Neutron Stars, Magnetars & Pulsars: Peter Mészáros
Magnetars are isolated neutron stars with surface dipole field strengths of ~ 10^15 Gauss, much higher than the ~ 10^12 Gauss of ordinary pulsars, and they manifest themselves in the form of soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs). Magnetars may be one possible central engine for gamma-ray bursts (GRB), in which case they would put out an MHD wind or jet which would, decaying as a power law, last much longer than the standard GRB gamma-radiation (Rees & Meszaros 2000). They may also produce late bumps in the GRB afterglow light curves (Zhang & Meszaros, 2001a,b). An interestig possibility is that the more common magnetars, such as AXP and SGRs, are able to accelerate protons in their inner ghaps, which via photo-meson interactions with the surface soft X-ray photons make TeV neutrinos. This magnetar TeV neutrino emission may be detectable with large km^3 detectors such as ICECUBE (Zhang, Dai, Meszaros & Waxman, 2003). An exciting possibility is that the recent giant flare of the Soft Gamma Repeater SGR 1806-20 recently detected (December 28 2005) in gamma-rays by Swift may also produce cosmic rays and neutrinos. Ioka, Razzaque, Kobayashi and Meszaros calculated the TeV neutrino flux expected from this SGR. Proton acceleration and p,gamma interactions could produce signals detectable with ICECUBE for a high enough baryon load fireball. This emission would be associated also with detectable TeV gamma-ray emission.
Young magnetars may be born with milisecond rotation periods, and the ultrastrong magnetic field will result in a Poynting dominated outgoing wavefield, which can accelerate cosmic rays to GZK energies through wake-field acceleration. In this case, one could probe the birth of fast rotating magnetars through high-energy neutrinos, (Murase, Meszaros and Zhang, 2009), which are produced when the hultra-high energy protons interact with the ejected outer stellar envelope (the supernova remnant).
An interesting direct generation mechanism of production of High Energy Neutrinos and Photons from Curvature Pions in Magnetars was investigated by Herpay, Razzaque, Patkós and Mészáros. This is expected through the curvature radiation of pions in strongly magnetized pulsars or magnetars. This mechanism operate only in magetars, since it requires the very high fields measured in these objects. The production of TeV energy neutrinos associated with this is expected to be detectable by cubic kilometer scale detectors, while the high energy photons are in the range of space detectors.
X-ray pulsars are strongly magnetized neutron stars in close binary systems. Their X-ray radiation is formed in the magnetic polar caps which are heated by accretion of the matter supplied by the binary companion, or in accretion columns above the polar caps. The radiating regions of these objects are much hotter than those of cooling NSs, typically, kT ~10 keV. The radiating plasma is fully ionized at these temperatures, but the radiative transfer problem is strongly complicated by the comptonization effects in strong magnetic field. The elementary radiative processes and the radiative transfer in the X-ray pulsars have been thoroughly investigated during the last decade. An essential part of these investigations was performed in our department, and a general overview of X- and gamma-ray emmision from accretion as well as rotation powered pulsars, including pre-1992 work on gamma-ray bursts and TeV-PeV sources is summarized in the book High-Energy Radiation from Magnetized Neutron Stars (Meszaros, 1992).
Accreting pulsars are a topic of major interest, and some of the most detailed models for the emission and beaming from these objects are being carried out in our department. The emitting atmosphere is modelled by means of a detailed finite-difference radiative transfer code, with the inclusion of polarization and the full angle and frequency dependence of both the continuum and the cyclotron resonant opacities. Additional effects arise as a consequence of the geometry, scattering and reprocessing by the accretion column, and propagation effects in the curved space-time of the neutron star. Detailed model pulse-shapes and spectra, when compared to phase-resolved data, can provide information not only about the physical conditions in the accreting polar cap, the binary parameters and aspect angles, but also about more fundamental parameters such as the mass-radius relation of neutron stars.
Bulik, Meszaros, Thomas and colleagues at Tokyo University derived the physical characteristics of the polar caps of the accreting pulsars Vela X-1 and 4U1538-52, by means of chi-squared to a detailed physical model of the accretion column involving asymmetries and cap structure. Ute Kraus and P. Meszaros, in collaboration with Blum, Schulte and Ruder from the University of Tuebingen (Germany) developed a method for deriving beam shapes of accreting X-ray pulsars. The method decomposes the observed light curves into their Fourier components and finds the minimum number of beam elements needed to achieve a fit to derive the polar cap magnetic geometry (Ap.J. subm.). Garmire, Meszaros and Pavlov collaborated with colleagues at NASA Marshall and Russia, calculating the scientific return prospects of a space-based X-ray polarimeter aimed at pulsars and AGN (Proc. Spie).
References
“High Energy Neutrinos and Photons from Curvature Pions in Magnetars”, Herpay, T., Razzaque, R., Patkós, A. and Mészáros, P., 2008, JCAP, JCAP08.025 (arXiv:0807.4914)
“Probing the Birth of Fast Rotating Magnetars through High-Energy Neutrinos”, Murase, K., Meszaros, P. and Zhang, B., 2009, PRD, 79:103001 (arXiv:0904.2509)
“TeV-PeV Neutrinos from Giant Flares of Magnetars and the Case of SGR 1806-20″, Ioka, K, Razzaque, S, Kobayashi, S, Meszaros, P, 2005, ApJ, 633, 1013 (astro-ph/0503279)
“TeV Neutrinos from Magnetars” , Zhang, B, Dai, Z.G, Meszaros, P, Waxman, E & Harding, A.K., 2003, ApJ, 595:346-351 (astro-ph/0210382)
“Limits on the high-energy gamma and neutrino fluxes from the SGR 1806-20 giant flare of December 27, 2004, with the AMANDA-II detector”, The IceCube Collaboration: Achterberg, A, et al, Astroparticle Phys., subm (astro-ph/0607233)
“Gamma-ray bursts with continuous energy injection and their afterglow signature”, Zhang, B & Meszaros, P, 2001, ApJ, 566, 712 (astro-ph/0108402)
“Gamma-ray Burst Afterglow with Continous Energy Injection: Signature of a Highly-Magnetized Millisecond Pulsar”, Zhang, B & Meszaros, P, 2001, ApJ(Letters), 552, L35 (astro-ph/0011133)
`Fe K-alpha Emission from a Decaying Magnetar Model of Gamma-Ray Bursts”, Rees, M.J & Meszaros, P, 2000, ApJ (Letters), 545, L73 (astro-ph/0010258)
“Geometry and Pulse Profiles of X-ray Pulsars: Asymmetric Relativistic Fits to 4U1538-52 and Vela X-1″, Bulik, T., Riffert, H., Meszaros, P., Makishima, K., Mihara, T. and Thomas, B., 1995, Ap.J., 444, 405
“A Quick, Cheap and Beautiful X-ray Polarimeter”, Weisskopf, M.C., Elsner, R.F., Joy, M.K., Ramsey, B.D., Garmire, G.P., Meszaros, P., Sunyaev, R., 1994, Spie Proc., vol 2283, 70.
“A Phenomenological Approach to X-ray Pulsar Light Curve Analysis”, Kraus, U., Blum, J., Schulte, T., Ruder, H. and Meszaros, P., 1996, Ap.J., 467, 794
High-Energy Radiation from Magnetized Neutron Stars , Meszaros, P., 1992 (University of Chicago Press).
Research sponsors: NASA, NSF
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