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

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 telescope 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 ± 0.5 days and 19.7 ± 1.2 days, are consistent with the radio time delay 26 +4 −5 days.

Microlensingconstraintson the size of the gamma-ray emission region in blazar B0218+357

“…An immediate consequence of the detection of time variability of µ γ is the conclusion in the detection of the microlensing effect in the γ-ray band. An alternative possibility for the variations of the magnification factor ratio (as discussed by Barnacka et al 2015 in the case of PKS 1830-211) would be the different locations of the 2012 and 2014 flaring regions inside the source. This, however, would require the displacements of the order of the Einstein radius of the (macro)lens, ∼1 kpc, even during the same flaring period.…”

Gravitational lenses as high-resolution telescopes

“…Thus, bins with a more prolonged integration time are necessary to have enough photon statistics to build a light curve including time before and after the flare. The short duration of gamma-ray flares relative to the expected time delays are an essential element (Barnacka et al, 2015a). Right: MERLIN image of PKS 1830-211 at 5 GHz (Jauncey et al, 1991). in the analysis of unresolved gamma-ray light curves.…”

“…Detection of time delay in data with sparse statistics is possible thanks to a signal processing procedure optimized using MC simulations. As (Barnacka et al, 2015a, Appendix A) demonstrates, without accurate signal processing, time delays would be difficult or even impossible to detect. Thus, the signal processing distinguishes between significant detections and no detections.…”

Multiply imaged time-varying sources behind galaxy clusters

“…As the spatial resolution of gamma-ray telescopes is limited to approximately 0.1 degrees by their detection mechanism, the localisation precision is too low to identify multiply-imaged GRBs as such. Instead, they are detected by light-curve matching as further detailed in Barnacka et al (2015); Davidson et al (2011). Being able to observe an afterglow in X-ray or optical and radio bands, the localisation precision is increased to 10 arcseconds and subarcseconds, respectively, Prochaska et al (2006).…”

“…7 Similar to the FRB internal emission rate, we assume that beaming effects are incorporated in this rate. tions, only two multiply-imaged GRBs caused by galaxy-scale lenses have been detected so far, Barnacka et al (2015Barnacka et al ( , 2016.…”