Program
10:00-12:00 (JST), [-1d] 17:00-19:00 (PST), [-1d] 20:00-22:00 (EST)
First week
Feb. 08 (Mon) Duncan Lorimer (40+10), Ziggy Pleunis (20+5), Pragya Chawla (20+5)
Feb. 09 (Tue) Bing Zhang (40+10), Wenbin Lu (40+10)
Feb. 10 (Wed) Adam Deller (40+10), Alvina Yee Lian On (20+5), Takuya Akahori (20+5)
Feb. 11 (Thu) Di Li (40+10), Kejia Lee (40+10)
Feb. 12 (Fri) Lin Lin (40+10), Teruaki Enoto (40+10), [Tea time 15:30 (JST)] Weiyang Wang (15+5)
Second week
Feb. 15 (Mon) Pawan Kumar (40+10), Shotaro Yamasaki (20+5)
Feb. 16 (Tue) Brian Metzger (40+10), Navin Sridhar (20+5)
Feb. 17 (Wed) Shri Kulkarni (40+10), Tetsuya Hashimoto (20+5)
Feb. 18 (Thu) Lorenzo Sironi (40+10), Masanori Iwamoto (20+5)
Feb. 19 (Fri) Shuta Tanaka (15+5), Ryuichi Takahashi (15+5), Tomoki Wada (15+5), Kazumi Kashiyama (15+5), Kunihito Ioka (15+5)
15:00-16:00 (JST) Tea time
Feb. 08 (Mon)
Chair: Kunihito Ioka
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Duncan Lorimer
Fast Radio Bursts -- Nature's Cosmological Probes
I review the current state of play in the rapidly evolving field of fast radio bursts. Starting with their discovery in 2007, I will focus on how the field has developed and what are the current open questions and prospects for current and future experiments over the next few years.
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Ziggy Pleunis
The first CHIME/FRB catalog: Fast Radio Burst morphologies and differentiating repeaters
The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a 4-cylinder 80-m x 100-m transit radio interferometer, located at the Dominion Radio Astrophysical Observatory near Penticton, B.C. CHIME was originally designed to map neutral hydrogen as a function of redshift to probe the expansion history of the Universe and operates the octave 400--800 MHz. Its high mapping speed and sensitivity and powerful correlator, moreover, make CHIME an excellent instrument to, commensally, search for Fast Radio Bursts (FRBs) and monitor pulsars. Indeed, the CHIME/FRB Project searches 1,024 digitally-formed beams, separated into 16K frequency channels with a 1-ms time resolution, for dispersed fast radio transients, in real-time, with the capability to save the buffered intensity and/or complex voltage data to disk on detection. We are set to release a first catalog of 517 FRBs, 60 of which are bursts from 18 different repeater sources. Here, I will present the construction of this catalog and a comparison between burst properties of repeaters and apparent non-repeaters. I will show how we can differentiate repeating sources of FRBs by their burst morphologies.
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Pragya Chawla
The first CHIME/FRB catalog: Interpreting FRB dispersion measures and scattering timescales
Over the past decade, population studies of fast radio bursts (FRBs) have been challenging to undertake due to the small number of known sources detected with different telescopes and detection pipelines. However, the large FRB sample detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) with a uniform selection function is well-suited for such studies. In this talk, I will present the distributions of dispersion measures and scattering timescales from the first CHIME/FRB catalog and describe the burst-fitting techniques used to determine these parameters. I will provide an overview of the framework that we have designed to simulate FRB populations located in different types of host galaxies and circumburst environments. I will then present constraints on the nature of FRB host galaxies and local environments derived by interpreting the CHIME-observed dispersion and scattering properties using the aforementioned framework.
Feb. 09 (Tue)
Chair: Kazumi Kashiyama
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Bing Zhang
The physical mechanisms of fast radio bursts
I will discuss several subjects on the physical mechanisms of FRBs. First, I will present several arguments in favor of the magnetospheric origin rather than the shock origin of FRBs in view of the latest observations. Second, I will discuss a type of off-beam FRBs, dubbed “slow radio bursts” or “SRBs” that might be detected from Galactic magnetars. Finally, I will discuss how one may address whether there exist genuinely non-repeating FRBs.
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Wenbin Lu
Towards Understanding FRBs
I will present a study of FRB cosmological volumetric rate density and provide evidence that cosmological and Galactic bursts belong to the same class of transients --- most likely all are repeaters. I will provide arguments that FRBs are most likely generated by the damping of Alfven waves propagating in the magnetosphere of strongly magnetized neutron stars. The Alfven waves are produced by crustal motion due to sudden energy release near the neutron star surface. If time allows, I will also address the polarization properties of FRBs.
