Variations of the dispersion (DM) and rotation (RM) measures of FRB 121102 indicate magnetic fields $\sim$ 3--17 mG in the dispersing plasma. The electron density may be $\sim 10^4\,$cm$^{-3}$. The observed time scales $\sim 1$ year constrain the size of the plasma cloud. Increasing DM excludes simple models involving an expanding supernova remnant, and the non-zero RM excludes spherical symmetry. The varying DM and RM may be attributable to the motion of plasma into or out of the line of sight or changing electron density within slower-moving plasma. The extraordinarily large RM of FRB 121102 implies an environment, and possibly also a formation process and source, qualitatively different from those of other FRB. The comparable and comparably varying RM of SGR/PSR J1745-2900 suggests it as an FRB candidate. An appendix discusses the age of FRB 121102 in the context of a "Copernican Principle".
The discovery that the Galactic SGR 1935$+$2154 emitted FRB 200428 simultaneous with a gamma-ray flare demonstrated the common source and association of these phenomena. If FRB radio emission is the result of coherent curvature radiation, the net charge of the radiating "bunches" or waves may be inferred from the radiated fields, independent of the mechanism by which the bunches are produced. A statistical argument indicates that the radiating bunches must have a Lorentz factor $\gtrapprox 10$. The observed radiation frequencies indicate that their phase velocity (pattern speed) corresponds to…
Accompanied by an X-ray burst, the fast radio burst (FRB) FRB 200428 was recently confirmed as originating from the Galactic magnetar soft gamma repeater (SGR) SGR J1935+2154. Just before and after FRB 200428 was detected, the Five-hundred-meter Aperture Spherical radio Telescope (FAST) had been monitoring SGR J1935+2154 for eight hours. From UTC 2020 April 27 23:55:00 to 2020 April 28 00:50:37, FAST detected no pulsed radio emission from SGR J1935+2154, while Fermi/Gamma-ray Burst Monitor registered 34 bursts in the X/soft $γ$-ray band, forming a unique sample of X-ray bursts in the absence o…
Fast radio bursts (FRBs) are millisecond-duration radio signals occurring at cosmological distances. However the physical model of FRBs is mystery, many models have been proposed. Here we study the frequency distributions of peak flux, fluence, duration and waiting time for the repeating FRB 121102. The cumulative distributions of peak flux, fluence and duration show power-law forms. The waiting time distribution also shows power-law distribution, and is consistent with a non-stationary Poisson process. These distributions are similar as those of soft gamma repeaters (SGRs). We also use the st…
The detection of a fast radio burst (FRB), FRB 200428, coincident with an X-ray burst (XRB) from the Galactic magnetar soft gamma repeater (SGR) SGR J1935+2154 suggests that magnetars can produce FRBs. Many XRBs have been detected from the source, but very few were found to be associated with bursty radio emission. Meanwhile, a number of weaker radio bursts have been detected from the source, which could in principle be slow radio bursts (SRBs): FRBs detected at viewing angles outside the FRB jet cone. In this paper, we use these X-ray and radio observations to constrain the geometric and rela…
In this paper, we present statistics of soft gamma repeater (SGR) bursts from SGR J1550-5418, SGR 1806-20 and SGR 1900+14 by adding new bursts from Kırmızıbayrak et al. (2017) detected with the Rossi X-ray Timing Explorer (RXTE). We find that the fluence distributions of magnetar bursts are well described by power-law functions with indices 1.84, 1.68, and 1.65 for SGR J1550-5418, SGR 1806-20 and SGR 1900+14, respectively. The duration distributions of magnetar bursts also show power-law forms. Meanwhile, the waiting time distribution can be described by a non-stationary Poisson process with a…
Two repeating FRB sources, FRB180916 (CHIME/FRB Collaboration, 2020a) and FRB121102 (Rajwade, et al., 2020, Cruces, et al., 2021) display periodic windowed behavior (PWB) in the times of FRB detections. In PWB, events only occur within a periodic window spanning some fraction of the period, but no events may occur during many of the periods. During UT 2020 April 28, two peaks of a soft gamma burst (Li, et al., 2021) were identified with two FRB peaks (CHIME/FRB Collaboration, et al., 2020b) from soft gamma repeater (SGR) 1935+2154. As SGRs are a type of magnetar, these observations establish a…
