MAXI J1957+032: an accreting neutron star possibly in a triple system

I present an optical characterization of the Galactic X-ray transient source MAXI J1957$+$032. This system flares by a factor of $\gtrsim10^{4}$ every few-hundred days, with each flare lasting $\sim5$ days. I identify its quiescent counterpart to be a late-K/early-M dwarf star at a distance of $5\pm2$ kpc. This implies that the peak $0.5-10$ keV luminosity of the system is $10^{36.4\pm0.4}$ erg s$^{-1}$. As found by Mata Sanchez et al., the outburst properties of MAXI J1957$+$032 are most consistent with the sample of accreting millisecond pulsars. However, the low inferred accretion rate, and the lack of evidence for a hydrogen-rich accretion flow, are difficult to reconcile with the late-K/early-M dwarf counterpart being the mass donor. Instead, the observations are best described by a low-mass hydrogen- and possibly helium-poor mass donor, such as a carbon-oxygen white dwarf, forming a tight interacting binary with a neutron star. The observed main-sequence counterpart would then likely be in a wide orbit around the inner binary.Comment: 12 pages, 3 figures, 4 tables, accepted by Ap

The impact of malaria control on infant mortality in Kenya

Since the early 2000s there has been a rapid intensification of malaria control efforts across Africa. I exploit baseline differences in the regional incidence of malaria coupled with the sharp timing of the intensified campaign to investigate the impact on infant mortality in Kenya. Post-intervention, I find a significant reduction in postneonatal mortality in the malarious regions relative to the non-malarious regions. In contrast, I find no evidence of impact on neonatal mortality which is consistent with epidemiological literature that finds neonates enjoy significant protection from malaria. I rule out alternative explanations such as differential pre-existing trends, changes in maternal and infant care, or the contemporaneous expansion of HIV/AIDS prevention and treatment. I find that the malaria campaign reduced postneonatal mortality by 33% in the malarious regions during 2004-2008

Flares from coalescing black holes in the centimeter-wavelength transient sky

Radio observations have resulted in some of the most fundamental and exciting discoveries in time-domain astronomy. Here I demonstrate the potential for the Next Generation Very Large Array (ngVLA) to localize prompt centimeter-wavelength counterparts to the coalescing binary supermassive black holes (SMBHs) to be detected by the LISA mission. The resulting redshift measurements of the hosts of LISA-detected coalescences will populate a Hubble diagram up to the epoch of the earliest galaxies. Analysis of the host environments and the electromagnetic coalescence signatures will provide crucial insight into the interactions between binary SMBHs and their environments, and the mechanisms of SMBH formation and growth.Comment: An ngVLA Science Book chapter. 10 pages, 3 figure