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Showing papers on "Magnetar published in 2021"


Journal ArticleDOI
C. K. Li1, Lin Lin2, Shaolin Xiong1, Ming-Yu Ge1, X. B. Li1, Tong Li3, Tong Li1, F. J. Lu1, S. N. Zhang1, Y. L. Tuo1, Y. Nang1, Bing Zhang4, S. Xiao1, Y. B. Chen1, Li-Ming Song1, Y. P. Xu1, C. Z. Liu1, S. M. Jia1, X. L. Cao1, J. L. Qu1, Songbo Zhang1, Yu-Dong Gu1, J. Y. Liao1, Xin-Fu Zhao1, Y. H. Tan1, J. Y. Nie1, H. S. Zhao1, S. J. Zheng1, Y. G. Zheng1, Y. G. Zheng5, Qiu-Yi Luo1, C. Cai1, Bo Li1, W. C. Xue1, Qingcui Bu6, Qingcui Bu1, Z. Chang1, Gang Chen1, L. Chen2, Tian-Xiang Chen1, Y. B. Chen3, Y. P. Chen1, Wei Cui3, Weiguang Cui1, J. K. Deng3, Yi-Qiao Dong1, Yuan-Yuan Du1, M. X. Fu3, G. H. Gao1, H. Gao1, Min Gao1, J. Guan1, Cheng-Cheng Guo1, Da-Wei Han1, Ya Fang Huang1, Jia Huo1, Luhua Jiang1, Wenhan Jiang1, J. Jin1, Y. J. Jin3, L. D. Kong1, Gang Li1, Mao-Shun Li1, Wenxiong Li1, X. X. Li1, Xuelong Li1, Y. G. Li1, Z. W. Li1, X. H. Liang1, B. S. Liu1, GuoQing Liu3, H. W. Liu1, X. J. Liu1, Yunchao Liu3, B. Lu1, Xue-Feng Lu1, Tao Luo1, X. H. Ma1, Bin Meng1, Ge Ou1, N. Sai1, R. C. Shang3, X. Y. Song1, Lei Sun1, Lian Tao1, Cunguo Wang1, G. F. Wang1, J. Z. Wang1, W. S. Wang1, Y. S. Wang1, XiangYang Wen1, B. B. Wu1, B. Y. Wu1, M. Wu1, G. C. Xiao1, H. Xu1, J. W. Yang1, Sisi Yang1, Y. J. Yang1, Y. J. Yang1, Qi-Bin Yi7, Qi-Bin Yi1, Q. Q. Yin1, Yuan You1, Aimei Zhang1, Chun-sheng Zhang1, Fuqin Zhang1, H. M. Zhang1, Junqiang Zhang1, T. Zhang1, W. C. Zhang1, Wan-Chang Zhang1, W. Z. Zhang2, Y. Zhang1, Yue Zhang1, Y. F. Zhang1, Y. J. Zhang1, Z. Zhang3, Zhi Zhang3, Z. L. Zhang1, D. K. Zhou1, J. F. Zhou3, Yu-Xuan Zhu1, Y. X. Zhu1, Y. X. Zhu8, R. L. Zhuang3 
TL;DR: In this article, the authors reported the detection of a non-thermal X-ray burst in the 1-250 keV energy band with the Insight-HXMT satellite, which they identify as having been emitted from SGR J1935+2154.
Abstract: Fast radio bursts (FRBs) are short pulses observed in the radio band from cosmological distances1. One class of models invokes soft gamma-ray repeaters (SGRs), or magnetars, as the sources of FRBs2. Some radio pulses have been observed from some magnetars3, but no FRB-like events have been detected in association with any magnetar burst, including one giant flare4. Recently, a pair of FRB-like bursts (termed FRB 200428) separated by 29 milliseconds were detected from the general direction of the Galactic magnetar SGR J1935+2154 (refs. 5,6). Here, we report the detection of a non-thermal X-ray burst in the 1–250 keV energy band with the Insight-HXMT satellite7, which we identify as having been emitted from SGR J1935+2154. The burst showed two hard peaks with a separation of 34 milliseconds, broadly consistent with that of the two bursts in FRB 200428. The delay time between the double radio peak and the X-ray peaks is about 8.62 s, fully consistent with the dispersion delay of FRB 200428. We thus identify the non-thermal X-ray burst to be associated with FRB 200428, whose high-energy counterpart is the two hard X-ray peaks. Our results suggest that the non-thermal X-ray burst and FRB 200428 share the same physical origin in an explosive event from SGR J1935+2154. Insight-HXMT detected a double-peaked X-ray burst from Galactic magnetar SGR J1935+2154, consistent with two fast radio bursts (FRBs) observed from the same object within seconds. This coincidence suggests a common physical origin, and gives insight into the mechanism behind the origin of FRBs.

117 citations


Journal ArticleDOI
TL;DR: In this paper, the authors reported the detection with Konus-Wind of a hard X-ray event of 28 April 2020 temporally coincident with a bright, two-peak radio burst in the direction of the Galactic magnetar SGR 1935+2154, with properties remarkably similar to those of FRBs.
Abstract: Fast radio bursts (FRBs) are bright, millisecond-scale radio flashes of unknown physical origin1. Young, highly magnetized, isolated neutron stars—magnetars—have been suggested as the most promising candidates for FRB progenitors owing to their energetics and high X-ray flaring activity2,3. Here we report the detection with Konus-Wind of a hard X-ray event of 28 April 2020 temporally coincident with a bright, two-peak radio burst4,5 in the direction of Galactic magnetar SGR 1935+2154, with properties remarkably similar to those of FRBs. We show that the two peaks of the double-peaked X-ray burst coincide in time with the radio peaks and infer a common source and the association of these phenomena. An unusual hardness of the X-ray spectrum strongly distinguishes the 28 April event among multiple ‘ordinary’ flares from SGR 1935+2154. A recent non-detection5–7 of radio emission from about 100 typical soft bursts from SGR 1935+2154 favours the idea that bright, FRB-like magnetar signals are associated with rare, hard-spectrum X-ray bursts. The implied rate of these hard X-ray bursts (~0.04 yr−1 magnetar−1) appears consistent with the rate estimate4 of SGR 1935+2154-like radio bursts (0.007–0.04 yr−1 magnetar−1). In April 2020, the Konus-Wind instrument registered two X-ray bursts temporally coincident with two radio bursts from the Galactic magnetar SGR 1935+2154. The unusual spectral hardness of the X-ray bursts may be an indicator of fast-radio-burst-like radio emission from magnetars.

