Early X-Ray Flares in GRBs

We analyze the early X-ray flares in the GRB ``flare--plateau--afterglow'' (FPA) phase observed by Swift-XRT. The FPA occurs only in one of the seven GRB subclasses the binary-driven hypernovae (BdHNe). This subclass consists of long GRBs with a carbon--oxygen core and a neutron star (NS) binary companion as progenitors. The hypercritical accretion of the supernova (SN) ejecta onto the NS can lead to the gravitational collapse of the NS into a black hole. Consequently, one can observe a GRB emission with isotropic energy {E}<SUB>{iso</SUB>}≳ {10}<SUP>52</SUP> erg, as well as the associated GeV emission and the FPA phase. Previous work had shown that gamma-ray spikes in the prompt emission occur at ~ {10}<SUP>15</SUP>{--}{10}<SUP>17</SUP> cm with Lorentz Gamma factors {{Gamma }}~ {10}<SUP>2</SUP>{--}{10}<SUP>3</SUP>. Using a novel data analysis, we show that the time of occurrence, duration, luminosity, and total energy of the X-ray flares correlate with E <SUB>iso</SUB>. A crucial feature is the observation of thermal emission in the X-ray flares that we show occurs at radii ~10<SUP>12</SUP> cm with {{Gamma }}≲ 4. These model-independent observations cannot be explained by the ``fireball'' model, which postulates synchrotron and inverse-Compton radiation from a single ultrarelativistic jetted emission extending from the prompt to the late afterglow and GeV emission phases. We show that in BdHNe a collision between the GRB and the SN ejecta occurs at ~=10<SUP>10</SUP> cm, reaching transparency at ~10<SUP>12</SUP> cm with {{Gamma }}≲ 4. The agreement between the thermal emission observations and these theoretically derived values validates our model and opens the possibility of testing each BdHN episode with the corresponding Lorentz Gamma factor.