TITLE: GCN CIRCULAR NUMBER: 29535 SUBJECT: GRB 210217A: Liverpool Telescope First Hour Observations DATE: 21/02/18 22:17:33 GMT FROM: Manisha Shrestha at Liverpool John Moores U M. Shrestha (Liverpool JMU), R. Smith (LJMU) , A. Melandri (INAF), I.A. Steele (LJMU), S. Kobayashi (LJMU), C. Mundell (Univ. Bath), A. Gomboc (Univ. Nova Gorica), C. Guidorzi (Univ. Ferrara) report on behalf of a wider collaboration: We observed the field of Swift GRB 210217A (GCN 29521) with the 2.0m Liverpool Telescope (LT), La Palma on 2021 Feb 17 starting at 23:28:51.056 UT using the IO:O optical camera in the r’, i’, and z’ bands. Data were calibrated with respect to nearby APASS secondary standard stars for r’ and i’ bands and SDSS secondary standard stars for z’ band. We confirm the optical counterpart reported by Swift UVOT and NEXT (GCN 29523). At T=194 seconds after the BAT trigger time, we measure r’ = 18.51 +/- 0.3 mag which is close to 18.6 +/- 0.2 mag detected by NEXT team (GCN 29523). The r’ band light curve made with IO:O observations show a power law decay over the first hour in flux vs time with alpha = 0.48. At T = 690 seconds after the BAT trigger time, we measure i’ = 18.77 +/- 0.1 mag and at T = 868 seconds after the trigger we measure z’ = 18.67 +/-0.1 mag. ________________________________ Important Notice: Liverpool John Moores University was established as a Higher Education Corporation under section 121 of the Education Reform Act 1988. Further information about Liverpool John Moores University can be found at https://www.ljmu.ac.uk/about-us The information in this email and any attachments is for the sole use of the intended recipient(s). If you are not an intended recipient, or a person responsible for delivering it to an intended recipient, you should delete it from your system immediately without disclosing its contents elsewhere and advise the sender by returning the email or by telephoning a number contained in the body of the email. No responsibility is accepted for loss or damage arising from viruses or changes made to this message after it was sent and the recipient must ensure that the email (and attachments) are virus free. The views contained in this email are those of the author and not necessarily those of Liverpool John Moores University. We will use the personal data information provided by you to respond to your email. For information about how we process personal data and monitor communications please see our Privacy Notice. https://www.ljmu.ac.uk/legal/privacy-and-cookies