There are insufficient catastrophic events (collapse, explosion or merger of stars or compact objects) to explain the cosmologically local rate of apparently non-repeating FRB if each such catastrophic event produces a single FRB. Unless produced by some novel and unsuspected but comparatively frequent event, apparently non-repeating FRB must actually repeat many times in the lifetimes of their sources. Yet no such infrequent repetitions (in contrast to the frequent activity of FRB known to repeat) have been observed, constraining their repetition rates and active lifetimes. The absence of mor…
Owing to the detection of an extremely bright fast radio burst (FRB) 200428 associated with a hard X-ray counterpart from the magnetar soft gamma-ray repeater (SGR) 1935+2154, the distance of SGR 1935+2154 potentially hosted in the supernova remnant (SNR) G57.2+0.8 can be revisited. Under the assumption that the SGR and the SNR are physically related, in this Letter, by investigating the dispersion measure (DM) of the FRB contributed by the foreground medium of our Galaxy and the local environments and combining with other observational constraints, we find that the distance of SGR 1935+2154 t…
Fast radio bursts (FRBs) are short pulses observed in radio frequencies usually originating from cosmological distances. The discovery of FRB 200428 and its X-ray counterpart from the Galactic magnetar SGR J1935+2154 suggests that at least some FRBs can be generated by magnetars. However, the majority of X-ray bursts from magnetars are not associated with radio emission. The fact that only in rare cases can an FRB be generated raises the question regarding the special triggering mechanism of FRBs. Here we report a giant glitch from SGR J1935+2154, which occurred approximately $3.1\pm2.5$\,day …
Recently, one fast radio burst, FRB 200428, was detected from the Galactic magnetar SGR J1935+2154 during one X-ray burst. This suggests that magnetars can make FRBs. On the other hand, the majority of X-ray bursts from SGR J1935+2154 are not associated with FRBs. One possible reason for such rarity of FRB-SGR-burst associations is that the FRB emission is much more narrowly beamed than the SGR burst emission. If such an interpretation is correct, one would expect to detect radio bursts with viewing angles somewhat outside the narrow emission beam. These "slow" radio bursts (SRBs) would have b…
The discovery of fast radio burst (FRB) 200428 from galactic SGR J1935+2154 makes it possible to measure rotational changes accompanied by FRBs and to test several FRB models which may be simultaneously associated with glitches. Inspired by this idea, we present order of magnitude calculations to the scenarios proposed. FRB models such as global starquakes, crust fractures and collisions between pulsars and asteroids/comets are discussed. For each mechanism, the maximum glitch sizes are constrained by the isotropic energy release during the X-ray burst and/or the SGR J1935+2154-like radio burs…
We present LOFAR imaging observations from the April/May 2020 active episode of magnetar SGR 1935+2154. We place the earliest radio limits on persistent emission following the low-luminosity fast radio burst FRB 200428 from the magnetar. We also perform an image-plane search for transient emission and find no radio flares during our observations. We examine post-FRB radio upper limits in the literature and find that all are consistent with the multi-wavelength afterglow predicted by the synchrotron maser shock model interpretation of FRB 200428. However, early optical observations appear to ru…
Very recently, an extremely bright fast radio burst (FRB) 200428 with two sub-millisecond pulses was discovered to come from the direction of the Galactic magnetar SGR 1935+2154, and an X-ray burst (XRB) counterpart was detected simultaneously. These observations favor magnetar-based interior-driven models. In this Letter, we propose a different model for FRB 200428 associated with an XRB from SGR 1935+2154, in which a magnetar with high proper velocity encounters an asteroid of mass $\sim10^{20}\,$g. This infalling asteroid in the stellar gravitational field is first possibly disrupted tidall…
