GCN Circular 32353
Subject
GRB 220706A : NICER detection of re-brightening 1 day after the Swift trigger
Event
Date
2022-07-09T00:07:58Z (4 years ago)
From
Motoko Serino at Aoyama Gakuin U. <serino@phys.aoyama.ac.jp>
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.