Magnetar

About: Magnetar is a research topic. Over the lifetime, 2905 publications have been published within this topic receiving 106806 citations.

Could electron-positron annihilation lines in the Galactic center result from pulsar winds?

Abstract: Observations of a strong and extended positron-electron annihilation line emission in the Galactic center (GC) region by the Spectrometer on the International Gamma-Ray Astrophysical Laboratory (SPI/INTEGRAL) are challenging to the existing models of positron sources in the Galaxy. In this paper, we study the possibility that pulsar winds in the GC produce the 511 keV line. We propose that three possible scenarios of pulsar winds may exist as the positron sources: normal pulsars, rapidly spinning strongly magnetized neutron stars (magnetars) in gamma-ray burst (GRB) progenitors, a population of millisecond pulsars in the Galactic center. These e ± pairs could be trapped in the region by the magnetic field in the Galactic center, and cool through synchrotron radiation and Coulomb interactions with the medium, thereby becoming non-relativistic particles. The cooling timescales are shorter than the diffuse timescale of positrons, so low-energy positrons could annihilate directly with electrons into 511 keV photons or could form positronium before annihilation. We find that normal pulsars cannot be a significant contributor to the positron sources. Although magnetars in the GC could be potential sources of positrons, their birth rate and birth locations may pose some problems for this scenario. We believe that the most likely candidates for positron sources in the GC may be a population of millisecond pulsars in the GC. Our preliminary estimations predict that the e ± annihilation rate in the GC is >5 x 10 42 s -1 , which is consistent with the present observational constraints. Therefore, the e ± pairs from pulsars winds can contribute significantly to the positron sources in the Galactic center region. Furthermore, since the diffusion length of positrons is short, we predict that the intensity distribution of the annihilation line should follow the distribution of millisecond pulsars, which should then correlate to the mass distribution in the GC.

1E 161348–5055 in the Supernova Remnant RCW 103: A Magnetar in a Young Low-Mass Binary System?

Abstract: We suggest that the unique X-ray source 1E 161348?5055 at the center of the supernova remnant RCW 103 consists of a neutron star in close orbit with a low-mass main-sequence star. The time signature of 6.67 hr is interpreted as the neutron star's spin period. This requires the neutron star to be endowed with a high surface magnetic field of ~1015 G. Magnetic or/and material (propeller) torques are able to rapidly spin the young neutron star down to an asymptotic, equilibrium spin period in close synchronism with the orbital period, similar to what happens in the Polar cataclysmic variables. 1E 161348?5055 could be the first case of a magnetar born in a young low-mass binary system.

Signature of a Newborn Black Hole from the Collapse of a Supra-massive Millisecond Magnetar

Abstract: The X-ray plateau followed by a steep decay (\"internal plateau\") has been observed in both long and short gamma-ray burst (GRBs), implying a millisecond magnetar operating in some GRBs. The sharp decay at the end of plateau, marking the abrupt cessation of the magnetar central engine, has been considered as the collapse of a supra-massive magnetar to a black hole (BH) when it spins down. If \"internal plateau\" is indeed the evidence of a magnetar central engine, a natural expectation is a signature from the new-born BH in some candidates. In this work, we find that GRB 070110 is a particular case, which shows a small X-ray bump following its \"internal plateau\". We interpret the plateau with a spin-down supra-massive magnetar and the X-ray bump with a fall-back BH accretion. This indicates that the new-born BH is likely active in some GRBs. Therefore, GRB 070110-like events may provide a further support to the magnetar central engine model and enable us to investigate the properties of the magnetar as well as the new-born BH.

Optical Transients Powered by Magnetars: Dynamics, Light Curves, and Transition to the Nebular Phase

Abstract: Millisecond magnetars can be formed via several channels: core-collapse of massive stars, accretion-induced collapse of white dwarfs (WDs), double WD mergers, double neutron star (NS) mergers, and WD-NS mergers. Because the mass of ejecta from these channels could be quite different, their light curves are also expected to be diverse. We evaluate the dynamic evolution of optical transients powered by millisecond magnetars. We find that the magnetar with short spin-down timescale converts its rotational energy mostly into the kinetic energy of the transient, while the energy of a magnetar with long spin-down timescale goes into radiation of the transient. This leads us to speculate that hypernovae could be powered by magnetars with short spin-down timescales. At late times the optical transients will gradually evolve into a nebular phase because of the photospheric recession. We treat the photosphere and nebula separately because their radiation mechanisms are different. In some cases the ejecta could be light enough that the magnetar can accelerate it to a relativistic speed. It is well known that the peak luminosity of a supernova (SN) occurs when the luminosity is equal to the instantaneous energy input rate, as shown by Arnett (1979). We show that photospheric recession and relativistic motion can modify this law. The photospheric recession always leads to a delay of the peak time $t_{\mathrm{pk}}$ relative to the time $t_{\times }$ at which the SN luminosity equals the instantaneous energy input rate. Relativistic motion, however, may change this result significantly.

Chandra and XMM-Newton imaging and spectroscopic study of the supernova remnant Kes 73 hosting the magnetar 1E 1841-045

Abstract: We present a Chandra and XMM-Newton study of the supernova remnant (SNR) Kes 73 hosting the anomalous X-ray pulsar 1E 1841-045. The Chandra image reveals clumpy structures across the remnant with enhanced emission along the western rim. The X-ray emission fills the radio shell and spatially correlates with the infrared image. The global X-ray spectrum is described by a two-component thermal model with a column density N_H ~ 2.6e22 cm^{-2} and a total luminosity of L_X ~ 3.3e37 ergs/s (0.5-10 keV, at an assumed distance of 8.5 kpc). The soft component is characterized by a temperature kT_s ~ 0.5 keV, a high ionization timescale, and enhanced Si and S abundances suggesting emission that is dominated by shocked ejecta. The hard component has a temperature kT_h ~ 1.6 keV, a relatively low ionization timescale, and mostly solar abundances suggesting emission that is dominated by interstellar/circumstellar shocked material. A spatially resolved spectroscopy study reveals no significant variations in the spectral properties. We infer an SNR age ranging between 750 yr and 2100 yr, an explosion energy of ~0.3e51 ergs and a shock velocity of 1200 km/s (under the Sedov phase assumption). We also discuss the possible scenario for Kes 73 expanding into the late red supergiant wind phase of its massive progenitor. Comparing the inferred metal abundances to core-collapse nucleosynthesis model yields, we estimate a progenitor mass >20 solar masses, adding a candidate to the growing list of highly magnetized neutron stars proposed to be associated with very massive progenitors.