TITLE:   GCN CIRCULAR
NUMBER:  31602
SUBJECT: ZTF22aaajecp/AT2022cmc: VLT/X-shooter redshift
DATE:    22/02/17 16:33:02 GMT
FROM:    Valerio D'Elia at ASDC  <valerio.delia@ssdc.asi.it>

N. R. Tanvir (Univ. Leicester), A. de Ugarte Postigo (Obs. Cote D’Azur), L. Izzo (DARK/NBI), S. D. Vergani (GEPI, Observatoire de Paris), V. D’Elia (ASI/SSDC, INAF/OAR), S. Campana (INAF-OAB), D. A. Perley (LJMU), K. Wiersema (Univ. Lancaster), A.J.  Levan (Radboud),  D. A. Kann (HETH/IAA-CSIC), A. Rossi (INAF-OAS), M. Della Valle (INAF-OAC) report on behalf of the Stargate Consortium:


We observed the fast and red optical transient ZTF22aaajecp/AT2022cmc (GCN Circ. 31590), also detected by VLA (GCN Circ. 31592), Zeiss-1000 (GCN Circ. 31593), LT (GCN Circ. 31594), GMOS-N (GCN Circ. 31595), GIT (GCN Circ. 31597), and NICER (GCN Circ. 31601), using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph.

A spectrum was secured covering the wavelength range 3000-21000 AA, and consisting of 4 exposures of 1200 s each. The observation was carried out about six days after the transient discovery.

In a preliminary reduction, the continuum is detected over the full spectral range. An emission line is detected at 10981 AA, which we interpret as due to OIII 5007 at a redshift of 1.193. The corresponding OIII 4959 line falls on a telluric feature, so it is not detected in our spectrum. Moreover, the Halpha emission line is in a telluric gap. However, a set of absorption lines from Mg (MgII 2796, MgII 2803 and MgI 2803), FeII (2344, 2383, 2586, 2600), and CaII (3934, 3969) are present at a consistent redshift. Thus we interpret it as the redshift of the transient. We note that the NICER X-ray detection (GCN Circ. 31601) is very bright if at this redshift.

We acknowledge excellent support from the ESO observing staff in Paranal, in particular Claudia Paladini and Ditte Slumstrup.