Early results from GLASS-JWST VIII: An Extremely Magnified Blue Supergiant Star at Redshift 2.65 in the Abell 2744 Cluster Field

Abstract

We report the discovery of an extremely magnified star at redshift $z=2.65$ in James Webb Space Telescope (JWST) NIRISS pre-imaging of the Abell 2744 galaxy-cluster field. The star's background host galaxy lies on a fold caustic of the foreground lens, and the cluster creates a pair of images of the region close to the lensed star. We identified the bright transient in one of the merging images at a distance of $\sim 0.15"$ from the critical curve, by subtracting the JWST F115W and F150W imaging from coadditions of archival Hubble Space Telescope (HST) F105W and F125W images and F140W and F160W images, respectively. Since the time delay between the two images should be only hours, the transient must be the microlensing event of an individual star, as opposed to a luminous stellar explosion which would persist for days to months. Analysis of individual exposures suggests that the star's magnification is not changing rapidly during the observations. From photometry of the point source through the F115W, F150W, and F200W filters, we identify a strong Balmer break, and modeling allows us to constrain the star's temperature to be approximately 7,000--12,000 K.

10 pages, 3 figures, submitted to ApJL

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Cited by in corpus (13)

• The James Webb Space Telescope Mission
• JWST's PEARLS: Prime Extragalactic Areas for Reionization and Lensing Science: Project Overview and First Results
• The GLASS-JWST Early Release Science Program. III. Strong lensing model of Abell 2744 and its infalling regions
• 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
• 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
• The GLASS-JWST Early Release Science Program. IV. Data release of 263 spectra from 245 unique sources
• A search for transients in the Reionization Lensing Cluster Survey (RELICS): Three new supernovae
• The GLASS-JWST Early Release Science Programme: The NIRISS Spectroscopic Catalogue
• Spectroscopic characterisation of gravitationally lensed stars at high redshifts
• Explanations for the two-component spectral energy distributions of gravitationally lensed stars at high redshifts