Magnetar Model Research Articles

Constraining the Ellipticity of the Newborn Magnetar with the Observational Data of Long Gamma-Ray Bursts

The X-ray plateau emission observed in many long gamma-ray bursts (LGRBs) has been usually interpreted as the spin-down luminosity of a rapidly spinning, highly magnetized neutron star (millisecond magnetar). If this is true, then the magnetar may emit extended gravitational wave (GW) emission associated with the X-ray plateau due to nonaxisymmetric deformation or various stellar oscillations. The advanced LIGO and Virgo detectors have searched for long-duration GW transients for several years; no evidence of GWs from any magnetar has been found until now. In this work, we attempt to search for signatures of GW radiation in the electromagnetic observation of 30 LGRBs under the assumption of the magnetar model. We utilize the observations of the LGRB plateau to constrain the properties of the newborn magnetar, including the initial spin period P 0, dipole magnetic field strength B p , and the ellipticity ϵ. We find that there are some tight relations between magnetar parameters, e.g., and . In addition, we derive the GW strain for the magnetar sample via their spin-down processes, and find that the GWs from these objects may not be detectable by the aLIGO and Einstein Telescope (ET) detectors. For a rapidly spinning magnetar (P ∼ 1 ms, B ∼ 1015 G), the detection horizon for the advanced LIGO O5 detector is ∼180 Mpc. The detection of such a GW signal associated with the X-ray plateau would be a smoking gun that the central engine of a GRB is a magnetar.

Arecibo observations of a burst storm from FRB 20121102A in 2016

ABSTRACT FRB 20121102A is the first known fast radio burst (FRB) from which repeat bursts were detected, and one of the best-studied FRB sources in the literature. Here we report on the analysis of 478 bursts (333 previously unreported) from FRB 20121102A using the 305-m Arecibo telescope – detected during approximately 59 hours of observations between December 2015 and October 2016. The majority of bursts are from a burst storm around September 2016. This is the earliest available sample of a large number of FRB 20121102A bursts, and it thus provides an anchor point for long-term studies of the source’s evolving properties. We observe that the bursts separate into two groups in the width-bandwidth-energy parameter space, which we refer to as the low-energy bursts (LEBs) and high-energy bursts (HEBs). The LEBs are typically longer duration and narrower bandwidth than the HEBs, reminiscent of the spectro-temporal differences observed between the bursts of repeating and non-repeating FRBs. We fit the cumulative burst rate-energy distribution with a broken power law and find that it flattens out toward higher energies. The sample shows a diverse zoo of burst morphologies. Notably, burst emission seems to be more common at the top than the bottom of our 1150–1730 MHz observing band. We also observe that bursts from the same day appear to be more similar to each other than to those of other days, but this observation requires confirmation. The wait times and burst rates that we measure are consistent with previous studies. We discuss these results, primarily in the context of magnetar models.

Bumpy Declining Light Curves Are Common in Hydrogen-poor Superluminous Supernovae

Recent work has revealed that the light curves of hydrogen-poor (Type I) superluminous supernovae (SLSNe), thought to be powered by magnetar central engines, do not always follow the smooth decline predicted by a simple magnetar spin-down model. Here we present the first systematic study of the prevalence and properties of “bumps” in the post-peak light curves of 34 SLSNe. We find that the majority (44%–76%) of events cannot be explained by a smooth magnetar model alone. We do not find any difference in supernova properties between events with and without bumps. By fitting a simple Gaussian model to the light-curve residuals, we characterize each bump with an amplitude, temperature, phase, and duration. We find that most bumps correspond with an increase in the photospheric temperature of the ejecta, although we do not see drastic changes in spectroscopic features during the bump. We also find a moderate correlation (ρ ≈ 0.5; p ≈ 0.01) between the phase of the bumps and the rise time, implying that such bumps tend to happen at a certain “evolutionary phase,” (3.7 ± 1.4)t rise. Most bumps are consistent with having diffused from a central source of variable luminosity, although sources further out in the ejecta are not excluded. With this evidence, we explore whether the cause of these bumps is intrinsic to the supernova (e.g., a variable central engine) or extrinsic (e.g., circumstellar interaction). Both cases are plausible, requiring low-level variability in the magnetar input luminosity, small decreases in the ejecta opacity, or a thin circumstellar shell or disk.

