Near-IR search for lensed supernovae behind galaxy clusters - II. First detection and future prospects

摘要

Aims. Powerful gravitational telescopes in the formof massive galaxy clusters can be used to enhance the light collectingpower over a limited field of view by about an order of magnitude influx. This effect is exploited here to increase the depth of a surveyfor lensed supernovae at near-IR wavelengths. Methods. We present a pilot supernova searchprogramme conducted with the ISAAC camera at VLT. Lensed galaxiesbehind the massive clusters A1689, A1835, and AC114 were observed for atotal of 20h divided into 2, 3, and 4 epochs respectively,separated by approximately one month to a limiting magnitude(Vega).Image subtractions including another 20h worth ofarchival ISAAC/VLT data were used to search for transients withlightcurve properties consistent with redshifted supernovae, both inthe new and reference data. Results. The feasibility of finding lensedsupernovae in our survey was investigated using synthetic lightcurvesof supernovae and several models of the volumetric type Ia andcore-collapse supernova rates as a function of redshift. We alsoestimate the number of supernova discoveries expected from the inferredstar-formation rate in the observed galaxies. The methods consistentlypredict a Poisson mean value for the expected number of supernovae inthe survey of between and 1.6 for all supernova types, evenly distributed between corecollapse and type Ia supernovae. One transient object was found behindA1689, from a galaxy with photometric redshift.The lightcurve and colors of the transient are consistent with being areddened type IIP supernova at.The lensing model predicts 1.4mag of magnification at thelocation of the transient, without which this object would not havebeen detected in the near-IR ground-based search described in thispaper (unlensed magnitude ). We perform a feasibility study of the potential for lensedsupernovae discoveries with larger and deeper surveys and conclude thatthe use of gravitational telescopes is a very exciting path for newdiscoveries. For example, a monthly rolling supernova search of asingle very massive cluster with the HAWK-I camera at VLT would yield$ }kern-0.75em{lower0.65exhbox{$sim$ }}10$ -->lensedsupernova lightcurves per year, where type Ia supernovae wouldconstitute about half of the expected sample. Key words: cosmology: observations -stars: supernovae: general - galaxies: clusters: general -gravitational lensing