Abstract
MAXI/GSC reported the detection of a faint X-ray transient in the direction of and likely associated with MAXI J1957+032 (ATel #15440). NICER proceeded to begin raster scan observations near the MAXI coordinates, finding a source position that is consistent with the Chandra coordinates of MAXI J1957+032 obtained during the previous outburst of the source in 2016 (ATel #9591): R.A. = 299.162950 deg. and Dec. = 3.445461 deg. (J2000). NICER collected a 1.3 ks pointed observation at these coordinates starting on 2022-06-19 14:54:14 UTC.
Coherent pulsation searches over 0.3-10.0 keV with a Fourier power spectrum and acceleration searches yielded a significant (over 10 sigma, single-trial) signal at 313.6 Hz. The acceleration search also yielded a weaker (2 sigma) signal at the second harmonic frequency of 627.2 Hz.
A broadband 0.4-10.0 keV spectral analysis found that an absorbed power law and disk blackbody provided a good fit, with a chi-squared value of 158 for 109 degrees of freedom. We find an absorption column density of nH = 0.072 (-0.011, +0.013) × 1022cm-2, a photon index of 1.32 (-0.16, +0.13), and an inner disk temperature of 0.79 (-0.02, +0.02) keV. This translates to a 0.3-10.0 keV absorbed flux of 2.57 (-0.07, +0.02) × 10-10 erg/s/cm-2 and an unabsorbed flux of about 2.8 × 10-10 erg/s/cm-2. Uncertainties are reported at 90% confidence.
NICER will continue to observe MAXI J1957+032. We encourage further observations of this source with other observatories.
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.
Coherent pulsation searches over 0.3-10.0 keV with a Fourier power spectrum and acceleration searches yielded a significant (over 10 sigma, single-trial) signal at 313.6 Hz. The acceleration search also yielded a weaker (2 sigma) signal at the second harmonic frequency of 627.2 Hz.
A broadband 0.4-10.0 keV spectral analysis found that an absorbed power law and disk blackbody provided a good fit, with a chi-squared value of 158 for 109 degrees of freedom. We find an absorption column density of nH = 0.072 (-0.011, +0.013) × 1022cm-2, a photon index of 1.32 (-0.16, +0.13), and an inner disk temperature of 0.79 (-0.02, +0.02) keV. This translates to a 0.3-10.0 keV absorbed flux of 2.57 (-0.07, +0.02) × 10-10 erg/s/cm-2 and an unabsorbed flux of about 2.8 × 10-10 erg/s/cm-2. Uncertainties are reported at 90% confidence.
NICER will continue to observe MAXI J1957+032. We encourage further observations of this source with other observatories.
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 language | English |
|---|---|
| Publication date | 19 Jun 2022 |
| Publication status | Published - 19 Jun 2022 |
| Series | The Astronomer's telegram |
|---|---|
| Number | ATel #15444 |
Keywords
- X-ray
- Neutron Star
- Transient
- Pulsar