GCN Circular 32353

W. Iwakiri (Chuo U.), M. Shidatsu (Ehime.U), M. Serino (AGU), K. C. Gendreau, Z. Arzoumanian (NASA/GSFC), 
T. Enoto, T. Mihara (RIKEN)

We report on initial NICER observations of GRB 220706A (GCN #32329) carried out on 2022 July 7. 
The observations were carried out in two parts. The first epoch began at 01:36 UT, approximately a half-day 
after the Swift/BAT trigger (GCN #32329), and ended at 03:34 UT, with ~1.5 ksec of exposure across two 
successive orbits of the International Space Station (ISS). The lightcurve shows a slow decay: 
the NICER-measured X-ray flux decreased from 8 x 10-13 to 6 x 10-13 erg/cm2/s in the 0.3-10 keV band. 
The emission overall was soft, with hardness ratio of 0.1 between the 0.3-2.0 and 2.0-10.0 keV bands. 
The second epoch was from 17:08 to 22:09 UT (~1 day after the Swift/BAT detection), with 3.4 ksec exposure 
in total. We found re-brightening of the afterglow: the NICER average flux during the second epoch 
was 6.5 x 10-12 erg/cm2/s in 0.3-10 keV, with a hardness ratio of 0.6. The result suggests that the spectrum 
has significantly hardened compared with the first-epoch results, unlike typical GRBs. 

NICER will continue to monitor this source. Multi-wavelength followup observations are strongly encouraged.

Note: Because the nature of the source is unknown, this message is cross-posted to ATel and GCN.