English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We present the spectroscopic evolution of AT 2017gfo, the optical counterpartof the first binary neutron star (BNS) merger detected by LIGO and Virgo,GW170817. While models have long predicted that a BNS merger could produce akilonova (KN), we have not been able to definitively test these models untilnow. From one day to four days after the merger, we took five spectra of AT2017gfo before it faded away, which was possible because it was at a distanceof only 39.5 Mpc in the galaxy NGC 4993. The spectra evolve from blue($\sim6400$K) to red ($\sim3500$K) over the three days we observed. The spectraare relatively featureless --- some weak features exist in our latest spectrum,but they are likely due to the host galaxy. However, a simple blackbody is notsufficient to explain our data: another source of luminosity or opacity isnecessary. Predictions from simulations of KNe qualitatively match the observedspectroscopic evolution after two days past the merger, but underpredict theblue flux in our earliest spectrum. From our best-fit models, we infer that AT2017gfo had an ejecta mass of $0.03M_\odot$, high ejecta velocities of $0.3c$,and a low mass fraction $\sim10^{-4}$ of high-opacity lanthanides andactinides. One possible explanation for the early excess of blue flux is thatthe outer ejecta is lanthanide-poor, while the inner ejecta has a higherabundance of high-opacity material. With the discovery and follow-up of thisunique transient, combining gravitational-wave and electromagnetic astronomy,we have arrived in the multi-messenger era.

The Rapid Reddening and Featureless Optical Spectra of the optical counterpart of GW170817, AT 2017gfo, During the First Four Days