Tight multi-messenger constraints on the neutron star equation of state from GW170817 and a forward model for kilonova light curve synthesis

We present a rapid analytic framework for predicting kilonova light curves following neutron star (NS) mergers, where the main input parameters are binary-based properties measurable by gravitational wave detectors (chirp mass and mass ratio, orbital inclination) and properties dependent on the nuclear equation of state (tidal deformability, maximum NS mass). This enables synthesis of a kilonova sample for any NS source population, or determination of the observing depth needed to detect a live kilonova given gravitational wave source parameters in low latency. We validate this code, implemented in the public MOSFiT package, by fitting it to GW170817. A Bayes factor analysis overwhelmingly ($B>10^{10}$) favours the inclusion of an additional luminosity source in addition to lanthanide-poor dynamical ejecta during the first day. This is well fit by a shock-heated cocoon model, though differences in the ejecta structure, opacity or nuclear heating rate cannot be ruled out as alternatives. The emission thereafter is dominated by a lanthanide-rich viscous wind. We find the mass ratio of the binary is $q=0.92\pm0.07$ (90% credible interval). We place tight constraints on the maximum stable NS mass, $M_{\rm TOV}=2.17^{+0.08}_{-0.11}$ M$_\odot$. For a uniform prior in tidal deformability, the radius of a 1.4 M$_\odot$ NS is $R_{1.4}\sim 10.7$ km. Re-weighting with a prior based on equations of state that support our credible range in $M_{\rm TOV}$, we derive a final measurement $R_{1.4}=11.06^{+1.01}_{-0.98}$ km. Applying our code to the second gravitationally-detected neutron star merger, GW190425, we estimate that an associated kilonova would have been fainter (by $\sim0.7$ mag at one day post-merger) and declined faster than GW170817, underlining the importance of tuning follow-up strategies individually for each GW-detected NS merger.Comment: Updated to match accepted version in MNRA

Multi‐instrument observations of SED during 24–25 October 2011 storm: Implications for SED formation processes

We present multiple instrument observations of a storm‐enhanced density (SED) during the 24–25 October 2011 intense geomagnetic storm. Formation and the subsequent evolution of the SED and the midlatitude trough are revealed by global GPS vertical total electron content maps. In addition, we present high time resolution Poker Flat Incoherent Scatter Radar (PFISR) observations of ionospheric profiles within the SED. We divided the SED observed by PFISR into two parts. Both parts are characterized by elevated ionospheric peak height ( h m F 2 ) and total electron content, compared to quiet time values. However, the two parts of the SED have different characteristics in the electron temperature ( T e ), the F region peak density ( N m F 2 ), and convection flows. The first part of the SED is associated with enhanced T e in the lower F region and reduced T e in the upper F region and is collocated with northward convection flows. The N m F 2 was lower than quiet time values. The second part of the SED is associated with significantly increased N m F 2 , elevated T e at all altitudes and is located near the equatorward boundary of large northwestward flows. Based on these observations, we suggest that the mechanisms responsible for the formation of the two parts of the SED may be different. The first part is due to equatorward expansion of the convection pattern and the projection of northward convection flows in the vertical direction, which lifts the ionospheric plasma to higher altitudes and thus reduces the loss rate of plasma recombination. The second part is more complicated. Besides equatorward expansion of the convection pattern and large upward flows, evidences of other mechanisms, including horizontal advection due to fast flows, energetic particle precipitation, and enhanced thermospheric wind in the topside ionosphere, are also present. Estimates show that contribution from precipitating energetic protons is at most ~10% of the total F region density. The thermospheric wind also plays a minor role in this case. Key Points SED formation during 24–25 October 2011 geomagnetic storm studied PFISR observations within the SED shown Electric field plays a major role in the formation of SED in this stormPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/102626/1/jgra50711.pd

On the generation/decay of the storm‐enhanced density plumes: Role of the convection flow and field‐aligned ion flow

