TITLE: GCN GRB OBSERVATION REPORT NUMBER: 2576 SUBJECT: GRB 040422: ROTSE-IIIb Prompt Optical Limits DATE: 04/04/23 04:02:23 GMT FROM: Eli Rykoff at Univ. of Michigan/ROTSE E. Rykoff reports on behalf of the ROTSE collaboration: The ROTSE-IIIb robotic telescope at McDonald Observatory, Texas, responded automatically to INTEGRAL Trigger #1756 (GRB040422) within 8 s of the receipt of the first alert, and 22.1 s after the beginning of the GRB. Our response sequence consists of 10 5 s exposures, 10 20 s exposures and 200 60 s exposures, all unfiltered. As the burst was behind the galactic plane, we expect significant extinction in our optical passband. Applying the formula from Finkbeiner, Schlegel and Davis (1998), we expect 4.4 magnitudes of extinction in the R-band, although they give a caveat that their calculations "should not be trusted" at galactic latitudes of |b|<5. Our first 5-s exposure started at 06:58:27.21 UT. We visually compared our images to the DSS using the revised error circle as reported by Mereghetti et. al (GCN 2572). We find no objects absent from the DSS to a limiting magnitude of R ~ 16.5, although field crowding creates significant source confusion. Coadding our first 10 images, with an effective exposure time of 110 s, also does not reveal any new objects to a limiting magnitude of R ~ 17.5. Furthermore, no objects in the error box varied significantly over the course of our 3.7 hours of observation.