GCN Circular 22201
E. Troja (UMD/GSFC), L. Piro (INAF/IAPS), G. Ryan (UMD), H. van Eeerten (U. Bath), T. Sakamoto (AGU), and S. B. Cenko (NASA/GSFC) report: The Chandra X-ray Observatory re-observed the field of GW170817/AT2017gfo (PI: B. Wilkes) starting on 2017-12-03 (~109 days after the LVC trigger) for a total exposure of 74 ks. A second shorter observation was performed on 2017-12-06 for a total exposure of 25 ks. Our preliminary analysis of the data clearly detects the X-ray counterpart of AT2017gfo at a flux level of ~1.5E-14 erg/cm^2/s (0.5-8.0 keV). The observed value is three times higher than the flux measured at earlier times (~5E-15 erg/cm^2/s at 15 days; Troja, E., et al. 2017, Nature, 551, 71) and implies a continued rise of the X-ray afterglow. We do not measure any significant spectral variation between these observations and our observations at earlier times. This behavior is hard to reconcile with the simple top-hat jet model and suggests a more complex structure of the GRB jet. We thank Belinda Wilkes, Andrea Prestwich and the entire Chandra for performing these observations.