[ Previous | Next | ADS ]

A Strong Increase in the Orbital Modulation of the X-ray flux of GX9+9

ATel #839; Alan M. Levine (MIT), Robert J. Harris (MIT), and Osmi Vilhu (U. of Helsinki)
on 16 Jun 2006; 19:13 UT
Credential Certification: Alan M. Levine (aml@space.mit.edu)

Subjects: X-ray, Request for Observations, Binary, Neutron Star

Referred to by ATel #: 940

Observations with the RXTE All-Sky Monitor (ASM) show that the modulation of the X-ray flux in the 2-12 keV band at the 4.19 hour orbital period of the LMXB GX9+9 has become strong since early in 2005. The modulation was originally discovered in HEAO 1 data by Hertz and Wood (ApJ 1988, 331, 764) and was detected with high significance in ASM data at a period P = 4.19344 +- 0.00007 hours (V. Shivamoggi, B. S. Thesis, M.I.T., 2005; Levine et al. 2005, AAS Meeting Abstracts, 207, 72.04). We have now looked for the orbital modulation in 1.05 year ASM data sets covering the 10 plus years of the RXTE mission and also in subdivisions of those data sets. We find that the peak-to-peak amplitude of the modulation expressed as a fraction of the average intensity was about 6% or less from the beginning of the mission until 2005 January after which it was much larger, i.e., the modulation was at most 6% in the interval 2004 Sep 14 (MJD 53262) to 2005 Jan 19 (MJD 53389) but was about 18% in the interval 2005 Jan 19 (MJD 53389) to 2005 May 25 (MJD 53515). The modulation strength appears to remain near 18% in 4 time intervals between 2005 May 25 and 2006 Jun 9 (MJD 53894) and was more or less independent of energy within the 1.5 to 12 keV band.

Observations of the orbital modulation of GX9+9 at all wavelengths are strongly encouraged.