Scattering of Ultrastrong Electromagnetic Waves by Magnetized Particles.

Observations of powerful radio waves from neutron star magnetospheres raise the question of how strong waves interact with particles in a strong background magnetic field B_{bg}. This problem is examined by solving the particle motion in the wave. Remarkably, waves with amplitudes E_{0}>B_{bg} pump particle energy via repeating resonance events, quickly reaching the radiation reaction limit. As a result, the wave is scattered with a huge cross section. This fact has implications for models of fast radio bursts and magnetars. Particles accelerated in the wave emit γ rays, which can trigger an e^{±} avalanche and, instead of silent escape, the wave will produce x-ray fireworks.

Optical Observations and Modeling of the Superluminous Supernova 2018lfe

We present optical imaging and spectroscopy of SN 2018lfe, which we classify as a Type I superluminous supernova (SLSN-I) at a redshift of z = 0.3501 ± 0.0004 with a peak absolute magnitude of M r = −22.1 ± 0.1 mag, one of the brightest SLSNe discovered. SN 2018lfe was identified for follow-up using our FLEET machine-learning pipeline. Both the light curve and the spectra of SN 2018lfe are consistent with the broad population of SLSNe. We fit the light curve with a magnetar central engine model and find an ejecta mass of M ej ≈ 3.8 M ⊙, a magnetar spin period of P ≈ 2.9 ms, and a magnetic field strength of B ⊥ ≈ 2.8 × 1014 G. The magnetic field strength is near the top of the distribution for SLSNe, while the spin period and ejecta mass are near the median values of the distribution for SLSNe. From late-time imaging and spectroscopy we find that the host galaxy of SN 2018lfe has an absolute magnitude of M r = −17.85 ± 0.24, (L B = 0.029 ± 0.007L*), and an inferred metallicity of Z ≈ 0.3 Z ⊙ and star formation rate of ≈0.8 M ⊙ yr−1.

Two years of optical and NIR observations of the superluminous supernova UID 30901 discovered by the UltraVISTA SN survey

ABSTRACT We present deep optical and near-infrared photometry of UID 30901, a superluminous supernova (SLSN) discovered during the UltraVISTA survey. The observations were obtained with VIRCAM (YJHKs) mounted on the VISTA telescope, DECam (griz) on the Blanco telescope, and SUBARU Hyper Suprime-Cam (HSC; grizy). These multiband observations comprise +700 d making UID 30901 one of the best photometrically followed SLSNe to date. The host galaxy of UID 30901 is detected in a deep HST F814W image with an AB magnitude of 27.3 ± 0.2. While no spectra exist for the SN or its host galaxy, we perform our analysis assuming z = 0.37, based on the photometric redshift of a possible host galaxy found at a projected distance of 7 kpc. Fitting a blackbody to the observations, the radius, temperature, and bolometric light curve are computed. We find a maximum bolometric luminosity of 5.4 ± 0.34 × 1043 erg s−1. A flattening in the light curve beyond 600 d is observed and several possible causes are discussed. We find the observations to clearly favour an SLSN type I, and plausible power sources such as the radioactive decay of 56Ni and the spin-down of a magnetar are compared to the data. We find that the magnetar model yields a good fit to the observations with the following parameters: a magnetic field B = 1.4 ± 0.3 × 1014 G, spin period of P = 6.0 ± 0.1 ms, and ejecta mass $M_{\mathrm{ ej}} = 11.9^{+4.8}_{-6.4} \,\mathrm{ M}_{\odot }$.

Early evolution of a newborn magnetar with strong precession motion in GRB 180620A

ABSTRACT The observed early X-ray plateau in the afterglow lightcurves of some gamma-ray bursts (GRBs) is attributed to the dipole radiations (DRs) of a newborn magnetar. A quasi-periodic oscillation (QPO) signal in the plateau would be strong evidence of the magnetar precession motion. By making a time-frequency domain analysis for the X-ray afterglow lightcurve of GRB 180620A, we find a QPO signal of ∼650 s in its early X-ray plateau. We fit the lightcurve with a magnetar precession model by adopting the Markov chain Monte Carlo algorithm. The observed lightcurve and the QPO signal are well represented with our model. The derived magnetic field strength of the magnetar is $B_{\rm p}= (1.02^{+0.59}_{-0.61})\times 10^{15}$ G. It rapidly spins down with angular velocity evolving as Ωs ∝ (1 + t/τsd)−0.96, where τsd = 9430 s. Its precession velocity evolution is even faster than Ωs, i.e. Ωp ∝ (1 + t/τp)−2.18 ± 0.11, where τp = 2239 ± 206 s. The inferred braking index is n = 2.04. We argue that the extra energy loss via the magnetospheric processes results in its rapid spin-down, low braking index, and strong precession motion of the magnetar.

