Abstract
We present temporal and time-resolved spectral analyses of all the
thermonuclear X-ray bursts observed from the neutron star low-mass X-ray
binary 4U 1728−34 with NICER from 2017 June to 2019 September. In
total, we detected 11 X-ray bursts from the source and performed
time-resolved spectroscopy. Unlike some of the earlier results for other
bursting sources from NICER, our spectral results indicate that the use
of a scaling factor for the persistent emission is not statistically
necessary. This is primarily a result of the strong interstellar
absorption in the line of sight toward 4U 1728−34, which causes the
count rates to be significantly lower at low energies. We also searched
for burst oscillations and detected modulations in six different bursts
at around the previously known burst oscillation frequency of 363 Hz.
Finally, we report the detection of oscillations prior to two bursts at
356 and 359 Hz, respectively. This is the first time in the literature
where burst oscillations are detected before the rapid rise in X-ray
flux, from any known burster. These oscillations disappear as soon as
the burst starts to rise and occur at a somewhat lower frequency than
the oscillations we detect during the bursts.
Original language | English |
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Article number | 55 |
Journal | Astrophysical Journal |
Volume | 958 |
Number of pages | 14 |
ISSN | 0004-637X |
DOIs | |
Publication status | Published - 2023 |
Keywords
- Neutron stars
- X-ray bursts
- Low-mass x-ray binary stars