Terzan 2

B. M. Belli, Istituto Astrofisica Spaziale, Frascati; F. d'Antona, Osservatorio Astronomico, Roma; D. Molteni, Istituto Fisica Universita, Palermo; and M. Morini, Istituto Fisica Cosmica e Informatica, Palermo, telex: "Analysis of an 11-hr observation, made with the EXOSAT medium-energy experiment and beginning 1985 Mar. 14.16 UT, of the x-ray source in the globular cluster Terzan 2 (= 4U 1722-30) shows evidence of quasi-periodic oscillations (QPOs) at a constant level of the source flux (1.3 x 10**-13 J m**-2 s**-1) in the energy range 2-8 keV. The average centroid frequency is 0.092 +/- 0.001 Hz, the FWHM is 0.0053 +/- 0.002 Hz, the rms (pulsed fraction) is 4.8 +/- 1.2, and the statistical significance > 5 sigma. Low- frequency noise and the second harmonic are also present. The QPOs show a hard spectrum, appearing with rms 5.6 +/- 1.6 significance > 4.5-sigma) in the hard part of the analyzed range (4-8 keV) and irrelevant (rms < 2, significance < 2-sigma) in the soft part (2-4 keV)."