Scorpius X-1
Abstract
A. G. Peele and N. E. White, Goddard Space Flight Center, NASA, write: "The public RXTE ASM lightcurve of Sco X-1 covering the interval 1996 Feb. 22-Nov. 28 shows an intensity modulation with a period of about 37 days. The period is detected using a Lomb-Scargle periodigram, and it has a false-alarm probablility of < 10E-6; it is also detected using minimum entropy and chi**2- folding techniques. Detection of the period is complicated by the well-known x-ray flaring from Sco X-1. The modulation is most evident in the low-energy (1.3-3.0-keV) channel, where the flaring amplitude is a minimum, and it is a sinusoidal-like modulation of the quiescent flux. Fitting a sine wave to the data in this channel gives an ephemeris of JD 2450160.9 (+/- 1.0) + (36.8 +/- 0.4)E, with phase zero defined as the modulation minimum and a full amplitude of 13 +/- 2 percent. The modulation amplitude for the quiescent flux decreases by a factor of 4-5 between the soft- and hard-energy (5.0-12.2-keV) channels. The 37-day modulation does not appear to be related to the flaring episodes. The modulation is not detected in archival Vela 5B and Ariel 5 ASM x-ray data (but upper limits do not rule out its presence). We encourage a search for the 37-day period in the optical and radio emission from Sco X-1 (= V818 Sco)."
- Publication:
-
International Astronomical Union Circular
- Pub Date:
- December 1996
- Bibcode:
- 1996IAUC.6524....2P