SIMBAD references

In this paper we discuss X-ray observations of γ Cas obtained in 1998 November with the Rossi X-Ray Timing Explorer (RXTE). The data were obtained nearly continuously over 54 hr, which is about twice the expected rotational period. An earlier RXTE light curve obtained in 1996 March over a 27 hr period showed X-ray flux arising from short-duration shots (flares) superimposed on an undulating ``basal'' component that was anticorrelated with fluctuations of the UV continuum over a timescale of ∼10 hr. The object of the present study was to (1) examine the long-term variations of the X-ray characteristics through comparisons with this earlier data and (2) to determine whether variations of the basal flux repeat during a second rotation period. A comparison of the results with the 1996 data set shows a number of similarities and differences in the X-ray behavior: (a) the mean X-ray level in 1998 was only 60% of the 1996 level, (b) the basal fluxes in 1998 vary over shorter timescales (less than 2 hr) than in 1996, (c) the shots were found to show a slightly softer (cooler) mean color than the basal component in 1998, although they were slightly hotter in 1996, (d) fluctuations in the colors of the shot and basal fluxes generally track one another in both data sets, (e) cyclical patterns of X-ray flux decrease with a period of about 7.5 hr occurred in both data sets, and (f) the frequency of shots with a given integrated energy was found to decrease exponentially with energy, although the rate of decrease in 1996 was slower than in 1998. There was only marginal evidence for a repetition during the second half of the time sequence of long-term basal flux variations seen during the first half of the observations. We suspect, however, that the large intrinsic variability of the X-ray source would have masked a true replication. We also present archival IUE data that shows the presence of UV continuum variations in 1982 with similar characteristics to those seen in 1996. This suggests that the regions responsible for the UV variability are very long lived. The data also provide the basis for a refined but still tentative rotational period of 1.12277 days. Assuming a flare paradigm and a very simple electron beam model, we examine the atmospheric heating expected for the shot events. We conclude that it is possible to explain how the measured shot temperature can be smaller than the temperature deduced for the basal X-ray emission. We also discover that if the beam model is correct then the electrons within the beam have relatively high energies (>200 keV) and are nearly monoenergetic. In three appendices we discuss arguments, first, against the idea that the X-ray emission from γ Cas arises from mass accretion onto a hypothetical white dwarf companion or from an active late-type star and, second, in favor of its origin from near the surface of γ Cas.