TITLE:   GCN CIRCULAR
NUMBER:  40995
SUBJECT: GRB 250706B: iTelescope optical observations
DATE:    25/07/06 20:59:09 GMT
FROM:    Filipp Dmitrievich Romanov at Amateur astronomer <filipp.romanov.27.04.1997@gmail.com>

On 2025-07-06 I observed the field of GRB 250706B (Palmerio et al.,
GCN Circ. 40989) remotely using the telescopes T33 (0.3-m f/9
reflector + CCD with Astrodon Series II Red filter) and T17 (0.43-m
f/6.8 reflector + CMOS with Astrodon Red-E filter) of iTelescope.Net
at Siding Spring Observatory, Australia.

The exposure times of the photographs were 300 seconds, observations
started at 19:56:23 UT (2h 50m after the trigger). I detected the
optical afterglow in all images with the position (J2000.0):
02:44:55.46 -50:03:40.1.

I measured the magnitudes (compared to r' magnitudes of nearby stars
from the APASS DR9 catalog: Henden et al., 2016):

Mid-time (UT) | Magnitude | Error | Telescope |
19:58:53.3  16.852  0.073  T33
20:04:55.9  16.790  0.046  T33
20:10:58.5  16.756  0.110  T33
20:17:00.3  16.752  0.071  T33

20:05:50.8  16.738  0.040  T17
20:11:47.9  16.875  0.054  T17
20:17:43.6  16.833  0.076  T17


Magnitudes were not corrected for Galactic extinction.

F. D. Romanov (AAVSO).