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Detection of coherent 7.6 HZ oscillations during a burst from Aquila X-1
Schoelkopf, R. J.; Kelley, R. L.
AA(California Institute of Technology, Pasadena), AB(NASA, Goddard Space Flight Center, Greenbelt, MD)
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 375, July 10, 1991, p. 696-700. (ApJ Homepage)
Publication Date:
NASA/STI Keywords:
Stellar Oscillations, X Ray Binaries, Coherent Radiation, Power Spectra
Bibliographic Code:


The results are reported of timing and spectral analysis of the X-ray source Aql X-1 (X1908 + 005) using data obtained with the Einstein SSS and MPC instruments. A classic type I burst was observed from Aql X-1 in both detectors, and a coherent modulation with a period of 131.66 + or - 0.02 (7.6 Hz) and a pulsed fraction of 10 percent was detected in the SSS data (0.64-4.5 keV) during the period of enhanced emission. The signal has a random occurrence probability of less than 5 x 10 to the -5th. The sensitivity of the MPC for high-resolution timing during the burst is greatly reduced because of the low-duty cycle during the burst, and the modulation is not detected. There is no evidence for a loss of coherence during the 80 s or so when it is observable. It is argued that an asymmetrical burst occurring on a neutron star rotating at 7.6 Hz offers a plausible explanation for the oscillation.

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