TITLE:   GCN CIRCULAR
NUMBER:  31594
SUBJECT: ZTF22aaajecp/AT2022cmc: Liverpool Telescope photometry
DATE:    22/02/15 23:25:52 GMT
FROM:    Daniel Perley at Liverpool JMU  <d.a.perley@ljmu.ac.uk>

D. A. Perley (LJMU) reports:

We acquired multicolor imaging of the fast optical transient ZTF22aaajecp (AT2022cmc; Andreoni et al. 2020, GCN 31590) using the IO:O camera of the 2m robotic Liverpool Telescope.  The afterglow was observed across four separate epochs in g, r, i, and z filters during the night ending 2022-02-15 UT, with the first epoch beginning at 00:50 and the last at 05:54.  The images show a clear detection of the transient in all bands.  Photometry with reference to SDSS secondary standard stars in the field gives the following magnitudes during the final epoch:

MJD         dt(d)   filter mag   unc
59625.2461  3.8003  g      20.72 0.16
59625.2501  3.8042  r      20.17 0.09
59625.2540  3.8082  i      20.16 0.07
59625.2580  3.8121  z      19.91 0.11

The dt column above is the time in days after the first detection as reported by Andreoni et al. (2022-02-11 10:42 UT).

The SED is consistent with a power-law with an index of beta=-1 (f_nu ~ nu^beta), similar to GRB afterglows.  This provides additional evidence in support of the interpretation of this event as a relativistic cosmological explosion (see also Perley et al., GCN 31592).  Spectroscopic confirmation is still required.




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