$i$) plane, using Model 1a: kerrbb + power law components. This was obtained by allowing the BH mass and mass accretion rate to vary. The red, green, and blue contours correspond to the 68%, 90%, and 99% confidence levels, respectively. The cross indicates the best-fit solution.