109 citations


Journal ArticleDOI
TL;DR: In this article, the authors detect two radio bursts from the Galactic magnetar SGR 1935+2154 with fluences of 112.5 and 22.7 µm on the Westerbork 25 µm dish.
Abstract: Fast radio bursts are millisecond-duration, bright radio signals (fluence 0.1–100 Jy ms) emitted from extragalactic sources of unknown physical origin. The recent CHIME/FRB and STARE2 detection of an extremely bright (fluence ~MJy ms) radio burst from the Galactic magnetar SGR 1935+2154 supports the hypothesis that (at least some) fast radio bursts are emitted by magnetars at cosmological distances. In follow-up observations totalling 522.7 h on source, we detect two bright radio bursts with fluences of 112 ± 22 Jy ms and 24 ± 5 Jy ms, respectively. Both bursts appear to be affected by interstellar scattering and we measure significant linear and circular polarization for the fainter burst. The bursts are separated in time by ~1.4 s, suggesting a non-Poissonian, clustered emission process—similar to those seen in some repeating fast radio bursts. Together with the burst reported by CHIME/FRB and STARE2, as well as a much fainter burst seen by FAST (fluence 60 mJy ms), our observations demonstrate that SGR 1935+2154 can produce bursts with apparent energies spanning roughly seven orders of magnitude, and that the burst rate is comparable across this range. This raises the question of whether these four bursts arise from similar physical processes, and whether the fast radio burst population distribution extends to very low energies (~1030 erg, isotropic equivalent). Two further radio bursts associated with magnetar SGR 1935+2154 have been detected with a Westerbork 25 m dish, bringing the total to four. These observations demonstrate that SGR 1935+2154, a putative Galactic analogue of a fast radio burst source, can emit bursts across seven orders of magnitude in energy.

77 citations


Journal ArticleDOI
TL;DR: In this paper, the AGILE satellite detected an X-ray burst in temporal coincidence with a bright FRB-like radio burst from the Galactic magnetar SGR 1935+2154.
Abstract: Fast radio bursts (FRBs) are millisecond radio pulses originating from powerful enigmatic sources at extragalactic distances. Neutron stars with large magnetic fields (magnetars) have been considered as the sources powering the FRBs, but the connection requires further substantiation. Here we report the detection by the AGILE satellite on 28 April 2020 of an X-ray burst in temporal coincidence with a bright FRB-like radio burst from the Galactic magnetar SGR 1935+2154. The burst observed in the hard X-ray band (18–60 keV) lasted about 0.5 s, it is spectrally cut off above 80 keV and implies an isotropically emitted energy of about 1040 erg. This event demonstrates that a magnetar can produce X-ray bursts in coincidence with FRB-like radio bursts. It also suggests that FRBs associated with magnetars can emit X-ray bursts. We discuss SGR 1935+2154 in the context of FRBs with low–intermediate radio energies in the range 1038–1040 erg. Magnetars with magnetic fields B ≈ 1015 G may power these FRBs, and new data on the search for X-ray emission from FRBs are presented. We constrain the bursting X-ray energy of the nearby FRB 180916 to be less than 1046 erg, smaller than that observed in giant flares from Galactic magnetars. In April 2020, the AGILE satellite registered an X-ray burst temporally coincident with a radio burst from the Galactic magnetar SGR 1935+2154. As seen in hard X-rays, the burst was cut off above 80 keV and had an isotropically emitted energy of about 1040 erg.

77 citations


Journal ArticleDOI
TL;DR: In this article, the authors presented sixteen FRB 121102 RMs from burst detections with the Arecibo 305m radio telescope, the Effelsberg 100m, and the Karl G. Jansky Very Large Array, providing a record of FRB's Faraday rotation measure (RM) over a 2.5-year timespan.
Abstract: The repeating fast radio burst source FRB 121102 has been shown to have an exceptionally high and variable Faraday rotation measure (RM), which must be imparted within its host galaxy and likely by or within its local environment. In the redshifted ($z=0.193$) source reference frame, the RM decreased from $1.46\times10^5$~rad~m$^{-2}$ to $1.33\times10^5$~rad~m$^{-2}$ between January and August 2017, showing day-timescale variations of $\sim200$~rad~m$^{-2}$. Here we present sixteen FRB 121102 RMs from burst detections with the Arecibo 305-m radio telescope, the Effelsberg 100-m, and the Karl G. Jansky Very Large Array, providing a record of FRB 121102's RM over a 2.5-year timespan. Our observations show a decreasing trend in RM, although the trend is not linear, dropping by an average of 15\% year$^{-1}$ and is $\sim9.7\times10^4$~rad~m$^{-2}$ at the most recent epoch of August 2019. Erratic, short-term RM variations of $\sim10^3$~rad~m$^{-2}$ week$^{-1}$ were also observed between MJDs 58215--58247. A decades-old neutron star embedded within a still-compact supernova remnant or a neutron star near a massive black hole and its accretion torus have been proposed to explain the high RMs. We compare the observed RMs to theoretical models describing the RM evolution for FRBs originating within a supernova remnant. FRB 121102's age is unknown, and we find that the models agree for source ages of $\sim6-17$~years at the time of the first available RM measurements in 2017. We also draw comparisons to the decreasing RM of the Galactic center magnetar, PSR J1745--2900.

