English: Timeline of the discovery of GW170817, GRB 170817A, SSS17a/AT 2017gfo, and the follow-up observations are shown by messenger and wavelength relative to the time tc of the gravitational-wave event. Two types of information are shown for each band/messenger. First, the shaded dashes represent the times when information was reported in a GCN Circular. The names of the relevant instruments, facilities, or observing teams are collected at the beginning of the row. Second, representative observations in each band are shown as solid circles with their areas approximately scaled by brightness; the solid lines indicate when the source was detectable by at least one telescope. Magnification insets give a picture of the first detections in the gravitational-wave, gamma-ray, optical, X-ray, and radio bands. They are respectively illustrated by the combined spectrogram of the signals received by LIGO-Hanford and LIGO-Livingston (see Section 2.1), the Fermi-GBM and INTEGRAL/SPI-ACS lightcurves matched in time resolution and phase, 1'5 × 1'5 postage stamps extracted from the initial six observations of SSS17a/AT 2017gfo and four early spectra taken with the SALT (at tc + 1.2 days; Buckley et al. 2017; McCully et al. 2017b), ESO-NTT (at tc + 1.4 days; Smartt et al. 2017), the SOAR 4 m telescope (at tc + 1.4 days; Nicholl et al. 2017d), and ESO-VLT-XShooter (at tc + 2.4 days; Smartt et al. 2017) as described in Section 2.3, and the first X-ray and radio detections of the same source by Chandra and JVLA. In order to show representative spectral energy distributions, each spectrum is normalized to its maximum and shifted arbitrarily along the linear y-axis (no absolute scale). The high background in the SALT spectrum below 4500 Å prevents the identification of spectral features in this band.