Donnarumma, Immacolata

A new insight into the innermost jet regions: probing extreme jet variability with LOFT.

Author list: I. Donnarumma on behalf of the LOFT Consortium

Blazars are highly variable sources over timescales that can be as low as minutes.This is  the case of the High Energy Peaked BL Lac objects which show strong variability in X-rays, which highly correlate with that of the TeV emission. The degree of this correlation is still debated, particularly when the flaring activity is followed down to very short time scales. This correlation could challenge the synchrotron-self-Compton scenario in which one relativistic electron population dominates the entire radiative output. We argue that the LOFT Large Area Detector (10 m^2, LAD), thanks to its unprecedented timing capability, should allow to detect the X-ray counterpart (2-50 keV) of the the very fast variability observed at TeV energies, sheding light on the nature of X-TeV connection.  We will discuss some test cases (e.g. PKS 2155-304), showing as it would be possible to look for any X-ray variability occurring at very short timescales, ever explored so far. This will put strong constraints on the size and the location of any additional electron population in the multi-zone scenario. Under this perspective, we will analyze the synergies between LOFT and the CTA observatories, planned to operate in the same time frame. Finally, perspectives  on the study of FSRQs will be also discussed.