IPTF 16asu Revisited: A Rapidly Evolving Superluminous Broad-lined Ic Supernova?

Abstract In this paper, we fit the spectral energy distributions of iPTF 16asu, which has so far been classified as a luminous rapidly evolving broad-lined Ic supernova (SN Ic-BL), and reconstruct its postpeak bolometric light curve. We find that the luminosity of the postpeak bolometric light curve of iPTF 16asu is about 3 times that of the pseudobolometric light curve derived in the literature, and the extrapolated peak luminosity exceeds ∼1044 erg s−1, which is higher than the threshold of superluminous supernovae (SLSNe). We then use the 56Ni model and the magnetar plus 56Ni model to fit the multiband light curves of iPTF 16asu, and construct the theoretical bolometric light curve using the best-fitting theoretical multiband light curves. We find that the magnetar plus 56Ni model can account for the photometry of iPTF 16asu, and the peak luminosity of its theoretical bolometric light curve is ∼1.06 × 1044 erg s−1. We suggest that iPTF 16asu and similar SNe (e.g., SN 2018gep) constitute the class of rapidly evolving SLSNe Ic-BL.

Fast Radio Bursts by High-frequency Synchrotron Maser Emission Generated at the Reverse Shock of a Powerful Magnetar Flare

Abstract We consider a magnetar flare model for fast radio bursts (FRBs). We show that millisecond bursts of sufficient power can be generated by synchrotron maser emission ignited at the reverse shock propagating through the weakly magnetized material that forms the magnetar flare. If the maser emission is generated in an anisotropic regime (due to the geometry of the production region or presence of an intense external source of stimulating photons), the duration of the maser flashes is similar to the magnetar flare duration even if the shock front radius is large. Our scenario allows for relaxing the requirements for several key parameters: the magnetic field strength at the production site, luminosity of the flare, and the production site bulk Lorentz factor. To check the feasibility of this model, we study the statistical relation between powerful magnetar flares and the rate of FRBs. The expected ratio is derived by convoluting the redshift-dependent magnetar density with its flare luminosity function above the energy limit determined by the FRB detection threshold. We obtain that only a small fraction, ∼10−5, of powerful magnetar flares trigger FRBs. This ratio agrees surprisingly well with our estimates: we obtained that 10% of magnetars should be in the evolutionary phase suitable for the production of FRBs, and only 10−4 of all flares are expected to be weakly magnetized, which is a necessary condition for the high-frequency maser emission.

Post maximum light and late time optical imaging polarimetry of type I superluminous supernova 2020znr

ABSTRACTOptical imaging polarimetry was conducted on the hydrogen poor superluminous supernova 2020znr during three phases after maximum light (≈ +34 d, +288 d, and +289 d). After instrumental and interstellar polarization correction, all measurements are consistent with null-polarization detection. Modelling the light curve with a magnetar spin-down model shows that SN2020znr has similar magnetar and ejecta parameters to other SLSNe. A comparison of the best-fitting values discussed in the literature on SN 2017egm and SN 2015bn, two hydrogen poor SLSNe showing an increase of polarization after maximum light, suggests that SN 2020znr has higher mass ejecta that may prevent access to the geometry of the inner ejecta with optical polarimetry. The combined information provided by spectroscopy and light-curve analysis of type I SLSNe may be an interesting avenue to categorize the polarization properties of this class of transients. This approach would require to expand the sample of SLSNe polarimetry data currently available with early and late time epochs new measurements.

