TITLE: GCN CIRCULAR NUMBER: 29808 SUBJECT: GRB 210411C: ePESSTO+ NTT optical observations DATE: 21/04/12 20:22:21 GMT FROM: Daniele B Malesani at DTU Space P. Pessi (ESO), G. Csoernyei, A. Holas, S. Taubenberger, C. Vogl (MPA Garching), A. Floers (GSI), G. Pignata (UNAB), J. Teffs (Liverpool), M. Dennefeld (IAP), D. B. Malesani (DTU Space), P. D'Avanzo (INAF/Brera), J. Anderson (ESO), T. Müller Bravo (Southampton), T.-W. Chen (Stockholm), M. Gromadzki (Warsaw), C. Inserra (Cardiff), E. Kankare (Turku), M. Nicholl (Birmingham), O. Yaron (Weizmann), D. Young (QUB), E. Zimmerman (Weizmann) report: We observed the optical afterglow of GRB 210411C (Sbarrato et al., GCN 29794; Strausbaugh & Cucchiara, GCN 29802; de Ugarte Postigo et al., GCN 29806) under the the advanced Public ESO Spectroscopic Survey for Transient Objects (ePESSTO+; see Smartt et al. 2015, A&A, 579, 40 and http://www.pessto.org ). The observations were performed on the ESO New Technology Telescope (NTT) at La Silla with the EFOSC2 instrument. A single 5-min exposure was acquired in the Gunn r filter, with mean epoch 2021 Apr 12.234 UT (14.55 hr after the GRB). The optical afterglow is well detected and we report the following coordinates (calibrated against the Gaia catalog): RA = 19:46:26.83 Dec = -39:23:52.7 For the afterglow, we measure a magnitude R = 21.28 +- 0.04 (Vega), assuming R = 17.31 for the USNO star at RA = 19:46:25.68, Dec = -39:23:48.9 . An extra uncertainty of ~0.3 mag should be added to account for the photometric calibration error of the USNO catalog.