X-Ray and Optical Microlensing in the Lensed Quasar PG 1115+080

TL;DR

This study uses microlensing observations of the lensed quasar PG 1115+080 to measure the sizes of its X-ray and optical emission regions, revealing that X-ray emission originates closer to the black hole than optical emission.

Contribution

It provides the first direct size measurements of X-ray and optical emission regions in PG 1115+080 using microlensing, highlighting differences in their spatial scales and implications for accretion disk models.

Findings

X-ray emission region is about 1.3 dex smaller than optical.

Optical disk scale length is approximately 10^16.6 cm.

X-ray emission is generated near the inner disk edge.

Abstract

We analyzed the microlensing of the X-ray and optical emission of the lensed quasar PG 1115+080. We find that the effective radius of the X-ray emission is 1.3(+1.1 -0.5) dex smaller than that of the optical emission. Viewed as a thin disk observed at inclination angle i, the optical accretion disk has a scale length, defined by the point where the disk temperature matches the rest frame energy of the monitoring band (kT=hc/lambda_rest with lambda_rest=0.3 micron), of log[(r_{s,opt}/cm)(cos(i) / 0.5)^{1/2}] = 16.6 \pm 0.4. The X-ray emission region (1.4-21.8 keV in the rest frame) has an effective half-light radius of log[r_{1/2,X}/cm] = 15.6 (+0.6-0.9}. Given an estimated black hole mass of 1.2 * 10^9 M_sun, corresponding to a gravitational radius of log[r_g/cm] = 14.3, the X-ray emission is generated near the inner edge of the disk while the optical emission comes from scales slightly larger than those expected for an Eddington-limited thin disk. We find a weak trend supporting models with low stellar mass fractions near the lensed images, in mild contradiction to inferences from the stellar velocity dispersion and the time delays.