GCN Circular 3915

D. Reichart reports on behalf of the UNC team of the FUN GRB Collaboration.

We have computed preliminary error bars on the temporal and spectral
indexes of Haislip et al. (GCN 3914
Not found
 
 
).  The temporal index is -1.20 +/- 0.17
and the spectral index is -0.35 +/- 0.33.  This disfavors the ISM-RED and
WIND-RED cases at the 2.2 sigma confidence level, the ISM-BLUE case at the
1.3 sigma confidence level, and the WIND-BLUE case only at the 0.3 sigma
confidence level (e.g., Sari, Piran & Narayan 1998; Chevalier & Li 2000).
If the WIND-BLUE case is borne out by further observations, this suggests
an electron-energy distribution index of p = 1.9 +/- 0.2, as well as a
massive-star origin.

If the NIR afterglow is strongly extinguished, and the intrinsic spectrum
is even shallower than -0.35, or even positive, then none of the standard
cases hold.  This also suggests that the afterglow is probably not strongly
extinguished, and supports the conclusion of Haislip et al. (GCN 3914
Not found
 
 
) that
the sharp spectral break between the J and i bands is likely due to
dropout.

Furthermore, given that the K to J spectral index is so shallow, and the J
to i spectral index is so steep, the redshift range is probably narrower
than that implied by the J and i filter centers (5.3 < z < 9.0), and is
probably between 6 and 8.  Careful modeling will better constrain this, but
z, Z and/or Y observations, preferably contemporaneous with addition NIR
observations would be most useful.