GRB 220706A : NICER detection of re-brightening 1 day after the Swift trigger
ATel #15507; W. Iwakiri (Chuo U.), M. Shidatsu (Ehime. U), M. Serino (AGU), K. C. Gendreau, Z. Arzoumanian (NASA/GSFC), T. Enoto, T. Mihara (RIKEN)
on 9 Jul 2022; 00:08 UT
Credential Certification: Wataru Iwakiri (wataru.iwakiri@riken.jp)
Subjects: X-ray, Gamma-Ray Burst, Transient
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 10-12erg/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.
