TY - JOUR
T1 - Flashlights
T2 - an off-caustic lensed star at redshift z = 1.26 in Abell 370
AU - Meena, Ashish Kumar
AU - Chen, Wenlei
AU - Zitrin, Adi
AU - Kelly, Patrick L.
AU - Golubchik, Miriam
AU - Zhou, Rui
AU - Alfred, Amruth
AU - Broadhurst, Tom
AU - Diego, Jose M.
AU - Filippenko, Alexei V.
AU - Li, Sung Kei
AU - Oguri, Masamune
AU - Smith, Nathan
AU - Williams, Liliya L.R.
N1 - Publisher Copyright: © 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.
PY - 2023/6/1
Y1 - 2023/6/1
N2 - We report the discovery of a transient seen in a strongly lensed arc at redshift zs = 1.2567 in Hubble Space Telescope imaging of the Abell 370 galaxy cluster. The transient is detected at 29.51 ± 0.14 AB mag in a WFC3/UVIS F200LP difference image made using observations from two different epochs, obtained in the framework of the Flashlights programme, and is also visible in the F350LP band (mF350LP ≈ 30.53 ± 0.76 AB mag). The transient is observed on the negative-parity side of the critical curve at a distance of ∼0.6 arcsec from it, greater than previous examples of lensed stars. The large distance from the critical curve yields a significantly smaller macromagnification, but our simulations show that bright, O/B-type supergiants can reach sufficiently high magnifications to be seen at the observed position and magnitude. In addition, the observed transient image is a trailing image with an observer-frame time delay of ∼+0.8 d from its expected counterpart, so that any transient lasting for longer than that should have also been seen on the minima side and is thus excluded. This, together with the blue colour we measure for the transient (mF200LP - mF350LP ≈ [-0.3, -1.6] AB), rules out most other transient candidates such as (kilo)novae, for example, and makes a lensed star the prime candidate. Assuming that the transient is indeed a lensed star as suggested, many more such events should be detected in the near future in cluster surveys with the Hubble Space Telescope and JWST.
AB - We report the discovery of a transient seen in a strongly lensed arc at redshift zs = 1.2567 in Hubble Space Telescope imaging of the Abell 370 galaxy cluster. The transient is detected at 29.51 ± 0.14 AB mag in a WFC3/UVIS F200LP difference image made using observations from two different epochs, obtained in the framework of the Flashlights programme, and is also visible in the F350LP band (mF350LP ≈ 30.53 ± 0.76 AB mag). The transient is observed on the negative-parity side of the critical curve at a distance of ∼0.6 arcsec from it, greater than previous examples of lensed stars. The large distance from the critical curve yields a significantly smaller macromagnification, but our simulations show that bright, O/B-type supergiants can reach sufficiently high magnifications to be seen at the observed position and magnitude. In addition, the observed transient image is a trailing image with an observer-frame time delay of ∼+0.8 d from its expected counterpart, so that any transient lasting for longer than that should have also been seen on the minima side and is thus excluded. This, together with the blue colour we measure for the transient (mF200LP - mF350LP ≈ [-0.3, -1.6] AB), rules out most other transient candidates such as (kilo)novae, for example, and makes a lensed star the prime candidate. Assuming that the transient is indeed a lensed star as suggested, many more such events should be detected in the near future in cluster surveys with the Hubble Space Telescope and JWST.
KW - galaxies: clusters: individual: Abell 370
KW - gravitational lensing: micro
KW - gravitational lensing: strong
UR - http://www.scopus.com/inward/record.url?scp=85154071054&partnerID=8YFLogxK
U2 - https://doi.org/10.1093/mnras/stad869
DO - https://doi.org/10.1093/mnras/stad869
M3 - Article
SN - 0035-8711
VL - 521
SP - 5224
EP - 5231
JO - MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
JF - MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
IS - 4
ER -