HESS J1507-622: A Plausible Young Galactic Kilonova Remnant

HESS J1507-622 is an unusual TeV gamma-ray source from the H.E.S.S. Galactic Plane Survey, notable for its off-plane location (b ≈ -3.5°) and compact angular extent (~0.3°). Its location and morphology challenge conventional pulsar wind nebula and supernova remnant interpretations, and the absence of a detected shell or associated pulsar leaves its origin unresolved.

The authors propose that HESS J1507-622 is a young Galactic kilonova remnant with gamma-ray emission of leptonic origin. In this scenario, the source's off-plane location is naturally explained by the natal kick imparted to the progenitor binary neutron star system. A leptonic kilonova remnant model can reproduce the observed GeV-TeV flux via inverse-Compton scattering from shock-accelerated electrons, while the corresponding synchrotron emission remains below current X-ray and radio upper limits. From the source's energetics and angular size, they infer a distance of 3.8-14.3 kpc and an age of 0.2-3.0 kyr, with the analysis favoring a remnant younger than 1 kyr.

The lack of a historical naked-eye record can be explained by the transient's rapid fading, far-southern declination, and potential line-of-sight extinction. The authors also assess detectability of unique multi-wavelength signatures that could confirm the hypothesis. They find promising prospects for detecting MeV gamma rays from the decay of r-process radioisotopes using future observatories, alongside complementary low-energy signatures from thermal dust emission and a possible optical light echo. These distinct signals would offer definitive tests of the kilonova remnant interpretation and motivate targeted observations with current and future facilities.