TITLE: GCN CIRCULAR NUMBER: 17513 SUBJECT: GRB 150301A: GROND Observations DATE: 15/03/01 14:29:55 GMT FROM: Corentin Delvaux at MPE M. Tanga, C. Delvaux, J. Greiner (all MPE Garching) and D. A. Kann (TLS Tautenburg) report on behalf of the GROND team: We observed the field of GRB 150301A (Swift trigger 632995; Lien et al., GCN #17510) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla Observatory (Chile). Observations started at 06:02 UT on 01-03-2015, 4.97 hrs after the GRB trigger. They were performed at an average seeing of 1.4" and at an average airmass of 1.5. We found two point sources within the 5.0" Swift-XRT error circle reported by Lien et al. (GCN #17510). The first source is at RA (J2000.0) = 16 h 17 m 13.08 s DEC (J2000.0) = -48d 42' 45.7" The second source is at RA (J2000.0) = 16 h 17 m 13.34 s DEC (J2000.0) = -48d 42' 49.7"  with an uncertainty of 0.3" in each coordinate for both sources. Based on the first 50 min of total exposures in g'r'i'z' and 40 min in JHK, we estimate the following preliminary magnitudes (all in AB system): For the first source: g' > 24.4 mag, r' > 24.5 mag, i' = 22.0 +/- 0.1 mag, z' = 21.0 +/- 0.3 mag, J = 18.8 +/- 0.2 mag, H = 18.3 +/- 0.2 mag, and K > 18.3 mag. For the second source: g' > 24.4 mag, r' > 24.5 mag, i' = 23.1 +/- 0.1 mag, z' = 22.2 +/- 0.1 mag, J = 19.6 +/- 0.3 mag, H = 19.1 +/- 0.4 mag, and K > 18.3 mag. Both objects appear to be constant over the duration of our observation. Therefore we suppose they are not related to the burst. We note the field is crowded. We also notice the presence of a bright star (~14 mag) west of the Swift-XRT error circle covering around 10% of the encircled region. Given magnitudes are calibrated against GROND zeropoints as well as 2MASS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)=3.31 mag in the direction of the burst (Schlafly & Finkbeiner 2011).