Resolving the High Energy Universe with Strong Gravitational Lensing: The Case of PKS 1830-211

TL;DR

This paper demonstrates how gravitational lensing and gamma-ray temporal analysis can significantly improve spatial resolution in identifying gamma-ray emission regions in distant blazars, exemplified by PKS 1830-211.

Contribution

It introduces and applies three techniques for analyzing unresolved gamma-ray light curves to measure time delays and localize emission regions with unprecedented precision.

Findings

Achieved a spatial resolution improvement factor of 10,000 at gamma-ray energies.

Identified emission from the core and displaced regions in PKS 1830-211.

Measured gamma-ray time delays consistent with radio observations for core emission.

Abstract

Gravitational lensing is a potentially powerful tool for elucidating the origin of gamma-ray emission from distant sources. Cosmic lenses magnify the emission from distance sources and produce time delays between mirage images. Gravitationally-induced time delays depend on the position of the emitting regions in the source plane. The Fermi/LAT satellite continuously monitors the entire sky and detects gamma-ray flares, including those from gravitationally-lensed blazars. Therefore, temporal resolution at gamma-ray energies can be used to measure these time delays, which, in turn, can be used to resolve the origin of the gamma-ray flares spatially. We provide a guide to the application and Monte Carlo simulation of three techniques for analyzing these unresolved light curves: the Autocorrelation Function, the Double Power Spectrum, and the Maximum Peak Method. We apply these methods to derive time delays from the gamma-ray light curve of the gravitationally-lensed blazar PKS 1830-211. The result of temporal analysis combined with the properties of the lens from radio observations yield an improvement in spatial resolution at gamma-ray energies by a factor of 10000. We analyze four active periods. For two of these periods, the emission is consistent with origination from the core and for the other two, the data suggest that the emission region is displaced from the core by more that ~1.5 kpc. For the core emission, the gamma-ray time delays, $23\pm0.5$ days and $19.7\pm1.2$ days, are consistent with the radio time delay $26^{+4}_{-5}$ days.