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Discovery of High Frequency Quasi-Periodic Oscillations in 4u1915-05

D. Barret·L. Boirin·J. F. Olive·J. E. Grindlay·P. F. Bloser·J. Swank·A. P. Smale
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Abstract

The type I X-ray burster and dipper 4U1915-05 (also known as XB1916-053) was monitored by the Rossi X-ray Timing Explorer between February and October, 1996. The source was observed in various spectral states; the highest luminosity state (LX ~ 1.5 10^37 ergs/s, 10 kpc, 1-20 keV) is associated with a soft spectrum, whereas for the lower luminosity state (down to ~5 10^36 ergs/s) the spectrum is significantly harder. Using the high time resolution data provided by the Proportional Counter Array (PCA), we have discovered High-Frequency Quasi-Periodic Oscillations (HFQPOs) in the persistent X-ray emission of 4U1915-05 while its luminosity was ~8 10^36 ergs/s. The QPO frequency ranges from 600 Hz up to ~1000 Hz, with typical Full Width at Half Maximum (FWHM) ~50-100 Hz and Root Mean Squared (RMS) values 15%. In addition, by using the ``shift and add'' technique, we have detected a twin HFQPO (5.5 sigma level) separated from the main peak by ~355 Hz. 4U1915-05 is the eighth Atoll source displaying simultaneous twin HFQPOs. Based on current knowledge of HFQPO sources, our observations suggest that 4U1915-05 might contain a 2.8 (or 5.6) millisecond rotating neutron star.

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D. Barret, L. Boirin, J. F. Olive, J. E. Grindlay, P. F. Bloser, J. Swank, A. P. Smale. 1998-11-15. Discovery of High Frequency Quasi-Periodic Oscillations in 4u1915-05. https://arxiv.org/abs/astro-ph/9811236

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