[vsnet-grb-info 27204] ZTF21aaeyldq: GTC Redshift and GRB afterglow nature confirmation
GCN Circulars
gcncirc at capella2.gsfc.nasa.gov
Sun Jan 17 11:19:54 JST 2021
TITLE: GCN CIRCULAR
NUMBER: 29307
SUBJECT: ZTF21aaeyldq: GTC Redshift and GRB afterglow nature confirmation
DATE: 21/01/17 02:18:08 GMT
FROM: Alexander Kann at IAA-CSIC <kann at iaa.es>
A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), D. A. Kann
(HETH/IAA-CSIC), D. A. Perley (LJMU), C. C. Thoene (HETH), M. Blazek, J.
F. Agui Fernandez (both HETH/IAA-CSIC), and R. Scarpa (GTC) report:
We observed the fast-fading hostless transient ZTF21aaeyldq (Ho et al.,
GCN #29305) with OSIRIS at the 10.4m Gran Telescopio Canarias (Roque de
los Muchachos Observatory, La Palma, Canary Islands, Spain), starting at
2021-01-16 23:35:54.359 UT (16.60 hours after the first optical
detection). The source is clearly detected. We obtained a 60 s r'-band
finder image and 4 x 900 s spectroscopy with the R1000B grism.
For the image starting at 2021-01-16 23:27:09.671 (0.68604 days after
the first optical detection), we measure r' = 21.64 +/- 0.03 (AB mag)
vs. a nearby SDSS star.
The spectrum shows a clear continuum over the full spectral range with
many strong absorption lines. We identify these lines as Ly-alpha, SII,
OI, SiII, SiIV, CII, CIV, FeII, AlII, and AlIII, at a mean redshift of z
= 2.514. We identify this as the redshift of the transient. Coupled with
the rapid decay, the moderately red color (Ho et al., GCN #29305) and
the lack of any broad spectral features, we also identify this transient
as a GRB afterglow for which no high-energy trigger has been reported
yet.
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