Gamma-Ray Bursts and Macronova (Summarized by Tsvi Piran)

Open questions concerning long GRBs progenitors: 
-What are the progenitors of long GRBs ? 
-Central engine models (either accreting Black Hole or magnetars) require rotation and possibly strong magnetic fields. Are these clues? 
-Low metallically is observed for the hosts. Is this a clue? Is this an observational bias? 
-Low metallicity favors faster rotation. Is this a clue? 

Open questions concerning Macronova (and short GRBs)
-Mass ejection in neutron star mergers and Macronova
  -The interpretation of the IR signal following GRB 130603B as a macronova requires significant mass ejection (> 0.02 Msun and possibly as much as 0.04 Msun).  Is this compatible with current theoretical estimates?  In simulations for neutron star mergers the largest tidally ejected mass is around 0.02Msun. Is this valid? 
  -What is the influence of EOS and other microphysics effects on mass ejection? As the EOS becomes harder there is less dynamical ejecta but more interaction component, the sum is roughly constant.
  -The disk mass is ~ 0.05-0.2 Msun. Possibly ~ .2-.25 of the disk is ejected via viscous ejection. Neutrino wind From the HMNS is  up to 0.01 Msun with higher Ye. Together there is about 0.04 Msun. 
  -The heating rate is critical in determining the luminosity of macronova and hence the required ejected mass. What is the exact heating rate and energy deposition? What are the effects on heating of leakage of gamma-rays? Heating from High Ye matter is stronger by a factor of 2.  This helps the mass problem.

-BH-ns mergers 
  -Another macronova candidate (submitted) requires ejection of >0.1 Msun.  Should we reject this outright or is BH-ns merger compatible? 
  -A BH in BH-ns merger that ejects significant mass should be rather small and fast rotating – is this possible? 
  -For an “interesting” BH-ns merger we need a low mass ns with a rapidly spinning Black hole. For a small mass ns the crust is larger hence slightly higher Ye.  More heating at late time? 

-Neutrino winds
  -Different neutrino luminosities in different simulations. Higher luminosities at a very early stage will impact the Ye of the ejecta. At the moment there is large discrepancy between 50 to 300 Bethe/sec.
  -The GRB jet has to cross the neutrino wind. This may depend on details of the wind structure. The neutrino wind may have a funnel around the axis. The wind may help collimating the GRB jet. 

-Rates and the origin of r-process material
  -What is the rate of mergers? Comparison of different estimates using different methods (note the critical dependence on assumed beaming and minimal energy for estimates based on observations of short GRBs). 
  -Do we need another fast source of r-process or are there enough early ns mergers to explain the observed r-process material in low metallicity stars? 
  -Does the excess of 244Pu in the early solar system imply a nearby r-process event? 
  -What is the lifetime of HMNS before it collapses to a black hole?