Searching for Highly Magnified Stars at Cosmological Distances: Discovery of a Redshift 0.94 Blue Supergiant in Archival Images of the Galaxy Cluster MACS J0416.1-2403
Kelly, Patrick L.
Diego, Jose M.
Williams, Liliya L. R.
Treu, Tommaso L.
Broadhurst, Thomas J.
Foley, Ryan J.
Filippenko, Alexei V.
AffiliationUniv Arizona, Dept Astron
Keywordsgalaxies: clusters: general
galaxies: clusters: individual: MACS J0416.1-2403
gravitational lensing: strong
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PublisherIOP PUBLISHING LTD
CitationWenlei Chen et al 2019 ApJ 881 8
RightsCopyright © 2019. The American Astronomical Society. All rights reserved.
Collection InformationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at firstname.lastname@example.org.
AbstractIndividual highly magnified stars have been recently discovered at lookback times of more than half the age of the universe, in lensed galaxies that straddle the critical curves of massive galaxy clusters. Having established their detectability, it is now important to carry out systematic searches for them in order to establish their frequency, and in turn learn about the statistical properties of high-redshift stars and of the granularity of matter in the foreground deflector. Here we report the discovery of a highly magnified star at redshift z = 0.94 in a strongly lensed arc behind a Hubble Frontier Field (HFF) galaxy cluster, MACS J0416.1-2403, discovered as part of a systematic archival search. The bright transient ( dubbed "Warhol") was discovered in Hubble Space Telescope data taken on 2014 September 15 and 16. The point source faded over a period of two weeks, and observations taken on 2014 September 1 show that the duration of the microlensing event was at most four weeks in total. The magnified stellar image that exhibited the microlensing peak may also exhibit slow changes over a period of years at a level consistent with that expected for microlensing by the stars responsible for the intracluster light of the cluster. Optical and infrared observations taken near peak brightness can be fit by a stellar spectrum with moderate host-galaxy extinction. A blue supergiant matches the measured spectral energy distribution near peak, implying a temporary magnification of at least several thousand. The short timescale of the event and the estimated effective temperature indicate that the lensed source is an extremely magnified star. Finally, we detect the expected counterimage of the background lensed star at an offset by similar to 0".1 in a deep coaddition of HFF imaging.
VersionFinal published version
SponsorsWorld Premier International Research Center Initiative (WPI Initiative), MEXT, Japan; JSPS KAKENHI [JP15H05892, JP18K03693]; NSF [AST-1518052, AST-1908823]; Gordon & Betty Moore Foundation; HeisingSimons Foundation; David and Lucile Packard Foundation; NASA/HST grants from the Space Telescope Science Institute (STScI) [GO-14922, GO-14872]; NASA [NAS 5-26555]; Christopher R. Redlich Fund; TABASGO Foundation; Miller Institute for Basic Research in Science (U.C. Berkeley); Ministerio de Economia y Competitividad [AYA2015-64508-P (MINECO/FEDER, UE)]; VILLUM FONDEN Investigator grant ; HST Frontier Fields program