Day 891

Friday.


1505.Nature
No signature of ejecta interaction with a stellar companion in three type Ia supernovae
Olling, ... Rest, ... Fillippenko, et al

Type Ia SNe are through to be the result of a thermonuclear runaway in C/O WDs, but it is uncertain whether the explosion is triggered by accretion from a non-degenerate companion star or by a merger with another WD.  Observations of a SN immediately following the explosion provide unique information on the distribution of ejected material and the progenitor system.  Models predict that the interaction of SN eject with a companion star or circumstellar debris lead to a sudden brightening lasting from hours to days.  Present data for 3 SNe that are likely to be type Ia observed during the Kepler mission with a time resolution of 30 min.  Find no signature of the SN ejecta interacting with nearby companions.  The lack of observable interaction signatures is consistent wit the idea that these three SNe resulted from the merger of binary WDs or other compact stars such as He stars.


1505.05809
Weak lensing by voids in modified lensing potentials
Barreira, Cautun, Li, Baugh, Pascoli

Study lensing by voids in Cubic Galileon and Nonlocal gravity cosmologies, which are examples of theories of gravity that modify the lensing potential.  Find voids in the DM and halo density fields of N-body sims and compute their lensing signal analytically from the void density profiles, which is shown to be well fit by a simple analytical formula.  In the Cubic Galileon model, the modifications to gravity inside voids are not screened and they approximately double the size of the lensing effects compared to GR.  The difference is largely determined by the direct effects of the fifth force on lensing and less so by the modified density profiles.  For this model, also discuss the subtle impact on the force and lensing calculations caused by the screening effects of haloes that exist in and around voids.  In the Nonlocal model, the impact of the modified density profiles and the direct modifications to lensing are comparable, but they boost the lensing signal by only ~10%, compared with that of GR.  Overall, the results suggest that lensing by voids is a promising tool to test models of gravity that modify lensing.