Young Magnetars Research Articles

A nebular origin for the persistent radio emission of fast radio bursts.

Fast radio bursts (FRBs) are millisecond-duration, bright (approximately Jy) extragalactic bursts, whose production mechanism is still unclear1. Recently, two repeating FRBs were found to have a physically associated persistent radio source of non-thermal origin2,3. These two FRBs have unusually large Faraday rotation measure values2,3, probably tracing a dense magneto-ionic medium, consistent with synchrotron radiation originating from a nebula surrounding the FRB source4-8. Recent theoretical arguments predict that, if the observed Faraday rotation measure mostly arises from the persistent radio source region, there should be a simple relation between the persistent radio source luminosity and the rotation measureitself7,9. Here we report the detection of a third, less luminous persistent radio source associated with the repeating FRB source FRB 20201124A at a distance of 413 Mpc, substantially expanding the predicted relation into the low luminosity-low Faraday rotation measure regime (<1,000 rad m-2). At lower values of the Faraday rotation measure, the expected radio luminosity falls below the limit-of-detection threshold for present-day radio telescopes. These findings support the idea that the persistent radio sources observed so far are generated by a nebula in the FRB environment and that FRBs with low Faraday rotation measure may not show a persistent radio source because of a weaker magneto-ionic medium. This is generally consistent with models invoking a young magnetar as the central engine of the FRB, in which the surrounding ionized nebula-or the interacting shock in a binary system-powers the persistent radio source.

FRBs from rapid spindown neutron stars

Abstract A fast radio burst (FRB) localized to a globular cluster (GC) challenges FRB models involving ordinary young magnetars. In this paper, we examine the rapid spindown millisecond neutron star (NS) scenario, which favours the dynamic environment in GCs. Fast spindown corresponds to a larger magnetic field than regular millisecond pulsars, which empirically favours giant pulse (GP) emission. The kinetic energy in millisecond NSs can readily exceed the magnetic energy in magnetars. The high inferred isotropic luminosity of most FRBs is challenging to explain in spin-down powered pulsars. A recent observation of a GP from the Crab pulsar, on the other hand, suggests highly Doppler-beamed emission, making the required energy orders of magnitude smaller than estimated with isotropic assumptions. Considering this strong beaming effect, GPs from a recycled pulsar with a modest magnetic field could explain the energetics and burst rates for a wide range of FRBs. The short life span accounts for a paucity of bright FRBs in the Milky Way neighbourhood. We point out that tidal disruption spin-up from a main sequence star can provide sufficient accretion rate to recycle a NS with mild magnetic field. It can also explain the observed source density and the spatial offset in the GC for FRB 20200120E. Frequency variation in the scattering tail for some of the brightest FRBs is expected in this scenario.

Periodic activities of Fast Radio Burst repeaters from precessing magnetars with evolving obliquity

Abstract Fast radio bursts (FRBs) are cosmological radio transients with millisecond durations and extremely high brightness temperatures. One FRB repeater, FRB 180916.J0158+65 (FRB 180916B), was confirmed to appear 16.35-day periodic activities with 5-day activity window. Another FRB repeater, FRB 121102, and two soft gamma-ray repeaters (SGRs), SGR 1935+2154 and SGR 1806-20, also show possible periodic activities. These periodicities might originate from the precession process of young magnetars due to the anisotropic pressure from the inner magnetic fields as proposed in the literature. In this work, we analyze a self-consistent model for the rotation evolution of magnetars and obtain the evolutions of magnetar precession and obliquity. We find that if the FRB repeaters and the SGRs with (possible) periodic activities originate from the magnetar precession, their ages would be constrained to be hundreds to tens of thousands of years, which is consistent with the typical ages of magnetars. Assuming that the FRB emission is beaming in the magnetosphere as proposed in the literature, we calculate the evolution of the observable probability and the duty cycle of the active window period. We find that for a given magnetar the observable probability increases with the magnetar age in the early stage and decreases with the magnetar age in the later stage, meanwhile, there are one or two active windows in one precession period if the emission is not perfectly axisymmetric with respect to the deformation axis of a magnetar, which could be tested by the future observation for repeating FRB sources.