56 citations


Journal ArticleDOI
TL;DR: In this article, the authors proposed a new scenario in which fast radio bursts are powered by short-lived relativistic outflows from accreting black holes or neutron stars, which propagate into the cavity of the pre-existing (quiescent'') jet.
Abstract: The discovery of periodicity in the arrival times of the fast radio bursts (FRBs) poses a challenge to the oft-studied magnetar scenarios. However, models that postulate that FRBs result from magnetized shocks or magnetic reconnection in a relativistic outflow are not specific to magnetar engines; instead, they require only the impulsive injection of relativistic energy into a dense magnetized medium. Motivated thus, we outline a new scenario in which FRBs are powered by short-lived relativistic outflows (``flares'') from accreting black holes or neutron stars, which propagate into the cavity of the pre-existing (``quiescent'') jet. In order to reproduce FRB luminosities and rates, we are driven to consider binaries of stellar-mass compact objects undergoing super-Eddington mass-transfer, similar to ultraluminous X-ray (ULX) sources. Indeed, the host galaxies of FRBs, and their spatial offsets within their hosts, show broad similarities with ULXs. Periodicity on timescales of days to years could be attributed to precession (e.g., Lens-Thirring) of the polar accretion funnel, along which the FRB emission is geometrically and relativistically beamed, which sweeps across the observer line of sight. Accounting for the most luminous FRBs via accretion power may require a population of binaries undergoing brief-lived phases of unstable (dynamical-timescale) mass-transfer. This will lead to secular evolution in the properties of some repeating FRBs on timescales of months to years, followed by a transient optical/IR counterpart akin to a luminous red nova, or a more luminous accretion-powered optical/X-ray transient. We encourage targeted FRB searches of known ULX sources.

44 citations


Journal ArticleDOI
04 Mar 2021-Universe
TL;DR: In this paper, the basic physics of coherent emission mechanisms proposed for fast radio bursts are reviewed, including the curvature emission of bunches, the synchrotron maser, and the emission of radio waves by variable currents during magnetic reconnection.
Abstract: Fast radio bursts (FRBs) are recently discovered mysterious single pulses of radio emission, mostly coming from cosmological distances (∼1 Gpc). Their short duration, ∼1 ms, and large luminosity demonstrate coherent emission. I review the basic physics of coherent emission mechanisms proposed for FRBs. In particular, I discuss the curvature emission of bunches, the synchrotron maser, and the emission of radio waves by variable currents during magnetic reconnection. Special attention is paid to magnetar flares as the most promising sources of FRBs. Non-linear effects are outlined that could place bounds on the power of the outgoing radiation.

42 citations


Journal ArticleDOI
TL;DR: The radio afterglow and near-infrared (NIR) counterpart of the Swift short GRB 200522A, located at a small projected offset of approximately 1$ kpc from the center of a young, star-forming host galaxy at $z=0.5536, was discovered by radio and X-ray luminosities consistent with those of on-axis cosmological short GRBs as mentioned in this paper.
Abstract: We present the discovery of the radio afterglow and near-infrared (NIR) counterpart of the Swift short GRB 200522A, located at a small projected offset of $\approx 1$ kpc from the center of a young, star-forming host galaxy at $z=0.5536$. The radio and X-ray luminosities of the afterglow are consistent with those of on-axis cosmological short GRBs. The NIR counterpart, revealed by our HST observations at a rest-frame time of $\approx2.3$ days, has a luminosity of $\approx (1.3-1.7) \times 10^{42}$ erg s$^{-1}$. This is substantially lower than on-axis short GRB afterglow detections, but is a factor of $\approx 8$-$17$ more luminous than the kilonova of GW170817, and significantly more luminous than any kilonova candidate for which comparable observations exist. The combination of the counterpart's color ($i-y = -0.08\pm 0.21$; rest-frame) and luminosity cannot be explained by standard radioactive heating alone. We present two scenarios to interpret the broad-band behavior of GRB 200522A: a synchrotron forward shock with a luminous kilonova (potentially boosted by magnetar energy deposition), or forward and reverse shocks from a $\approx14^{\circ}$, relativistic ($\Gamma_0 \gtrsim 80$) jet. Models which include a combination of enhanced radioactive heating rates, low-lanthanide mass fractions, or additional sources of heating from late-time central engine activity may provide viable alternate explanations. If a stable magnetar was indeed produced in GRB 200522A, we predict that late-time radio emission will be detectable starting $\approx 0.3$-$6$ years after the burst for a deposited energy of $\approx 10^{53}$ erg. Counterparts of similar luminosity to GRB 200522A associated with gravitational wave events will be detectable with current optical searches to $\approx\!250$ Mpc.

39 citations


Journal ArticleDOI
14 Jan 2021-Nature
TL;DR: In this paper, the authors reported observations of the γ-ray burst GRB 200415A, which was localized to a 20-square-arcmin region of the starburst galaxy NGC-253, located about 3.5 million parsecs away.
Abstract: Soft γ-ray repeaters exhibit bursting emission in hard X-rays and soft γ-rays. During the active phase, they emit random short (milliseconds to several seconds long), hard-X-ray bursts, with peak luminosities1 of 1036 to 1043 erg per second. Occasionally, a giant flare with an energy of around 1044 to 1046 erg is emitted2. These phenomena are thought to arise from neutron stars with extremely high magnetic fields (1014 to 1015 gauss), called magnetars1,3,4. A portion of the second-long initial pulse of a giant flare in some respects mimics short γ-ray bursts5,6, which have recently been identified as resulting from the merger of two neutron stars accompanied by gravitational-wave emission7. Two γ-ray bursts, GRB 051103 and GRB 070201, have been associated with giant flares2,8–11. Here we report observations of the γ-ray burst GRB 200415A, which we localized to a 20-square-arcmin region of the starburst galaxy NGC 253, located about 3.5 million parsecs away. The burst had a sharp, millisecond-scale hard spectrum in the initial pulse, which was followed by steady fading and softening over 0.2 seconds. The energy released (roughly 1.3 × 1046 erg) is similar to that of the superflare5,12,13 from the Galactic soft γ-ray repeater SGR 1806−20 (roughly 2.3 × 1046 erg). We argue that GRB 200415A is a giant flare from a magnetar in NGC 253. The γ-ray burst GRB 200415A is probably a giant flare emitted from a magnetar in the nearby starburst galaxy NGC 253.

