A kilonova associated with GRB 070809

For on-axis typical short gamma-ray bursts (sGRBs), the forward shock emission is usually so bright that renders the identification of kilonovae (also known as macronovae) in the early afterglow ($t<0.5$ d) phase rather challenging. This is why previously no thermal-like kilonova component has been identified at such early time except in the off-axis dim GRB 170817A associated with GW170817. Here we report the identification of an unusual optical radiation component in GRB 070809 at $t\sim 0.47$ d, thanks plausibly to the very-weak/subdominant forward shock emission. The optical emission with a very red spectrum is well in excess of the extrapolation of the X-ray emission that is distinguished by an unusually hard spectrum, which is at odds with the forward shock afterglow prediction but can be naturally interpreted as a kilonova. Our finding supports the speculation that kilonovae are ubiquitous , and demonstrates the possibility of revealing the neutron star merger origin with the early afterglow data of some typical sGRBs that take place well beyond the sensitive radius of the advanced gravitational wave detectors and hence the opportunity of organizing dedicated follow-up observations for events of interest.Comment: 20 pages, 5 figures, published in Nature Astronom

Discovery of gamma-ray emission from a strongly lobe-dominated quasar 3C 275.1

We systematically analyze the 6-year {\it Fermi}/LAT data of the lobe-dominated quasars (LDQs) in the complete LDQ sample from 3CRR survey and report the discovery of high-energy $\gamma$-ray emission from 3C 275.1. The $\gamma$-ray emission of 3C 207 is confirmed and significant variability of the lightcurve is identified. We do not find statistically significant $\gamma$-ray emission from other LDQs. 3C 275.1 is the known $\gamma$-ray quasar with the lowest core dominance parameter (i.e., $R=0.11$). We also show that both the northern radio hotspot and parsec jet models can reasonably reproduce the $\gamma$-ray data. The parsec jet model, however, is favored by the potential $\gamma$-ray variability at the timescale of months. We suggest that some dimmer $\gamma$-ray LDQs will be detected in the future and LDQs could contribute non-negligibly to the extragalactic $\gamma$-ray background.Comment: 26 pages, 10 figures, 3 tables; ApJ in pres

5-(4-Chloro­anilinomethyl­ene)-2,2-dimethyl-1,3-dioxane-4,6-dione

The title compound, C13H12ClNO4, is approximately planar, with a dihedral angle of 8.23 (4)° between the mean plane of the amino­methyl­ene unit and the planar part of the dioxane ring. The dioxane ring has a half-boat conformation, in which the C atom between the dioxane O atoms is −0.464 (8) Å out of the plane of the other five atoms. In the mol­ecule there is an intra­molecular N—H⋯O hydrogen bond, involving the NH H atom and the adjacent dioxane carbonyl O atom. In the crystal, weak intermolecular C—H⋯O hydrogen-bonding contacts, result in the formation of sheets parallel to the ab plane