Kavli Affiliate: Kohei Inayoshi
| First 5 Authors: Christa DeCoursey, Eiichi Egami, Fengwu Sun, Arshia Akhtarkavan, Rachana Bhatawdekar
| Summary:
The James Webb Space Telescope (JWST) discovered 79 transients out to
$z$$sim$4.8 through the JADES Transient Survey (JTS), but the JTS did not find
any $z$$>$5 transients. Here, we present the first photometric evidence of a
$z$$>$5 transient/variable source with JWST. The source, AT 2023adya, resides
in a $z_{mathrm{spec}}$$=$5.274 galaxy in GOODS-N, which dimmed from $m_{rm
F356W}$$=$26.05$pm$0.02 mag to 26.24$pm$0.02 mag in the rest-frame optical
over approximately two rest-frame months, producing a clear residual signal in
the difference image ($m_{rm F356W}$$=$28.01$pm$0.17 mag;
SN$_mathrm{var}$$=$6.09) at the galaxy center. Shorter-wavelength bands
(F090W/F115W) show no rest-frame ultraviolet brightness change. Based on its
rest-frame V-band absolute magnitude of M$_mathrm{V}$$=$$-$18.48 mag, AT
2023adya could be any core-collapse supernova (SN) subtype or an SN Ia.
However, due to low SN Ia rates at high redshift, the SN Ia scenario is
unlikely. Alternatively, AT 2023adya may be a variable active galactic nucleus
(AGN). However, the JWST NIRCam/Grism spectrum shows no broad H$alpha$
emission line (FWHM$=$130$pm$26 km s$^{-1}$), disfavoring the variable AGN
scenario. It is also unlikely that AT 2023adya is a tidal disruption event
(TDE) because the TDE models matching the observed brightness changes have low
event rates. Although it is not possible to determine AT 2023adya’s nature
based on the two-epoch single-band photometry alone, this discovery indicates
that JWST can push the frontier of transient/variable science past $z$$=$5 and
towards the epoch of reionization.
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