GRB 210323A:Signature of Long-lasting Lifetime of Supra-massive Magnetar as the Central Engine from the Merger of Binary Neutron Star

Theoretically,a supra-massive neutron star or magnetar may be formed after the merger of binary neutron stars.GRB210323A is a short-duration gamma-ray burst(GRB)with a duration of lasting~1 s.The light curve of the prompt emission of GRB 210323A shows a signal-peaked structure and a cutoff power-law model can adequately fit the spectra with E_p=1826±747.More interestingly,it has an extremely long-lasting plateau emission in the X-ray afterglow with a duration of~10^(4)s,and then follows a rapid decay with a decay slope~3.2.This temporal feature is challenging by invoking the external shock mode.In this paper,we suggest that the observed long-lasting X-ray plateau emission is caused by the energy injection of dipole radiation from supra-massive magnetar,and the abrupt decay following the longlasting X-ray plateau emission is explained by supra-massive magnetar collapsing into a black hole.It is the short GRB(SGRB)with the longest X-ray internal plateau emission powered by a supra-massive neutron star.If this is the case,one can estimate the physical parameters of a supra-massive magnetar,and compare with other SGRBs.We also discuss the possible gravitational-wave emission,which is powered by a supra-massive magnetar and its detectability,and the possible kilonova emission,which is powered by r-process and magnetar spin-down to compare with the observed data.

GRB 200612A:An Ultralong Gamma-Ray Burst Powered by Magnetar Spinning Down

GRB 200612A could be classified as an ultralong gamma-ray burst due to its prompt emission lasting up to~1020 s and the true timescale of the central engine activity t_(burst)≥4×10^(4) s.The late X-ray light curve with a decay index ofα=7.53 is steeper than the steepest possible decay from an external shock model.We propose that this X-ray afterglow can be driven by dipolar radiation from the magnetar spindown during its early stage,while the magnetar collapsed into the black hole before its spindown,resulting in a very steep decay of the late X-ray light curve.The optical data show that the light curve is still rising after 1.1 ks,suggesting a late onset.We show that GRB 200612A’s optical afterglow light curve is fitted with the forward shock model by Gaussian structured off-axis jet.This is a special case among GRBs,as it may be an ultralong gamma-ray burst powered by a magnetar in an off-axis observation scenario.

Effect of rapid evolution of magnetic tilt angle on a newborn magnetar's dipole radiation

We study the electromagnetic radiation from a newborn magnetar whose magnetic tilt angle decreases rapidly. We calculate the evolution of the angular spin frequency, the perpendicular component of the surface magnetic field strength, and the energy loss rate through magnetic dipole radiation. We show that the spin-down of the magnetar experiences two stages characterized by two different timescales. The apparent magnetic field decreases with the decrease of the tilt angle. We further show that the energy loss rate of the magnetar is very different from that in the case of a fixed tilt angle. The evolution of the energy loss rate is consistent with the overall light curves of gamma-ray bursts which show a plateau structure in their afterglow stage. Our model supports the idea that some gamma-ray bursts with a plateau phase in their afterglow stage may originate from newborn millisecond magnetars.

An accreting low magnetic field magnetar for the ultraluminous X-ray source in M82

One ultraluminous X-ray source in M82 has recently been identified as an accreting neutron star （named NuSTAR J095551＋6940.8）. It has a super-Eddington luminosity and is spinning up. An aged magnetar is more likely to be a low magnetic field magnetar. An accreting low magnetic field magnetar may explain both the super- Eddington luminosity and the rotational behavior of this source. Considering the effect of beaming, the spin-up rate is understandable using the traditional form of accretion torque. The transient nature and spectral properties of M82 X-2 are discussed. The theoretical range of periods for accreting magnetars is provided. Three observational appearances of accreting magnetars are summarized.

Effect of strong magnetic field on chemical potential and electron capture in magnetar

The chemical potential of electrons in a strong magnetic field is investigated. It is shown that the magnetic field has only a slight effect on electron chemical potential when B 〈 10^11 T, but electron chemical potential will decrease greatly when B 〉 10^11 T. The effects of a strong magnetic field on electron capture rates for ^60Fe are discussed, and the result shows that the electron capture sharply decreases because of the strong magnetic field.

