Detection of GeV Gamma-rays from HESS J1534-571 and Multiwavelength Implications for the Origin of the Non-thermal Emission

Abstract

HESS J1534-571 is a very high energy gamma-ray source that was discovered by the H.E.S.S. observatory and reported as one of several new sources with a shell-like morphology at TeV energies, matching in size and location with the supernova remnant G323.7-1.0 discovered in radio observations by the Molonglo Galactic Plane Survey. Many known TeV shells also show X-ray emission, however, no X-ray counterpart has been seen for HESS J1534-571. The detection of a new GeV source using data from the \emph{Fermi} satellite that is compatible in extension with the radio supernova remnant and shows a very hard power-law spectrum ($\frac{dN}{dE} \propto E^{-1.35}$) is presented here, together with the first broadband modeling of the nonthermal emission from this source. It is shown that leptonic emission is compatible with the known multiwavelength data and a corresponding set of physical source parameters is given. The required total energy budget in leptons is reasonable, $\sim 1.5\times10^{48}$ erg for a distance to the object of $5$ kpc. The new GeV observations imply that a hadronic scenario, on the other hand, requires a cosmic ray spectrum that deviates considerably from theoretical expectations of particle acceleration.