[vsnet-grb-info 16475] GRB 150424A: NOT optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17756
SUBJECT: GRB 150424A: NOT optical observations
DATE:    15/04/24 23:08:53 GMT
FROM:    Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani at dark-cosmology.dk>

D. Malesani (DARK/NBI), D. Xu (NAOC/CAS), D. J. Watson (DARK/NBI), and 
P. Blay (IAC/NOT), report on behalf of a larger collaboration:

We observed the optical counterpart (Perley, GCN 17745; Marshall & 
Beardmore, GCN 17751) of the short GRB 150424A (Beardmore et al., GCN 
Circ. 17743), using the Nordic Optical Telescope equipped with the 
AlFOSC camera. The first 300-s R-band exposure was taken starting at 
20:57 UT (13.2 hr after the GRB)

We clearly detect the counterpart with a magnitude R = 20.67 +- 0.06 
(assuming R = 16.27 for the USNO star at RA = 10:09:11.09, Dec = 
-26:36:58.4).

This magnitude is just slightly fainter than the value reported by 
Perley (GCN 17745) 1.6 hr after the trigger, indicating a very slow 
decay - consistent with the UVOT report. The brightness of the afterglow 
is unprecedented for a short GRB this late after the GRB. Such a 
behaviour is unusual and we encourage further observations.