Speaker
Description
Circumstantial evidence points to binary neutron star (BNS) mergers as the principal source of ultrahigh energy cosmic rays (UCRs), as will be briefly reviewed. This motivates trying to predict consequences of the BNS merger scenario for the UCR spectrum and composition, and also multi-messenger implications in particular gravitational wave-EHE neutrino coincidences. In this talk I will
1) Report briefly on the recent PIC simulation of Comisso et al (2024) showing that acceleration in magnetized turbulence produces the spectrum E^{-2.1} sech[(E/E_cut)^2]. This gives a good fit to UCR spectrum and composition data — much better than the exponential cutoff associated with diffusive shock acceleration (Protheroe&Stanev 1999).
2) Calculate the UCR cutoff rigidity, assuming acceleration occurs in the turbulent outflow (not the jets), initializing the outflow magnetic field with the ultrahigh resolution neutrino-GRMHD simulation of Kiuchi et al 2024 and using a simple treatment of synchrotron emission. The analysis predicts a rigidity (E/Ze) cutoff of 5.5 - 7 EV, consistent with the value 6.8 EV from fitting the Auger spectrum and composition data with the spectrum of magnetized turbulence.
3) Calculate the time delay of an EHE neutrino relative to the associated gravitational wave. The analysis 2) shows that UCRs are predominantly accelerated at a radius of about 10^{14} cm, implying a time-delay of order one day for neutrinos relative to the arrival time of the gravitational wave produced by the merger. With next-generation gravitaional wave and EHE neutrino detectors, such coincidences may be detectable and would provide decisive evidence of this scenario. Coincidences with short GRBs are also a possibility.
4) Outline the calculation required for predicting the composition of UCRs in the BNS merger scenario, and discuss the prediction that UCRs with energies >~ 150 EeV originated as r-process elements such as Tellurium and Xenon.
5) Discuss the principle challenges to this scenario and the most pressing studies which need to be done.