Feb. 10 (Wed)
Chair: Bing Zhang
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Adam Deller
The FRB population as seen by ASKAP
The Australian SKA Pathfinder (ASKAP) combines a wide field of view with a voltage buffer and a real-time detection system. Collectively, these create a powerful FRB instrument: the wide field of view ensures a high detection rate, while the real-time triggering system ensures that detected FRBs can be localised to arcsecond precision and studied at microsecond time resolution with offline analysis. I will present the latest results on the FRB population as seen by ASKAP, including studies of the emission mechanism, host galaxy properties, and the use of localised FRBs to study the intergalactic medium and the cosmic web.
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Alvina Yee Lian On
Probing the magnetic Universe with fast radio bursts
Extragalactic fast radio bursts may be used as beacons to probe the large-scale magnetic field and its origin(s). The length scales on which magnetic field varies are often inferred from correlations in the observed Faraday rotation measure (RM). RM is a variable derived from the polarised radiative transfer equations under restrictive conditions. In this talk, we assess the usage of rotation measure fluctuation (RMF) analyses for magnetic field diagnostics in the framework of polarised radiative transfer. We show how density fluctuations could affect the correlation length of magnetic field inferred from the conventional RMF analyses. In particular, we caution against the interpretations of RMF analyses when a characteristic density is ill-defined. Moreover, the spatial correlations are generally dissimilar along the line-of-sight and across the sky plane, hence the context of RMF must be clarified when inferring from observational data. In complex situations, a covariant polarised radiative transfer calculation is essential to properly track the radiative and transport processes, otherwise the interpretations of magnetism in galaxy clusters and larger scale structures would be ambiguous. Lastly, we discuss the implications of our work on future radio observations, particularly with the Square Kilometre Array (SKA).
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Takuya Akahori
Linearly-polarized FRB as a tool of exploring cosmic magnetism
Linear polarization is one of only a few promising tools of exploring cosmic magnetism. In the last decades, linear polarization from cosmological objects such as quasars and radio galaxies has been used to diagnose magnetic fields of not only the sources and the Milky Way but also intervening galaxies and even the intergalactic medium. In my talk, I briefly review these previous works and discuss extensions of the works with linearly-polarized FRBs. Particularly, with a state-of-the-art polarimetric technique called Faraday tomography, linearly-polarized FRB could be a powerful probe of the intergalactic magnetic field.
Feb. 11 (Thu)
Chair: Susumu Inoue
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Di Li
Is FRB 121102 Alone?
The first known and localized repeater, FRB 121102, is the touchstone of measuring ensemble characteristics of FRB pulses. Is FRB 121102 a representative source or an exotic outlier? Such question has direct implication on the current debate of whether all FRBs repeat. I report here a large event set with more than 1600 individual bursts within 60 days from FRB 121102. Our analysis reveals a characteristic peak energy ~ 5E37 erg, below which the burst rate drops precipitously. During the apex of activity, the burst rate reached 122 bursts per hour. Despite the decent sampling in time, no periodicity nor QPO was seen for between 1ms to 1000s. I will discuss the implication of these results on understanding the FRB population.
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Kejia Lee
FRB searches with Chinese radio telescope
In the talk, we will summarise the FRB searching activity carried out using three Chinese radio telescopes, Nanshan 26m, Kunming 40m, and FAST 500m. Works on peryton following cold-plasma dispersion, FRB 180301 and SGR 1935+2154 will be covered.
Feb. 12 (Fri)
Chair: Kohta Murase
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Lin Lin
How does a Magnetar look in X-rays?
In this talk I will briefly review the observational properties of magnetars in X-ray band, and discuss in detail the X-ray behavior of SGR J1935+2154.
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Teruaki Enoto
Highly-magnetized neutron stars as one of the potential origins of FRBs
Highly magnetized neutron stars, including magnetars, young pulsars, and rotating radio transients (RRATs), are thought to be one of the potential candidates of the origin of fast radio bursts (FRBs). These neutron stars exhibit sporadic radiations, such as magnetar giant flares, short bursts, and intensive short-duration radio bursts of RRATs and giant radio pulses (GRPs). I will provide an overview of observational similarities between FRBs and highly magnetized neutron stars in my talk. Then, I will report recent results from the NICER X-ray observatory, follow-up observations of the Galactic FRB source, SGR 1935+2154, and the discovery of enhanced X-ray emission associated with GRPs of the Crab pulsar with their implications to the FRB science.
