Multiply imaged time-varying sources behind galaxy clusters

Abstract

With upcoming (continuum) surveys of high-resolution radio telescopes, detection rates of fast radio bursts (FRBs) might approach 10 5 per sky per day by future extremely large observatories, such as the possible extension of the Square Kilometer Array (SKA) to a phase 2 array. Depending on the redshift distribution of FRBs and using the repeating FRB121102 as a model, we calculate a detection rate of multiply-imaged FRBs with their multiply-imaged hosts caused by the distribution of galaxy-cluster scale gravitational lenses of the order of 10 −4 per square degree per year for a minimum total flux of the host of 10 µJy at 1.4 GHz for SKA phase 2. Our comparison of estimated detection rates for quasars, supernovae, gamma ray bursts, and FRBs shows that multiple images of FRBs could be more numerous than those of gamma ray bursts and supernovae and as numerous as multiple images of quasars. Time delays between the multiple images of an FRB break degeneracies in model-based and model-independent lens reconstructions as other time-varying sources do, yet without a microlensing bias as FRBs are more point-like and have shorter duration times. We estimate the relative imprecision of FRB time-delay measurements to be 10 −10 for time delays on the order of 100 days for galaxy-cluster scale lenses, yielding more precise (local) lens properties than time delays from the other time-varying sources. Using the lens modelling software Grale, we show the increase in accuracy and precision of the reconstructed scaled surface mass density map of a simulated cluster-scale lens when adding time delays for one set of multiple images to the set of observational constraints.

Free-form grale lens inversion of galaxy clusters with up to 1000 multiple images

“…I and II, the central peaks are not reconstructed very well but for one of the peaks, which had fewer images near it, the reconstruction is worse compared to the other peak. In general having more images is always beneficial, however, the presence of central images (maxima in the arrival time surface) does not always guarantee better constrained central regions (Wagner et al 2019). For a circularly symmetric lens the deflection angle is determined only by the total mass interior to a point, and the more central a point is, the less mass is enclosed by it.…”

Generalised model-independent characterisation of strong gravitational lenses – VI. The origin of the formalism intrinsic degeneracies and their influence on H0

“…Available cases are still rare, yet, multiply-imaged quasars or supernovae behind clusters may be detected more frequently with future surveys. As investigated in Wagner et al (2019), fast radio bursts could be equally likely found as multiple images in a galaxy cluster. Advantages in favour of employing cluster-scale lenses are the higher relative precision of the time delay measurements and the numerous constraints on the lens model coming from a multitude of multiple-image systems.…”

Extended lens reconstructions with grale: exploiting time-domain, substructural, and weak lensing information

“…Time delays can provide very useful information about the overall lensing potential, and the time delay fitness measure proposed in Liesenborgs et al (2009) was evaluated more thoroughly. The test was similar to the one used in Liesenborgs & De Rijcke (2012); Wagner et al (2019), where a lens with an elliptical version of a Navarro-Frenk-White (NFW; Navarro et al (1996)) mass distribution was used to gauge the effect of the addition of time delay information to the images of only a single source. Here, it was found that when adding time delay information to the images of all sources, the old fitness measure can over-focus the images whereas a newly proposed expression appears to avoid this.…”