We analyse archival data from the Parkes radio telescope which was observing a location 35.6$^\circ$ away from SGR 1806-20 during its giant $γ$-ray flare of 2004 December 27. We show that no FRB-like burst counterpart was detected, and set a radio limit of 110\,MJy at 1.4 GHz, including the estimated 70\,dB suppression of the signal due to its location in the far side lobe of Parkes and the predicted scattering from the interstellar medium. The upper limit for the magnetar giant flare radio to $γ$-ray fluence ratio is $η_\mathrm{SGR} \lesssim 10^{7}\,\mathrm{Jy\,ms\,erg^{-1}\,cm^{2}}$. Based o…
Fast radio bursts (FRBs) are mysterious millisecond-duration radio transients of unknown origin observed at extragalactic distances. It has been long speculated that magnetars are the engine powering repeating bursts from FRB sources, but no convincing evidence has been collected so far\cite{sun19}. Recently, the Galactic magnetar SGR J1935+2154 entered an active phase by emitting intense soft Gamma-ray bursts. One FRB-like event with two peaks (FRB 200428) and a luminosity slightly lower than the faintest extragalactic FRBs was detected from the source, in association with a soft Gamma-ray / …
Fast radio bursts (FRBs) are millisecond-duration, bright radio signals (fluence $\mathrm{0.1 - 100\,Jy\,ms}$) emitted from extragalactic sources of unknown physical origin. The recent CHIME/FRB and STARE2 detection of an extremely bright (fluence $\sim$MJy$\,$ms) radio burst from the Galactic magnetar SGR~1935$+$2154 supports the hypothesis that (at least some) FRBs are emitted by magnetars at cosmological distances. In follow-up observations totalling 522.7$\,$hrs on source, we detect two bright radio bursts with fluences of $112\pm22\mathrm{\,Jy\,ms}$ and $24\pm5\mathrm{\,Jy\,ms}$, respecti…
Finding the Particularity of the Active Episode of SGR J1935+2154 during Which FRB 20200428 Occurred: Implication from Statistics of Fermi/GBM X-Ray Bursts
Central China Normal University（华中师范大学）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）；Key Laboratory of Quark and Lepton Physics (Central China Normal University), Ministry of Education（教育部夸克与轻子物理重点实验室（华中师范大学））；Beijing Normal University（北京师范大学）；Dezhou University（德州学院）；Qufu Normal University（曲阜师范大学）
GECAM discovery of the second FRB-associated Magnetar X-ray Burst from SGR J1935+2154
State Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所粒子天体物理国家重点实验室）；University of Chinese Academy of Sciences, Chinese Academy of Sciences（中国科学院大学）；Department of Astronomy, Tsinghua University（清华大学天文系）
The discovery of a fast radio burst (FRB) associated with a magnetar in the Milky Way by the Canadian Hydrogen Intensity Mapping Experiment FRB collaboration (CHIME/FRB) and the Survey for Transient Astronomical Radio Emission 2 (STARE2) has provided an unprecedented opportunity to refine FRB emission models. The burst discovered by CHIME/FRB shows two components with different spectra. We explore interstellar scintillation as the origin for this variation in spectral structure. Modeling a weak scattering screen in the supernova remnant associated with the magnetar, we find that a superluminal…
Recently, a fast radio burst (FRB)-like event is found to be associated with a Galactic magnetar, SGR 1935+2154, accompanied by an X-ray burst. We find this radio burst challenges the typical emission mechanisms involving magnetars, which includes coherent curvature radiation from charged bunches, fast magnetosonic (FMS) wave, synchrotron maser from shocks, and the pulsar-like mechanism for low-twist magnetars. More specifically, we find that (1) the X-rays are most-likely to be produced inside the magnetosphere. (2) For the coherent curvature radiation from the decay of Alfvén wave, it will g…
Magnetars are highly magnetized neutron stars that are characterized by recurrent emission of short-duration bursts in soft gamma-rays/hard X-rays. Recently, FRB 200428 were found to be associated with an X-ray burst from a Galactic magnetar. Two fast radio bursts (FRBs) show mysterious periodic activity. However, whether magnetar X-ray bursts are periodic phenomena is unclear. In this paper, we investigate the period of SGR 1806-20 activity. More than 3000 short bursts observed by different telescopes are collected, including the observation of RXTE, HETE-2, ICE and Konus. We consider the obs…
Fast radio bursts, magnetars and earthquakes: their "family feud"?
