arXiv subjects

R. Mckinven

Publications and source records attributed to R. Mckinven.

22 records · Page 2Linked to original sources

arXiv2019

CHIME/FRB Detection of the Original Repeating Fast Radio Burst Source FRB 121102

We report the detection of a single burst from the first-discovered repeating Fast Radio Burst source, FRB 121102, with CHIME/FRB, which operates in the frequency band 400-800 MHz. The detected burst occurred on 2018 November 19 and its emission extends down to at least 600 MHz, the lowest frequency detection of this source yet. The burst, detected with a significance of 23.7$σ$, has fluence 12$\pm$3 Jy ms and shows complex time and frequency morphology. The 34 ms width of the burst is the largest seen for this object at any frequency. We find evidence of sub-burst structure that drifts downward in frequency at a rate of -3.9$\pm$0.2 MHz ms$^{-1}$. Our best fit tentatively suggests a dispersion measure of 563.6$\pm$0.5 pc cm$^{-3}$, which is ${\approx}$1% higher than previously measured values. We set an upper limit on the scattering time at 500 MHz of 9.6 ms, which is consistent with expectations from the extrapolation from higher frequency data. We have exposure to the position of FRB 121102 for a total of 11.3 hrs within the FWHM of the synthesized beams at 600 MHz from 2018 July 25 to 2019 February 25. We estimate on the basis of this single event an average burst rate for FRB 121102 of 0.1-10 per day in the 400-800 MHz band for a median fluence threshold of 7 Jy ms in the stated time interval.

astro-ph.HE↗

arXiv2019

A Second Source of Repeating Fast Radio Bursts

The discovery of a repeating Fast Radio Burst (FRB) source, FRB 121102, eliminated models involving cataclysmic events for this source. No other repeating FRB has yet been detected in spite of many recent FRB discoveries and follow-ups, suggesting repeaters may be rare in the FRB population. Here we report the detection of six repeat bursts from FRB 180814.J0422+73, one of the 13 FRBs detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) FRB project during its pre-commissioning phase in July and August 2018. These repeat bursts are consistent with originating from a single position on the sky, with the same dispersion measure (DM), ~189 pc cm-3. This DM is approximately twice the expected Milky Way column density, and implies an upper limit on the source redshift of 0.1, at least a factor of ~2 closer than FRB 121102. In some of the repeat bursts, we observe sub-pulse frequency structure, drifting, and spectral variation reminiscent of that seen in FRB 121102, suggesting similar emission mechanisms and/or propagation effects. This second repeater, found among the first few CHIME/FRB discoveries, suggests that there exists -- and that CHIME/FRB and other wide-field, sensitive radio telescopes will find -- a substantial population of repeating FRBs.

astro-ph.HE↗

arXiv2018

Polycrystalline Crusts in Accreting Neutron Stars

The crust of accreting neutron stars plays a central role in many different observational phenomena. In these stars, heavy elements produced by H-He burning in the rapid proton capture (rp-) process continually freeze to form new crust. In this paper, we explore the expected composition of the solid phase. We first demonstrate using molecular dynamics that two distinct types of chemical separation occur, depending on the composition of the rp-process ashes. We then calculate phase diagrams for three-component mixtures and use them to determine the allowed crust compositions. We show that, for the large range of atomic numbers produced in the rp-process ($Z\sim 10$--$50$), the solid that forms has only a small number of available compositions. We conclude that accreting neutron star crusts should be polycrystalline, with domains of distinct composition. Our results motivate further work on the size of the compositional domains, and have implications for crust physics and accreting neutron star phenomenology.

astro-ph.HE↗

arXiv2017

Simulating the Novel Phase Separation of a Rapid Proton Capture Ash Composition

Nucleosynthesis in the oceans of accreting neutron stars can produce novel mixtures of nuclides, whose composition is dependent on the exact astrophysical conditions. Many simulations have now been done to determine the nucleosynthesis products in the ocean, but the phase separation at the base of the ocean, which determines the composition of the crust, has not been as well studied. In this work, we simulate the phase separation of a composition, which was predicted to produce a crust enriched in light nuclei, in contrast with past work which predicts that crust is enriched in heavy nuclei. We perform molecular dynamics simulations of the phase separation of this mixture using the methods of Horowitz $\textit{et. al.}$ (2007). We find good agreement with the predictions of Mckinven $\textit{et al.}$ (2016) for the phase separation of this mixture. Moreover, this supports their method as a computationally efficient alternative to molecular dynamics for calculating phase separation for a wider regime of astrophysical conditions.

astro-ph.HE↗