Magnetars in the Metagalaxy: An Origin for Ultra-High-Energy Cosmic Rays in the Nearby Universe

By J. Arons. 2002

230 citations recorded by the source corpus.

I show that the relativistic winds of newly born magnetars (neutron stars with petagauss surface magnetic fields) with initial spin rates close to the centrifugal breakup limit, occurring in all normal galaxies with massive star formation, can provide a source of ultrarelativistic light ions with an E-1 injection spectrum, steepening to E-2 at higher energies, with an upper cutoff at 1021-1022 eV. Interactions with the cosmic microwave background yield a spectrum at the Earth that compares favorably with the spectrum of ultra-high-energy cosmic rays (UHECRs) observed at energies up to a few times 1020 eV. The fit to the observations suggests that ~5%-10% of the magnetars are born with rotation rates and voltages sufficiently high to allow the acceleration of the UHECR. The form the spectrum incident on the Earth takes depends sensitively on the mechanism and the magnitude of gravitational wave losses during the early spin-down of these neutron stars: pure electromagnetic spin-down (the E-1 injection spectrum) yields a GZK feature [a flattening of the E3J(E) spectrum] below 1020 eV, rather than a cutoff, while a moderate GZK cutoff appears if gravitational wave losses are strong enough to steepen the injection spectrum above 1020 eV. The flux above 1020 eV comes from magnetars in relatively nearby galaxies (D < 50 Mpc). I outline the probable physics of acceleration of such particles in a magnetar's wind: it is a form of "surf-riding" in the approximately force-free fields of the wind. I also show how the high-energy particles can escape with small energy losses from the magnetars' natal supernovae. In particular, I show that the electromagnetic energy emitted by the magnetar "shreds" the supernova envelope in times short enough to allow most of the relativistic energy to escape largely unimpeded into the surrounding interstellar medium, where it drives a relativistic blast wave that expands to parsec scale before slowing down to nonrelativistic speeds. I also show that since the ions are accelerated in a region where the magnetic field has the structure of a strong electromagnetic wave but propagate at larger radii through a region of weaker magnetic field near the rotational equator of the outflow, the ultra-high-energy particles escape with negligible adiabatic and radiation losses. The requirement that the magnetars' relativistic winds not overproduce interstellar supershells and unusually large supernova remnants suggests that most of the initial spin-down energy is radiated in kilohertz gravitational waves for several hours after each supernova. For typical distances to events that contribute to E > 100 EeV air showers, the model predicts gravitational wave strains ~3 × 10-21. Such bursts of gravitational radiation should correlate with bursts of ultra-high-energy particles. The Auger experiment should see bursts of particles with energy above 100 EeV every few years.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/49391551ef5a10cb669348a1ceb6964b66934217

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In Astronomy and Astrophysics

1. B. Metzger
2. E. Quataert
3. T. Thompson
4. D. Kasen
5. Bing Zhang
6. D. Giannios
7. A. Spitkovsky
8. E. Berger

In Nuclear and High Energy Physics

1. B. Metzger
2. E. Quataert
3. A. Spitkovsky
4. Tim Huege
5. D. Giannios
6. T. Thompson
7. J. Arons
8. Kumiko Kotera

Citations in the corpus

• Open Questions in Cosmic-Ray Research at Ultrahigh Energies (2019, unknown): “Pulsars, the smallest and most highly-magnetized objects shown in Figure 10 , induce strong magnetic potentials that can potentially also accelerate UHECRs (Gunn and Ostriker, 1969; Blasi et al., 2000; Arons, 2003; Murase et al., 2009; Philippov and Spitkovsky, 2018).”
• The Astrophysics of Ultrahigh-Energy Cosmic Rays (2011, background): “A detailed discussion for magnetar winds can also be found in Arons (2003).”
• The strongest cosmic magnets: soft gamma-ray repeaters and anomalous X-ray pulsars (2008, background): “Furthermore, ultra high-energy cosmic rays could be produced in the relativistic winds of rapidly spinning magnetars immediately after their birth (Arons 2003).”
• BLAZARS AS ULTRA-HIGH-ENERGY COSMIC-RAY SOURCES: IMPLICATIONS FOR TeV GAMMA-RAY OBSERVATIONS (2011, background): “…that could potentially accelerate UHECRs, including, for example, GRBs (Waxman 1995; Vietri 1995; Murase et al. 2008a), fast rotating magnetars (Arons 2003), structure formation shocks in galaxy clusters (Norman et al. 1995; Kang et al. 1996; Inoue et al. 2007), and quasar remnants (Boldt &…”
• Physics, Astrophysics and Cosmology with Gravitational Waves (2009, background): “In this connection the suggestion of Arons [43] that at least some magnetars are formed in events of some kind that involve strong magnetic field braking but also strong gravitational wave emission, and that these events are the source of the ultra-high–energy cosmic rays whose source, is so far une”
• SUPERNOVA LIGHT CURVES POWERED BY YOUNG MAGNETARS (2009, background): “Cases this extreme may also be sources for ultra-high energy cosmic rays (Arons 2003) or deposit enough energy in the collapsing stellar envelope to favorably shape the deep interior (Uzdensky & MacFadyen 2007; Bucciantini et al. 2009) for the production of a collimated relativistic flow needed for…”
• Combined fit of spectrum and composition data as measured by the Pierre Auger Observatory (2016, background): “rd spectra up to some characteristic maximal energy. This is also the case if cosmic rays are accelerated in an unipolar inductor that can arise in the polar caps of rotating magnetized neutron stars [33, 38, 39], or black holes [40]. If interactions in the magnetospheres can be neglected this also ”
• The Proto-Magnetar Model for Gamma-Ray Bursts (2010, background): “In equation (3) we neglect angular momentum losses due to gravitational waves, which become important if the NS is sufficiently aspherically distorted by its strong interior magnetic field (e.g. Cutler 2002; Arons 2003; Stella et al. 2005; Dall’Osso et al. 2009).”
• Ultra high energy cosmic rays: implications of Auger data for source spectra and chemical composition (2013, background): “The hard injection spectra required to fit the PAO data are reminiscent of models of the origin of UHECRs associated to acceleration in rapidly rotating neutron stars [45, 46, 47, 48], although hard spectra are a more general characteristic of acceleration scenarios where regular electric fields are”
• Magnetized relativistic jets and long-duration GRBs from magnetar spin-down during core-collapse supernovae (2009, methodology): “…discs, such as are seen in simulations of accretion discs relevant to GRBs (e.g. Proga et al. 2003), will form a magnetized bubble that will escape via the polar channel rather than transferring energy to the SN shock as has been previously hypothesized (Arons 2003; Kohri, Narayan & Piran 2005).”
• Ab-initio Pulsar Magnetosphere: Particle Acceleration in Oblique Rotators and High-energy Emission Modeling (2017, background): “For the parameters of millisecond magnetars, this makes energetic ions interesting candidates for the ultra high-energy cosmic rays (Arons 2003).”