TITLE:   GCN CIRCULAR
NUMBER:  23319
SUBJECT: GRB 181010A: ePESSTO NTT optical observations
DATE:    18/10/10 18:48:11 GMT
FROM:    Paolo D'Avanzo at INAF-OAB  <paolo.davanzo@brera.inaf.it>

T. Reynolds (Turku), S. Moran (Turku/NOT), P. D'Avanzo (INAF-OAB), D. B. Malesani (DAWN/NBI and DARK/NBI), M. De Pasquale (Istanbul Univ.), 
S. Campana, A. Melandri (INAF-OAB), J. Harmanen, H. Kuncarayakti (Turku), R. Cartier (CTIO), M. Dennefeld (IAP), C. Inserra (Southampton), 
E. Kankare (QUB), K. Maguire (QUB), S. J. Smartt (QUB), O. Yaron (Weizmann), D. R. Young (QUB), I. Manulis (Weizmann) report:


We observed the optical counterpart of GRB 181010A (Melandri et al. GCN 23309; Gorbovskoy et al. GCN 23310; Martone et al. GCN 23311; 
Troja et al. GCN 23312; Vielfaure et al. GCN 23315; Emery et al. GCN 23317) under the extended Public ESO Spectroscopic Survey for Transient 
Objects (ePESSTO; see Smartt et al. 2015, A&A, 579, 40; http://www.pessto.org <http://www.pessto.org/> ). The observations were performed on the ESO New Technology 
Telescope at La Silla with the EFOSC2 instrument in imaging mode starting from 2018-10-10 at 08:37:50 UT (i.e. 2.7 hours from the burst). 
The observations ended at 08:53:03 UT and were carried out with the R and i filters. 
The optical afterglow is clearly detected in the R-band image. From preliminary photometry, we find a magnitude of R ~ 22.9 +/- 0.1 
(Vega, calibrated against the USNOB1 catalogue). The afterglow is marginally detected in the i-band. From preliminary forced photometry 
at the afterglow position, we derive a magnitude of i ~ 21.4 +/- 0.4 (AB, calibrated against the Pan-STARRS catalogue). These results, 
compared to previous reports (e.g. Martone et al. GCN 23311; Troja et al. GCN 23312; Vielfaure et al. GCN 23315), suggest for a significant fading 
of the optical afterglow flux.