TITLE:   GCN CIRCULAR
NUMBER:  42363
SUBJECT: GRB 251018A: BOOTES-5 and BOOTES-7 early optical detections
DATE:    25/10/18 20:48:38 GMT
FROM:    I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg@iaa.es>

Y.-D. Hu (GXU), I. Perez-Garcia, A. J. Castro-Tirado, E. J. Fernandez-Garcia, M. D. Caballero-Garcia, S.-Y. Wu, R. Sanchez-Ramirez, and S. Guziy (IAA-CSIC), I. M. Carrasco (SMA), M. Gritsevich (Univ. of Helsinki), C. Perez del Pulgar (Univ. of Malaga), S. Jeong (ADD, Daejeon), G. Garcia-Segura and D. Hiriart (IA-UNAM, Ensenada), W. H. Lee (UNAM, Mexico DF), D.-R. Xiong (YNAO), B.-B. Zhang (NJU), and A. Maury (Space Obs., San Pedro de Atacama) on behalf of a larger collaboration, report:

Following the detection of GRB251018A by Swift (Gupta et al., GCN 42343) and Fermi (Fermi GBM team, GCN 42342), the 0.6m BOOTES-5/JGU robotic telescope at San Pedro Martir Observatory (Mexico) automatically responded to this high-energy event starting on Oct 18, 03:12:45 UT (i.e., 43 sec after detection). Series of images in clear filter were gathered and we detect an optical source. Using USNO B-1.0 as a reference, we measure an initial magnitude of 16.78 +/- 0.16 in the first 1 x 5 s stacked image. 

Meanwhile, the 0.6m BOOTES-7 robotic telescope at Space Observatory (San Pedro de Atacama, Chile) also automatically observed the GRB location starting on Oct. 18, 03:13:22 UT (i.e. 80 s after trigger). The afterglow is also detected with 16.04 +/- 0.11. These detections are consistent with the one reported by MASTER (Lipunov et al., GCN 42346), TRT (Fu et al., GCN 42345), and UVOT (Kuin et al., GCN 42353). Further analysis of the additional images is ongoing.

We would like to thank the staff at San Pedro Martir Observatory and San Pedro de Atacama Space Observatory for their excellent support.