Fast Radio Bursts in the disks of Active Galactic Nuclei

Abstract Fast radio bursts (FRBs) are luminous millisecond-duration radio pulses with extragalactic origin, which were discovered more than a decade ago. Despite the numerous samples, the physical origin of FRBs remains poorly understood. FRBs have been thought to originate from young magnetars or accreting compact objects (COs). Massive stars or COs are predicted to be embedded in the accretion disks of active galactic nuclei (AGNs). The dense disk absorbs FRBs severely, making them difficult to observe. However, progenitors’ ejecta or outflow feedback from the accreting COs interact with the disk material to form a cavity. The existence of the cavity can reduce the absorption by the dense disk materials, making FRBs escape. Here we investigate the production and propagation of FRBs in AGN disks and find that the AGN environments lead to the following unique observational properties, which can be verified in future observation. First, the dense material in the disk can cause large dispersion measure (DM) and rotation measure (RM). Second, the toroidal magnetic field in the AGN disk can cause Faraday conversion. Third, during the shock breakout, DM and RM show non-power-law evolution patterns over time. Fourth, for accreting-powered models, higher accretion rates lead to more bright bursts in AGN disks, accounting for up to 1 % of total bright repeating FRBs.

Searching for Associations between Short Gamma-Ray Bursts and Fast Radio Bursts

The physical origin of fast radio bursts (FRBs) is still unclear. However, young magnetars associated with short-duration gamma-ray bursts (SGRBs) have been thought to be possible central engines for some FRBs. In this paper, we perform a systematic search for SGRBs that are associated with FRBs in a sample including 623 FRBs (601 one-off bursts and 22 repeaters) and 168 SGRBs with precise localizations. We find that FRB 190309A is spatially associated with GRB 060502B, with a chance probability of 0.05 when temporal and redshift information is taken into account. Considering the high chance probability (the statistical significance is <3σ), we examine other observational properties such as the host galaxy, the dispersion measure, and the energy budget of the central engine to check the possibility of their association. Although the available observational information is insufficient to determine whether they are physically associated, it does not rule out such a possibility. As the only pair of FRB and GRB that are spatially associated, it remains an interesting case worthy of further attention.

Cosmic Baby and the r-process Nucleosynthesis

Astrophysical origin of the rapid neutron capture process (i.e., r-process) remains a mystery. Among the known r-process sites radio-actively powered kilonova, produced by binary neutron star mergers, attracted the astronomers a promising source in the light of gravitational wave radiation. The first detected binary neutron star merger event GW170817 confirmed the existence of binary neutron star (BNS) in nature while its associated properties such as transient electro-magnetic emission in the form of x-rays, long and short gamma ray bursts (l, s GRBs), First Radio Bursts (FRBs) offer the astronomer to rethink about the origin of the r-process abundances in the light of Magnetars, created in both supernova explosion and also in neutron star merger, as a r-process contributor. Recently detected Cosmic Baby i.e. Swift J1818.0 – 1607 is a young magnetar of 240 years aged with super-strong magnetic fields ~ 8.9424 x 1017 G and ellipticity ~ 9 x 10-3. Due to its youngness among the 31 detected magnetars till today, it may provide x-ray lines emitted by the r-process abundances which makes it as an important promising source in the eyes of LOFT, NuSTAR detectors. This author proposes that this cosmic baby can be considered as a suitable astrophysical source decoding of its observed results may unravel the realistic situations of the magnetar at the time of merger, supernova explosion, etc. for generation of super heavy elements like Eu, Ti.

