NICER observations the new X-ray transient SWIFT J174038.1-273712

A. Sanna*, D. Altamirano, Keith C. Gendreau, L. Burderi, A. Riggio, T. Di Salvo, G. K. Jaisawal, M. Ng

*Corresponding author for this work

Research output: Other contributionNet publication - Internet publicationCommunication


Referred to by ATel #: 14550, 14552Following the discovery of the new X-ray transient SWIFT J174038.1-273712 by the Neil Gehrels Swift Observatory (ATels #14536), we triggered observations with the Neutron Star Interior Composition Explorer (NICER) that started on 2021 April 9 at 14:52 UT (total exposure of ~27 ksec).NICER's average source count rate was 4.2 cts/sec (0.5-10 keV). The 0.5-10 keV power spectrum does not present significant periodic or quasi-periodic signals in the frequency range 0.005Hz - 2.500 Hz. The power spectrum shows low-frequency variability (red noise) with a fractional rms amplitude of 28+/-1% (0.5-10 keV as measured in the 0.007-1.7 Hz range).The continuum X-ray spectrum extracted from the NICER data in the 0.5-10 keV energy range is well described (red. chi^2 1.24 for 639 d.o.f.) by an absorbed blackbody and a thermally comptonized continuum ((Tbabs(bbody+nthcomp) in XSPEC). The absorption column density derived from the spectral fit is N_H = 0.93(2)E22 cm^-2. The blackbody component is described by a temperature kT=0.39(2) keV while the thermally comptonized component is characterized by a photon index Gamma=2.3(3) produced by an electron population with temperature kTe<=4 keV and seed photon temperature linked to the blackbody component. There is marginal evidence of a broad (sigma 0.54(13) keV) Fe line feature at 6.64(14) keV. The absorbed 0.5-10 keV source flux is 1.5(2)E-11 erg cm^-2 s^-1, that implies a relatively low-luminosity (L~2e35 erg/s) system, even assuming a source distance of 10 kpc.Currently, the temporal and spectral properties of SWIFT J174038.1-273712 do not allow us to unambiguously identify the compact object's nature in the binary X-ray system. The observed source flux is either compatible with the beginning/ending of a standard outburst from a Low-mass X-ray binary or the beginning of the outburst of a so-called very faint X-ray transient (Wijnands et al. 2006, A&A, 449, 1117). 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.
Original languageEnglish
Publication date13 Apr 2021
Number of pages1
Publication statusPublished - 13 Apr 2021
SeriesThe Astronomer's telegram
NumberATel #14545


  • X-ray
  • Transient


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