Fermi GRB 240828A: Bassano Bresciano Observatory upper limit

We performed optical follow-up observations of the GRB 240828A discovered by the Fermi satellite. We used the Baker-Schmidt telescope (Diam 250mm F/3) of the (IAU station 565) Bassano Bresciano Astronomical Observatory (Italy). The single Field of the telescope is 41.2' x 30.7' To cover the uncertainty zone of the satellite position, we performed a mosaic of 9 images in order to cover a rectangle with sides of 2.1 x 1.5 degrees centered on the coordinates J2000 14h 36m, 35d 47' We performed a total of 9 pointings to cover an area of 3.9 square degrees. For each pointing, 10 images were taken with duration of 20 seconds each. The limiting magnitude is CR 17 (CR= Unfiltered with R zero point). The sequence of pointing and the taking of images were automated by means of a telescope control software developed at our observatory. The image analysis was performed using the subtraction method, with the template from POSS2/UKTSU Red images. The observations started 4 hour after the GRB trigger. For each field, we co-added 10 exposures of 20 sec each. Start T0+ End T0+ CR lim 4.03 hour 4.81 hour 17 We did not found any credible optical counterpart in the error box of the Fermi Satellite. Magnitudes were estimated with the pan-STARRS cat and are derived using Lupton (2005) equations. Not corrected for galactic dust extinction. Reference: http://www.osservatoriobassano.org The message may be cited.