Title:
Origin and Equation-of-State of young nearby neutron stars
Abstract:
Recently, 60Fe was found in the Earth crust, which is believed
to have formed in a recent nearby supernova. If the time, distance,
and mass of the progenitor of that supernova would be known,
then one can test and constrain supernova ejecta models.
Knowing the positions, proper motions, and distances of dozens of
young nearby neutron stars (within a few kpc), we can determine
their past flight path and possible kinematic origin. For such
calculations, we have to assume the otherwise unknown radial velocity
through Monte-Carlo simulations. By tracing back its motion, we can
then find the stellar association, in which the neutron star may have
been formed by a recent supernova. If a neutron star seems to have flown
through a nearby young stellar association, where at least one supernova
may have taken place given its current mass function, it may have formed
there. We search for additional indications for such events, like
run-away stars ejected in supernovae in binaries, 26Al emission, etc.
Once the birth place of a neutron star in a supernova is found,
we would have determined the distance of the supernova
and the age of the neutron star (flight time as kinematic age).
If all stars in such an association have formed roughly at the
same time, as assumed by star formation theories and often observed,
we also know the life-time and, hence, mass of the supernova
progenitor star.
In this way, we also try to find the neutron star, which was born
in the nearby recent supernova, which may have ejected the 60Fe
found in the Earth crust. We can then test and calibrate supernova
ejecta models. If 244Pu can be found in the Earth crust with the same
age, too, this would be evidence for the r-process to form 244Pu.
We will also present briefly other neutron stars projects at University
Jena: We study in detail the seven known young nearby isolated, thermally
emitting radio-quiet neutron stars (called Magnificent Seven, M7 NSs),
in order to determine masses and radii to constrain the equation-of-state.
With X-ray observations, we can determine temperatures of the M7.
With optical observations, we can obtain the brightness and, in two
cases (RXJ1856 and RXJ0720), the distance of these NSs. From those values,
we can determine the radii of two NSs. We also try to determine masses of
the NSs from either future gravitational microlensing effects, when the
NSs happen to pass in front of a background star, or by detection and
orbital motion of sub-stellar companions like planets around NSs.
From rotational phase-resolved X-ray spectroscopy, we can now also
determine the compactness (mass/radius), so that it seems feasible
to determine both mass and radius for a few NSs, e.g. RXJ1856 and RXJ0720.