SIMBAD references

We investigate the constraints imposed on the luminosity function (LF) of long duration gamma ray bursts (LGRBs) by the flux distribution of bursts detected by the GBM at ∼1MeV, and the implications of the non detection of the vast majority, ∼95%, of the LGRBs at higher energy, ∼1GeV, by the LAT detector. We find a LF that is consistent with those determined by BATSE and Swift. The non detections by LAT set upper limits on the ratio R of the prompt fluence at ∼1GeV to that at ∼1MeV. The upper limits are more stringent for brighter bursts, with upper limits on R<{0.1,0.3,1} for {5,30,60}% of the bursts. This implies that for most bursts the prompt ∼1GeV emission may be comparable to the ∼1MeV emission, but can not dominate it. The value of R is not universal: the measured values and upper limits imply that R ranges over (at least) an order of magnitude around 0.1. For several bright bursts with reliable determination of the photon spectral index at ∼1MeV, the LAT non detection implies an upper limit to the ∼100MeV flux which is <0.1 of the flux obtained by extrapolating the ∼1MeV flux to high energy. For the widely accepted models, in which the ∼1MeV power-law photon spectrum reflects the power-law energy distribution of fast cooling electrons, this suggests that either the electron energy distribution does not follow a power-law over a wide energy range, or that the high energy photons are absorbed. Requiring an order unity pair production optical depth at 100MeV sets an upper limit for the Lorentz factor, Γ≲10^2.5.