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Weiyang Wang
On the sub-pulse drifting of repeating FRBs
A bright radio burst was newly discovered in SGR 1935+2154, which exhibits some fast radio burst (FRB)-like temporal and frequency properties, suggesting a neutron star (NS)/magnetar magnetospheric origin of FRBs. We propose an explanation of the temporal and frequency properties of sub-pulses of repeating FRBs based on the generic geometry within the framework of charged-bunching coherent curvature radiation in the magnetosphere. The sub-pulses in a radio burst come from bunches of charged particles moving along different magnetic field lines. Their radiation beams sweep across the line of sight at different times, and those radiating at the more curved part tend to be seen earlier and at higher frequency. However, by considering bunches generated at slightly different times, we find there is also a small probability that the emission from the less curved part can be seen earlier. We simulate the time–frequency structures by deriving various forms of the electric acceleration field in the magnetosphere. This structure of sub-pulses is a natural consequence of coherent curvature radiation from an NS/magnetar magnetosphere with suddenly and violently triggered sparks. We apply this model to explain the time–frequency structure within a specific dipolar configuration by invoking the transient pulsar-like sparking from the inner gap of a slowly rotating NS, and we have also applied it to more generic configurations.
Feb. 15 (Mon)
Chair: Kunihito Ioka
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Pawan Kumar
FRB radiation mechanism and cosmology
Fast radio bursts (FRBs) are short duration (~ms), very bright, radio transients. Their detection in 2007 was a major unexpected discovery in astronomy in decades. Hunting for FRBs and measuring their physical properties have become one of the leading scientific goals in astronomy. It is now well established that many FRBs are located at a distance of several billion lightyears, and therefore they are the brightest known transients in the universe in the radio band. Using very general arguments, I will show that the radio emission is coherent, the magnetic field strength associated with the source of these events should be 10^{14}Gauss or more. Recently, an FRB was discovered in the Galaxy and it confirmed that at least some FRBs are associated with magnetars. I will describe my recent work that disturbances close to the surface of a magnetar launch Alfven waves into the magnetosphere, which propagate to a distance of a few tens of neutron star radii and then produce coherent radio emission. The coincident hard X-rays associated with the Galactic-FRB can be understood in this scenario. This model provides a unified picture for weak Galactic FRBs as well as the bright bursts seen at cosmological distances.
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Shotaro Yamasaki
Multi-Wavelength Constraints on the Outflow Properties of the Extremely BrightMillisecond Radio Bursts from the Galactic Magnetar SGR 1935+2154
A bright coherent radio burst with millisecond duration, reminiscent of cosmological fast radio bursts (FRBs), was co-detected with an anomalously-hard X-ray burst from a Galactic magnetar SGR 1935+2154 on April 28, 2020. We investigate the possibility that the event was triggered by a deposition of a magnetic energy in a localized region of the magnetosphere, thereby producing a so-called trapped fireball (FB) and simultaneously launching relativistic outflows. We show that the thermal component of the X-ray burst spectrum is consistent with a trapped FB with an average temperature of a few hundred keV and a size of ∼10^5cm. Meanwhile, the non-thermal component of the X-ray burst and the coherent radio burst may arise from relativistic outflows. We calculate the dynamical evolution of the outflow, launched with an energy budget ∼10^{39}-10^{40} erg comparable to that of the trapped FB for a variety of baryon load (eta) and initial magnetization (sigma_0) parameters. If both the hard X-ray and radio bursts are produced by the energy dissipation of the outflow, the properties can be constrained by the conditions for photon escape and the intrinsic timing offset of about 10ms among the radio and X-ray burst spikes. We show that the hard X-ray bursts need to be generated at r_{X} >10^{8}cm from the stellar surface, irrespective of the emission mechanism. Particularly in the case of shock dissipation, the outflow should accelerate up to a Lorentz factor of about 10^3 by the time it reaches the outer edge of the magnetosphere and the shock dissipation should take place at 10^{12} cm < r_{X,radio} < 10^{14} cm. In this case, extremely clean (eta ~>10^4) and/or highly magnetized (sigma_0 ~> 10^3) outflows are implied, which may be consistent with the rarity of this phenomenon.
