A likely optical counterpart of the G292.0+1.8 pulsar wind nebula. ⋆

Abstract

Context. G292.0+1.8 is the Cas A-like supernova remnant containing the young pulsar PSR J1124-5916, which powers a compact torus-like pulsar wind nebula with a jet visible in X-rays. Aims. We have performed deep optical observations of the pulsar fie ld to detect the optical counterpart of the pulsar and its neb ula. Methods. The observations were carried out using the direct imaging mode of FORS2 at the ESO VLT/UT1 telescope in the V, R, and I bands. We also analyzed archival images obtained with the Chandra/ACIS-I, ACIS-S, and HRC-S in X-rays. Results. In all three optical bands we detect a faint elliptical nebul osity, whose brightness peak and center position are consistent at a sub-arcsecond level with the X-ray position of the pulsar. The field is densely packed with background stars, but after s ubtraction of these stars the morphology of the object and the orientation of its major axis appear to be in a good agreement with the brightest inner part of the pulsar nebula torus region seen almost edge on in X-rays. Within the nebulosity we do not resolve any point-like optical object that could be identified with the pulsar and estimate i ts contribution to the observed nebulosity flux as <20%. Extracting the X-ray spectrum from the physical region equivalent to the optical source position and extent and combining that with the measured optical fluxes, we compile a tentative multi-wavelength spe ctrum of the inner part of the nebula. Within uncertainties of the interstellar extinction towards G292.0+1.8 it is reminiscent of either the Crab or PSR B540-69 and J0205+6449 pulsar wind nebula spectra. Conclusions. The position, morphology, and spectral properties of the detected nebulosity suggest that it is the likely optical coun terpart of the pulsar plus its wind nebula system in G292.0+1.8. Higher spatial resolution optical observations and th e extension of the broad-band spectrum of the proposed counterpart candidate towards the IR and UV are necessary to confirm its origin.