Abstract
Astrophys.J. 579 (2002) L29-L32 Using a very deep observation with HST/STIS, we have searched for an optical
counterpart to the nearby radio-quiet isolated neutron star RX J1308.6+2127
(RBS 1223). We have identified a single object in the 90% Chandra error circle
that we believe to be the optical counterpart. This object has
$m_{50CCD}=28.56\pm0.13$ mag, which translates approximately to an unabsorbed
flux of $F_{\lambda}=(1.7 \pm 0.3)e-20$ ergs/s/cm^2/A at 5150 A or an
X-ray-to-optical flux ratio of $log(f_X/f_opt)=4.9$. This flux is a factor of
$\approx 5$ above the extrapolation of the black-body fit to the X-ray
spectrum, consistent with the optical spectra of other isolated neutron stars.
Without color information we cannot conclude that this source is indeed the
counterpart of RX J1308.6+2127. If not, then the counterpart must have
$m_{50CCD} > 29.6$ mag, corresponding to a flux that is barely consistent with
the extrapolation of the black-body fit to the X-ray spectrum.