Fitting XMM-Newton observations of the AXP 1RXS J170849.0−400910 with four magnetar surface emission models, and predictions for X-ray polarization observations with IXPE

Context. Phase-resolved spectral and spectropolarimetric X-ray observations of magnetars present us with the opportunity to test models of the origin of the X-ray emission from these objects, and to constrain the properties of the neutron star surface and atmosphere. Aims. Our first aim is to use archival XMM-Newton observations of the magnetar 1RXS J170849.0−400910 to ascertain how well four emission models describe the phase-resolved XMM-Newton energy spectra. Our second aim is to evaluate the scientific potential of future spectropolarimetric observations of 1RXS J170849.0−400910 with the Imaging X-ray Polarimetry Explorer (IXPE) scheduled for launch in late 2021. The most salient questions are whether IXPE is able to distinguish between the different emission models, and whether IXPE can unambiguously detect the signatures of quantum electrodynamics (QED) effects in strong magnetic fields. Methods. We used numerical radiation transport calculations for a large number of different system parameters to predict the X-ray flux and polarization energy spectra of the source 1RXS J170849.0−400910. Based on the numerical results, we developed a new model to fit phase-resolved and phase-averaged X-ray spectral (i.e., XMM-Newton and IXPE) and spectropolarimetric (IXPE) data. In order to test the sensitivity of IXPE to strong-field QED effects, we fit a simulated IXPE observation with two versions of the model, i.e., with and without QED effects accounted for. Results. The fixed-ions condensed surface model gives the best description of the phase-resolved XMM-Newton spectra, followed by the blackbody and free-ions condensed surface models. The magnetized atmosphere model gives a poor description of the data and seems to be largely excluded. Simulations show that the IXPE observations of sources such as 1RXS J170849.0−400910 will allow us to cleanly distinguish between high-polarization (blackbody, magnetized atmosphere) and low-polarization (condensed surface) models. If the blackbody or magnetized atmosphere models apply, IXPE can easily prove QED effects based on ∼200 ksec observations as studied here; longer IXPE observation times will be needed for a clear detection in the case of the condensed surface models. Conclusions. The XMM-Newton data have such a good signal-to-noise ratio that they reveal some limitations of the theoretical models. Notwithstanding this caveat, the fits clearly favor the fixed-ions condensed surface and blackbody models over the free-ions condensed surface and magnetized atmosphere models. The IXPE polarization information will greatly help us to figure out how to improve the models. The first detection of strong-field QED effects in the signal from astrophysical sources seems possible if an adequate amount of time is dedicated to the observations.

A Decade and a Half of Fast Radio Burst Observations

Fast radio bursts (FRBs) have a story which has been told and retold many times over the past few years as they have sparked excitement and controversy since their pioneering discovery in 2007. The FRB class encompasses a number of microsecond- to millisecond-duration pulses occurring at Galactic to cosmological distances with energies spanning about 8 orders of magnitude. While most FRBs have been observed as singular events, a small fraction of them have been observed to repeat over various timescales leading to an apparent dichotomy in the population. ∼50 unique progenitor theories have been proposed, but no consensus has emerged for their origin(s). However, with the discovery of an FRB-like pulse from the Galactic magnetar SGR J1935+2154, magnetar engine models are the current leading theory. Overall, FRB pulses exhibit unique characteristics allowing us to probe line-of-sight magnetic field strengths, inhomogeneities in the intergalactic/interstellar media, and plasma turbulence through an assortment of extragalactic and cosmological propagation effects. Consequently, they are formidable tools to study the Universe. This review follows the progress of the field between 2007 and 2020 and presents the science highlights of the radio observations.

