AstroSat /LAXPC Detection of Millisecond Phenomena in 4U 1728-34
- Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai (India)
- Inter-University Centre for Astronomy and Astrophysics, Pune 411007 (India)
- UM-DAE Center of Excellence for Basic Sciences, University of Mumbai, Kalina, Mumbai-400098 (India)
- Indian Institute of Science Education and Research, Bhauri, Bhopal 462066 (India)
- University of Mumbai, Kalina, Mumbai-400098 (India)
- Dept. of Astronomy and Astrophysics, Raman Research Institute, Bengaluru-560080 (India)
The low-mass X-ray binary 4U 1728-24 was observed with AstroSat /LAXPC on 2016 March 8th. Data from a randomly chosen orbit of over 3 ks was analyzed for detection of rapid intensity variations. We found that the source intensity was nearly steady but, toward the end of the observation, a typical Type-1 burst was detected. Dynamical power spectrum of the data in the 3–20 keV band, reveals the presence of a kHz Quasi-Periodic Oscillation (QPO) for which the frequency drifted from ∼815 Hz at the beginning of the observation to about 850 Hz just before the burst. The QPO is also detected in the 10–20 keV band, which was not obtainable by earlier RXTE observations of this source. Even for such a short observation with a drifting QPO frequency, the time lag between the 5–10 and 10–20 keV bands can be constrained to be less than 100 microseconds. The Type-1 burst that lasted for about 20 s had a typical profile. During the first four seconds, dynamic power spectra reveal a burst oscillation for which the frequency increased from ∼361.5 to ∼363.5 Hz. This is consistent with the earlier results obtained with RXTE /PCA, showing the same spin frequency of the neutron star. The present results demonstrate the capability of the LAXPC instrument for detecting millisecond variability even from short observations. After RXTE ceased operation, LAXPC on AstroSat is the only instrument at present with the capability of detecting kHz QPOs and other kinds of rapid variations from 3 keV to 20 keV and possibly at higher energies as well.
- OSTI ID:
- 22663580
- Journal Information:
- Astrophysical Journal, Vol. 841, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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