TY - JOUR
T1 - Searching for Highly Magnified Stars at Cosmological Distances
T2 - Discovery of a Redshift 0.94 Blue Supergiant in Archival Images of the Galaxy Cluster MACS J0416.1-2403
AU - Chen, Wenlei
AU - Kelly, Patrick L.
AU - Diego, Jose M.
AU - Oguri, Masamune
AU - Williams, Liliya L.R.
AU - Zitrin, Adi
AU - Treu, Tommaso L.
AU - Smith, Nathan
AU - Broadhurst, Thomas J.
AU - Kaiser, Nick
AU - Foley, Ryan J.
AU - Filippenko, Alexei V.
AU - Salo, Laura
AU - Hjorth, Jens
AU - Selsing, Jonatan
N1 - Publisher Copyright:
© 2019. The American Astronomical Society. All rights reserved..
PY - 2019/8/10
Y1 - 2019/8/10
N2 - Individual 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 ∼0.″1 in a deep coaddition of HFF imaging.
AB - Individual 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 ∼0.″1 in a deep coaddition of HFF imaging.
KW - galaxies: clusters: general
KW - galaxies: clusters: individual: MACS J0416.1-2403
KW - gravitational lensing: strong
KW - stars: massive
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U2 - 10.3847/1538-4357/ab297d
DO - 10.3847/1538-4357/ab297d
M3 - Article
AN - SCOPUS:85071968146
SN - 0004-637X
VL - 881
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
M1 - 8
ER -