TITLE:   GCN CIRCULAR
NUMBER:  6967
SUBJECT: GRB 071021: possible high-z burst
DATE:    07/10/21 22:08:21 GMT
FROM:    Takanori Sakamoto at NASA/GSFC  <takanori@milkyway.gsfc.nasa.gov>

T. Sakamoto (GSFC/UMBC), N. Gehrels (GSFC) and Kim Page (U. Leicester)

We point out that GRB 071021 has several signatures of high redshift.
As pointed out in GCN 6966, it has BAT high-redshift indicators
(Sakamoto et al. 2007 in prep.) as follows:

- long duration T90 = 225 sec
- relatively few (two) significant peaks
- peak flux (1 s) < 1.0 ph/cm2/s
- power-law photon index (1.70) < 2

Since May 2007, only this burst and GRB 071018 (GCN 6933) have
satisfied all four indicators.  GRB 071021 also has an X-ray
afterglow lightcurve with strong late-time flares (GCN 6963; see
http://gcn.gsfc.nasa.gov/gcn/other/071021_xrtlc.gif) reminiscent 
of high-redshift burst GRB 050904.  It also has optical observations 
without detection (GCN 6961, 6962).

Deep IR observations are strongly encouraged.