A Search for Cataclysmic Variables in the EGRET All-Sky Survey

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Session 55 -- Interacting Binaries: CVs and XRBs
Display presentation, Thursday, January 13, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[55.11] A Search for Cataclysmic Variables in the EGRET All-Sky Survey

P. Barrett, E.M. Schlegel (USRA), O.C. DeJager (PU CHE), G. Chanmugam (LSU)

We present results from {\sl Compton/EGRET} observations of the entire class of magnetic Cataclysmic Variables (CV) and many recent novae. The result from this initial survey is negative with no detection greater than $2\sigma$. The average upper limit of the luminosity of a typical (distance $\sim 100pc$) CV is $\approx 7 \times 10^{30}~ergs~ s^{-1}$ which implies a conversion efficiency of accretion luminosity to $\gamma$-ray luminosity of $<1$\% for $\gamma$-rays above $100 MeV$.

This low conversion efficiency places tight constraints on non-thermal models of $\gamma$-ray production from accretion-powered, magnetic compact binaries. For diffusive shock acceleration of protons which is the only process possible for the AM Herculis subclass of CVs, we obtain upper limits to the flux above $100 MeV$ from VV Puppis, V834 Cen (E1405-451), and AM Herculis of about 10, 5, and 3$\times 10^{30}~ ergs~ s^{-1}$, respectively. These flux upper limits are more than a factor of ten less than the fluxes claimed by Bhat et al. (1989) using COS-B data for VV Puppis and V834 Cen and about 100 less than the TeV flux from AM Her (Bhat et al. 1991). These results may mean that the diffusive shock process is not as important in AM Her binaries as is proposed. For the dynamo mechanism of particle acceleration which is the putative process occuring in the DQ Herculis subclass of CVs, the efficiency of converting angular momentum to $\gamma$-rays must be less than optimal. This result may be important for the production of $\gamma$-rays from neutron star binaries where the dynamo mechanism was first proposed.

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