NICER follow-up observations of MAXI J1803-298

P. M. Bult, K. C. Gendreau, T. Enoto, J. Homan, D. Altamirano, A. Sanna, G. K. Jaisawal, M. Ng, W. Iwakiri, T. E. Strohmayer, Zaven Arzoumanian, J. Steiner

Research output: Other contributionNet publication - Internet publicationCommunication

Abstract

Continuing the ongoing efforts to observe the new X-ray transient MAXI J1803-298 (ATels #14587, #14588, #14591, #14594, #14597, #14598, #14601), we have collected further observations with the Neutron Star Interior Composition Explorer (NICER). We observed the source on May 2nd (1 ks) and May 4th (0.5 ks), finding the 0.5-10 keV count-rate to be increasing from 770 ct/s to 1100 ct/s, respectively.

The energy spectra could be reasonably well described with an absorbed disk plus power-law continuum model. The absorption column density is measured at 3.2 x 1021 cm-2. Between the two sets of observations we further observe the disk temperature to decrease from 0.34 +/- 0.01 keV to 0.29 +/- 0.01 keV, while the power law photon index increases from 1.56 +/- 0.02 to 1.63 +/- 0.02. Strong residuals are observed between 6-8 keV likely associated with Fe emission lines. Further investigation of these features is under way. The 1-10 keV flux was 2.5 x 10-9 and 3.3 x 10-9 erg/s/cm2, respectively.

Considering the temporal variability in the 0.5-10 keV band, we find that on May 2nd the power spectrum showed band limited noise below 10 Hz with an amplitude of about 23% rms. Additionally, we see a sharp QPO at ~0.13 Hz. By May 4th, the QPO frequency had increased to ~0.26 Hz, while the amplitude of the noise component decreased to 18% rms.

The spectral and temporal properties are more in line with those of a hard state accreting stellar-mass black hole than with those of an accreting neutron star. However, further observations are needed to unambiguously identify the nature of the compact object.

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 date5 May 2021
Publication statusPublished - 5 May 2021
SeriesThe Astronomer's telegram
NumberATel #14602

Keywords

  • X-ray
  • Transient

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