NICER detection of periodicity in the new X-ray transient MAXI J0901-531

P. S. Ray*, A. Sanna, K. C. Gendreau, G. K. Jaisawal, J. Kennea, W. Iwakiri, T. Mihara, T. E. Strohmayer, D. Chakrabarty, M. T. Wolff, D. Altamirano, Zaven Arzoumanian, P. Jenke, C. A Wilson-Hodge

*Corresponding author for this work

Research output: Other contributionNet publication - Internet publicationCommunication

Abstract

Referred to by ATel #: 14564 Tweet Following the discovery of the new X-ray transient MAXI J0901-531 (ATel #14555), we triggered observations with the Neutron Star Interior Composition Explorer (NICER) that started on 2021 April 16 at 19:48 UT and obtained a total exposure of ~9.25 ks. The pointing direction was the Swift localization from ATel #14557. NICER's average measured count rate was 19.6 cts/s (0.5-8 keV), including a background contribution of < 1 c/s. The power spectrum exhibits a low-frequency noise component extending to about 0.1 Hz, plus a coherent periodicity with a fundamental frequency of 0.07 Hz with at least four significant harmonics. A pulse timing analysis gives a frequency of 0.0711477(2) Hz (P = 14.055 seconds). No significant frequency derivative is seen with a limit of |F1| < 4E-12 Hz/s. The frequency value is consistent with the Fermi/GBM measurement obtained by integrating data collected in the time interval April 13-16. We fitted the 0.5-10 keV spectrum with an absorbed power-law model. This model failed to describe the NICER energy continuum. To better fit the spectrum, an additional blackbody (bbodyrad in XSPEC) was added along with the power-law component. Following are preliminary spectral parameters derived from this analysis: absorption column density N_H = (4.1+/-0.2) x 10^21 cm^-2 (Wilms abundance), black body temperature kT = 0.61+/-0.02 keV, blackbody normalization BBnorm = 14+/-1, and photon index = 0.13+/-0.06. The best fit reduced chi-squared is 1.13 for 827 degrees of freedom. The 0.5-10 keV unabsorbed flux is 1.83x10^{-10} erg/s/cm^2. No iron line feature is observed between 6-7 keV though we see some excess around 7.5 keV. Further investigation is required. 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 date18 Apr 2021
Publication statusPublished - 18 Apr 2021
SeriesThe Astronomer's telegram
NumberATel #14559

Keywords

  • X-ray
  • Gamma Ray
  • Binary
  • Neutron Star
  • Transient
  • Pulsar

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