Storm‐enhanced density (SED) plumes are prominent ionospheric electron density increases at the dayside middle and high latitudes. The generation and decay mechanisms of the plumes are still not clear. We present observations of SED plumes during six storms between 2010 and 2013 and comprehensively analyze the associated ionospheric parameters within the plumes, including vertical ion flow, field‐aligned ion flow and flux, plasma temperature, and field‐aligned currents, obtained from multiple instruments, including GPS total electron content (TEC), Poker Flat Incoherent Scatter Radar (PFISR), Super Dual Auroral Radar Network, and Active Magnetosphere and Planetary Electrodynamics Response Experiment. The TEC increase within the SED plumes at the PFISR site can be 1.4–5.5 times their quiet time value. The plumes are usually associated with northwestward E  ×  B flows ranging from a couple of hundred m s −1 to > 1 km s −1 . Upward vertical flows due to the projection of these E  ×  B drifts are mainly responsible for lifting the plasma in sunlit regions to higher altitude and thus leading to plume density enhancement. The upward vertical flows near the poleward part of the plumes are more persistent, while those near the equatorward part are more patchy. In addition, the plumes can be collocated with either upward or downward field‐aligned currents (FACs) but are usually observed equatorward of the peak of the Region 1 upward FAC, suggesting that the northwestward flows collocated with plumes can be either subauroral or auroral flows. Furthermore, during the decay phase of the plume, large downward ion flows, as large as ~200 m s −1 , and downward fluxes, as large as 10 14  m −2  s −1 , are often observed within the plumes. In our study of six storms, enhanced ambipolar diffusion due to an elevated pressure gradient is able to explain two of the four large downward flow/flux cases, but this mechanism is not sufficient for the other two cases where the flows are of larger magnitude. For the latter two cases, enhanced poleward thermospheric wind is suggested to be another mechanism for pushing the plasma downward along the field line. These downward flows should be an important mechanism for the decay of the SED plumes. Key Points Vertical plasma lifting leads to density increase during plume generation phase Large downward field‐aligned ion flow/flux seen during plume decay phase Complex‐induced plasma drifts seen indicating plumes' highly dynamic naturePeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/1/StormB_tec_20121113.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/2/QuietTimeF_tec_20100821.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/3/StormD_tec_20120423.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/4/QuietTimeC_tec_20120928.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/5/SupplementaryMaterial_Figure3_quiet.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/6/QuietTimeE_tec_20110203.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/7/StormC_tec_20120930.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/8/StormA_tec_20130423.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/9/StormF_tec_20100803.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/10/jgra51348.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/11/SupplementaryMaterial_Figure4_quiet.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/12/QuietTimeA_tec_20130421.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/13/QuietTimeD_tec_20120429.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/14/QuietTimeB_tec_20121109.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/15/StormE_tec_20110204.pd

PFISR observation of intense ion upflow fluxes associated with an SED during the 1 June 2013 geomagnetic storm

The Earth’s ionosphere plays an important role in supplying plasma into the magnetosphere through ion upflow/outflow, particularly during periods of strong solar wind driving. An intense ion upflow flux event during the 1 June 2013 storm has been studied using observations from multiple instruments. When the open‐closed field line boundary (OCB) moved into the Poker Flat incoherent scatter radar (PFISR) field of view, divergent ion fluxes were observed by PFISR with intense upflow fluxes reaching ~1.9 × 1014 m−2 s−1 at ~600 km altitude. Both ion and electron temperatures increased significantly within the ion upflow, and thus, this event has been classified as a type 2 upflow. We discuss factors contributing to the high electron density and intense ion upflow fluxes, including plasma temperature effect and preconditioning by storm‐enhanced density (SED). Our analysis shows that the significantly enhanced electron temperature due to soft electron precipitation in the cusp can reduce the dissociative recombination rate of molecular ions above ~400 km and contributed to the density increase. In addition, this intense ion upflow flux event is preconditioned by the lifted F region ionosphere due to northwestward convection flows in the SED plume. During this event, the OCB and cusp were detected by DMSP between 15 and 16 magnetic local times, unusually duskward. Results from a global magnetohydrodynamics simulation using the Space Weather Modeling Framework have been used to provide a global context for this event. This case study provides a more comprehensive mechanism for the generation of intense ion upflow fluxes observed in association with SEDs.Key PointsA more comprehensive mechanism for the generation of intense ion upflow fluxes observed in association with SEDs has been providedNorthwestward convection flows lift the F region ionosphere within SED and provide seed population for intense ion upflow fluxesSignificantly elevated electron temperature reduces recombination rate contributing to density increasePeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136519/1/jgra53328.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136519/2/jgra53328_am.pd

Towards discovery of gravitationally lensed explosive transients: the brightest galaxies in massive galaxy clusters from Planck-SZ2

We combine the Planck-SZ2 galaxy cluster catalogue with near-infrared photometry of galaxies from the VISTA Hemisphere Survey to identify candidate brightest cluster galaxies (BCGs) in 306 massive clusters in the Southern skies at redshifts of $z>0.1$. We find that 91% of these clusters have at least one candidate BCG within the 95% confidence interval on the cluster centers quoted by the Planck collaboration, providing reassurance that our analyses are statistically compatible, and find 92% to be reasonable candidates following a manual inspection. We make our catalog publicly available to assist colleagues interested in multi-wavelength studies of cluster cores, and the search for gravitationally lensed explosive transients in upcoming surveys including the Legacy Survey of Space and Time by the Vera C. Rubin Observatory.Comment: Published in RNAAS in March 2023. 3 pages, 1 figur

Adjunctive rifampicin for Staphylococcus aureus bacteraemia (ARREST): a multicentre, randomised, double-blind, placebo-controlled trial.

