Gravitational microlensing of high-redshift supernovae by compact objects

An analysis of the effect of microlensing by a cosmologically dominant density of compact objects is performed, using high-redshift Type Ia supernovae (SN Ia's) as probes. The compact objects are modeled as a three-dimensional distribution of point masses, and Monte Carlo simulations are done to calculate the resulting amplification probability distributions for several column densities and cosmologies. By combining these distributions with the intrinsic SN Ia luminosity function and comparing with the results for a perfectly smooth universe, estimates are made of the number of supernovae that would need to be observed to confirm or rule out this lensing scenario. It is found that ~ 1000 SN Ia's with redshifts of z ~ 1 would be needed to perform this test, which is beyond what current searches can hope to accomplish. Observations of many fewer high- redshift supernovae, used merely as standard candles, appears a promising way of distinguishing between different cosmological models. Although not detectable in current supernova surveys, the high- redshift SN Ia's should be present in deep CCD images made for other purposes; we estimate that in an ω = 1 universe with H₀_ = 50 km s^-1^ Mpc^-1^ approximately 8 SN Ia's arcmin^-2^ should be present at any instant at redshifts of z <= 0. 5 (mB_ <= 25). They would be distinguished from other objects (e. g. , galaxies) by their transient nature. By simply counting the number of variable objects in frames taken at different epochs, an upper limit on the number of supernovae (or the fraction of variable objects which can be attributed to supernova events) can be made.