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An upper limit to the energy of gamma-ray bursts indicates that GRB/SNe are powered by magnetars  [PDF]
P. Mazzali,A. MacFadyen,S. Woosley,E. Pian,M. Tanaka
Physics , 2014, DOI: 10.1093/mnras/stu1124
Abstract: The kinetic energy of supernovae (SNe) accompanied by gamma-ray bursts (GRBs) tends to cluster near E52 erg, with 2.E52 erg an upper limit to which no compelling exceptions are found (assuming a certain degree of asphericity), and it is always significantly larger than the intrinsic energy of the GRB themselves (corrected for jet collimation). This energy is strikingly similar to the maximum rotational energy of a neutron star rotating with period 1 ms. It is therefore proposed that all GRBs associated with luminous SNe are produced by magnetars. GRBs that result from black hole formation (collapsars) may not produce luminous SNe. X-ray Flashes (XRFs), which are associated with less energetic SNe, are produced by neutron stars with weaker magnetic field or lower spin.
Magnetars and Gamma Ray Bursts  [PDF]
N. Bucciantini
Physics , 2012, DOI: 10.1017/S1743921312013075
Abstract: In the last few years, evidences for a long-lived and sustained engine in Gamma Ray Bursts (GRBs) have increased the attention to the so called millisecond-magnetar model, as a competitive alternative to the standard collapsar scenario. I will review here the key aspects of the {\it millisecond magnetar} model for Long Duration Gamma Ray Bursts (LGRBs). I will briefly describe what constraints, present observations put on any engine model, both in term of energetic, outflow properties, and the relation with the associated Supernova (SN). For each of these I will show how the millisecond magnetar model satisfies the requirements, what are the limits of the model, how can it be further tested, and what observations might be used to discriminate against it. I will also discuss numerical results that show the importance of the confinement by the progenitor star in explaining the formation of a collimated outflow, how a detailed model for the evolution of the central engine can be built, and show that a wide variety of explosive events can be explained by different magnetar parameters. I will conclude with a suggestion that magnetars might be at the origin of the Extended Emission (EE) observed in a significant fraction of Short GRBs.
Quasi-Periodic Oscillations in Short Recurring Bursts of the magnetars SGR 1806-20 and SGR 1900+14 Observed With RXTE  [PDF]
D. Huppenkothen,L. M. Heil,A. L. Watts,E. G??ü?
Physics , 2014, DOI: 10.1088/0004-637X/795/2/114
Abstract: Quasi-periodic oscillations (QPOs) observed in the giant flares of magnetars are of particular interest due to their potential to open up a window into the neutron star interior via neutron star asteroseismology. However, only three giant flares have been observed. We therefore make use of the much larger data set of shorter, less energetic recurrent bursts. Here, we report on a search for QPOs in a large data set of bursts from the two most burst-active magnetars, SGR 1806-20 and SGR 1900+14, observed with the Rossi X-ray Timing Explorer (RXTE). We find a single detection in an averaged periodogram comprising 30 bursts from SGR 1806-20, with a frequency of 57 Hz and a width of 5 Hz, remarkably similar to a giant flare QPO observed from SGR 1900+14. This QPO fits naturally within the framework of global magneto-elastic torsional oscillations employed to explain the giant flare QPOs. Additionally, we uncover a limit on the applicability of Fourier analysis for light curves with low background count rates and strong variability on short timescales. In this regime, standard Fourier methodology and more sophisticated Fourier analyses fail in equal parts by yielding an unacceptably large number of false positive detections. This problem is not straightforward to solve in the Fourier domain. Instead, we show how simulations of light curves can offer a viable solution for QPO searches in these light curves.
