James Webb Space Telescope Feed Post

Webb's PEARLS: Transients in the MACS J0416.1-2403 Field Published: 7/14/2023 10:05:24 PM Updated: 7/14/2023 10:05:24 PM

Paper abstract: With its unprecedented sensitivity and spatial resolution, the James WebbSpace Telescope (JWST) has opened a new window for time-domain discoveries inthe infrared. Here we report observations in the only field that has receivedfour epochs (over 126 days) of JWST NIRCam observations in Cycle 1. This fieldis towards MACS J0416.1-2403, which is a rich galaxy cluster at z=0.397 and isone of the Hubble Frontier Fields. We have discovered 14 transients from thesedata. Twelve of these transients happened in three galaxies (with redshiftsz=0.94, 1.01, and 2.091) crossing a lensing caustic of the cluster, and thesetransients are highly magnified by gravitational lensing. These 12 transientsare likely of a similar nature to those previously reported based on the HubbleSpace Telescope (HST) data in this field, i.e., individual stars in the highlymagnified arcs. However, these twelve could not have been found by the HSTbecause they are too red and too faint. The other two transients are associatedwith background galaxies (z=2.205 and 0.7093) that are only moderatelymagnified, and they are likely supernovae. They indicate a de-magnifiedsupernova surface density of 0.5 per sq.arcmin integrated up to z ~ 2 whenmonitored at the time cadence of a few months. Such a high surface density isachieved at the ~3--4 micron survey limit of AB ~ 28.5 mag, which, while beyondthe capability of HST, can be easily reached by JWST.