Flashlights: An Off-Caustic Lensed Star at Redshift $z$ = 1.26 in Abell 370

Abstract

We report the discovery of a transient seen in a strongly lensed arc at redshift $z_{\mathrm{s}}=1.2567$ in \emph{Hubble Space Telescope} imaging of the Abell 370 galaxy cluster. The transient is detected at $29.51\pm 0.14$ AB mag in a WFC3/UVIS F200LP difference image made using observations from two different epochs, obtained in the framework of the \emph{Flashlights} program, and is also visible in the F350LP band ($m_{F350LP}\approx 30.53\pm 0.76$ AB mag). The transient is observed on the negative-parity side of the critical curve at a distance of $\sim 0.6"$ 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 $\sim +0.8$ days 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 ($m_{F200LP}-m_{F350LP}\approx [-0.3,-1.6]$ AB), rules out most other transient candidates such as (kilo)novae, for example, and makes a lensed star the prime candidate. Assuming 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 \emph{Hubble Space Telescope} and \emph{James Webb Space Telescope}.

9 pages. 5 figures. Accepted in MNRAS

References in corpus (18)

• Array Programming with NumPy
• An ultra-deep near-infrared spectrum of a compact quiescent galaxy at z=2.2
• Discovery and properties of ultra-high redshift galaxies ($9<z<12$) in the JWST ERO SMACS 0723 Field
• Understanding caustic crossings in giant arcs: characteristic scales, event rates, and constraints on compact dark matter
• Mass and magnification maps for the Hubble Space Telescope Frontier Fields clusters: implications for high redshift studies
• Revealing Galaxy Candidates out to $z\sim 16$ with JWST Observations of the Lensing Cluster SMACS0723
• Lens models and magnification maps of the six Hubble Frontier Fields clusters
• A Highly Magnified Star at Redshift 6.2
• Modelling the spectra of the kilonova AT2017gfo -- I: The photospheric epochs
• Microlensing of Extremely Magnified Stars near Caustics of Galaxy Clusters
• JWST Imaging of Earendel, the Extremely Magnified Star at Redshift $z=6.2$
• Two lensed star candidates at $z\simeq 4.8$ behind the galaxy cluster MACS J0647.7+7015
• JWST's PEARLS: a new lens model for ACT-CL J0102$-$4915, "EL Gordo'', and the first red supergiant star at cosmological distances discovered by JWST
• Evolution of the stellar-merger red nova V1309 Scorpii: SED analysis
• An Efficient Method for Simulating Light Curves of Cosmological Microlensing and Caustic Crossing Events
• Geometric Corroboration of the Earliest Lensed Galaxy at z~10.8 from Robust Free-Form Modelling
• Flashlights: More than A Dozen High-Significance Microlensing Events of Extremely Magnified Stars in Galaxies at Redshifts z=0.7-1.5
• Multiwavelength modeling the SED of nova V339~Del: Stopping the wind and long-lasting super-Eddington luminosity with dust emission

Cited by in corpus (9)

• UNCOVERing the extended strong lensing structures of Abell 2744 with the deepest JWST imaging
• JWST's PEARLS: Mothra, a new kaiju star at z=2.091 extremely magnified by MACS0416, and implications for dark matter models
• Imaging dark matter at the smallest scales with $z\approx 1$ lensed stars
• Statistics of magnification for extremely lensed high redshift stars
• A search for transients in the Reionization Lensing Cluster Survey (RELICS): Three new supernovae
• Flashlights: Prospects for constraining the Initial Mass Function around cosmic noon with caustic-crossing events
• Transient star B/R ratio and star formation in $z\gtrsim 1$ lensed galaxies
• Extending the cosmic distance ladder two orders of magnitude with strongly lensed Cepheids, carbon AGB, and RGB stars
• Lensed stars in galaxy-galaxy strong lensing -- a JWST prediction for the Cosmic Horseshoe