Day 1521

Friday.

1901.00507
Detecting dark matter cores in galaxy clusters with strong lensing
Andrade, Minor, Nierenberg, Kaplinghat

Test the ability of strong lensing data to constrain the size of a central core in the DM halo of galaxy clusters, using Abell 611 as a prototype.  Using simulated data, show that modeling a cluster halo with ellipticity in the gravitational potential can bias the inferred mass and concentration, which may bias the inferred central density when weak lensing or X-ray data are added.  Also highlight the possibility for spurious constraints on the core size if the radial density profile is different from the assumed model.  These systematics can be ameliorated if central images are present in the data.  Applying the methodology to Abell 611 and imposing a reasonable prior on the stellar mass-to-light ratio restricts the core size to be less than about 4 kpc, with a minimum reduced chi^2 of 0.28 for 0."2 positional errors  Such small cores imply a constraint on the dark matter self-interaction cross section of the order of 0.1 cm^2/g at relative velocities of about 1500 km/s.


1901.00508
Turning up the heat on `Oumuamua
Forbes, Loeb

Explore what may be learned by close encounters between extrasolar minor bodies like `Oumuamua and the Sun.  These encounters may yield strong constraints on the bulk composition and possible origin of `Oumuamua-like objects.  Find that such objects collide with the Sun once every 30 years, while about 2 pass pithing the orbit of Mercury each year.  Identify preferred orientations for the orbits of extrasolar objects and point out known SS bodies with these orientations.  Conclude using a simple Bayesian analysis that about one of these objects is extrasolar in origin, even if we cannot tell which.


1901.00627
Filaments of galaxies as a clue to the origin of ultra-high-energy cosmic rays
Kim, et al

UHECRs are known to come from outside of our Galaxy, but their origin still remains unknown.  The Telescope Array (TA) experiment recently identified a high concentration in the arrival directions of UHECRs with energies above 5.7e19 eV, called the hotspot.  Here, report the presence of filaments of galaxies, connected to the Virgo Cluster, on the sky around the hotspot, and a statistically significant correlation between hotspot events and the filaments.  With 5-year TA data, the maximum significance of binomial statistics for the correlation is estimated to be 6.1 sigma at correlation angle 3.4 degree.  The probability that the above significance appears by chance is ~2e-8 (5.6 sigma).  Based on this finding, suggest a model for the origin of TA hotspot UHECRs; they are produced at sources in the Virgo Cluster, and escape to and propagate along filaments, before they are scattered towards us.  This picture requires the filament magnetic fields of strength >~20 nG, which needs to be confirmed in future observations.