Highly magnified stars in lensing clusters: New evidence in a galaxy lensed by MACS J0416.1-2403

Alexander A. Kaurov, Liang Dai, Tejaswi Venumadhav, Jordi Miralda-Escudé, Brenda Frye

Research output: Contribution to journalArticlepeer-review


We examine a caustic-straddling arc at z = 0.9397 in the field of the galaxy cluster MACS J0416.1-2403 (z = 0.397) using archival multiband HST images and show that its surface brightness exhibits anomalies that can be explained by a single highly magnified star undergoing microlensing. First, we show that the surface brightness pattern is not perfectly symmetric across the cluster critical curve, which is inconsistent with a locally smooth lens model; the location of the candidate star exhibits the most significant asymmetry. Second, our analysis indicates that the asymmetric feature has ∼ 30% higher flux in the 2012 visits compared to the Frontier Fields program visits in 2014. Moreover, the variable asymmetric feature shows an anomalous color between the F814W and F105W filters in 2014. These anomalies are naturally explained by microlensing induced variability of a caustic-transiting blue supergiant in a star-forming region, with a mean magnification factor around µ ∼ 200. We extend this study to a statistical analysis of the whole arc image and find tentative evidence of the increased mismatch of the two images in the proximity of the critical line. Robust detection of one or multiple caustic-transiting stars in this arc will enable detailed follow-up studies that can shed light on the small-scale structure of the dark matter inside the cluster halo.

Original languageEnglish (US)
JournalUnknown Journal
StatePublished - Feb 26 2019


  • Gravitational lensing: micro, galaxies: clusters: individual (MACS J0416.1-2403)

ASJC Scopus subject areas

  • General

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