National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；University of Chinese Academy of Sciences（中国科学院大学）；Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学天文与前沿科学研究院）；Tsinghua University（清华大学）
Since April 28, 2020, Insight-HXMT has implemented a dedicated observation on the magnetar SGR J1935+2154. Thanks to the wide energy band (1-250 keV) and high sensitivity of Insight-HXMT, we obtained 75 bursts from SGR J1935+2154 during a month-long activity episode after the emission of FRB 200428. Here, we report the detailed time-integrated spectral analysis of these bursts and the statistical distribution of the spectral parameters. We find that for 15%(11/75) of SGR J1935+2154 bursts, the CPL model is preferred, and most of them occurred in the latter part of this active epoch. In the cum…
GECAM discovery of a peculiar magnetar X-ray burst (MXB 221120) from SGR J1935+2154 associated with a fast radio burst
State Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所粒子天体物理国家重点实验室）；University of Chinese Academy of Sciences, Chinese Academy of Sciences（中国科学院大学）；College of Physics and Hebei Key Laboratory of Photophysics Research and Application, Hebei Normal University（河北师范大学物理学院河北省光物理研究与应用重点实验室）；College of Electronic and Information Engineering, Tongji University（同济大学电子与信息工程学院）；Department of Nuclear Science and Technology, School of Energy and Power Engineering, Xi’an Jiaotong University（西安交通大学能源与动力工程学院核科学与技术系）；Yunnan Observatories, Chinese Academy of Sciences（中国科学院云南天文台）；Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences（中国科学院天体结构与演化重点实验室）；Department of Astronomy, Peking University（北京大学天文学系）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；Beijing Laser Acceleration Innovation Center, Huairou, Beijing（北京激光加速创新中心）；School of Physical Science and Technology, Southwest Jiaotong University（西南交通大学物理科学与技术学院）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）；School of Physics and Electronic Science, Guizhou Normal University（贵州师范大学物理与电子科学学院）；Guizhou Provincial Key Laboratory of Radio Astronomy and Data Processing, Guizhou Normal University（贵州师范大学贵州省射电天文与数据处理重点实验室）；Institute of Astrophysics, Central China Normal University（华中师范大学天体物理研究所）
The observed rotation measures (RMs) towards the galactic centre magnetar and towards Sagittarius A* provide a strong constraint on MHD models of the galactic centre accretion flow, probing distances from the black hole separated by many orders of magnitude. We show, using 3D simulations of accretion via magnetized stellar winds of the Wolf-Rayet stars orbiting the black hole, that the large, time-variable RM observed for the pulsar PSR J1745-2900 can be explained by magnetized wind-wind shocks of nearby stars in the clockwise stellar disc. In the same simulation, both the total X-ray luminosi…
Recently, the discovery of Galactic FRB 200428 associated with a X-ray burst (XRB) of SGR 1935+2154 has built a bridge between FRBs and magnetar activities. In this paper, we assume that the XRB occurs in the magnetar magnetosphere. We show that the observational properties of FRB 200428 and the associated XRB are consistent with the predictions of synchrotron maser emission at ultrarelativistic magnetized shocks, including radiation efficiency, similar energy occurrence frequency distributions, and simultaneous arrive times. It requires that the upstream medium is a mildly relativistic baryon…
The origin(s) and mechanism(s) of fast radio bursts (FRBs), which are short radio pulses from cosmological distances, have remained a major puzzle since their discovery. We report a strong Quasi-Periodic Oscillation(QPO) of 40 Hz in the X-ray burst from the magnetar SGR J1935+2154 and associated with FRB 200428, significantly detected with the Hard X-ray Modulation Telescope (Insight-HXMT) and also hinted by the Konus-Wind data. QPOs from magnetar bursts have only been rarely detected; our 3.4 sigma (p-value is 2.9e-4) detection of the QPO reported here reveals the strongest QPO signal observe…