New Astronomy with the Swift Observatory: Discovery of Cosmic Baby, Supernova explosion and other Extremes

Analysis of Swift observed data offer us a new concept on supernova explosion and gamma ray bursts moulding on our old ideas. Swift space telescope observatory was launched in 2004 mainly for observation of gamma ray bursts (GRBs) with an operational active duration of two years. According to the new picture of supernova explosion — firstly shocks break out with the emission of x-rays and then exploding will occur while conventional idea was a new born neutron star compresses, rebounds and then triggers a shock wave that finally blows the star’s gaseous outer layers. Another invaluable discovery of Swift observatory was detection of Cosmic Baby, i.e. Swift J1818.0 – 1607 which is a young magnetar of ~ 240 years aged. It is also exhibiting triaxiality (as a triaxial star) having interior core magnetic field and ellipticity are 8.9424 x 1017 G and ~ 9 x 10–3, respectively. Nearly twenty years in service after its launching Swift is in good health and expected will remain active for few years also. So, new astronomy awaits from the Swift mission.

3D evolution of neutron star magnetic fields from a realistic core-collapse turbulent topology

ABSTRACT We perform the first 3D fully coupled magneto-thermal simulations of neutron stars (including the most realistic background structure and microphysical ingredients so far) applied to a very complex initial magnetic field topology in the crust, similar to what was recently obtained by proto-neutron stars dynamo simulations. In such configurations, most of the energy is stored in the toroidal field, while the dipolar component is a few per cent of the mean magnetic field. This initial feature is maintained during the long-term evolution (∼106 yr), since the Hall term favours a direct cascade (compensating for Ohmic dissipation) rather than a strong inverse cascade, for such an initial field topology. The surface dipolar component, responsible for the dominant electromagnetic spin-down torque, does not show any increase in time, when starting from this complex initial topology. This is in contrast to the timing properties of young pulsars and magnetars which point to higher values of the surface dipolar fields. A possibility is that the deep-seated magnetic field (currents in the core) is able to self-organize in large scales (during the collapse or in the early life of a neutron star). Alternatively, the dipolar field might be lower than is usually thought, with magnetosphere substantially contributing to the observed high spin-down, via e.g. strong winds or strong coronal magnetic loops, which can also provide a natural explanation to the tiny surface hotspots inferred from X-ray data.

Distribution of Fast Radio Burst Dispersion Measures in CHIME/FRB Catalog 1: Implications on the Origin of FRBs

Recently, CHIME/FRB project published its first fast radio burst (FRB) catalog (hereafter, Catalog 1), which contains in total 536 unique bursts. With the help of the latest set of FRBs in this large-size catalog, we aim to investigate the dispersion measure (DM) or redshift ( $$z$$ ) distribution of the FRB population, and solution of this problem could be used to clarify the question of FRB origin. In this study, we adopted the M&E 2018 model to fit the observed $$z$$ distribution of FRBs in Catalog 1. In the M&E 2018 model, we are mostly interested in the $$\Phi (z)$$ function, i.e., number of bursts per proper time per comoving volume, which is represented by the star formation rate (SFR) with a power-law index $$n$$ . Our estimated value of $$n$$ is $$0.0_{{ - 0.0}}^{{ + 0.6}}$$ ( $$0.0_{{ - 0.0}}^{{ + 2.1}}$$ ) at the 68 (95) per cent confidence level, implying that the FRB population evolves with redshift consistent with, or faster than, the SFR. Specially, the consistency of the $$n$$ values estimated by this study and the SFR provides a potential support for the hypothesis of FRBs originating from young magnetars.

Evolutionary implications of a magnetar interpretation for GLEAM-X J162759.5–523504.3

ABSTRACT The radio pulsar GLEAM-X J162759.5–523504.3 has an extremely long spin period ($P = 1091.17\, \mbox{s}$), and yet seemingly continues to spin-down rapidly ($\dot{P} &amp;lt; 1.2 \times 10^{-9}\, \mbox{ss}^{-1}$). The magnetic field strength that is implied, if the source is a neutron star undergoing magnetic dipole braking, could exceed $10^{16}\, \mbox{G}$. This object may therefore be the most magnetized neutron star observed to date. In this paper, a critical analysis of a magnetar interpretation for the source is provided. (i) A minimum polar magnetic field strength of $B \sim 5 \times 10^{15}\, \mbox{G}$ appears to be necessary for the star to activate as a radio pulsar, based on conventional ‘death valley’ assumptions. (ii) Back-extrapolation from magnetic braking and Hall–plastic–Ohm decay suggests that a large angularize momentum reservoir was available at birth to support intense field amplification. (iii) The observational absence of X-rays constrains the star’s field strength and age, as the competition between heating from field decay and Urca cooling implies a surface luminosity as a function of time. If the object is an isolated, young ($\sim 10\, \mbox{kyr}$) magnetar with a present-day field strength of $B \gtrsim 10^{16}\, \mbox{G}$, the upper limit ($\approx 10^{30}\, \mbox{erg s}^{-1}$) set on its thermal luminosity suggests it is cooling via a direct Urca mechanism.