37 citations


Journal ArticleDOI
TL;DR: In this paper, the authors reported the unambiguous identification of a distinct population of four local (999% confidence) magnetar giant flares (MGFs) from the Milky Way and its satellite galaxies, and they have long been suspected to constitute a third class of extragalactic GRBs.
Abstract: Cosmological gamma-ray bursts (GRBs) are known to arise from distinct progenitor channels: short GRBs mostly from neutron star mergers and long GRBs from a rare type of core-collapse supernova (CCSN) called collapsars Highly magnetized neutron stars called magnetars also generate energetic, short-duration gamma-ray transients called magnetar giant flares (MGFs) Three have been observed from the Milky Way and its satellite galaxies, and they have long been suspected to constitute a third class of extragalactic GRBs We report the unambiguous identification of a distinct population of four local ( 999% confidence These properties, the host galaxies, and nondetection in gravitational waves all point to an extragalactic MGF origin Despite the small sample, the inferred volumetric rates for events above 4 × 1044 erg of Gpc−3 yr−1 make MGFs the dominant gamma-ray transient detected from extragalactic sources As previously suggested, these rates imply that some magnetars produce multiple MGFs, providing a source of repeating GRBs The rates and host galaxies favor common CCSN as key progenitors of magnetars

33 citations


Journal ArticleDOI
TL;DR: Observations of the γ-ray burst GRB 200415A have a rapid onset, very fast time variability, flat spectra and substantial sub-millisecond spectral evolution, which match well with those expected for a giant flare from an extragalactic magnetar.
Abstract: Magnetars are slowly-rotating neutron stars with extremely strong magnetic fields ($10^{13-15}$ G), episodically emitting $\sim100$ ms long X-ray bursts with energies of $\sim10^{40-41}$ erg. Rarely, they produce extremely bright, energetic giant flares that begin with a short ($\sim0.2$ s), intense flash, followed by fainter, longer lasting emission modulated by the magnetar spin period (typically 2-12 s), thus confirming their origin. Over the last 40 years, only three such flares have been observed in our local group; they all suffered from instrumental saturation due to their extreme intensity. It has been proposed that extra-galactic giant flares likely constitute a subset of short gamma-ray bursts, noting that the sensitivity of current instrumentation prevents us from detecting the pulsating tail, while the initial bright flash is readily observable out to distances $\sim 10-20$ Mpc. Here, we report X- and gamma-ray observations of GRB 200415A, which exhibits a rapid onset, very fast time variability, flat spectra and significant sub-millisecond spectral evolution. These attributes match well with those expected for a giant flare from an extra-galactic magnetar, noting that GRB 200415A is directionally associated with the galaxy NGC 253 ($\sim$3.5 Mpc away). The detection of $\sim3$ MeV photons provides definitive evidence for relativistic motion of the emitting plasma. The observed rapid spectral evolution can naturally be generated by radiation emanating from such rapidly-moving gas in a rotating magnetar.

Journal ArticleDOI
TL;DR: In this article, the authors used a sample of fast radio bursts (FRBs) host galaxies and a complete sample of corecollapse supernova (CCSN) hosts to determine whether FRB progenitors are consistent with a population of magnetars born in CCSNe.
Abstract: With the localization of fast radio bursts (FRBs) to galaxies similar to the Milky Way and the detection of a bright radio burst from SGR J1935+2154 with energy comparable to extragalactic radio bursts, a magnetar origin for FRBs is evident. By studying the environments of FRBs, evidence for magnetar formation mechanisms not observed in the Milky Way may become apparent. In this Letter, we use a sample of FRB host galaxies and a complete sample of core-collapse supernova (CCSN) hosts to determine whether FRB progenitors are consistent with a population of magnetars born in CCSNe. We also compare the FRB hosts to the hosts of hydrogen-poor superluminous supernovae (SLSNe-I) and long gamma-ray bursts (LGRBs) to determine whether the population of FRB hosts is compatible with a population of transients that may be connected to millisecond magnetars. After using a novel approach to scale the stellar masses and star formation rates of each host galaxy to be statistically representative of z = 0 galaxies, we find that the CCSN hosts and FRBs are consistent with arising from the same distribution. Furthermore, the FRB host distribution is inconsistent with the distribution of SLSNe-I and LGRB hosts. With the current sample of FRB host galaxies, our analysis shows that FRBs are consistent with a population of magnetars born through the collapse of giant, highly magnetic stars.

