NICER follow up of the new X-ray transient Swift J1729.5-3223
ATel #14818; A. Sanna (Univ. Cagliari), D. Altamirano (Univ. of Southampton), M. Ng (MIT), L. Burderi, A. Riggio (Univ. Cagliari), T. Di Salvo (Univ. Palermo)
on 30 Jul 2021; 19:39 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Andrea Sanna (andrea.sanna@dsf.unica.it)
Subjects: X-ray, Binary, Transient
Following the announcement of the new X-ray transient Swift J1729.5-3223 discovered by Swift (ATel #14791), we started observing the source with the Neutron star Interior Composition Explorer (NICER) starting from 2021 July 28 at 11:12 UT, for a total exposure of approximately 5 ksec.
The average source count rate measured by NICER was 4.2 cts/sec (0.5-10 keV). The 0.5-10 keV power spectrum does not present significant periodic or aperiodic signals in the frequency range 5E-3Hz - 2.5E+3 Hz.
The continuum X-ray spectrum extracted from the NICER data in the 0.5-10 keV energy range is well described (red. chi^2 1.10 for 108 d.o.f.) by an absorbed power-law. The absorption column density derived from the spectral fit is N_H = 2.14(4)E+22 cm^-2, while the power-law photon index is 1.52(3). The absorbed 0.5-10 keV source flux is 3.4(1)E-11 erg cm^-2 s^-1. There is no evidence of a spectral Fe line feature in the energy range 6.4-7 keV.
At the moment, the temporal and spectral properties of Swift J1729.5-3223 do not allow us to unambiguously identify the nature of the compact object in the X-ray binary system. ATCA radio observations performed closely with X-ray Swift observations placed the source at a position on the radio/X-ray plane consistent with it being either a black hole or neutron star X-ray binary (ATel #14815). Therefore, further X-ray, as well as multi-wavelength observations, are strongly encouraged.
NICER is a 0.2-12 keV X-ray telescope operating on the International Space Station. The NICER mission and portions of the NICER science team activities are funded by NASA.