Magnetars are neutron stars with extreme magnetic field and sometimes manifest as soft gamma-ray repeaters (SGRs). SGR J1935+2154 is one of the most prolific bursters and the first confirmed source of fast radio burst (i.e. FRB 200428). Encouraged by the discovery of the first X-ray counterpart of FRB, Insight-Hard X-ray Modulation Telescope (Insight-HXMT) implemented a dedicated 33-day long ToO observation of SGR J1935+2154 since April 28, 2020. With the HE, ME, and LE telescopes, Insight-HXMT provides a thorough monitoring of burst activity evolution of SGR J1935+2154, in a very broad energy…
There are several phenomenological similarities between Soft Gamma Repeaters and Fast Radio Bursts, including duty factors, time scales and probable repetition. The sudden release of magnetic energy in a neutron star magnetosphere, as in popular models of SGR, can meet the energy requirements of FRB but requires both the presence of magnetospheric plasma in order that dissipation occur in a transparent region and a mechanism for releasing much of that energy quickly. FRB sources and SGR are distinguished by long-lived (up to thousands of years) current-carrying coronal arches remaining from fo…
Constraints on the Low-frequency Radio Emission of the Galactic FRB Source SGR 1935+2154
Nanjing University（南京大学）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；University of Chinese Academy of Sciences（中国科学院大学）；Lebedev Physical Institute of Astro Space Center of Pushchino Radio Astronomy Observatory（普希奇诺射电天文观测站太空物理中心列别捷夫物理研究所）；State Key Laboratory of Radio Astronomy and Technology, NAOC, Chinese Academy of Sciences（中国科学院国家天文台射电天文与技术重点实验室）；Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学前沿天文与天体物理研究院）；Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education（教育部现代天文与天体物理重点实验室（南京大学））；Institute of Mathematical Problems of Biology, Branch of Keldysh Institute of Applied Mathematics of Russian Academy of Sciences（俄罗斯科学院凯尔迪什应用数学研究所生物数学问题研究所）
A luminous radio burst was recently detected in temporal coincidence with a hard X-ray flare from the Galactic magnetar SGR 1935+2154 with a time and frequency structure consistent with cosmological fast radio bursts (FRB) and a fluence within a factor of $\lesssim 10$ of the least energetic extragalactic FRB previously detected. Although active magnetars are commonly invoked FRB sources, several distinct mechanisms have been proposed for generating the radio emission which make different predictions for the accompanying higher frequency radiation. We show that the properties of the coincident…
Fast radio bursts (FRBs) are short pulses observed in radio band from cosmological distances. One class of models invoke soft gamma-ray repeaters (SGRs), or magnetars, as the sources of FRBs. Some radio pulses have been observed from some magnetars, however, no FRB-like events had been detected in association any magnetar burst, including one giant flare. Recently, a pair of FRB-like bursts (FRB 200428 hereafter) separated by milliseconds (ms) were detected from the general direction of the Galactic magnetar SGR J1935+2154. Here we report the detection of a non-thermal X-ray burst in the 1-250…
Very recently a fast radio burst (FRB) 200428 associated with a strong X-ray burst from the Galactic magnetar SGR 1935+2154 has been detected, which is direct evidence supporting the magnetar progenitor models of FRBs. Assuming the FRB radiation mechanism is synchrotron maser emission from magnetized shocks, we develop a specific scenario by introducing a density jump structure of upstream medium, and thus the double-peaked character of FRB 200428 is a natural outcome. The luminosity and emission frequency of two pulses can be well explained in this scenario. Furthermore, we find that the sync…
