  Dilepton production in In+In collisions at 158 AGeV is studied within the
microscopic parton-hadron-string dynamics (PHSD) transport approach that
incorporates explicit partonic degrees-of-freedom, dynamical hadronization as
well as the more familiar hadronic dynamics in the final reaction stages. A
comparison to the data of the NA60 Collaboration shows that the measured
dilepton yield is well described by including the collisional broadening of
vector mesons, while simultaneously accounting for the electromagnetic
radiation of the strongly coupled quark-gluon plasma (sQGP) via off-shell
quark-antiquark annihilation, quark annihilation with additional gluon
Bremsstrahlung and the gluon-Compton scattering mechanisms. In particular, the
spectra in the intermediate mass range (1 GeV < M < 2.5 GeV) are dominated by
quark-antiquark annihilation in the nonperturbative QGP. Also, the observed
softening of the transverse mass spectra at intermediate masses (1 GeV < M <
2.5 GeV) is approximately reproduced. Furthermore, for dileptons of low masses
(M < 0.6 GeV), we find a sizable contribution from the quark annihilation with
additional gluon bremsstrahlung, thus providing another possible window for
probing the properties of the sQGP.
