A Wolf-Rayet-like progenitor of SN 2013cu from spectral observations of a stellar wind.

The explosive fate of massive Wolf-Rayet stars (WRSs) is a key open question in stellar physics. An appealing option is that hydrogen-deficient WRSs are the progenitors of some hydrogen-poor supernova explosions of types IIb, Ib and Ic (ref. 2). A blue object, having luminosity and colours consistent with those of some WRSs, has recently been identified in pre-explosion images at the location of a supernova of type Ib (ref. 3), but has not yet been conclusively determined to have been the progenitor. Similar work has so far only resulted in non-detections. Comparison of early photometric observations of type Ic supernovae with theoretical models suggests that the progenitor stars had radii of less than 10(12) centimetres, as expected for some WRSs. The signature of WRSs, their emission line spectra, cannot be probed by such studies. Here we report the detection of strong emission lines in a spectrum of type IIb supernova 2013cu (iPTF13ast) obtained approximately 15.5 hours after explosion (by 'flash spectroscopy', which captures the effects of the supernova explosion shock breakout flash on material surrounding the progenitor star). We identify Wolf-Rayet-like wind signatures, suggesting a progenitor of the WN(h) subclass (those WRSs with winds dominated by helium and nitrogen, with traces of hydrogen). The extent of this dense wind may indicate increased mass loss from the progenitor shortly before its explosion, consistent with recent theoretical predictions

The Evolution of Compact Binary Star Systems

We review the formation and evolution of compact binary stars consisting of white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and BHs are thought to be the primary astrophysical sources of gravitational waves (GWs) within the frequency band of ground-based detectors, while compact binaries of WDs are important sources of GWs at lower frequencies to be covered by space interferometers (LISA). Major uncertainties in the current understanding of properties of NSs and BHs most relevant to the GW studies are discussed, including the treatment of the natal kicks which compact stellar remnants acquire during the core collapse of massive stars and the common envelope phase of binary evolution. We discuss the coalescence rates of binary NSs and BHs and prospects for their detections, the formation and evolution of binary WDs and their observational manifestations. Special attention is given to AM CVn-stars -- compact binaries in which the Roche lobe is filled by another WD or a low-mass partially degenerate helium-star, as these stars are thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure

Predictive Crime Mapping: Arbitrary Grids or Street Networks?

OBJECTIVES: Decades of empirical research demonstrate that crime is concentrated at a range of spatial scales, including street segments. Further, the degree of clustering at particular geographic units remains noticeably stable and consistent; a finding that Weisburd (Criminology 53:133–157, 2015) has recently termed the ‘law of crime concentration at places’. Such findings suggest that the future locations of crime should—to some extent at least—be predictable. To date, methods of forecasting where crime is most likely to next occur have focused either on area-level or grid-based predictions. No studies of which we are aware have developed and tested the accuracy of methods for predicting the future risk of crime at the street segment level. This is surprising given that it is at this level of place that many crimes are committed and policing resources are deployed. METHODS: Using data for property crimes for a large UK metropolitan police force area, we introduce and calibrate a network-based version of prospective crime mapping [e.g. Bowers et al. (Br J Criminol 44:641–658, 2004)], and compare its performance against grid-based alternatives. We also examine how measures of predictive accuracy can be translated to the network context, and show how differences in performance between the two cases can be quantified and tested. RESULTS: Findings demonstrate that the calibrated network-based model substantially outperforms a grid-based alternative in terms of predictive accuracy, with, for example, approximately 20 % more crime identified at a coverage level of 5 %. The improvement in accuracy is highly statistically significant at all coverage levels tested (from 1 to 10 %). CONCLUSIONS: This study suggests that, for property crime at least, network-based methods of crime forecasting are likely to outperform grid-based alternatives, and hence should be used in operational policing. More sophisticated variations of the model tested are possible and should be developed and tested in future research