BACKGROUND: Staphylococcus aureus bacteraemia is a common cause of severe community-acquired and hospital-acquired infection worldwide. We tested the hypothesis that adjunctive rifampicin would reduce bacteriologically confirmed treatment failure or disease recurrence, or death, by enhancing early S aureus killing, sterilising infected foci and blood faster, and reducing risks of dissemination and metastatic infection. METHODS: In this multicentre, randomised, double-blind, placebo-controlled trial, adults (≥18 years) with S aureus bacteraemia who had received ≤96 h of active antibiotic therapy were recruited from 29 UK hospitals. Patients were randomly assigned (1:1) via a computer-generated sequential randomisation list to receive 2 weeks of adjunctive rifampicin (600 mg or 900 mg per day according to weight, oral or intravenous) versus identical placebo, together with standard antibiotic therapy. Randomisation was stratified by centre. Patients, investigators, and those caring for the patients were masked to group allocation. The primary outcome was time to bacteriologically confirmed treatment failure or disease recurrence, or death (all-cause), from randomisation to 12 weeks, adjudicated by an independent review committee masked to the treatment. Analysis was intention to treat. This trial was registered, number ISRCTN37666216, and is closed to new participants. FINDINGS: Between Dec 10, 2012, and Oct 25, 2016, 758 eligible participants were randomly assigned: 370 to rifampicin and 388 to placebo. 485 (64%) participants had community-acquired S aureus infections, and 132 (17%) had nosocomial S aureus infections. 47 (6%) had meticillin-resistant infections. 301 (40%) participants had an initial deep infection focus. Standard antibiotics were given for 29 (IQR 18-45) days; 619 (82%) participants received flucloxacillin. By week 12, 62 (17%) of participants who received rifampicin versus 71 (18%) who received placebo experienced treatment failure or disease recurrence, or died (absolute risk difference -1·4%, 95% CI -7·0 to 4·3; hazard ratio 0·96, 0·68-1·35, p=0·81). From randomisation to 12 weeks, no evidence of differences in serious (p=0·17) or grade 3-4 (p=0·36) adverse events were observed; however, 63 (17%) participants in the rifampicin group versus 39 (10%) in the placebo group had antibiotic or trial drug-modifying adverse events (p=0·004), and 24 (6%) versus six (2%) had drug interactions (p=0·0005). INTERPRETATION: Adjunctive rifampicin provided no overall benefit over standard antibiotic therapy in adults with S aureus bacteraemia. FUNDING: UK National Institute for Health Research Health Technology Assessment

Systematic light-curve modelling of TDEs:statistical differences between the spectroscopic classes

With the sample of observed tidal disruption events (TDEs) now reaching several tens, distinct spectroscopic classes have emerged: TDEs with only hydrogen lines (TDE-H), only helium lines (TDE-He), or hydrogen in combination with He II and often N III/O III (TDE-H+He). Here we model the light curves of 32 optically-bright TDEs using the Modular Open Source Fitter for Transients (MOSFiT) to estimate physical and orbital properties, and look for statistical differences between the spectroscopic classes. For all types, we find a shallow distribution of star masses, compared to a typical initial mass function, between $\sim 0.1-1$ M$_\odot$, and no TDEs with very deep ($\beta \gg 1$) encounters. Our main result is that TDE-H events appear to come from less complete disruptions (and possibly lower SMBH masses) than TDE-H+He, with TDE-He events fully disrupted. We also find that TDE-H events have more extended photospheres, in agreement with recent literature, and argue that this could be a consequence of differences in the self-intersection radii of the debris streams. Finally, we identify an approximately linear correlation between black hole mass and radiative efficiency. We suggest that TDE-H may be powered by collision-induced outflows at relatively large radii, while TDE-H+He could result from prompt accretion disks, formed more efficiently in closer encounters around more massive SMBHs.Comment: Submitted to MNRA