November 2013 – January 2015, Japan Society for Promotion of Science Fellowship, Riken, Japan

Conduct a full time research project from the title “GRB relations and their theoretical interpretation”. Mentored 1 student in summer and in winter. Participation as a local organizer for the Conferences held at Riken in this period and participation to the Open House at Riken.

Key achievements:

  • Devised a general method to build mock datasets, which takes into account selection effects on both the time and the luminosity (Dainotti et al. 2015a). This method shows how not knowing the efficiency function of the instrument detecting GRBs could influence the evaluation of the intrinsic slope of any correlation and the GRB density rate. Dainotti et al. (2015a) showed that the intrinsic slope of the LT correlation is -1.0. This method is general, therefore relevant to investigate if any other GRB relation is generated by the biases themselves. Moreover, Dainotti et al. (2015a) evaluated the redshift-dependent ratio Psi(z)=(1+z)^alpha of the GRB rate to the star formation rate. They found a modest evolution -0.2< alpha< 0.5 consistent with Swift GRB afterglow plateau in the redshift range 0.99<z<9.4.
  • The interpretation of the La-Ta intrinsic correlation, corrected by selection bias, within the context of a central engine origin (Rownlinson et al. 2014). Rownlinson et al. (2014) suggested that the magnetar model predicts an observable plateau phase, with plateau durations and luminosities being determined by the magnetic fields and spin periods of the newly formed magnetar. This paper analytically shows that the magnetars can explain, within the 1 sigma uncertainties, the La-Ta intrinsic correlation.
  • The use of the La-Ta relation as a possible cosmological tool is presented in Postnikov et al. (2014), where they constrained the cosmological equation of state as a function of redshift, w(z), up to z=9.4 in a completely non-parametric way, without imposing any a priori functional form for w(z). To avoid the circularity problem, Postnikov et al. (2014) calibrated the GRBs at high redshift using the slope and normalization of the La-Ta correlation at low redshift in the same range of the SNe Ia. Within the assumption of a flat Friedmann-Lemaître-Robertson-Walker universe and combining SNe Ia data with baryonic acoustic oscillation constraints, the resulting maximum likelihood solutions are close to a constant w = -1.