Journal ArticleDOI
01 Sep 2021-Universe
TL;DR: In this article, the formation and evolution of the magnetic field of a neutron star is discussed, paying special attention to the field decay processes and its magnetic field properties, and a subjective list of open problems is presented.
Abstract: Neutron stars are natural physical laboratories allowing us to study a plethora of phenomena in extreme conditions. In particular, these compact objects can have very strong magnetic fields with non-trivial origin and evolution. In many respects, its magnetic field determines the appearance of a neutron star. Thus, understanding the field properties is important for the interpretation of observational data. Complementing this, observations of diverse kinds of neutron stars enable us to probe parameters of electro-dynamical processes at scales unavailable in terrestrial laboratories. In this review, we first briefly describe theoretical models of the formation and evolution of the magnetic field of neutron stars, paying special attention to field decay processes. Then, we present important observational results related to the field properties of different types of compact objects: magnetars, cooling neutron stars, radio pulsars, and sources in binary systems. After that, we discuss which observations can shed light on the obscure characteristics of neutron star magnetic fields and their behaviour. We end the review with a subjective list of open problems.


Journal ArticleDOI
TL;DR: In this article, the authors show that the presence of a strong toroidal magnetic field is enough to explain the strong modulation of thermal X-ray emission in quiescence and allow their rotational orientation to be further constrained.
Abstract: Magnetars are neutron stars (NSs) with extreme magnetic fields1 of strength 5 × 1013−1015 G. These fields are generated by dynamo action during the proto-NS phase, and are expected to have both poloidal and toroidal components2–6, although the energy of the toroidal component could be ten times larger7. Only the poloidal dipolar field can be measured directly, via NS spin-down8. The magnetic field provides heating and governs how this heat flows through the crust9. Magnetar thermal X-ray emission in quiescence is modulated with the rotational period of the NS, with a typical pulsed fraction 10–58%, implying that the surface temperature is substantially non-uniform despite the high thermal conductivity of the star’s crust. Poloidal dipolar fields cannot explain this large pulsed fraction10,11. Previous two-dimensional simulations12,13 have shown that a strong, large-scale toroidal magnetic field pushes a hot region into one hemisphere and increases the pulsed fraction. Here, we report three-dimensional magneto-thermal simulations of magnetars with strong, large-scale toroidal magnetic fields. These models, combined with ray propagation in curved spacetime, accurately describe the observed light curves of 10 out of 19 magnetars in quiescence and allow us to further constrain their rotational orientation. We find that the presence of a strong toroidal magnetic field is enough to explain the strong modulation of thermal X-ray emission in quiescence. Realistic three-dimensional magneto-thermal simulations of magnetars with strong, large-scale toroidal magnetic fields accurately describe the observed light curves of 10 out of 19 magnetars in quiescence and allow their rotational orientation to be further constrained.

Journal ArticleDOI
TL;DR: In this article, spectral and temporal analyses of 24 X-ray bursts emitted 13 hours prior to the FRB and seen simultaneously with the Neutron Star Interior Composition Explorer (NICER) mission of the National Aeronautics and Space Administration and with the Fermi Gamma-ray Burst Monitor (GBM) mission in their combined energy range of 0.2
Abstract: Magnetars are young, magnetically powered neutron stars that possess the strongest magnetic fields in the Universe. Fast radio bursts (FRBs) are extremely intense millisecond-long radio pulses of primarily extragalactic origin, and a leading attribution for their genesis focuses on magnetars. A hallmark signature of magnetars is their emission of bright, hard X-ray bursts of sub-second duration. On 27 April 2020, the Galactic magnetar SGR J1935+2154 emitted hundreds of X-ray bursts within a few hours. One of these temporally coincided with an FRB, the first known detection of an FRB from the Milky Way. Here, we present spectral and temporal analyses of 24 X-ray bursts emitted 13 hours prior to the FRB and seen simultaneously with the Neutron Star Interior Composition Explorer (NICER) mission of the National Aeronautics and Space Administration and with the Fermi Gamma-ray Burst Monitor (GBM) mission in their combined energy range of 0.2 keV to 30 MeV. These broadband spectra permit direct comparison with the spectrum of the FRB-associated X-ray burst (FRB-X). We demonstrate that all 24 NICER and GBM bursts are very similar temporally to the FRB-X, but strikingly different spectrally. The singularity of the FRB-X burst is perhaps indicative of an uncommon locale for its origin. We suggest that this event originated in quasi-polar open or closed magnetic field lines that extend to high altitudes. Twenty-four X-ray bursts from a Galactic magnetar simultaneously observed with NICER and Fermi permit a direct comparison to a later X-ray burst that was coincident with a fast radio burst (FRB). The FRB-related burst is spectrally distinct, pointing to an unusual point of emission.

Journal ArticleDOI
TL;DR: In this paper, the energy spectrum of photons resulting from conversion of axion-like-particles (ALPs) in the magnetosphere was compared with hard X-ray data from NuSTAR, INTEGRAL, and XMM-Newton for a set of eight magnetars for which such data exists.
Abstract: Quiescent hard X-ray and soft gamma-ray emission from neutron stars constitute a promising frontier to explore axion-like-particles (ALPs). ALP production in the core peaks at energies of a few keV to a few hundreds of keV; subsequently, the ALPs escape and convert to photons in the magnetosphere. The emissivity goes as $\sim T^6$ while the conversion probability is enhanced for large magnetic fields, making magnetars, with their high core temperatures and strong magnetic fields, ideal targets for probing ALPs. We compute the energy spectrum of photons resulting from conversion of ALPs in the magnetosphere and then compare it against hard X-ray data from NuSTAR, INTEGRAL, and XMM-Newton for a set of eight magnetars for which such data exists. Upper limits are placed on the product of the ALP-nucleon and ALP-photon couplings. For the production in the core, we perform a careful calculation of the ALP emissivity in degenerate nuclear matter modeled by a relativistic mean field theory. The reduction of the emissivity due to improvements to the one-pion exchange approximation is incorporated, as is the strong suppression of the emissivity due to nucleon superfluidity in the neutron star core. A range of core temperatures is considered, corresponding to different models of the steady heat transfer from the core to the stellar surface. Our treatment also includes the first calculation of the emissivity due to $n+p \rightarrow n+p+a$ processes in the limit of strongly degenerate nuclear matter. For the subsequent conversion, we solve the coupled differential equations mixing ALPs and photons in the magnetosphere. The conversion occurs due to a competition between the dipolar magnetic field and the photon refractive index induced by the external magnetic field. Semi-analytic expressions are provided alongside the full numerical results.

