Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...436l...9v&link_type=abstract
Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X), vol. 436, no. 1, p. L9-L13
Astronomy and Astrophysics
Astronomy
39
Accretion Disks, Eclipsing Binary Stars, Pulsars, Spaceborne Astronomy, X Ray Astronomy, X Ray Binaries, Companion Stars, Light Curve, Stellar Luminosity, X Ray Spectra
Scientific paper
We present first results from a multiwavelength campaign to observe the binary pulsar system Her X-1/ HZ Her. The campaign spanned 4 days during 1993 August: observations were taken with five satellites (IUE, EUVE, ROSAT, ASCA, and CGRO/BATSE) and several ground-based 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 significant reduction in UV flux observed around eclipse implies 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.
Agerer Franz
Charles Phil A.
Cheng Fu-Hua
Dennerl Konrad
Hu Esther M.
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