A possible origin of the Galactic Center magnetar SGR 1745–2900

Since there is a large population of massive O/B stars and putative neutron stars （NSs） located in the vicinity of the Galactic Center （GC）, intermediate-mass X-ray binaries （IMXBs） constituted by an NS and a B-type star probably exist there. We investigate the evolutions of accreting NSs in IMXBs （similar to M82 X-2） with a - 5.2 M companion and orbital period 2.53 d. By adopting a mildly super-Eddington rate M = 6 × 10-8 M yr-1 for the early Case B Roche-lobe overflow （RLOF） accretion, we find that only in accreting NSs with quite elastic crusts （slippage factor s = 0.05） can the toroidal magnetic fields be amplified within 1 Myr, which is assumed to be the longest duration of the RLOF. These IMXBs will evolve into NS＋white dwarf （WD） binaries if they are dynamically stable. However, before the formation of NS＋WD binaries, the high stellar density in the GC will probably lead to frequent encounters between the NS＋evolved star binaries （in post-early Case B mass transfer phase） and NSs or exchange encounters with other stars, which may produce single NSs. These NSs will evolve into magnetars when the amplified poloidal magnetic fields diffuse out to the NS surfaces. Consequently, our results provide a possible expianation for the origin of the GC magnetar SGR 1745-2900. Moreover, the accreting NSs with s 〉 0.05 will evolve into millisecond pulsars （MSPs）. Therefore, our model reveals that the GC magnetars and MSPs could both originate from a special kind of IMXB.

On the possible wind nebula of magnetar Swift J1834.9-0846:a magnetism-powered synchrotron nebula

Recently, the magnetar Swift J1834.9-0846 has been reported to have a possible wind nebula. It is shown that both the magnetar and its wind nebula are understandable in the wind braking scenario. The magnetar＇s rotational energy loss rate is not enough to power the particle luminosity. The required particle luminosity should be about 10^36 erg s^- 1 to 10^38 erg s^-1. It is obtained in three different approaches： considering wind braking of Swift J1834.9-0846; the spectral and spatial observations of the wind nebula; and an empirical upper bound on wind nebula X-ray luminosity. The nebula magnetic field is about 10-4 G. The possible wind nebula of Swift J1834.9-0846 should be a magnetar wind nebula. It is powered by the magnetic energy released from the magnetar.

Magnetar giant flare originating from GRB 200415A:transient GeV emission, time-resolved E_(p)-L_(iso) correlation and implications

Giant flares(GFs)are unusual bursts from soft gamma-ray repeaters(SGRs)that release an enormous amount of energy in a fraction of a second.The afterglow emission of these SGR-GFs or GF candidates is a highly beneficial means of discerning their composition,relativistic speed and emission mechanisms.GRB 200415A is a recent GF candidate observed in a direction coincident with the nearby Sculptor galaxy at 3.5 Mpc.In this work,we searched for transient gamma-ray emission in past observations by Fermi-LAT in the direction of GRB 200415A.These observations confirm that GRB 200415A is observed as a transient GeV source only once.A pure pair-plasma fireball cannot provide the required energy for the interpretation of GeV afterglow emission and a baryonic poor outflow is additionally needed to explain the afterglow emission.A baryonic rich outflow is also viable,as it can explain the variability and observed quasi-thermal spectrum of the prompt emission if dissipation is happening below the photosphere via internal shocks.Using the peak energy(Ep)of the time-resolved prompt emission spectra and their fluxes(Fp),we found a correlation between Ep and Fp or isotropic luminosity Liso for GRB 200415A.This supports the intrinsic nature of Ep-Liso correlation found in SGRs-GFs,hence favoring a baryonic poor outflow.Our results also indicate a different mechanism at work during the initial spike,and that the evolution of the prompt emission spectral properties in this outflow would be intrinsically due to the injection process.

Are There Magnetars in High-mass X-Ray Binaries?

Magnetars form a special population of neutron stars with strong magnetic fields and long spin periods. About 30 magnetars and magnetar candidates known currently are probably isolated, but the possibility that magnetars are in binaries has not been excluded. In this work, we perform spin evolution of neutron stars with different magnetic fields in wind-fed high-mass X-ray binaries and compare the spin period distribution with observations, aiming to find magnetars in binaries. Our simulation shows that some of the neutron stars, which have long spin periods or are in widely-separated systems, need strong magnetic fields to explain their spin evolution. This implies that there are probably magnetars in high-mass X-ray binaries. Moreover, this can further provide a theoretical basis for some unclear astronomical phenomena, such as the possible origin of periodic fast radio bursts from magnetars in binary systems.

