The isolated neutron star RBS1774 revisited Revised XMM-Newton X-ray parameters and an optical counterpart from deep LBT-observations

We report optical B-band observations with the Large Binocular Telescope LBT of the isolated neutron star RBS1774. The stacked image with total exposure 2. h5 reveals a candidate optical counterpart at mB = 26.96 ± 0.20 at position α(2000) = 21h43m03. s40, δ(2000) = +06◦54′17. ′′5, within the joint Chandra and XMM-Newton error circles. We analyse archival XMM-Newton observations and derive revised spectral and positional parameters. The predicted optical flux from the extrapolated X-ray spectrum is likely twice as high as reported before. The measured optical flux exceeds the extrapolated X-ray spectral flux by a factor ∼ 40 (15 – 60 at 1σ confidence). We interpret our detection and the spectral energy distribution as further evidence of a temperature structure over the neutron star’s surface and present a pure thermal model reflecting both the SED and the pulsed fraction of the light curve.