TITLE:   GCN CIRCULAR
NUMBER:  11578
SUBJECT: GRB 101219B: GROND detection of a SN signature
DATE:    11/01/19 16:57:31 GMT
FROM:    Felipe Olivares Estay at MPE  <felipe@mpe.mpg.de>

F. Olivares E., P. Schady, T. Kruehler, J. Greiner (all MPE Garching),
S. Klose, and D. A. Kann (Tautenburg Observatory) report on behalf of
the GROND team:

GROND continues to observe the field of the Swift GRB 101219B (Gelbord
et al., GCN #11473) simultaneously in g'r'i'z'JHK. The light curve of
the optical transient associated with this GRB (Olivares E. et al.,
GCN #11478, Kuin & Gelbord, GCNs 11482, 11516, 11575, 11576) started
as a single power-law decay, but flattens at around day five at a
preliminary AB magnitude of r' ~ 22.7. In addition there is a clear
color change associated with the flattening.

Starting at day 15, the light curve again decreases in all optical
bands to a magnitude of r' ~ 23.7 at 27 days after the burst. This
light curve shape is typical for GRB/SN events (e.g., Zeh et al. 2004,
ApJ, 609, 952), and we hence interpret these observational features as
signatures of an emerging and decaying supernova underlying the
afterglow emission of GRB 101219B.

Assuming a luminosity equal to that of SN 1998bw for the SN component,
as well as negligible dust extinction along the line of sight, a
conservative redshift range of 0.4 < z < 0.7 is derived for GRB
101219B. We note that the peak time rather short (around 14 days after
burst, see Ferrero et al. 2006, A&A, 457, 857), which further suggests
a low redshift for this GRB.

We stress that at this stage, a possible host contribution and the SN
component cannot be accurately disentangled and all results should be
considered preliminary.

Photometric and in particular spectroscopic observations with larger
aperture telescopes aiming at the detection of the fading SN and/or
host galaxy are highly encouraged.