A Possible Conection Between Magnetars and Gamma-Ray Bursts  [cached]
M. P. Allen,J. E. Horvath,J. A. Pacheco de Freitas
Revista mexicana de astronomía y astrofísica , 2001,
Abstract: We argue that magnetars, neutron stars with strong magnetic fields, can be the powerhouses behind some gamma-ray bursts (GRBs), thanks to effects only possible in presence of high magnetic fields. The production of axions in supernova cores by pair anihilation e+e- -> a is possible in such intense magnetic fields. A fraction of the ~ 1053 erg of binding energy of the newly created neutron star escapes with this axion flux. However, axions in high magnetic fields decay through a -> e+e- with mean life tau ~ 10-4 s, therefore close to the magnetar, producing the relativistic shock with ~ 1051 erg ("fireball") and the GRB. At least one GRB was coincident with an "anomalous" supernova Ic, supporting this scenario.
Conference Summary: Supernovae and Gamma-Ray Bursts  [PDF]
J. Craig Wheeler
Physics , 1999,
Abstract: There are hints that nearby Type Ia supernovae may be a little different than those at large redshift. Confidence in the conclusion that there is a cosmological constant and an accelerating Universe thus still requires the hard work of sorting out potential systematic effects. Polarization data show that core-collapse supernovae (Type II and Ib/c) probably depart strongly from spherical symmetry. Evidence for exceedingly energetic supernovae must be considered self-consistently with evidence that they are asymmetric, a condition that affects energy estimates. Jets arising near the compact object can produce such asymmetries. There is growing conviction that gamma-ray bursts intrinsically involve collimated or jet-like flow and hence that they are also strongly asymmetric. SN 1998bw is a potential rosetta stone that will help to sort out the physics of explosive events. Are events like SN 1998bw more closely related to "ordinary" supernovae or "hypernovae?" Do they leave behind neutron stars as "ordinary" pulsars or "magnetars" or is the remnant a black hole? Are any of these events associated with classic cosmic gamma-ray bursts as suggested by the supernova-like modulation of the afterglows of GRB 970228, GRB 980326 and GRB 990712?
Central compact objects, superslow X-ray pulsars, gamma-ray bursts: do they have anything to do with magnetars?  [PDF]
H. Tong,W. Wang
Physics , 2014,
Abstract: Magnetars and many of the magnetar-related objects are summarized together and discussed. It is shown that there is an abuse of language in the use of "magnetar". Anomalous X-ray pulsars and soft gamma-ray repeaters are well-known magnetar candidates. The current so called anti-magnetar (for central compact objects), accreting magnetar (for superslow X-ray pulsars in high mass X-ray binaries), and millisecond magnetar (for the central engine of some gamma-ray bursts), they may not be real magnetars in present understandings. Their observational behaviors are not caused by the magnetic energy. Many of them are just neutron stars with strong surface dipole field. A neutron star plus strong dipole field is not a magnetar. The characteristic parameters of the neutron stars for the central engine of some gamma-ray bursts are atypical from the neutron stars in the Galaxy. Possible signature of magnetic activities in accreting systems are discussed, including repeated bursts and a hard X-ray tail. China's future hard X-ray modulation telescope may contribute to finding some magnetic activities in accreting neutron star systems.
Magnetars  [PDF]
Paolo Cea
Physics , 2005,
Abstract: P-stars are compact stars made of up and down quarks in beta-equilibrium with electrons in a chromomagnetic condensate. P-stars are able to account for compact stars like RXJ 1856.5-3754 and RXJ 0720.4-3125, stars with radius comparable with canonical neutron stars, as well as super massive compact objects like SgrA*. We discuss p-stars endowed with super strong dipolar magnetic field which, following consolidated tradition in literature, are referred to as magnetars. We show that soft gamma-ray repeaters and anomalous X-ray pulsars can be understood within our theory. We find a well defined criterion to distinguish rotation powered pulsars from magnetic powered pulsars. We show that glitches, that in our magnetars are triggered by magnetic dissipative effects in the inner core, explain both the quiescent emission and bursts in soft gamma-ray repeaters and anomalous X-ray pulsars. We are able to account for the braking glitch from SGR 1900+14 and the normal glitch from AXP 1E 2259+586 following a giant burst. We discuss and explain the observed anti correlation between hardness ratio and intensity. Within our magnetar theory we are able to account quantitatively for light curves for both gamma-ray repeaters and anomalous X-ray pulsars. In particular we explain the puzzling light curve after the June 18, 2002 giant burst from AXP 1E 2259+586, so that we feel this last event as the Rosetta Stone for our theory. Finally, in Appendix we discuss the origin of the soft emission not only for soft gamma-ray repeaters and anomalous X-ray pulsars, but also for isolated X-ray pulsars. We also offer an explanation for the puzzling spectral features in 1E 1207.4-5209.
