GCN Circular 18279

Z. Cano (U. Iceland), D. Malesani (DARK/NBI), A. de Ugarte Postigo
(IAA-CSIC, DARK/NBI), D. Xu (NAOC/CAS), J. Saario (NOT, U. Turku) and P.
Jakobsson (U. Iceland) report on behalf of a larger collaboration:

We observed the field of GRB 150910A (Pagani et al., GCN Circ. 18264
Not found
 
 
) with
the 2.5-m Nordic Optical Telescope (NOT) equipped with MOSCA in two epochs
on the morning of 11-Sept-2015, at 01:10 and 04:45 UT, respectively.  In
SDSS filters r (epoch 1) and ugrz (epoch 2) we clearly detect the optical
afterglow (e.g. Zheng & Filippenko, GCN Circ. 18265
Not found
 
 
).

A summary of our photometry is as follows:

-------------------------------------------------------
filter (SDSS)        t-t0 (hr)            mag +- merr
-------------------------------------------------------
   r                  16.27              20.85 +- 0.18
   r                  20.18              21.24 +- 0.21
   u                  20.05              21.82 +- 0.24
   g                  20.24              21.49 +- 0.22
   z                  19.84              20.78 +- 0.24

These magnitudes are calibrated to SDSS and are not corrected for
foreground extinction.  We note that these magnitudes are in good agreement
with those obtained by GROND (Schmidl et al., GCN Circ. 18277
Not found
 
 
) at a
contemporaneous post-explosion epoch.  Compared with other datasets, e.g.
Xu et al. (GCN Circ. 18269
Not found
 
 
), our second epoch of r-band observations
implies a power-law like decay in time, e.g. f(t)=t^-alpha, with a decay
slope of alpha=1.
���1.