Magnetar

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

Magnetic field decay in neutron stars: from soft gamma repeaters to ‘weak-field magnetars’

Abstract: The recent discovery of the ‘weak-field, old magnetar’ soft gamma repeater (SGR) J0418+5729, whose dipole magnetic field, Bdip, is less than 7.5 × 10 12 G, has raised perplexing questions: how can the neutron star produce SGR-like bursts with such a low magnetic field? What powers the observed X-ray emission when neither the rotational energy nor the magnetic dipole energy is sufficient? These observations, which suggest either a much larger energy reservoir or a much younger true age (or both), have renewed the interest in the evolutionary sequence of magnetars. We examine here a phenomenological model for the magnetic field decay: u Bdip ∝ B 1+α dip and compare its predictions with the observed period, P, the period derivative, u P , and the X-ray luminosity, LX, of magnetar candidates. We find a strong evidence for a dipole field decay on a time-scale of ∼10 3 yr for the strongest (Bdip ∼ 10 15 G) field objects, with a decay index within the range 1 ≤ α< 2 and more likely within 1.5 α 1.8. The decaying field implies a younger age than what is implied by P/ 2 u P . Surprisingly, even with the younger age, the energy released in the dipole field decay is insufficient to power the X-ray emission, suggesting the existence of a stronger internal field, Bint. Examining several models for the internal magnetic field decay, we find that it must have a very large ( 10 16 G)

The Gamma-Ray Giant Flare from SGR 1806?20: Evidence of Crustal Cracking via Initial Timescales

Abstract: Soft γ-ray repeaters (SGRs) are neutron stars that emit short (1 s) and energetic (1042 ergs s-1) bursts of soft γ-rays. Only four of them are currently known. Occasionally, SGRs have been observed to emit much more energetic "giant flares" (~1044-1045 ergs s-1). These are exceptional and rare events. We report here on serendipitous observations of the intense γ-ray flare from SGR 1806-20 that occurred on 2004 December 27. Unique data from the Cluster and Double Star TC-2 satellites, designed to study the Earth's magnetosphere, provide the first observational evidence of three separate timescales within the early (first 100 ms) phases of this class of events. These observations reveal that in addition to the initial very steep (<0.25 ms) X-ray onset, there is first a 4.9 ms exponential rise timescale followed by a continued exponential rise in intensity on a timescale of 70 ms. These three timescales are a prominent feature of current theoretical models, including the timescale (several milliseconds) for fracture propagation in the crust of the neutron star.

Accreting magnetars: a new type of high-mass X-ray binaries?

Abstract: The discovery of very slow pulsations (Pspin = 5560 s) has solved the long-standing question of the nature of the compact object in the high-mass X-ray binary 4U 2206+54 but has posed new ones. According to spin evolutionary models in close binary systems, such slow pulsations require a neutron star magnetic field strength larger than the quantum critical value of 4.4 × 10 13 G, suggesting the presence of a magnetar. We present the first XMM–Newton observations of 4U 2206+54 and investigate its spin evolution. We find that the observed spin-down rate agrees with the magnetar scenario. We analyse Integral Spacecraft GammaRay Imager (ISGRI)/INTErnational Gamma-RAy Laboratory (INTEGRAL) observations of 4U 2206+54 to search for the previously suggested cyclotron resonance scattering feature at ∼30 keV. We do not find a clear indication of the presence of the line, although certain spectra display shallow dips, not always at 30 keV. The association of these dips with a cyclotron line is very dubious because of its apparent transient nature. We also investigate the energy spectrum of 4U 2206+54 in the energy range 0.3–10 keV with unprecedented detail and report for the first time the detection of very weak 6.5 keV fluorescence iron lines. The photoelectric absorption is consistent with the interstellar value, indicating very small amount of local matter, which would explain the weakness of the florescence lines. The lack of matter locally to the source may be the consequence of the relatively large orbital separation of the two components of the binary. The wind would be too tenuous in the vicinity of the neutron star.

Fast radio bursts at the dawn of the 2020s

Abstract: Since the discovery of the first fast radio burst (FRB) in 2007, and their confirmation as an abundant extragalactic population in 2013, the study of these sources has expanded at an incredible rate. In our 2019 review on the subject we presented a growing, but still mysterious, population of FRBs -- 60 unique sources, 2 repeating FRBs, and only 1 identified host galaxy. However, in only a few short years new observations and discoveries have given us a wealth of information about these sources. The total FRB population now stands at over 600 published sources, 24 repeaters, and 19 host galaxies. Higher time resolution data, sustained monitoring, and precision localisations have given us insight into repeaters, host galaxies, burst morphology, source activity, progenitor models, and the use of FRBs as cosmological probes. The recent detection of a bright FRB-like burst from the Galactic magnetar SGR~1935+2154 provides an important link between FRBs and magnetars. There also continue to be surprising discoveries, like periodic modulation of activity from repeaters and the localisation of one FRB source to a relatively nearby globular cluster associated with the M81 galaxy. In this review, we summarise the exciting observational results from the past few years. We also highlight their impact on our understanding of the FRB population and proposed progenitor models. We build on the introduction to FRBs in our earlier review, update our readers on recent results, and discuss interesting avenues for exploration as the field enters a new regime where hundreds to thousands of new FRBs will be discovered and reported each year.