Fermi Gamma-ray Space Telescope

Testing the closure relations for GRBs presenting plateau emission

Maria Dainotti
(Giacomo Vianello, Nicola Omodei,Vahe' Petrosian)


Very surprisingly the analysis of the LAT lightcurves shows the presence of breaks (Omodei et al. 2012), providing a possible difficulty for the synchrotron models. The Swift Satellite provides a rapid follow up of the afterglows in several wavelengths, that reveals even a more complex behavior of the lightcurves. In fact, a large number of afterglows are considerably deviating from the broken power-law seen in the past (OBrien et al. 2006, Sakamoto et al. 2007), and in a significant fraction of GRBs, a ``Steep--Flat--Steep" trend (Tagliaferri et al. 2005, Nousek et al. 2006) shows the existence of a plateau lasting from hundreds to a few thousands seconds (Willingale et al. 2007; Dainotti et al. 2008,2010). The presence of the plateu emission in the X-ray band, whose nature remains still a mystery, arises a natural question: whether or not the late flattening seen in the $gamma$-ray emission is the beginning of the same plateau seen in X-ray. The plateau emission observed in BAT+XRT gives a fundamental tool to understand if the $gamma$-ray and the X-ray emissions are correlated and if the breaks we see in these two bands are achromatic. Another important question is whether the mechanism that powers the plateau in X-rays is the same as in $gamma$-rays.We will test for a handful of LAT lightcurves consistent with the X-ray plateaus if they obey the closure relations.