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

TL;DR

This study identifies a potential optical counterpart to the neutron star RBS1774, revises its X-ray parameters, and suggests a complex surface temperature structure based on combined optical and X-ray data.

Contribution

It provides the first optical detection of RBS1774 and offers revised X-ray spectral and positional parameters with a thermal model explaining the spectral energy distribution.

Findings

Optical counterpart candidate at mB = 26.96 ± 0.20

Revised XMM-Newton spectral and positional parameters

Optical flux exceeds X-ray extrapolation by factor ~40

Abstract

We report optical B-band observations with the Large Binocular Telescope LBT of the isolated neutron star RBS1774. The stacked image with total exposure 2.5h reveals a candidate optical counterpart at mB = 26.96 +- 0.20 at position RA(2000) = 21:43:03.4, DEC(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 1sigma 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.