NOAO >   Observing Info >   Approved Programs >   2007A-0092

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Proposal Information for 2007A-0092


PI: Bernard McNamara, New Mexico State University, bmcnamar@nmsu.edu
Address: Department of Astronomy, William and Frenger, Las Cruces, New Mexico 88003, US

CoI: Thomas Harrison, New Mexico State University
CoI: Jillian Bornak, New Mexico State University
CoI: Doug Hoffman, New Mexico State University

Title: The Origin of the IR Variability in GX17+2 and GX5-1

Abstract: GX 17+2 and GX 5-1 are Low Mass X-ray Binaries (LMXBs). LMXBs consist of a neutron star (or black hole) accreting material from a low mass star. Both GX 17+2 and GX 5-1 are also members of the subclass of ``Z-sources'', LMXBs that trace out a Z pattern in their X-ray color- color diagrams as the mass transfer rate fluctuates. While all Z sources are variable from the X-ray to the radio, GX 17+2 and GX 5-1 are unusual in that their K band emission varies by >3 mag and >1 mag respectively. The two most likely causes of this variability are a jet or large instabilities within their accretion disks. We propose a simple test of these two hypotheses using the KP2.1m SQIID and Andicam on the CTIO 1.3 m telescope. If the infrared variability arises from a jet it should be periodic, smoothly varying, and uncorrelated with the X- ray fluxes measured by the RXTE all-sky-monitor. If the infrared variability arises from an accretion disk instability, it should be non- periodic, highly non-uniform, but correlated with the X-ray emission. Longer term Andicam K-band measurements are requested to allow the duty cycle of these objects to be determined.


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