Journal ArticleDOI
TL;DR: In this paper, the authors reported a universal correlation between X-ray luminosity and radio luminosity over twenty orders of magnitude among solar type III radio bursts, XTE J1810-197 and Galactic FRB 200428.
Abstract: Fast radio bursts (FRBs) are bright milliseconds radio transients with large dispersion measures. Recently, FRB 200428 was detected in temporal coincidence with a hard X-ray flare from the Galactic magnetar SGR 1935+2154, which supports that at least some FRBs are from magnetar activity. Interestingly, a portion of X-ray flares from magnetar XTE J1810-197 and the Sun are also accompanied by radio bursts. Many features of Galactic FRB 200428 and cosmological FRBs resemble solar radio bursts. However, a common physical origin among FRBs, magnetar radio pulses and solar radio bursts has not yet been established. Here we report a universal correlation between X-ray luminosity and radio luminosity over twenty orders of magnitude among solar type III radio bursts, XTE J1810-197 and Galactic FRB 200428. This universal correlation reveals that the energetic electrons which produce the X-ray flares and those which cause radio emissions have a common origin, which can give stringent limits on the generation process of radio bursts. Moreover, we find similar occurrence frequency distributions of energy, duration and waiting time for solar radio bursts, SGR 1935+2154 and repeating FRB 121102, which also support the tight correlation and the X-ray flares temporally associated with radio bursts. All of these distributions can be understood by avalanche models of self-organized criticality systems. The universal correlation and statistical similarities indicate that the Galactic FRB 200428 and FRBs seen at cosmological distances can be treated as scaled-up solar radio bursts.

Journal ArticleDOI
TL;DR: In this paper, the authors explore dynamical formation scenarios for objects in old globular clusters that may plausibly power fast radio burst (FRB) models, using N-body simulations.
Abstract: The repeating fast radio burst (FRB) localized to a globular cluster in M81 challenges our understanding of FRB models. In this Letter, we explore dynamical formation scenarios for objects in old globular clusters that may plausibly power FRBs. Using N-body simulations, we demonstrate that young neutron stars may form in globular clusters at a rate of up to $\sim50\,\rm{Gpc}^{-3}\,\rm{yr}^{-1}$ through a combination of binary white dwarf mergers, white dwarf--neutron star mergers, binary neutron star mergers, and accretion induced collapse of massive white dwarfs in binary systems. We consider two FRB emission mechanisms: First, we show that a magnetically-powered source (e.g., a magnetar with field strength $\gtrsim10^{14}\,$G) is viable for radio emission efficiencies $\gtrsim10^{-4}$. This would require magnetic activity lifetimes longer than the associated spin-down timescales and longer than empirically-constrained lifetimes of Galactic magnetars. Alternatively, if these dynamical formation channels produce young rotation-powered neutron stars with spin periods of $\sim10\,$ms and magnetic fields of $\sim10^{11}\,$G (corresponding to spin-down lifetimes of $\gtrsim10^5\,$yr), the inferred event rate and energetics can be reasonably reproduced for order unity duty cycles. Additionally, we show that recycled millisecond pulsars or low-mass X-ray binaries similar to those well-observed in Galactic globular clusters may also be plausible channels, but only if their duty cycle for producing bursts similar to the M81 FRB is small.

Journal ArticleDOI
TL;DR: In this article, the authors track the evolution of photons and matter in a coupled two-zone ("wind/nebula" and "ejecta") model, accounting for the range of radiative processes, and identify a mechanism by which gamma-gamma pair creation in the upstream pulsar wind regulates the mean energy of particles entering the nebula over the first several years after the explosion.
Abstract: Superluminous supernovae (SLSNe) are massive star explosions too luminous to be powered by traditional energy sources, such as radioactive 56Ni. These transients may instead be powered by a central engine, such as a millisecond pulsar or magnetar, whose relativistic wind inflates a nebula of high energy particles and radiation behind the expanding ejecta. We present 3D Monte Carlo radiative transfer calculations which follow the production and thermalization of high energy radiation from the nebula into optical radiation and, conversely, determine the gamma-ray emission that escapes the ejecta without thermalizing. We track the evolution of photons and matter in a coupled two-zone ("wind/nebula" and "ejecta") model, accounting for the range of radiative processes. We identify a novel mechanism by which gamma-gamma pair creation in the upstream pulsar wind regulates the mean energy of particles entering the nebula over the first several years after the explosion, rendering our results on this timescale insensitive to the (uncertain) intrinsic wind pair multiplicity. To explain the observed late-time steepening of SLSNe optical light curves as being the result of gamma-ray leakage, the nebular magnetization must be very low, epsB ~ 1 yr, inconsistent with observations. For magnetars to remain viable contenders for powering SLSNe, we conclude that either magnetic dissipation in the wind/nebula is extremely efficient, or that the spin-down luminosity decays significantly faster than the canonical dipole rate ~1/t^2 in a way that coincidentally mimicks gamma-ray escape.

