GROJ1750-27: a neutron star far behind the Galactic Center switching into the propeller regime. (arXiv:1902.05153v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Lutovinov_A/0/1/0/all/0/1">A.Lutovinov</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Tsygankov_S/0/1/0/all/0/1">S.Tsygankov</a> (2,1), <a href="http://arxiv.org/find/astro-ph/1/au:+Karasev_D/0/1/0/all/0/1">D.Karasev</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Molkov_S/0/1/0/all/0/1">S.Molkov</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Doroshenko_V/0/1/0/all/0/1">V.Doroshenko</a> (3) (1 – Space Research Institute, Moscow, 2 – University of Turku, 3 – Institut f&#xfc;r Astronomie und Astrophysik, T&#xfc;bingen)

We report on analysis of properties of the X-ray binary pulsar GROJ1750-27
based on X-ray (Chandra, Swift, and Fermi/GBM), and near-infrared (VVV and
UKIDSS surveys) observations. An accurate position of the source is determined
for the first time and used to identify its infrared counterpart. Based on the
VVV data we investigate the spectral energy distribution (SED) of the
companion, taking into account a non-standard absorption law in the source
direction. A comparison of this SED with those of known Be/X-ray binaries and
early type stars has allowed us to estimate a lower distance limit to the
source at $>12$ kpc. An analysis of the observed spin-up torque during a giant
outburst in 2015 provides an independent distance estimate of $14-22$ kpc, and
also allows to estimate the magnetic field on the surface of the neutron star
at $Bsimeq(3.5-4.5)times10^{12}$ G. The latter value is in agreement with the
possible transition to the propeller regime, a strong hint for which was
revealed by Swift/XRT and Chandra. We conclude that GROJ1750-27 is located far
behind the Galactic Center, which makes it one of the furthest Galactic X-ray
binaries known.

We report on analysis of properties of the X-ray binary pulsar GROJ1750-27
based on X-ray (Chandra, Swift, and Fermi/GBM), and near-infrared (VVV and
UKIDSS surveys) observations. An accurate position of the source is determined
for the first time and used to identify its infrared counterpart. Based on the
VVV data we investigate the spectral energy distribution (SED) of the
companion, taking into account a non-standard absorption law in the source
direction. A comparison of this SED with those of known Be/X-ray binaries and
early type stars has allowed us to estimate a lower distance limit to the
source at $>12$ kpc. An analysis of the observed spin-up torque during a giant
outburst in 2015 provides an independent distance estimate of $14-22$ kpc, and
also allows to estimate the magnetic field on the surface of the neutron star
at $Bsimeq(3.5-4.5)times10^{12}$ G. The latter value is in agreement with the
possible transition to the propeller regime, a strong hint for which was
revealed by Swift/XRT and Chandra. We conclude that GROJ1750-27 is located far
behind the Galactic Center, which makes it one of the furthest Galactic X-ray
binaries known.

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