Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics

We present new observations of the early X-ray afterglows of the first 27 gamma-ray bursts (GRBs) detected with the Swift X-ray Telescope (XRT). The early X-ray afterglows show a canonical behavior, where the light curve broadly consists of three distinct power law segments: (i) an initial very steep decay (t^{-alpha} with 34, and augments the already severe requirements for the efficiency of the prompt gamma-ray emission.Comment: 35 pages, 8 figures, accepted for publication in Ap

GROWTH observations of GW170817: The gravitational wave event GW170817 was caused by the merger of two neutron stars (see the Introduction by Smith). In three papers, teams associated with the GROWTH (Global Relay of Observatories Watching Transients Happen) project present their observations of the event at wavelengths from x-rays to radio waves. Evanset al.used space telescopes to detect GW170817 in the ultraviolet and place limits on its x-ray flux, showing that the merger generated a hot explosion known as a blue kilonova. Hallinanet al.describe radio emissions generated as the explosion slammed into the surrounding gas within the host galaxy. Kasliwalet al.present additional observations in the optical and infrared and formulate a model for the event involving a cocoon of material expanding at close to the speed of light, matching the data at all observed wavelengths.Science, this issue p.1565, p.1579, p.1559; see also p.1554