SGR 1833-0832 was discovered on 2010 March 19 thanks to the Swift detection of a short hard X-ray burst and follow-up X-ray observations. Since then, it was repeatedly observed with Swift, Rossi X-ray Timing Explorer, and XMM-Newton. Using these data, which span about 225 days, we studied the long-term spectral and timing characteristics of SGR 1833-0832. We found evidence for diffuse emission surrounding SGR 1833-0832, which is most likely a halo produced by the scattering of the point source X-ray radiation by dust along the line of sight, and we show that the source X-ray spectrum is well d…
We measure the proper motion of the pulsar PSR J1745-2900 relative to the Galactic Center massive black hole, Sgr A*, using the Very Long Baseline Array (VLBA). The pulsar has a transverse velocity of 236 +/- 11 km s^-1 at position angle 22 +/- 2 deg East of North at a projected separation of 0.097 pc from Sgr A*. Given the unknown radial velocity, this transverse velocity measurement does not conclusively prove that the pulsar is bound to Sgr A*; however, the probability of chance alignment is very small. We do show that the velocity and position is consistent with a bound orbit originating i…
The most common form of magnetar activity is short X-ray bursts, with durations from milliseconds to seconds, and luminosities ranging from $10^{36}$ to $10^{43}\ {\rm erg}\,{\rm s}^{-1}$. Recently, an X-ray burst from the galactic magnetar SGR 1935+2154 was detected to be coincident with two fast radio burst (FRB) like events from the same source, providing evidence that FRBs may be linked to magnetar bursts. Using fully 3D force-free electrodynamics simulations, we show that such magnetar bursts may be produced by Alfvén waves launched from localized magnetar quakes: a wave packet propagates…
The statistical properties of the repeating fast radio burst FRB 121102 are investigated. We find that the cumulative distributions of fluence, flux density, total energy and waiting time can be well fitted by the bent power law. In addition, the probability density functions of fluctuations of fluence, flux density and total energy well follow the Tsallis $q$-Gaussian distribution. The $q$ values keep steady around $q\sim 2$ for different scale intervals, indicating a scale-invariant structure of the bursts. The statistical properties of FRB 121102 are very similar to that of the soft gamma r…
We analyze 134 ks Chandra ACIS-I observations of the Galactic Centre (GC) performed in July 2011. The X-ray image with the field of view $17' \times 17'$ contains the hot plasma surrounding the Sgr~A*. The obtained surface brightness map allow us to fit Bondi hot accretion flow to the innermost hot plasma around the GC. We have fitted spectra from region up to $5"$ from Sgr~A* using a thermal bremsstrahlung model and four Gaussian profiles responsible for K$_α$ emission lines of Fe, S, Ar, and Ca. The X-ray surface brightness profile up to $3"$ from Sgr~A* found in our data image, was successf…
Giant radio pulses in the magnetar XTE J1810-197 detected with the IAR's telescopes
Instituto de Astronomía Teórica y Experimental, CONICET-UNC（理论与实验天文学研究所）；Facultad de Matemática, Astronomía, Física y Computación, UNC（数学、天文学、物理与计算学院）；Instituto Argentino de Radioastronomía（阿根廷射电天文研究所）；Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata（拉普拉塔国立大学天文与地球物理科学学院）；Department of Space, Earth and Environment, Chalmers University of Technology（查尔姆斯理工大学空间、地球与环境系）
SGR J1745-2900 was detected from its outburst activity in April 2013 and it was the first soft gamma repeater (SGR) detected near the center of the Galaxy (Sagittarius A$^*$). We use 3.5-year Chandra X-ray light-curve data to constrain some neutron star (NS) geometric parameters. We assume that the flux modulation comes from hot spots on the stellar surface. Our model includes the NS mass, radius, a maximum of three spots of any size, temperature and positions, and general relativistic effects. We find that the light-curve of SGR J1745-2900 could be described by either two or three hot spots. …
