Discovery of Extended Infrared Emission around the Neutron Star RXJ0806.4–4123

Abstract

Following up on a faint detection of a near-infrared (NIR) source at the position of the X-ray thermal isolated neutron star RXJ0806.4-4123, we present new Hubble Space Telescope observations in the H-band. The NIR source is unambiguously detected with a Vega magnitude of 23.7 +/- 0.2 (flux density of 0.40 +/- 0.06 mu Jy at lambda = 1.54 mu m). The source position is coincident with the neutron star position, and the implied NIR flux is strongly in excess of what one would expect from an extrapolation of the optical-UV spectrum of RXJ0806.4-4123. The NIR source is extended, with a size of at least 0 8, and shows some asymmetry. The conservative upper limit on the flux contribution of a point source is 50%. Emission from gas and dust in the ambient diffuse interstellar medium can be excluded as a cause for the extended emission. The source parameters are consistent with an interpretation as either the first NIR-only detected pulsar wind nebula or the first resolved disk around an isolated neutron star.