Deep X-Ray and Radio Observations of the First Outburst of the Young Magnetar Swift J1818.0−1607

Swift J1818.0−1607 is a radio-loud magnetar with a spin period of 1.36 s and a dipolar magnetic field strength of B ∼ 3 × 1014 G, which is very young compared to the Galactic pulsar population. We report here on the long-term X-ray monitoring campaign of this young magnetar using XMM-Newton, NuSTAR, and Swift from the activation of its first outburst in 2020 March until 2021 October, as well as INTEGRAL upper limits on its hard X-ray emission. The 1–10 keV magnetar spectrum is well modeled by an absorbed blackbody with a temperature of kT BB ∼ 1.1 keV and apparent reduction in the radius of the emitting region from ∼0.6 to ∼0.2 km. We also confirm the bright diffuse X-ray emission around the source extending between ∼50″ and ∼110″. A timing analysis revealed large torque variability, with an average spin-down rate −2.3 × 10−11 Hz2 that appears to decrease in magnitude over time. We also observed Swift J1818.0−1607 with the Karl G. Jansky Very Large Array on 2021 March 22. We detected the radio counterpart to Swift J1818 measuring a flux density of S v = 4.38 ± 0.05 mJy at 3 GHz and a half-ringlike structure of bright diffuse radio emission located at ∼90″ to the west of the magnetar. We tentatively suggest that the diffuse X-ray emission is due to a dust-scattering halo and that the radio structure may be associated with the supernova remnant of this young pulsar, based on its morphology.

The most probable host of CHIME FRB 190425A, associated with binary neutron star merger GW190425, and a late-time transient search

ABSTRACT The identification and localization of fast radio bursts (FRBs) to their host galaxies have revealed important details about the progenitors of these mysterious, millisecond-long bursts of coherent radio emission. In this work, we study the most probable host galaxy of the apparently non-repeating CHIME/FRB event FRB 20190425A – a particularly high-luminosity, low-dispersion measure event that was demonstrated in a recent paper to be temporally and spatially coincident with the LIGO-Virgo-KAGRA binary neutron star merger GW190425, suggesting an astrophysical association (p-value 0.0052). In this paper, we remain agnostic to this result, and we confirm UGC10667 as the most probable host galaxy of FRB 20190425A, demonstrating that the host galaxies of low-dispersion measure, one-off CHIME FRBs can be plausibly identified. We then perform multiwavelength observations to characterize the galaxy and search for any afterglow emission associated with the FRB and its putative GW counterpart. We find no radio or optical transient emission in our observations $2.5\, \mathrm{yr}$ post-burst. UGC10667 is a spiral galaxy at z ∼ 0.03, dominated by an old stellar population. We find no evidence of a large population of young stars, with nebular emission dominated by star formation at a rate of $1\!-\!2\, ~\mathrm{M_\odot \, yr^{-1}}$. While we cannot rule out a young magnetar as the origin of FRB 20190425A, our observations are consistent with an origin in a long delay-time neutron star binary merger.

