INVERSE COMPTON GAMMA-RADIATION OF FAINT SYNCHROTRON X-RAY NEBULAE AROUND PULSARS

The fluxes of the inverse Compton gamma-rays expected from synchrotron X-ray nebulae are calculated and the observability of this radiation is discussed. The main emphasis is given to the pulsar driven nebulae (plerions), although the results and conclusions are equally applicabl e to the extended non-thermal X-ray sources produced by shock-accelera ted electrons in the shell-type supernovae remnants. The existence of the non-thermal (synchrotron) component of X-radiation in these object s implies an effective acceleration of electrons up to energies E-e si milar to 100B(-5)(1/2) epsilon(keV) TeV (B-5=B/10(-5) G; epsilon(keV)= epsilon/1keV). The inverse Compton scattering of the same electrons on the ambient photon fields may result in observable TeV gamma-radiatio n as well. The 2.7-K microwave background radiation is, as a rule, the dominant target photon field for production of gamma-rays. This provi des a direct relation, for the given magnetic field, between the typic al energies of the synchrotron (epsilon) and inverse Compton (E) photo ns produced by the same electrons: epsilon(keV)similar or equal to 0.0 7(E/1 TeV)B-5. The ratio of relevant energy fluxes at these energies i s about f(gamma)(greater than or equal to E)/f(x)(greater than or equa l to epsilon)similar or equal to 0.1 B(-5)(-2)xi, where the f(x)(great er than or equal to E) is the energy flux of soft X-rays corrected for absorption, and the factor xi greater than or equal to 1 is introduce d in order to take into account possible differences in the source siz es responsible for the fluxes observed by X-ray and gamma-ray detector s. Since the fluxes of X-ray nebulae with angular size less than a few arcmin are typically at the level of f(x) less than or equal to 10(-1 1) erg cm(-2) s(-1), then the detectability of these objects in TeV ga mma-rays, by current atmospheric Cherenkov telescopes with sensitiviti es a few times 10(-12) erg cm(-2) s(-1), would significantly depend on the ambient magnetic field. In particular, the gamma-ray observabilit y of these X-ray nebulae becomes problematic even for the lowest possi ble magnetic field, i.e. B similar to B(ISM)similar or equal to 3-5 mu G. Otherwise, the detection of gamma-rays from such sources would req uire xi>>1, which implies that in fact the relativistic electrons occu py a significantly larger region around the accelerator than the great er than or equal to 1 arcmin X-ray nebulae resolved by the ROSAT and A SCA satellites. We argue that the invocation of such an hypothesis all ows us to explain satisfactorily the flux of TeV gamma-rays detected f rom the direction of the recently discovered faint X-ray nebula around the pulsar PSR B1706-44.