X-Ray Afterglow Plateaus of Long Gamma-Ray Bursts: Further Evidence for Millisecond Magnetars  [PDF]
S. X. Yi,Z. G. Dai,X. F. Wu,F. Y. Wang
Physics , 2014,
Abstract: Many long-duration gamma-ray bursts (GRBs) were observed by {\it Swift}/XRT to have plateaus in their X-ray afterglow light curves. This plateau phase has been argued to be evidence for long-lasting activity of magnetar (ultra-strongly magnetized neutron stars) central engines. However, the emission efficiency of such magnetars in X-rays is still unknown. Here we collect 24 long GRB X-ray afterglows showing plateaus followed by steep decays. We extend the well-known relationship between the X-ray luminosity ${L_{\mathrm{X}}}$ and spin-down luminosity $L_{\mathrm{sd}}$ of pulsars to magnetar central engines, and find that the initial rotation period $P_{0}$ ranges from 1 ms to 10 ms and that the dipole magnetic field $B$ is centered around $10^{15}$ G. These constraints not only favor the suggestion that the central engines of some long GRBs are very likely to be rapidly rotating magnetars but also indicate that the magnetar plateau emission efficiency in X-rays is close to 100%.
Magnetars, Gamma-ray Bursts, and Very Close Binaries  [PDF]
A. I. Bogomazov,S. B. Popov
Physics , 2009, DOI: 10.1134/S1063772909040052
Abstract: We consider the possible existence of a common channel of evolution of binary systems, which results in a gamma-ray burst during the formation of a black hole or the birth of a magnetar during the formation of a neutron star. We assume that the rapid rotation of the core of a collapsing star can be explained by tidal synchronization in a very close binary. The calculated rate of formation of rapidly rotating neutron stars is qualitatively consistent with estimates of the formation rate of magnetars. However, our analysis of the binarity of newly-born compact objects with short rotational periods indicates that the fraction of binaries among them substantially exceeds the observational estimates. To bring this fraction into agreement with the statistics for magnetars, the additional velocity acquired by a magnetar during its formation must be primarily perpendicular to the orbital plane before the supernova explosion, and be large.
Magnetars: the physics behind observations  [PDF]
Roberto Turolla,Silvia Zane,Anna Watts
Physics , 2015, DOI: 10.1088/0034-4885/78/11/116901
Abstract: Magnetars are the strongest magnets in the present universe and the combination of extreme magnetic field, gravity and density makes them unique laboratories to probe current physical theories (from quantum electrodynamics to general relativity) in the strong field limit. Magnetars are observed as peculiar, burst--active X-ray pulsars, the Anomalous X-ray Pulsars (AXPs) and the Soft Gamma Repeaters (SGRs); the latter emitted also three "giant flares," extremely powerful events during which luminosities can reach up to 10^47 erg/s for about one second. The last five years have witnessed an explosion in magnetar research which has led, among other things, to the discovery of transient, or "outbursting," and "low-field" magnetars. Substantial progress has been made also on the theoretical side. Quite detailed models for explaining the magnetars' persistent X-ray emission, the properties of the bursts, the flux evolution in transient sources have been developed and confronted with observations. New insight on neutron star asteroseismology has been gained through improved models of magnetar oscillations. The long-debated issue of magnetic field decay in neutron stars has been addressed, and its importance recognized in relation to the evolution of magnetars and to the links among magnetars and other families of isolated neutron stars. The aim of this paper is to present a comprehensive overview in which the observational results are discussed in the light of the most up-to-date theoretical models and their implications. This addresses not only the particular case of magnetar sources, but the more fundamental issue of how physics in strong magnetic fields can be constrained by the observations of these unique sources.
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