A Possible 250 s X-Ray Quasi-periodicity in the Fast Blue Optical Transient AT2018cow

The fast blue optical transients (FBOTs) are a new population of extragalactic transients of unclear physical origin. A variety of mechanisms has been proposed including failed supernova explosion, shock interaction with a dense medium, young magnetar, accretion onto a compact object and stellar tidal disruption event, but none is conclusive. Here we report the discovery of a possible X-ray quasi-periodicity signal with a period of ∼250 s (at a significance level of 99.76%) in the brightest FBOT AT2018cow through the analysis of XMM-Newton/PN data. The signal is independently detected at the same frequency in the average power density spectrum from data taken from the Swift telescope, with observations covering from 6 to 37 days after the optical discovery, though the significance level is lower (94.26%). This suggests that the quasi-periodic oscillation (QPO) frequency may be stable over at least 1.1 × 104 cycles. Assuming the ∼250 s QPO to be a scaled-down analog of that typically seen in stellar mass black holes, a black hole mass of ∼103–105 solar masses could be inferred. The overall X-ray luminosity evolution could be modeled with a stellar tidal disruption by a black hole of ∼104 solar masses, providing a viable mechanism to produce AT2018cow. Our findings suggest that other bright FBOTs may also harbor intermediate-mass black holes.

Thermal luminosity degeneracy of magnetized neutron stars with and without hyperon cores

ABSTRACT The dissipation of intense crustal electric currents produces high Joule heating rates in cooling neutron stars. Here, it is shown that Joule heating can counterbalance fast cooling, making it difficult to infer the presence of hyperons (which accelerate cooling) from measurements of the observed thermal luminosity Lγ. Models with and without hyperon cores match Lγ of young magnetars (with poloidal–dipolar field Bdip ≳ 1014 G at the polar surface and Lγ ≳ 1034 erg s−1 at t ≲ 105 yr) as well as mature, moderately magnetized stars (with Bdip ≲ 1014 G and 1031 erg s−1 ≲ Lγ ≲ 1032 erg s−1 at t ≳ 105 yr). In magnetars, the crustal temperature is almost independent of hyperon direct Urca cooling in the core, regardless of whether the latter is suppressed or not by hyperon superfluidity. The thermal luminosities of light magnetars without hyperons and heavy magnetars with hyperons have Lγ in the same range and are almost indistinguishable. Likewise, Lγ data of neutron stars with Bdip ≲ 1014 G but with strong internal fields are not suitable to extract information about the equation of state as long as hyperons are superfluid, with maximum amplitude of the energy gaps of the order ≈1 MeV.

Burst timescales and luminosities as links between young pulsars and fast radio bursts

Fast radio bursts (FRBs) are extragalactic radio flashes of unknown physical origin. Their high luminosities and short durations require extreme energy densities, such as those found in the vicinity of neutron stars and black holes. Studying the burst intensities and polarimetric properties on a wide range of timescales, from milliseconds down to nanoseconds, is key to understanding the emission mechanism. However, high-time-resolution studies of FRBs are limited by their unpredictable activity levels, available instrumentation and temporal broadening in the intervening ionized medium. Here we show that the repeating FRB 20200120E can produce isolated shots of emission as short as about 60 nanoseconds in duration, with brightness temperatures as high as 3 × 1041 K (excluding relativistic effects), comparable with ‘nano-shots’ from the Crab pulsar. Comparing both the range of timescales and luminosities, we find that FRB 20200120E observationally bridges the gap between known Galactic young pulsars and magnetars and the much more distant extragalactic FRBs. This suggests a common magnetically powered emission mechanism spanning many orders of magnitude in timescale and luminosity. In this Article, we probe a relatively unexplored region of the short-duration transient phase space; we highlight that there probably exists a population of ultrafast radio transients at nanosecond to microsecond timescales, which current FRB searches are insensitive to. The range of timescales and luminosities measured from the nearby fast radio burst FRB 20200120E observationally connects these extreme extragalactic transients with studies of Galactic neutron stars.

A repeating fast radio burst source in a globular cluster.

Fast radio bursts (FRBs) are flashes of unknown physical origin1. The majority of FRBs have been seen only once, although some are known to generate multiple flashes2,3. Many models invoke magnetically powered neutron stars (magnetars) as the source of the emission4,5. Recently, the discovery6 of another repeater (FRB 20200120E) was announced, in the direction of the nearby galaxy M81, with four potential counterparts at other wavelengths6. Here we report observations that localized the FRB to a globular cluster associated with M81, where it is 2 parsecs away from the optical centre of the cluster. Globular clusters host old stellar populations, challenging FRB models that invoke young magnetars formed in a core-collapse supernova. We propose instead that FRB 20200120E originates from a highly magnetized neutron star formed either through the accretion-induced collapse of a white dwarf, or the merger of compact stars in a binary system7. Compact binaries are efficiently formed inside globular clusters, so a model invoking them could also be responsible for the observed bursts.