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TL;DR: In this paper, the authors report on simultaneous and non-simultaneous observing campaigns using the Arecibo, Effelsberg, LOFAR, MeerKAT, MK2 and Northern Cross radio telescopes and the MeerLICHT optical telescope in the days and months after the April 28 event.
Abstract: Magnetars are a promising candidate for the origin of Fast Radio Bursts (FRBs). The detection of an extremely luminous radio burst from the Galactic magnetar SGR J1935+2154 on 2020 April 28 added credence to this hypothesis. We report on simultaneous and non-simultaneous observing campaigns using the Arecibo, Effelsberg, LOFAR, MeerKAT, MK2 and Northern Cross radio telescopes and the MeerLICHT optical telescope in the days and months after the April 28 event. We did not detect any significant single radio pulses down to fluence limits between 25 mJy ms and 18 Jy ms. Some observing epochs overlapped with times when X-ray bursts were detected. Radio images made on four days using the MeerKAT telescope revealed no point-like persistent or transient emission at the location of the magnetar. No transient or persistent optical emission was detected over seven days. Using the multi-colour MeerLICHT images combined with relations between DM, NH and reddening we constrain the distance to SGR J1935+2154, to be between 1.5 and 6.5 kpc. The upper limit is consistent with some other distance indicators and suggests that the April 28 burst is closer to two orders of magnitude less energetic than the least energetic FRBs. The lack of single-pulse radio detections shows that the single pulses detected over a range of fluences are either rare, or highly clustered, or both. It may also indicate that the magnetar lies somewhere between being radio-quiet and radio-loud in terms of its ability to produce radio emission efficiently.

Posted Content
TL;DR: In this paper, a family of model invoking coherent inverse Compton scattering (ICS) of bunched particles that may operate within or just outside of the magnetosphere of a flaring magnetar was proposed.
Abstract: The extremely high brightness temperature of fast radio bursts (FRBs) requires that their emission mechanism must be "coherent", either through concerted particle emission by bunches or through an exponential growth of a plasma wave mode or radiation amplitude via certain maser mechanisms. The bunching mechanism has been mostly discussed within the context of curvature radiation or cyclotron/synchrotron radiation. Here we propose a family of model invoking coherent inverse Compton scattering (ICS) of bunched particles that may operate within or just outside of the magnetosphere of a flaring magnetar. Crustal oscillations during the flaring event may excite low-frequency electromagnetic waves near the magnetar surface. The X-mode of these waves could penetrate through the magnetosphere. Bunched relativistic particles in the charge starved region inside the magnetosphere or in the current sheet outside of the magnetosphere would upscatter these low-frequency waves to produce GHz emission to power FRBs. The ICS mechanism has a much larger emission power for individual electrons than curvature radiation. This greatly reduces the required degree of coherence in bunches, alleviating several criticisms to the bunching mechanism raised in the context of curvature radiation. The emission is $\sim 100\%$ linearly polarized (with the possibility of developing circular polarization) with a constant or varying polarization angle across each burst. The mechanism can account for a narrow-band spectrum and a frequency downdrifting pattern, as commonly observed in repeating FRBs.

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TL;DR: In this article, the optical spectro-photometric observations of the nearby Type I superluminous supernova (SLSN I) SN 2017gci, whose peak K-corrected absolute magnitude reaches Mg=-21.5 mag.
Abstract: We present and discuss the optical spectro-photometric observations of the nearby (z=0.087) Type I superluminous supernova (SLSN I) SN 2017gci, whose peak K-corrected absolute magnitude reaches Mg=-21.5 mag. Its photometric and spectroscopic evolution includes features of both slow and of fast evolving SLSN I, thus favoring a continuum distribution between the two SLSN-I subclasses. In particular, similarly to other SLSNe I, the multi-band light curves of SN 2017gci show two rebrightenings at about 103 and 142 days after the maximum light. Interestingly, this broadly agrees with a broad emission feature emerging around 6520 A after 51 days from the maximum light, which is followed by a sharp knee in the light curve. If we interpret this feature as Halpha, this could support the fact that the bumps are the signature of late interactions of the ejecta with a (hydrogen rich) circumstellar material. Then we fitted magnetar and CSM-interaction powered synthetic light curves onto the bolometric one of SN 2017gci. In the magnetar case, the fit suggests a polar magnetic field Bp = 6 x 1e14 G, an initial period of the magnetar Pinitial=2.8 ms, an ejecta mass Mejecta=9 Msun and an ejecta opacity k = 0.08 cm g^{-1} . A CSM interaction scenario would imply a CSM mass of 5 Msun and an ejecta mass of 12 Msun. Finally, the nebular spectrum of phase 187 days was modeled, deriving a mass of 10 Msun for the ejecta. Our models suggest that either a magnetar or CSM interaction might be the power sources for SN 2017gci and that its progenitor was a massive (40 Msun) star.

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TL;DR: In this article, altitude-dependent radio emission from magnetar curvature radiation, with bursts emitted from regions which are asymmetric with respect to the magnetic dipole axis, can lead to burst activity windows and polarization consistent with the recent observations.
Abstract: Recent observations of the periodic Fast Radio Burst source 180916.J0158+65 (FRB 180916) find small linear polarization position angle swings during and between bursts, with a burst activity window that becomes both narrower and earlier at higher frequencies. Although the observed chromatic activity window disfavors models of periodicity in FRB 180916 driven by the occultation of a neutron star by the optically-thick wind from a stellar companion, the connection to theories where periodicity arises from the motion of a bursting magnetar remains unclear. In this paper, we show how altitude-dependent radio emission from magnetar curvature radiation, with bursts emitted from regions which are asymmetric with respect to the magnetic dipole axis, can lead to burst activity windows and polarization consistent with the recent observations. In particular, the fact that bursts arrive systematically earlier at higher frequencies disfavors theories where the FRB periodicity arises from forced precession of a magnetar by a companion or fallback disk, but is consistent with theories where periodicity originates from a slowly-rotating or freely-precessing magnetar. Several observational tests are proposed to verify/differentiate between the remaining theories, and pin-down which theory explains the periodicity in FRB 180916.

Posted Content
TL;DR: In this article, the authors present the first systematic study of the prevalence and properties of "bumps" in the post-peak light curves of 34 superluminous supernovae (SLSNe).
Abstract: 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 the 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 ($\rho\approx0.5$; $p\approx0.01$) between the phase of the bumps and the rise time, implying that such bumps tend to happen at a certain "evolutionary phase," $(3.7\pm1.4)t_\mathrm{rise}$. 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.

