The broadening of the hydrogen lines during flares is thought to result from increased charge (electron, proton) density in the flare chromosphere. However, disagreements between theory and modeling prescriptions have precluded an accurate diagnostic of the degree of ionization and compression resulting from flare heating in the chromosphere. To resolve this issue, we have incorporated the unified theory of electric pressure broadening of the hydrogen lines into the non-LTEradiative-transfer code RH. This broadening prescription produces a much more realistic spectrum of the quiescent, A0 star Vega compared to the analytic approximations used as a damping parameter in the Voigt profiles. We test recent radiative-hydrodynamic (RHD) simulations of the atmospheric response to high nonthermal electron beam fluxes with the new broadening prescription and find that the Balmer lines are overbroadened at the densest times in the simulations. Adding many simultaneously heated and cooling model loops as a "multithread" model improves the agreement with the observations. We revisit the threecomponent phenomenological flare model of the YZ CMi Megaflare using recent and new RHD models. The evolution of the broadening, line flux ratios, and continuum flux ratios are well-reproduced by a multithread model with high-flux nonthermal electron beam heating, an extended decay phase model, and a "hot spot" atmosphere heated by an ultrarelativistic electron beam with reasonable filling factors: ∼0.1%, 1%, and 0.1% of the visible stellar hemisphere, respectively. The new modeling motivates future work to understand the origin of the extended gradual phase emission.

We present NUV flare spectra from the Hubble Space Telescope/Cosmic Origins Spectrograph during two moderateamplitude U -band flares on the dM4e star GJ 1243. These spectra are some of the first accurately flux-calibrated, NUV flare spectra obtained over the impulsive phase in M dwarf flares. We observed these flares with a fleet of nine ground-based telescopes simultaneously, which provided broadband photometry and low-resolution spectra at the Balmer jump. A broadband continuum increase occurred with a signal-to-noise > 20 in the HST spectra, while numerous Fe II lines and the Mg II lines also increased but with smaller flux enhancements compared to the continuum radiation. These two events produced the most prominent Balmer line radiation and the largest Balmer jumps that have been observed to date in dMe flare spectra. A T = 9000 K blackbody under-estimates the NUV continuum flare flux by a factor of two and is a poor approximation to the white-light in these types of flare events. Instead, our data suggest that the peak of the specific continuum flux density is constrained to U -band wavelengths near the Balmer series limit. A radiative-hydrodynamic simulation of a very high energy deposition rate averaged over times of impulsive heating and cooling better explains the λ > 2500Å flare continuum properties. These two events sample only one end of the empirical color-color distribution for dMe flares, and more time-resolved flare spectra in the NUV, U -band, and optical from 2000 − 4200Å are needed during more impulsive and/or more energetic flares.

In this article, we examine how communities can maximize deterrence of crime while minimizing cost and police intrusion on public life. Using 3,720 hot spot-days, we show that the “sweet spot” duration of police absence, to maximize the residual deterrence of crime, was a full four days after the last day of targeting police patrol at each hot spot. Over a 248-day period, we randomly reshuffled 15 separate hot spots daily into either treatment (targeted police patrols) or control (no targeted patrols) for that day, so that all locations repeatedly switched between randomly assigned groups. This repeated crossover design (Cochrane & Cox, 1957; Fienberg et al., 1980) included random periods of up to 20 consecutive days in which individual hot spots remained in the control condition, allowing us to measure how soon, and by what trajectory, the residual deterrent effect of targeted patrolling wore off. After four days without patrolling, there was a sudden termination of residual deterrence, marked by a 66% rise in offense frequency, and a 395% spike in our index of crime harm (House & Neyroud 2018), compared to the treatment condition. It may be possible to deploy less, not more policing and still maximize deterrent effects.

Aims. The hydrogen Lyman lines provide important diagnostic information about the dynamics of the chromosphere, but there have been few systematic studies of their variability during flares. We investigate Doppler shifts in these lines in several flares, and use these to calculate plasma speeds. Methods. We use spectral data from the Multiple EUV Grating Spectrograph B (MEGS-B) detector of the Extreme-Ultraviolet Variability Experiment (EVE) instrument on the Solar Dynamics Observatory. MEGS-B obtains full-disk spectra of the Sun at a resolution of 0.1 nm in the range 37-105 nm, which we analyse using three independent methods. The first method performs Gaussian fits to the lines, and compares the quiet-Sun centroids with the flaring ones to obtain the Doppler shifts. The second method uses crosscorrelation to detect wavelength shifts between the quiet-Sun and flaring line profiles. The final method calculates the "center-of-mass" of the line profile, and compares the quiet-Sun and flaring centroids to obtain the shift. Results. In a study of 6 flares we find strong signatures of both upflow and downflow in the Lyman lines, with speeds measured in Sun-as-a-Star data of around 10 km s −1 , and speeds in the flare excess signal of around 30 km s −1 . Conclusions. All events showing upflows in Lyman lines are associated with some kind of eruption or coronal flow in imaging data, which may be responsible for the net blueshifts. Events showing downflows in the Lyman lines may be associated with loop contraction or faint downflows, but it is likely that chromospheric condensation flows are also contributing.

The hydrogen Lyman lines (91.2 nm < λ<121.6 nm) are significant contributors to the radiative losses of the solar chromosphere, and they are enhanced during flares. We have shown previously that the Lyman lines observed by the Extreme Ultraviolet Variability instrument onboard the Solar Dynamics Observatory exhibit Doppler motions equivalent to speeds on the order of 30 km s −1 . However, contrary to expectations, both redshifts and blueshifts were present and no dominant flow direction was observed. To understand the formation of the Lyman lines, particularly their Doppler motions, we have used the radiative hydrodynamic code, RADYN, along with the radiative transfer code, RH, to simulate the evolution of the flaring chromosphere and the response of the Lyman lines during solar flares. We find that upflows in the simulated atmospheres lead to blueshifts in the line cores, which exhibit central reversals. We then model the effects of the instrument on the profiles, using the Extreme Ultraviolet Variability Experiment (EVE) instrumentʼs properties. What may be interpreted as downflows (redshifted emission) in the lines, after they have been convolved with the instrumental line profile, may not necessarily correspond to actual downflows. Dynamic features in the atmosphere can introduce complex features in the line profiles that will not be detected by instruments with the spectral resolution of EVE, but which leave more of a signature at the resolution of the Spectral Investigation of the Coronal Environment instrument onboard the Solar Orbiter.