Simultaneous Multiwavelength Observations of Her X-1

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Session 37 -- Pulsars
Display presentation, Thursday, January 13, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[37.08] Simultaneous Multiwavelength Observations of Her X-1

S.D. Vrtilek (CfA, UMD), P. Charles (Oxford), E. Hu (IfA), P. Kahabka (MPE), C. la Dous (ESA), H. Marshall (MIT), T. Mihara (Riken), F. Primini (CfA), R. Rutten (RGO), Y. Soong (GSFC), J. Stull (Alfred University), J. Tr\"umper (MPE), W. Voges (MPE), R. M. Wagner (OSU), R. Wilson (MSFC)

We present preliminary results from a multiwavelength campaign to observe the binary pulsar system Hercules X-1/HZ Herculis. The campaign spanned four days during August 1993 and involved EUVE, IUE, ROSAT, ASCA, and COMPTON/BATSE, as well as several ground-based optical observatories. During the observation (TJD 9210-9214) Her X-1 appeared to make a transition from the normal 35-day `high-on' state to one of the anomalous low states reported by Parmar \etal~(1985). The drop in countrate is most pronounced for the ASCA (1.0 - 12.0 keV) energy band; the effect becomes less for the ROSAT and EUVE bands with no apparent effect in the IUE and optical bands. The IUE observations continued to show the 1.7 day orbital modulation. The observed drop in medium energy X-ray countrate (a factor of 100) is considerably greater than that observed by Parmar \etal~(a factor of 20). Fits to the ROSAT and ASCA spectra determine that the decrease in countrate cannot be attributed to excess absorbing material: the hydrogen column densities do not increase during the low state observations.

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