MUSE observations of the optical nebula surrounding the central compact object in the Vela Junior Supernova Remnant

Abstract

Central Compact Objects (CCOs), neutron stars found near the centre of some Supernova Remnants (SNRs), have been almost exclusively studied in X-rays and are thought to lack the wind nebulae typically seen around young, rotation-powered pulsars. We present the first, spatially-resolved, morphological and spectroscopic study of the optical nebula observed at the location of CXOU J085201.4-461753, the CCO in the heart of the Vela Junior SNR. It is currently the only Galactic CCO with a spatially coincident nebula detected at optical wavelengths, whose exact nature remains uncertain. New MUSE integral field spectroscopy data confirm that the nebula, shaped like a smooth blob extending 8" in diameter, is dominated by [N II]$\lambda\lambda$6548,6583 emission. The data reveals a distinct and previously unobserved morphology of the H$\alpha$ emission, exhibiting an arc-like shape reminiscent of a bow shock nebula. We observe a significantly strong [N II] emission relative to H$\alpha$, with the [N II]$\lambda\lambda$6548,6583 up to 34 times the intensity of the H$\alpha$ emission within the optical nebula environment. Notably, the [N II] and H$\alpha$ structures are not spatially coincident, with the [N II] nebula concentrated to the south of the CCO and delimited by the H$\alpha$ arc-like structure. We detect additional emission in [N I], He I, [S II], [Ar III], [Fe II], and [S III]. We discuss our findings in the light of a photoionization or Wolf-Rayet nebula, pointing to a very massive progenitor and further suggesting that very massive stars do not necessarily make black holes.