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.

Sudden discharge of young charged magnetars as a new model for FRBs

ABSTRACT We propose a new model for Fast Radio Bursts (FRBs) based on a sudden discharge of a charged young magnetar, caused by the short falling time-scale of oppositely charged particles on to the magnetar. In this scenario, curvature radiation is emitted by particles accelerated at relativistic by the strong electric fields produced by the disconnection and the subsequent reconnection of the magnetic field lines, a process triggered by the sudden discharge. We modelled the magnetars as charged neutron stars in the static approximation using the exterior metric by the Reissner–Nordström. We also adopted an electrical charge distribution proportional to the mass-energy density, although our results are not strongly sensitive to the specific star’s charge distribution, only to the total charge. Our calculations show that the discharge and emission time-scales are several milliseconds, compatible with the FRB phenomena for magnetars with a total charge of ∼1020 C and mass and radius in the range of 1.5–3.0 M⊙ and 10–45 km, respectively. Furthermore, the calculated total emitted power of a coherent pulse is $P_{\mathrm{ tot}}\sim 10^{42-43} \, \mathrm{erg\, s}^{-1}$, and the frequency range and time-scale are also consistent with FRBs astronomical observations. Finally, if the magnetar does not collapse after the discharge, the existence of FRB repeater sources cannot rule out the existence of a blast repetition after the time needed to magnetosphere recharges and produce a new discharge.

INTEGRAL Limits on Past High-energy Activity from FRB 20200120E in M81

Abstract The repeating fast radio burst FRB 20200120E is located in a globular cluster belonging to the nearby M81 galaxy. Its small distance (3.6 Mpc) and accurate localization make it an interesting target to search for bursting activity at high energies. From 2003 November to 2021 September, the INTEGRAL satellite has obtained an exposure time of 18 Ms on the M81 sky region. We used these data to search for hard X-ray bursts from FRB 20200120E using the IBIS/ISGRI instrument, without finding any significant candidate, down to an average fluence limit of ∼10−8 erg cm−2 (20–200 keV). The corresponding limit on the isotropic luminosity for a burst of duration Δt is ∼ 10 45 10 ms Δ t erg s−1, the deepest limit obtained for an extragalactic FRB in the hard X-ray range. This rules out the emission of powerful flares at a rate higher than 0.1 yr−1 that could be expected in models invoking young hyperactive magnetars.

A Local Universe Host for the Repeating Fast Radio Burst FRB 20181030A

Abstract We report on the host association of FRB 20181030A, a repeating fast radio burst (FRB) with a low dispersion measure (103.5 pc cm−3) discovered by the CHIME/FRB Collaboration et al. Using baseband voltage data saved for its repeat bursts, we localize the FRB to a sky area of 5.3 arcmin2 (90% confidence). Within the FRB localization region, we identify NGC 3252 as the most promising host with an estimated chance-coincidence probability &lt;2.5 × 10−3. Moreover, we do not find any other galaxy with M r &lt; −15 AB mag within the localization region to the maximum estimated FRB redshift of 0.05. This rules out a dwarf host 5 times less luminous than any FRB host discovered to date. NGC 3252 is a star-forming spiral galaxy and at a distance of ≈20 Mpc, it is one of the closest FRB hosts discovered thus far. From our archival radio data search, we estimate a 3σ upper limit on the luminosity of a persistent compact radio source (source size &lt; 0.3 kpc at 20 Mpc) at 3 GHz to be 2 × 1026 erg s−1 Hz−1, at least 1500 times smaller than that of the FRB 20121102A persistent radio source. We also argue that a population of young millisecond magnetars alone cannot explain the observed volumetric rate of repeating FRBs. Finally, FRB 20181030A is a promising source for constraining FRB emission models due to its proximity and we strongly encourage its multi-wavelength follow-up.