Evidence for a decreasing X-ray afterglow emission of GW170817A and GRB 170817A in XMM-Newton [HEAP]

http://arxiv.org/abs/1801.06164


We report our observation of the short GRB 170817A, associated to the binary neutron star merger event GW 170817, perfomed in the X-ray band with XMM-Newton 135 d after the event (on the 29th December 2017). We find that the X-ray light curve started to decrease with respect to the previous steadily brightening trend. This is also supported by a nearly simultaneous optical Hubble Space Telescope observation. Since the optical-to-X-ray spectral slope did not change with respect to previous observations, we exclude that the decrease in flux is due to the passage of the cooling frequency: its origin must be geometric or dynamical. We interpret all the existing afterglow data with two models: i) a structured jet and ii) a jet-less isotropic fireball with some stratification in its radial velocity structure. Both models fit the data and predict that the radio flux must decrease simultaneously with the optical and the X-ray one, making hard to distinguish between them at the present stage. Polarimetric measures and the rate of short GRB-GW association in future LIGO/Virgo runs will be key to disentangle these two geometrically different scenarios.

Read this paper on arXiv…

P. DAvanzo, S. Campana, G. Ghisellini, et. al.
Fri, 19 Jan 18
51/68

Comments: Letter submitted to Astronomy & Astrophysics. Other authors will be added to the present author list as soon as they have permission from the respective collaborations