HEAD 2000, November 2000
Session 22. Accreting X-Ray Pulsars
Display, Wednesday, November 8, 2000, 8:00am-6:00pm, Bora Bora Ballroom

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[22.04] USA Observations of Hercules X-1 During an Extended Low State

M. N. Lovellette, K. S. Wood, P. S. Ray, R. M. Bandyopadhyay, M. T. Wolff, G. Fritz, P. Hertz, M. P. Kowalski, D. Yentis (E. O. Hulburt Center for Space Research, Naval Research Laboratory), P. Saz Parkinson, E. Bloom, W. Focke, B. Giebels, G. Godfrey, K.T. Reilly, G. Shabad (Stanford Linear Accelerator Center, Stanford University), L. Titarchuk (George Mason U.), J. Scargle (NASA/ Ames Research Center, Moffett Field), USA Experiment Science Working Group

Hercules X-1 has been in a prolonged low state during most of 1999--2000. We have used the USA instrument on ARGOS to observe the source. Because we are able to use the USA offset pointing system to modulate the signal we obtain both pulsed fluxes (or upper limits) and accurate measurements of the unpulsed flux. The frequency of observation permits good sampling of phases in both the orbital cycle and the 35-day cycle. USA data are merged with those from the RXTE/ASM. We discuss these measurements and compare with the observations made during the earlier extended low of 1983, which was observed using EXOSAT. The fluxes and spectrum are used to constrain models for how the disk geometry changes during extended lows.

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The author(s) of this abstract have provided an email address for comments about the abstract: lovellette@xip.nrl.navy.mil

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