Posted Content
TL;DR: In this article, the authors apply novel, recently developed plasma ray-tracing techniques to model the propagation of radio photons produced by axion dark matter in neutron star magnetospheres and combine this with both archival and new data for the galactic centre magnetar PSR J1745-2900.
Abstract: We apply novel, recently developed plasma ray-tracing techniques to model the propagation of radio photons produced by axion dark matter in neutron star magnetospheres and combine this with both archival and new data for the galactic centre magnetar PSR J1745-2900. The emission direction to the observer and the magnetic orientation are not constrained for this object leading to parametric uncertainty. Our analysis reveals that ray-tracing greatly reduces the signal sensitivity to this uncertainty, contrary to previous calculations where there was no emission at all in some directions. Based on a Goldreich-Julian model for the magnetosphere and a Navarro-Frank-White model for axion density in the galactic centre, we obtain the most robust limits on the axion-photon coupling, to date. These are comparable to those from the CAST solar axion experiment in the mass range $\sim 4.2-60\,\mu{\rm eV}$. If the dark matter density is larger, as might predicted by a "spike" model, the limits could be much stronger. The dark matter density in the region of the galactic centre is now the biggest uncertainty in these calculations.


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TL;DR: In this article, the authors studied soft-gamma-ray emission from magnetars with the Fermi-GBM and derived upper limits on the product of the ALP-nucleon and ALP-photon couplings.
Abstract: Axion-like-particles (ALPs) emitted from the core of a magnetar can convert to photons in its magnetosphere. The resulting photon flux is sensitive to the product of (i) the ALP-nucleon coupling ${G}_{an}$ which controls the production cross section in the core and (ii) the ALP-photon coupling ${g}_{a\ensuremath{\gamma}\ensuremath{\gamma}}$ which controls the conversion in the magnetosphere. We study such emissions in the soft-gamma-ray range (300 keV to 1 MeV), where the ALP spectrum peaks and astrophysical backgrounds from resonant Compton up scattering are expected to be suppressed. Using published quiescent soft-gamma-ray flux upper limits in five magnetars obtained with CGRO COMPTEL and INTEGRAL SPI/IBIS/ISGRI, we put limits on the product of the ALP-nucleon and ALP-photon couplings. We also provide a detailed study of the dependence of our results on the magnetar core temperature. We further show projections of our result for future Fermi-GBM observations. Our results motivate a program of studying quiescent soft-gamma-ray emission from magnetars with the Fermi-GBM.

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TL;DR: In this paper, the authors used radiative transfer simulations to calculate the generated X-ray emission in a magnetized neutron star binary nearing merger, and compared the results with observed magnetar bursts, including the recent activity of SGR 1935+2154 accompanied by fast radio burst.
Abstract: Magnetar bursts can be emitted by Alfven waves growing in the outer magnetosphere to nonlinear amplitudes, $\delta B/B\sim 1$, and triggering magnetic reconnection. Similar magnetic flares should occur quasi-periodically in a magnetized neutron star binary nearing merger. In both cases, fast dissipation in the magnetic flare creates optically thick $e^\pm$ plasma, whose heat capacity is negligible compared with the generated radiation energy. Magnetic dissipation then involves photon viscosity and acts through Compton drag on the plasma bulk motions in the reconnection region. The effective temperature of the resulting Comptonization process is self-regulated to tens of keV. The generated X-ray emission is calculated using time-dependent radiative transfer simulations, which follow the creation of $e^\pm$ pairs and the production, Comptonization, and escape of photons. The simulations show how the dissipation region becomes dressed in an $e^\pm$ coat, and how the escaping spectrum is shaped by radiative transfer through the coat. The results are compared with observed magnetar bursts, including the recent activity of SGR 1935+2154 accompanied by a fast radio burst. Predictions are made for X-ray precursors of magnetized neutron star mergers.

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TL;DR: In this article, the authors reported on the extremely bright gamma-ray flare GRB 200415A of April 15, 2020, which they localize, using the Interplanetary Network, to a tiny (20 sq. arcmin) area on the celestial sphere, that overlaps the central region of the Sculptor galaxy at 3.5 Mpc from the Milky Way.
Abstract: Magnetars are young, highly magnetized neutron stars that produce extremely rare giant flares of gamma-rays, the most luminous astrophysical phenomena in our Galaxy. The detection of these flares from outside the Local Group of galaxies has been predicted, with just two candidates so far. Here we report on the extremely bright gamma-ray flare GRB 200415A of April 15, 2020, which we localize, using the Interplanetary Network, to a tiny (20 sq. arcmin) area on the celestial sphere, that overlaps the central region of the Sculptor galaxy at 3.5 Mpc from the Milky Way. From the Konus-Wind detections, we find a striking similarity between GRB 200415A and GRB 051103, the even more energetic flare that presumably originated from the M81/M82 group of galaxies at nearly the same distance (3.6 Mpc). Both bursts display a sharp, millisecond-scale, hard-spectrum initial pulse, followed by an approximately 0.2 s long steadily fading and softening tail. Apart from the huge initial pulses of magnetar giant flares, no astrophysical signal with this combination of temporal and spectral properties and implied energy has been reported previously. At the inferred distances, the energy released in both flares is on par with that of the December 27, 2004 superflare from the Galactic magnetar SGR 1806-20, but with a higher peak luminosity. Taken all together, this makes GRB 200415A and its twin GRB 051103 the most significant candidates for extragalactic magnetar giant flares, both a factor of five more luminous than the brightest Galactic magnetar flare observed previously, thus providing an important step towards a better understanding of this fascinating phenomenon.