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S.D. Vrtilek (1,2), T. Mihara (3), F.A. Primini (1), P. Kahbda (4), H. Marshall (5), F. Agerer (6), P.A. Charles (7), F.H. Cheng (2), K. Dennerl (4), C. la Dous (8), E.M. Hu (9), R. Rutten (10), P. Serlemitsos (11), Y. Soong (11), J. Stull(12), J. Trümper (4), W. Voges (4), R.M. Wagner (13), R. Wilson (14)
1) Harvard-Smithsonian Center for Astrophysics, 60 Garden
Street, Cambridge MA 02138.
2) Dept. of Astronomy, University of
Maryland, College Park, MD 20742.
3) The Institute of Physical and Chemical Research, 2-1 Hirosawa
Wako Saitama 351-01 Japan.
4) Max Planck Institut für extraterrestrische Physik, D-85740
Garching bei München, Germany
5) Eureka Scientific, Inc., 2452 Delmer St., Suite 100 Oakland, CA
94602
6) Dorfstr. 19, D-84184 Zweikirchen, Germany
7) Department of Physics, Oxford University, Keble Road, Oxford OX1
3RH, UK
8) ESA/IUE Observatory, Villafranca, Apartado 50727, 28080
Madrid, Spain
9) Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, HI
96822
10) Royal Greenwich Observatory/ NFRA, Apartado de Correos 321,
E-38780 Santa Cruz de la Palma, Islas Canarias, Spain
11) NASA/GSFC
LHEA Code 666, Greenbelt, MD 20771
12) Alfred University Observatory, 26 North Main St, Alfred, NY
14802
13) Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ
86001
14 ) NASA/MSFC, Code ES-84, Huntsville, AL 35812
We present first results from a multiwavelength campaign to observe the binary pulsar system Her X-1/HZ Her. The campaign spanned four days during August 1993: observations were taken with 5 satellites and several ground-based optical facilities. A substantial, unexpected drop in flux at X-ray energies, with no change in absorbing column density, was observed. The pulse period has increased from the previous measurement, contrary to the usual spin-up, and no pulsed emission is detected above 0.9 keV in the low state. The optical and UV fluxes continued to show 1.7 day modulation attributed to X-ray heating of the companion star. However, the UV flux around eclipse was significantly reduced implying an absence of the normally observed excess attributed to X-ray heating of the disk. We conclude that we have observed an anomalous low state, seen only once before (Parmar, et.al. 1985), in which the X-ray flux is not redistributed but obscured. We suggest explanations for the behavior of the flux at different wavelengths.
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