Fast Radio Bursts as Crustal Dynamical Events Induced by Magnetic Field Evolution in Young Magnetars

We revisit in this work a model for repeating Fast Radio Bursts based of the release of energy provoked by the magnetic field dynamics affecting a magnetar’s crust.We address the basics of such a model by solving the propagation of the perturbation approximately,and quantify the energetics and the radiation by bunches of charges in the so-called charge starved region in the magnetosphere.The(almost)simultaneous emission of newly detected X-rays from SGR 1935+2154 is tentatively associated with a reconnection behind the propagation.The strength of f-mode gravitational radiation excited by the event is quantified,and more detailed studies of the nonlinear(spiky)soliton solutions are suggested.

X-ray flares raising upon magnetar plateau as an implication of a surrounding disk of newborn magnetized neutron star

The X-ray flares have usually been ascribed to long-lasting activities of the central engine of gamma-ray bursts(GRBs),e.g.,fallback accretion.The GRB X-ray plateaus,however,favor a millisecond magnetar central engine.The fallback accretion can be significantly suppressed due to the propeller effect of a magnetar.Therefore,if the propeller regime cannot resist the mass flow onto the surface of the magnetar efficiently,the X-ray flares raising upon the magnetar plateau would be expected.In this work,such peculiar cases are connected to the accretion process of the magnetars,and an implication for magnetar-disc structure is given.We investigate the repeated accretion process with multi-flare GRB 050730,and give a discussion for the accretion-induced variation of the magnetic field in GRB 111209 A.Two or more flares exhibit in the GRB 050730,060607 A and 140304 A;by adopting magnetar mass M=1.4 M_(⊙)and radius R=12 km,the average mass flow rates of the corresponding surrounding disk are 3.53×10^(-4)M_(⊙)s^(-1).4.23×10^(-4)M_(⊙)s^(-1),and 4.33×10^(-4)M_(⊙)s^(-1),and the corresponding average sizes of the magnetosphere are 5.01×10^(6)cm,6.45 x 10^(-6)cm,and 1.09×10^(-7)cm,respectively.A statistic analysis that contains eight GRBs within 12 flares shows that the total mass loading in single flare is~2×10^(-5)M_(⊙).In the lost mass of a disk,there are about 0.1%used to feed a collimated jet.

Statistical properties of fast radio bursts elucidate their origins:magnetars are favored over gamma-ray bursts

Fast radio bursts(FRBs) are extremely strong radio flares lasting several milliseconds,most of which come from unidentified objects at a cosmological distance.They can be apparently repeating or not.In this paper,we analyzed 18 repeaters and 12 non-repeating FRBs observed in the frequency bands of 400–800 MHz from Canadian Hydrogen Intensity Mapping Experiment(CHIME).We investigated the distributions of FRB isotropic-equivalent radio luminosity,considering the K correction.Statistically,the luminosity distribution can be better fitted by Gaussian form than by power-law.Based on the above results,together with the observed FRB event rate,pulse duration,and radio luminosity,FRB origin models are evaluated and constrained such that the gamma-ray bursts(GRBs) may be excluded for the non-repeaters while magnetars or neutron stars(NSs) emitting the supergiant pulses are preferred for the repeaters.We also found the necessity of a small FRB emission beaming solid angle(about 0.1 sr) from magnetars that should be considered,and/or the FRB association with soft gamma-ray repeaters(SGRs) may lie at a low probability of about 10%.Finally,we discussed the uncertainty of FRB luminosity caused by the estimation of the distance that is inferred by the simple relation between the redshift and dispersion measure(DM).

Electron capture rates for iron group nuclei at the surface of magnetar

Effects of an ultra-strong magnetic field on electron capture rates for 55Co are analyzed in the nuclear shell model and under the Landau energy levels quantized approximation in the ultra-strong magnetic field, and the electron capture rates on 10 abundant iron group nuclei at the surface of a magnetar are given. The results show that electron capture rates on 55Co are increased greatly in the ultra-strong magnetic field, by about 3 orders of magnitude generally. These conclusions play an important role in future study of the evolution of magnetars.

High Energy Emission from Magnetar Due to Giant Flare

We propose a theoretical model for magnetar giant flare to explain the flaring activity on 2004 December 27 from SGR1806-20 comprehensively. A global rearrangement is expected by the magnetic reconnection that requires explaining the giant SGR flares. In this paper we propose two regions of flares: preflare on the surface of magnetar and main burst at a distance of light cylinder radius. Acquiring the maximum potential drop on the magnetar surface, adopting space charge limited flow model, and using magnetic field B ≈ 1015 G, the luminosities of flare energies release for the preflare phase and main burst phase are found to be in the order of 1041 erg·sˉ1 and 1044 erg·sˉ1 respectively, conforming to magnetar burst energy and flare temperature is determined by considering black body radiation.

