TITLE: GCN CIRCULAR NUMBER: 18552 SUBJECT: GRB 151027A: Correction to GCN 18519 DATE: 15/11/02 19:12:53 GMT FROM: Zach Cano at U of Iceland ​Z. Cano (U. Iceland) reports on behalf of a larger collaboration: Upon further investigation, it was discovered that the magnitudes given in GCN Circ. 18519 are incorrect. The presented photometry was not for the optical and NIR afterglow of GRB 151027A, but rather the fainter object that is 3.1 arcsec SW of the afterglow (Dichiara et al. GCN Circ. 18510). A revised summary of the NOT observations follows: Filter t-t0 (hr) Mag +- Merr ----------------------------------------- B 17.94 18.2 +- 0.1 R 18.17 17.9 +- 0.1 I 18.28 17.4 +- 0.1 J 16.92 16.4 +- 0.1 H 17.38 15.5 +- 0.1 K 17.60 15.1 +- 0.1 The optical filters are calibrated to USNO-B1 and the NIR filters to 2MASS, where a single star that appears in both catalogs was used for the zeropoint calculation. These magnitudes are not corrected for foreground extinction. When these extinguished magnitudes are converted to monochromatic fluxes (using the zeropoints from Fukugita et al. 1995; Hewett et al. 2006), a single power-law with an exponent of -0.8 provides a good fit to the optical-to-NIR spectral energy distribution. My apologies for the confusion.​