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DECAYING DARK-MATTER; COSMOLOGICAL CONSTRAINTS; CDMAstronomy & Astrophysics; stars: neutron; pulsars: general; X-rays: individuals: eRASSU
J131716.9-402647;
Abstract:
The X-ray source eRASSU J131716.9-402647 was recently identified from observations with Spectrum Roentgen Gamma (SRG)/eROSITA as a promising X-ray dim isolated neutron star (XDINS) candidate on the premise of a soft energy distribution, absence of catalogued counterparts, and a high X-ray-to-optical flux ratio. Here, we report the results of a multi-wavelength observational campaign with XMM-Newton, NICER and the FORS2 instrument at the ESO-VLT. We found in both the XMM-Newton and NICER data that the X-ray emission is strongly pulsed at a period of 12.757 s (pulsed fraction pf = (29.1 +/- 2.6)% in the 0.2-2 keV band). The pulse profile is double-humped, and the pulsed fraction increases with energy. The XMM-Newton and NICER epochs allow us to derive a 3 sigma upper limit of. P <= 8 x 10(-11) s s(-1) on the spin-down rate of the neutron star. The source spectrum is well described by a purely thermal continuum, either a blackbody with kT similar to 95 eV or a magnetised neutron star atmosphere model with kT similar to 35 eV. Similarly to other thermally emitting isolated neutron stars, we found in either case strong deviations from the continuum, a broad absorption feature at energy similar to 260 eV and a narrow one around 590 eV. The FORS2 instrument at ESO-VLT has not detected the optical counterpart (mR > 27.5 mag, 5 sigma detection limit), implying an X-ray-to-optical flux ratio of 104 at least. The properties of eRASSU J131716.9-402647 strongly resemble those of a highly magnetised isolated neutron star and favour an XDINS or high-B pulsar nature.