Spindown of magnetars:quantum vacuum friction?

Magnetars are proposed to be peculiar neutron stars which could power their X-ray radiation by super-strong magnetic fields as high as 〉 10^（14） G.However,no direct evidence for such strong fields has been obtained till now,and the recent discovery of low magnetic field magnetars even indicates that some more efficient radiation mechanism than magnetic dipole radiation should be included.In this paper,quantum vacuum friction（QVF） is suggested to be a direct consequence of super-strong surface fields,therefore the magnetar model could then be tested further through QVF braking.The high surface magnetic field of a pulsar interacting with the quantum vacuum results in a significantly high spindown rate（P）.It is found that a QVF dominates the energy loss of pulsars when the pulsar＇s rotation period and its first derivative satisfy the relationship P^3P 〉 0.63 ×10^（-16）ξ^（-4） s^2,whereξ is the ratio of the surface magnetic field over the dipole magnetic field.In the ＂QVF ＋ magnetodipole＂ joint braking scenario,the spindown behavior of magnetars should be quite different from that in the pure magnetodipole model.We are expecting these results could be tested by magnetar candidates,especially low magnetic field cases,in the future.

Non-detection of pulsed radio emission from magnetar Swift J1834.9-0846: constraint on the fundamental plane of magnetar radio emission

The magnetar Swift J1834.9-0846 is observed using the Nanshan 25 m radio telescope. No pulsed radio emission is detected. The upper limit on the pulsed radio emission from this source is 0.5 mJy. According to the ＂fundamental plane＂ for radio magnetars, this source should have radio emission. Therefore, our results put constraints on the existence of a fundamental plane of magnetar radio emission. We argue that a magnetar＇s ability to emit radio emission may have little to do with the spin down luminosity and is related to the magnetar＇s X-ray luminosity. The only necessary condition is a relatively low X-ray luminosity.

A note on the puzzling spindown behavior of the Galactic center magnetar SGR J1745-2900

SGR J1745-2900 is a magnetar near the Galactic center. X-ray observations of this source found a decreasing X-ray luminosity accompanied by an enhanced spindown rate. This negative correlation between X-ray luminosity and spindown rate is hard to understand. The wind braking model of magnetars is employed to explain this puzzling spindown behavior. During the release of magnetic energy of magnetars, a system of particles may be generated. Some of these particles remain trapped in the magnetosphere and may contribute to the X-ray luminosity. The rest of the particles can flow out and take away the rotational energy of the central neutron star. A smaller polar cap angle will cause the decrease of X-ray luminosity and enhanced spindown rate of SGR J1745-2900. This magnetar is shortly expected to have a maximum spindown rate.

Tunneling of Relativistic Bosons Induced by Magnetic Fields in the Magnetar’s Crust

The present work is devoted to the study of bosons evolving in the frozen magnetar＇s crust endowed with an ultra-strong magnetic field orthogonal to an electric field, both described by periodic functions. We discuss the quantum tunneling process through the one-dimensional potential barrier along Oz. The solutions to the Klein- Gordon equation are expressed in terms of Mathieu＇s functions which, for computable particle＇s energy range, are turning from oscillatory to exponentially growing modes along Oz. Within the Jeffreys Wentzel Kramers- Brillouin framework, the transmission coefficient is computed for the particle momentum in the middle of the instability range.

The timing behavior of magnetar Swift J1822.3—1606: timing noise or a decreasing period derivative?

The different timing results of the magnetar Swift J1822.3—1606 are analyzed and understood theoretically.It is noted that different timing solutions are caused not only by timing noise,but also because the period derivative is decreasing after the outburst.Both the decreasing period derivative and the large timing noise may originate from wind braking associated with the magnetar.Future timing of Swift J1822.3—1606 will help clarify whether or not its period derivative is decreasing with time.

Role of magnetic fields on the outer crust in a magnetar

We explore the properties of 4110 nuclides from Z=5 to Z=82 with the Sky3D code and the composition of the outer crust in magnetars under extreme magnetic fields.The effects of the variation in nuclear masses due to magnetic fields on the outer crust are comprehensively studied.The neutron-drip transition pressure,equation of state,and neutron fraction in the outer crust are also discussed.