3-Cyano­anilinium hydrogen oxalate hemihydrate

In the title hydrated mol­ecular salt, C7H7N2 +·C2HO4 −·0.5H2O, contains a 3-cyano­anilinium cation, a hydrogen oxalate anion and half a water mol­ecule in an asymmetric unit. The dihedral angle between the CO2(H) and CO2 planes of the hydrogen oxalate ion is 7.96 (1)°. In the crystal, the components are linked by N—H⋯O and O—H⋯O hydrogen bonds, forming a layer lying parallel to the ac plane

Dyson-Schwinger Equations with a Parameterized Metric

We construct and solve the Dyson-Schwinger equation (DSE) of quark propagator with a parameterized metric, which connects the Euclidean metric with the Minkowskian one. We show, in some models, the Minkowskian vacuum is different from the Euclidean vacuum. The usual analytic continuation of Green function does not make sense in these cases. While with the algorithm we proposed and the quark-gluon vertex ansatz which preserves the Ward-Takahashi identity, the vacuum keeps being unchanged in the evolution of the metric. In this case, analytic continuation becomes meaningful and can be fully carried out.Comment: 10 pages, 7 figures. To appear in Physical Review

Nonplanar On-shell Diagrams and Leading Singularities of Scattering Amplitudes

Bipartite on-shell diagrams are the latest tool in constructing scattering amplitudes. In this paper we prove that a Britto-Cachazo-Feng-Witten (BCFW)-decomposable on-shell diagram process a rational top-form if and only if the algebraic ideal comprised of the geometrical constraints is shifted linearly during successive BCFW integrations. With a proper geometric interpretation of the constraints in the Grassmannian manifold, the rational top-form integration contours can thus be obtained, and understood, in a straightforward way. All rational top-form integrands of arbitrary higher loops leading singularities can therefore be derived recursively, as long as the corresponding on-shell diagram is BCFW-decomposable.Comment: 13 pages with 12 figures; final version appeared in Eur.Phys.J. C77 (2017) no.2, 8

5-(Pyridinium-3-yl)tetra­zol-1-ide hexa­aqua­magnesium dichloride

In the title compound, (C6H5N5)2[Mg(H2O)6]Cl2, the asymmetric unit contains one zwitterionic 5-(pyridinium-3-yl)tetra­zol-1-ide mol­ecule, one half of an [Mg(H2O)6]2+ cation ( symmetry) and one chloride ion. The MgII ion is surrounded by six water mol­ecules, with their O atoms located at the apices, exhibiting a slightly distorted octa­hedral coordination. Mg—O bond lengths range from 2.0526 (14) to 2.0965 (16) Å [mean value = 2.068 Å]. The pyridine and tetra­zole rings are nearly coplanar and only twisted from each other by a dihedral angle of 5.68 (1)°. The zwitterionic organic mol­ecules, anions and cations are connected by O—H⋯Cl, O—H⋯N and N—H⋯Cl hydrogen bonds, leading to the formation of a three-dimensional network

Revisiting the distance, environment and supernova properties of SNR G57.2+0.8 that hosts SGR 1935+2154

We have performed a multi-wavelength study of supernova remnant (SNR) G57.2+0.8 and its environment. The SNR hosts the magnetar SGR 1935+2154, which emitted an extremely bright ms-duration radio burst on 2020 Apr 28 (The Chime/Frb Collaboration et al. 2020; Bochenek et al. 2020). We used the 12CO and 13CO J=1-0 data from the Milky Way Image Scroll Painting (MWISP) CO line survey to search for molecular gas associated with G57.2+0.8, in order to constrain the physical parameters (e.g., the distance) of the SNR and its magnetar. We report that SNR G57.2+0.8 is likely impacting the molecular clouds (MCs) at the local standard of rest (LSR) velocity V_{LSR} ~ 30 km/s and excites a weak 1720 MHz OH maser with a peak flux density of 47 mJy/beam. The chance coincidence of a random OH spot falling in the SNR is <12%, and the OH-CO correspondence chance is 7% at the maser spot. This combines to give < 1% false probability of the OH maser, suggesting a real maser detection. The LSR velocity of the MCs places the SNR and magnetar at a kinematic distance of d=6.6 +/- 0.7 kpc. The nondetection of thermal X-ray emission from the SNR and the relatively dense environment suggests G57.2+0.8 be an evolved SNR with an age $t>1.6 \times 10^4$ (d/6.6 kpc) yr. The explosion energy of G57.2+0.8 is lower than $2 \times 10^{51}(n_0/10 cm^{-3})^{1.16} (d/~6.6 kpc)^{3.16}$ erg, which is not very energetic even assuming a high ambient density $n_0$ = 10 cm$^{-3}$. This reinforces the opinion that magnetars do not necessarily result from very energetic supernova explosions.Comment: 9 pages, 5 figures, accepted for publication in the Astrophysical Journa