The Gubser solution to inviscid relativistic fluid dynamics is used to
examine the role of transverse expansion on the energy spectrum of photons
radiated by quark-gluon plasma. Transverse flow is shown to be a modest effect
on the energy spectrum of photons as a whole, despite its large effect on rare
high-energy photons produced at low temperatures. An exact expression is
derived for the volume of the plasma as a function of its temperature. A simple
formula is obtained for the energy spectrum of high-energy thermal photons,
which is used to relate the inverse slope Teff of the photon
spectrum at energy E to the maximum temperature of the plasma T0, finding
Teff≈T0/(1+25ET0).Comment: 6 pages, 5 figures; v2: added exact formula for Gubser volume, fixed
definition of effective temperature, updated text accordingl