MAXI J2320-268: Swift/XRT observations reveal likely link to HD 220096
ATel #16145; J. A. Kennea (PSU), W. Iwakiri (Chuo U) and H. Negoro (Nihon U) report on behalf of a larger collaboration
on 22 Jul 2023; 15:09 UT
Credential Certification: Jamie A. Kennea (kennea@astro.psu.edu)
Subjects: Optical, X-ray, Star
MAXI reported the detection of a new transient source, MAXI J2320-268 (ATEL #16144) on July 20th, 2023. Starting on July 22nd, 2023 @ 01:01UT, Swift
performed a series of 12 tiling observations in order to cover the MAXI error region. We detect one, bright X-ray source inside the MAXI error region at
the following localization: RA/Dec(J2000) = 350.3154, -26.9876, which is equivalent to:
RA(J2000) = 23h 21m 15.70s,
Dec(J2000) = -26d 59m 15.3s,
with an error radius 10.5## (90% confidence). This X-ray source is consistent with the localization of the star HD 220096, which is a known X-ray
source (e.g. Giommi et al, 1991) and has been previously seen to produce stellar flares (Schmitt et al, 2021).
The observed count rate, corrected for pile-up, is 1.01 +/- 0.16 count/s. Looking at historical XRT data taken on this source, we find a high degree
of variability over observations taken by Swift in December 2004, 2017 and 2023, varying between 0.16 - 1.8 count/s.
The spectrum is well described by a power law with photon index of 1.7(+0.8/-0.4) with a flux of 4.1 (+1.8/-1.5) x 10^-11 erg/s/cm^-2 (0.3 - 10 keV).
Assuming a distance to HD 220096 of 101pc (e.g. Bailer-Jones et al, 2021), this relates to an X-ray luminosity of 5 x 10^29 erg/s (0.3 - 10 keV). We note
that Gunter et al (2020) reported on TESS observations of stellar flares, and with a flare with energy 10^36.9 erg, HD 220096 AKA TIC332487879 was the
source of the brightest flare in their sample.
Therefore we tentatively suggest that MAXI J2320-268 may be due to a stellar flare from HD 220096 AKA TIC332487879.
This work was supported by the Swift GI program with NASA Grant
