TITLE: GCN CIRCULAR NUMBER: 24763 SUBJECT: GRB 190530A: Further OAJ/OSN photometry and analysis DATE: 19/06/06 16:58:21 GMT FROM: Alexander Kann at IAA-CSIC D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), L. Izzo, M. Blazek, C. C. Thoene, K. Bensch (all HETH/IAA-CSIC) report: We checked the magnitude of our second-epoch OSN observation (Kann et al., GCN 24700) of the Fermi GBM/LAT GRB 190530A (Fermi GBM team, GCN 24676; Longo et al., GCN 24679) and found a calculation error which resulted in an incorrect zero-point. Remeasuring the magnitude against four SDSS stars (once again transformed to Rc via the equations of Lupton 2005) we now derive Rc(AB) = 19.51 +/- 0.04 mag. This is in good agreement with the value obtained by Moskvitin & Uklein (GCN 24708). The magnitude of Belkin et al. (GCN 24698) is still overly bright compared to our new result, and the revised value from Vinko et al. (GCN 24751) is now significantly fainter. We obtained 7 x 300 s images in SDSS r' with the 0.8m telescope of the Observatorio Astrofisico de Javalambre (Teruel, Spain). The first three images were taken too early in twilight and were discarded. The afterglow is clearly detected in the stack of the four last images, and we measure: r'(AB) = 20.27 +/- 0.06 mag at 2.43735 days after the GRB. This is in good agreement with an earlier value from Vinko et al. (GCN 24751) combined with a steep decay. Using the further photometry published since Kann et al. (GCN 24700) (Moskvitin et al., GCN 24708; Belkin et al., GCN 24712; Kumar et al., GCN 24729; Nandi et al., GCN 24745; Vinko et al., GCN 24751) we find: - The steep decay between the observation of Watson et al. (GCN 24690) and Xin et al. (GCN 24697) remains, and is not significantly affected by our revised OSN measurement. - There may be a small flare at 1.4 days (this GCN [OSN]; Moskvitin et al., GCN 24708). - Starting at 2.2 days (Belkin et al., GCN 24712; Vinko et al., GCN 24751; this GCN [OAJ]; Nandi et al., GCN 24745; Kumar et al., GCN 24729), yet another steep decay sets in, for which we measure alpha = 3.72 +/- 0.43. This value is perfectly in agreement with the one derived in Kann et al. (GCN 24700) at an earlier time, but now based on significantly more measurements. Further follow-up is warranted, if possible.