SN 2019hcc: a Type II supernova displaying early O ii lines

ABSTRACT We present optical spectroscopy together with ultraviolet, optical, and near-infrared photometry of SN 2019hcc, which resides in a host galaxy at redshift 0.044, displaying a sub-solar metallicity. The supernova spectrum near peak epoch shows a ‘w’ shape at around 4000 Å which is usually associated with O ii lines and is typical of Type I superluminous supernovae. SN 2019hcc post-peak spectra show a well-developed H α P-Cygni profile from 19 d past maximum and its light curve, in terms of its absolute peak luminosity and evolution, resembles that of a fast-declining Hydrogen-rich supernova (SN IIL). The object does not show any unambiguous sign of interaction as there is no evidence of narrow lines in the spectra or undulations in the light curve. Our tardis spectral modelling of the first spectrum shows that carbon, nitrogen, and oxygen (CNO) at 19 000 K reproduce the ‘w’ shape and suggests that a combination of non-thermally excited CNO and metal lines at 8000 K could reproduce the feature seen at 4000 Å. The Bolometric light-curve modelling reveals that SN 2019hcc could be fit with a magnetar model, showing a relatively strong magnetic field (B > 3 × 1014 G), which matches the peak luminosity and rise time without powering up the light curve to superluminous luminosities. The high-energy photons produced by the magnetar would then be responsible for the detected O ii lines. As a consequence, SN 2019hcc shows that a ‘w’ shape profile at around 4000 Å, usually attributed to O ii, is not only shown in superluminous supernovae and hence it should not be treated as the sole evidence of the belonging to such a supernova type.

Studying magnetic fields of ultraluminous X-ray pulsars using different accretion torques

The magnetic field of ultraluminous X-ray (ULX) pulsars is the key parameter to understand the nature and accretion physics. However, the typical magnetic field values in these ULX pulsars are still under debate. We used six different torque models to study the magnetic fields of ULX pulsars, to see how derived magnetic fields change with different models, and to determine which models are more suitable for ULX pulsars. We took the currently available period, period derivative, and flux data of 7 confirmed ULX pulsars, M82 X-2, ULX NGC 7793 P13, ULX NGC 5907, NGC 300 ULX1, NGC 1313 X-2, M51 ULX-7, Swift J0243.6+6124, plus one potential ULX pulsars, SMC X-3. The magnetic fields of these ULX pulsars were constrained from two physical conditions: the spin-up process and near equilibrium. We checked possible dependence of the magnetic field estimations on the different torque models. The calculations suggest the accretion torque models by Ghosh and Lamb (1979), Wang (1995), Kluźniak and Rappaport (2007) and Campbell (2012) are more likely to support magnetar models for ULX pulsars, while Lovelace et al. (1995)'s model generally predicts the magnetic field in normal neutron stars. Implications of our results combined with other independent methods are also discussed, which will help us to understand the nature and rotational behavior of these ULX pulsars.

Late-time radio observations of the short GRB 200522A: constraints on the magnetar model

ABSTRACT GRB 200522A is a short duration gamma-ray burst (GRB) at redshift z= 0.554 characterized by a bright infrared counterpart. A possible, although not unambiguous, interpretation of the observed emission is the onset of a luminous kilonova powered by a rapidly rotating and highly magnetized neutron star, known as magnetar. A bright radio flare, arising from the interaction of the kilonova ejecta with the surrounding medium, is a prediction of this model. Whereas the available data set remains open to multiple interpretations (e.g. afterglow, r-process kilonova, magnetar-powered kilonova), long-term radio monitoring of this burst may be key to discriminate between models. We present our late-time upper limit on the radio emission of GRB 200522A, carried out with the Karl G. Jansky Very Large Array at 288 d after the burst. For kilonova ejecta with energy Eej $\approx 10^{53}\, \rm erg$, as expected for a long-lived magnetar remnant, we can already rule out ejecta masses $M_{\rm ej}\lesssim 0.03\, \mathrm{M}_\odot$ for the most likely range of circumburst densities n ≳ 10−3 cm−3. Observations on timescales of ≈ 3–10 yr after the merger will probe larger ejecta masses up to Mej ∼ 0.1 M⊙, providing a robust test to the magnetar scenario.

Variability of Late-time Radio Emission in the Superluminous Supernova PTF10hgi

Abstract We report the time variability of the late-time radio emission in a Type I superluminous supernova (SLSN), PTF10hgi, at z = 0.0987. The Karl G. Jansky Very Large Array 3 GHz observations at 8.6 and 10 yr after the explosion both detected radio emission with a ∼40% decrease in flux density in the second epoch. This is the first report of a significant variability of the late-time radio light curve in an SLSN. Through combination with previous measurements in two other epochs, we constrained both the rise and decay phases of the radio light curve over three years, peaking at approximately 8–9 yr after the explosion with a peak luminosity of L 3 GHz = 2 × 1021 W Hz−1. Possible scenarios for the origin of the variability are an active galactic nucleus (AGN) in the host galaxy, an afterglow caused by the interaction between an off-axis jet and circumstellar medium, and a wind nebula powered by a newly born magnetar. Comparisons with models show that the radio light curve can be reproduced by both the afterglow model and magnetar wind nebula model. Considering the flat radio spectrum at 1–15 GHz and an upper limit at 0.6 GHz obtained in previous studies, plausible scenarios are a low-luminosity flat-spectrum AGN or a magnetar wind nebula with a shallow injection spectral index.

