Multiwavelength observations of GX 339-4 in 1996. I. Daily light curves and X-ray and gamma-ray spectroscopy

As part of our multiwavelength campaign of GX 339-4 observations in 1996, we present our radio, X-ray, and gamma-ray observations made in July, when the source was in a hard state (=soft X-ray low state). The radio observations were made at the time when there was a possible radio jet. We show that the radio spectrum was hat and significantly variable and that the radio spectral shape and amplitude at this time were not anomalous for this source. Daily light curves from our pointed observation on July 9-23 using the Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Gamma-Ray Observatory (GGRO), from the Burst and Transient Source Experiment (BATSE) on CGRO, and from the All-Sky Monitor on the Rossi X-Ray Timing Explorer (RXTE) also show that there was no significant change in the X-ray and gamma-ray flux or hardness during the time when the possible radio jetlike feature was seen. The higher energy portion of our pointed RXTE observation made on July 26 can be equally well fitted using simple power law times exponential (PLE) and Sunyaev-Titarchuk (ST) functions. An additional soft component, is required, as well as a broad emission feature centered on similar to 6.4 keV. This may be an iron line that: is broadened by orbital Doppler motions and/or scattering off a hot medium. Its equivalent width is similar to 600 eV. Our simplistic continuum fitting does not require an extra reflection component. Both a PLE and an ST model also fit our OSSE spectrum on its own. Although the observations are not quite simultaneous, combining the RXTE and CGRO spectra we find that the PLE model easily fits the joint spectrum. However, the ST model drops off too rapidly with increasing energies to give an acceptable joint fit.