TITLE: GCN CIRCULAR NUMBER: 31626 SUBJECT: ZTF22aaajecb/AT 2022cmc: CAHA 2.2m/CAFOS detection, luminous transient DATE: 22/02/21 21:16:30 GMT FROM: Alexander Kann at IAA-CSIC D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (Obs. Cote d'Azur), C. C. Thoene (HETH/ASU CAS Ondrejov), M. Blazek (HETH), J. F. Agui Fernandez (HETH/IAA-CSIC), I. Vico, and A. Guijarro (both CAHA) report: We observed the red ZTF transient ZTF22aaajecp/AT 2022cmc (Andreoni et al., GCN #31590), likely a GRB afterglow at z = 1.193 (Tanvir et al., GCN #31602; Lundquist et al., GCN #31612) with CAFOS, mounted on the 2.2m telescope, at the Calar Alto Observatory (Almeria, Spain). The observation started at 04:54:04 UT on 18 February 2022 (6.76 days after the first ZTF detection) and consisted of 12 x 120 s integrations in the r' and i' bands, each. Observations were hampered by the full Moon, but otherwise conditions were very good (1".3 seeing, very good transparency). The transient is clearly detected in each of the stacked images. Compared to a nearby Pan-STARRS comparison star, we measure r' = 21.12 +/- 0.03 mag (AB) 6.772 days after first detection. Gathering data from other GCNs (Andreoni et al., GCN #31590; Lipunov et al., GCN #31600; Kumar et al., GCN #31597; Pankov et al., GCNs #31593, #31625; Perley, GCN #31594), and assuming a GRB time one hour before the first detection (note the exact choice of time has little influence on the late decay slope), we find the transient is described by an achromatic decay with slope alpha = 1.05 +/- 0.05. The SED is described, similar to the result Perley (GCN #31594) found, by a simple power-law with slope beta = 1.29 +/- 0.22. This is slightly steeper than usual for synchrotron radiation from a typical GRB afterglow, indicating some extra extinction may play a role, as might be expected from the high X-ray column density found by NICER (Pasham et al., GCN #31601). Using the known redshift and the spectral slope, we shift the afterglow into the z = 1 frame (following Kann, Klose & Zeh 2006, ApJ, 641, 993). We find that at 6.2 days (z = 1 frame), this transient is among the ten most luminous GRB afterglows, yielding further evidence that it itself is a bona fide GRB afterglow. The long rise indicates an off-axis origin, and the luminous afterglow makes it likely the initial GRB was very energetic. So far no viable candidates have been reported by the IPN (it is not positionally coincident with the short GRB 220211A, Andreoni et al., GCN #31590; also we note a short GRB at such a high redshift would not be expected to have such a luminous afterglow), leading to the conclusion that the off-axis angle was large enough to strongly suppress the prompt emission - a true orphan afterglow.