A comparison between repeating bursts of FRB 121102 and giant pulses from Crab pulsar and its applications

There are some similarities between bursts of repeating fast radio bursts (FRBs) and giant pulses (GPs) of pulsars. To explore possible relations between them, we study the cumulative energy distributions of these two phenomena using the observations of repeating FRB 121102 and the GPs of Crab pulsar. We find that the power-law slope of GPs (with fluence ≥130 Jy·ms) is 2.85±0.10. The energy distribution of FRB 121102 can be well fitted by a smooth broken power-law function. For the bursts of FRB 121102 above the break energy (1.22 · 1037 erg), the best-fitting slope is 2.90 +0.55−0.44 , similar to the index of GPs at the same observing frequency (<1.4 GHz). We further discuss the physical origin of the repeating FRB 121102 in the framework of the super GPs model. And we find that the super GPs model involving a millisecond pulsar is workable and favored for explaining FRB 121102 despite that the magnetar burst model is more popular.

Rotating vector model for magnetars

ABSTRACT The modification of the rotating vector model in the case of magnetars are calculated. Magnetars may have twisted magnetic field compared with normal pulsars. The polarization position angle of magnetars will change in the case of a twisted magnetic field. For a twisted dipole field, we found that the position angle will change both vertically and horizontally. During the untwisting process of the magnetar magnetosphere, the modifications of the position angle will evolve with time monotonously. This may explain the evolution of the position angle in magnetar PSR J1622-4950 and XTE J1810-197. The relation between the emission point and the line of sight will also change. We suggest every magnetospheric models of magnetars also calculate the corresponding changes of position angle in their models. Order of magnitude estimation formula for doing this is given. This opens the possibility to extract the magnetic field geometry of magnetars from their radio polarization observations.

A Search for Hard X-Ray Bursts Occurring Simultaneously with Fast Radio Bursts in the Repeating FRB 121102

Abstract The nature of fast radio bursts (FRBs) is currently unknown. Repeating FRBs offer better observation opportunities than nonrepeating FRBs because their simultaneous multiwavelength counterparts might be identified. The magnetar flare model of FRBs is one of the most promising models that predict high-energy emission in addition to radio burst emission. To investigate such a possibility, we have searched for simultaneous and quasi-simultaneous short-term hard X-ray bursts in all Swift/BAT event mode data, which covered the periods when FRB detections were reported in the repeating FRB 121102, by making use of BAT’s arcminute-level spatial resolution and wide field of view. We did not find any significant hard X-ray bursts that occurred simultaneously with those radio bursts. We also investigated potential short X-ray bursts that occurred quasi-simultaneously with those radio bursts (occurrence time differs in the range from hundreds of seconds to thousands of seconds) and concluded that even the best candidates are consistent with background fluctuations. Therefore, our investigation concluded that there were no hard X-ray bursts detectable with Swift/BAT that occurred simultaneously or quasi-simultaneously with those FRBs in the repeating FRB 121102.

Double-peaked Pulse Profile of FRB 200428: Synchrotron Maser Emission from Magnetized Shocks Encountering a Density Jump

Abstract Very recently a fast radio burst (FRB) 200428 associated with a strong X-ray burst from the Galactic magnetar SGR 1935+2154 was detected; this provides direct evidence supporting the magnetar progenitor models of FRBs. Assuming that the FRB radiation mechanism is synchrotron maser emission from magnetized shocks, we develop a specific scenario by introducing a density-jump structure of upstream medium, thus making the double-peaked character of FRB 200428 a natural outcome. The luminosity and emission frequency of two pulses can be well explained in this scenario. Furthermore, we find that the synchrotron emission of shock-accelerated electrons is in the X-ray band, and therefore can be responsible for at least a portion of observed X-ray fluence. With the proper upgrade, in the future this density-jump scenario could be applied to FRBs with multiple peaks.