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Multi-dimensional models of proto-magnetar winds: spindown, nucleosynthesis, and gamma-ray bursts

Prasanna, Tejas
http://orcid.org/0000-0002-9886-7504
http://rave.ohiolink.edu/etdc/view?acc_num=osu1720757575398456

Abstract Details

2024, Doctor of Philosophy, Ohio State University, Physics.
In the seconds following their formation in core-collapse supernovae, `proto'-neutron stars (PNSs) drive neutrino-heated magneto-centrifugal winds. The neutrino-driven wind phase during the cooling of the PNS lasts $\sim 1-100$\,s. We construct unprecedentedly realistic models of the PNS cooling phase using two-dimensional axisymmetric magnetohydrodynamic simulations. We include the effects of neutrino heating and cooling, employ a general equation of state, consider strong magnetic fields along with a dynamic PNS magnetosphere, and include the effects of PNS rotation. We show that relatively slowly rotating magnetars (strongly magnetized PNSs) with initial spin periods $P_{\star0} \gtrsim 100$\,ms spin down rapidly during the cooling epoch. For polar magnetic field strengths $B_0\gtrsim10^{15}$\,G, we show that the spindown timescale is of the order seconds in early phases. We show that magnetars with mass $M$ born with $B_0$ greater than $\simeq1.3\times10^{15}\,{\rm\,G}\,(P_{\star0}/{400\,\rm\,ms})^{-1.4}(M/1.4\,{\rm M}_\odot)^{2.2}$ spin down to periods $> 1$\,s in just the first few seconds of evolution. We discuss the implications for observed magnetars, including the discrepancy between their characteristic ages and supernova remnant ages. On the other hand, we show that rapidly rotating magnetars with initial spin periods $P_{\star 0}\lesssim 4$\,ms and $B_0\gtrsim 10^{15}$\,G can release $10^{50}-5\times 10^{51}$\,ergs of energy during the first $\sim2$\,s of the cooling phase. Based on this result, it is plausible that sustained energy injection by magnetars through the relativistic wind phase can power gamma-ray bursts (GRBs). We also show that magnetars with moderate field strengths of $B_0\lesssim 5\times 10^{14}$\,G do not release a large fraction of their rotational kinetic energy during the cooling phase and hence, are not likely to power GRBs. We hypothesize that moderate field strength magnetars can be central engines of superluminous supernovae. We also focus on the prospects for detecting PNS rotation and potential spindown using supernova neutrinos. Provided that there are neutrino emission `hot-spots' or `cold-spots' on the surface of the rotating PNS, we can expect a periodic modulation in the number of neutrinos observable by detectors. We propose a modified Discrete Fourier Transform (DFT) technique with three frequency parameters to detect spindown. Due to lack of neutrino data from a nearby supernova except the $\sim20$ neutrinos detected from SN1987A, we use toy models to generate neutrino arrival times. We use the false alarm rate (FAR) to quantify the significance of the Fourier power spectrum peaks. We show that PNS rotation and spindown are detected with $\rm FAR<2\%$ ($2\sigma$) for periodic signal content $\rm M\gtrsim 13-15\%$ if $5\times 10^{3}$ neutrinos are detected in $\sim 3$\,s and with $\rm FAR<1\%$ for $\rm M\geq 5\%$ if $5\times 10^{4}$ neutrinos are detected in $\sim 3$\,s. Finally, we focus on heavy element nucleosynthesis in magnetar winds. We show that high entropy material is quasi-periodically ejected from the closed zone of the PNS magnetosphere with the required thermodynamic conditions to produce heavy elements. We show for the first time that the PNS rotation rate significantly affects the thermodynamic conditions of the wind. We show that maximum entropy $S$ of the material ejected depends systematically on the magnetar spin period $P_{\star}$ and scales as $S \propto P_{\star}^{-5/6}$ for sufficiently rapid rotation. We show that PNS winds can have favorable conditions to produce $r-$process nuclei as well as $p-$nuclei.
Todd Thompson (Advisor)
James Beatty (Committee Member)
Samir Mathur (Committee Member)
Christopher Hirata (Committee Member)
259 p.
Astronomy; Astrophysics; Nuclear Physics; Physics; Plasma Physics; Theoretical Physics
neutron stars; magnetars; neutrinos; spindown; gamma-ray bursts; supernovae; hypernovae; Discrete Fourier Transform (DFT); heavy element nucleosynthesis; r-process; p-nuclei; quasi-periodic eruptions; plasmoids; magnetosphere; magnetohydrodynamics (MHD); magnetic field; Equation of State (EOS); computer simulations; plasma

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Citations

  • Prasanna, T. (2024). Multi-dimensional models of proto-magnetar winds: spindown, nucleosynthesis, and gamma-ray bursts [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1720757575398456

    APA Style (7th edition)

  • Prasanna, Tejas. Multi-dimensional models of proto-magnetar winds: spindown, nucleosynthesis, and gamma-ray bursts. 2024. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1720757575398456.

    MLA Style (8th edition)

  • Prasanna, Tejas. "Multi-dimensional models of proto-magnetar winds: spindown, nucleosynthesis, and gamma-ray bursts." Doctoral dissertation, Ohio State University, 2024. http://rave.ohiolink.edu/etdc/view?acc_num=osu1720757575398456

    Chicago Manual of Style (17th edition)

osu1720757575398456
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This open access ETD is published by The Ohio State University and OhioLINK.