Feb. 16 (Tue)
Chair: Kazumi Kashiayama
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Brian Metzger
FRBs from Flaring Magnetars
I will overview magnetar models for fast radio bursts. I will focus on an emission model which invokes synchrotron maser emission from an ultra-relativistic shock (generated e.g. by flaring activity) propagating into a slowly expanding upstream medium. I will describe the motivation for this model in the context of giant flares from Galactic magnetars, the persistent source properties of the repeating source FRB121102, and the observed properties of repeating FRB sources more generally. I will describe possible extensions of the model to other source classes, such as neutron star binary mergers.
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Navin Sridhar
Shock-powered radio precursors of neutron star mergers from accelerating relativistic binary winds
If at least one neutron star (NS) in a merging binary NS system is magnetized, then the orbital motion of the conducting companion during the final inspiral induces a strong current along the magnetic field lines connecting the stars. One consequence of this interaction is to substantially expand the primary's open magnetic flux and hence increase the luminosity of its wind relative to that of an isolated pulsar. As the binary orbit shrinks due to gravitational radiation, the power and speed of this binary-induced spiral wind may increase, leading to self-interaction and internal shocks in the outflow outside the binary orbit. The magnetized forward shock can generate an observable radio emission via the synchrotron maser process. We present 1D relativistic hydrodynamical simulations of shock interaction in the accelerating binary NS wind, which we combine with the results of particle-in-cell simulations of the shock maser emission, to generate synthetic FRB light curves. We predict ~60 FRBs/day to be detected through this channel by the current radio facilities, and ~2 of them per year, coincident with GW detections.
Feb. 17 (Wed)
Chair: Bing Zhang
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Shri Kulkarni
Low luminosity end of FRBs
Search for FRBs in Milky Way and nearby galaxies
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Tetsuya Hashimoto
Origins of fast radio bursts and their future applications
Fast radio bursts (FRBs) are a new type of astronomical transients with millisecond time scales, occurring at cosmological distances. Constraining their origins is one of the most important tasks in astronomy. Except for one confirmed case, the origins of the remaining >99% of the current FRB sample are still unknown. To overcome this problem, I performed unique statistical approaches to constrain their origins. Here I show, for the first time, the number density evolutions of non-repeating and repeating FRBs towards the distant Universe. The number density of non-repeating FRBs is almost constant during the past ~10 Gyr. The nearly-constant density is consistent with a flat trend of cosmic stellar-mass density traced by old stellar populations with ~Gyr time-scales. Our finding strongly narrows down the progenitor candidates of non-repeating FRBs to old objects, e.g., neutron stars. In contrast, the number density of repeating FRBs increases towards the distant Universe in a similar way to the cosmic star formation-rate density or supermassive black hole accretion-rate density. Short-living objects with <~Myr time-scales associated with young-stellar populations (or their remnants, e.g., magnetars) or active galactic nuclei are progenitor candidates of repeating FRBs. I, also for the first time, constrained the progenitors of FRBs statistically, bringing a breakthrough in understanding the origins of FRBs (TH+2020a,c). Additionally, I will discuss important applications of future FRBs. I discovered the non-repeating FRBs to be the new standard candle over the traditional type Ia supernovae (TH+2019a). Future FRBs to be detected with the Square Kilometre Array (TH+2020b) will allow us to address the time variability of the dark energy for the first time. I also propose a new method to investigate the cosmic reionization history using future FRBs (TH+2020d). In contrast to the cosmic microwave background observations, the new method will allow us to measure the reionization history as it is without any assumption on its functional shape. These applications clearly indicate the capability of future FRBs in broad areas in astronomy.
Feb. 18 (Thu)
Chair: Susumu Inoue
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Lorenzo Sironi
Coherent emission from relativistic shocks
The emission process of Fast Radio Bursts (FRBs) remains unknown. Electromagnetic precursor waves generated by the synchrotron maser instability at relativistic magnetized shocks have been recently invoked to explain the FRB coherent radio emission. By means of multi-dimensional particle-in-cell (PIC) simulations, we investigate the properties of the precursor waves radiated by relativistic perpendicular shocks propagating in strongly magnetized pair plasmas. We characterize the efficiency, spectrum and polarization of the resulting emission as a function of the flow magnetization, bulk Lorentz factor, and temperature, and we discuss implications for FRB models based on the synchrotron maser scenario.
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Masanori Iwamoto
2D PIC Simulations of Synchrotron Maser Instability in Relativistic Shocks
The origin of fast radio bursts (FRBs) is one of the unsolved problems in astrophysics. Since the high intensity and short duration of FRBs suggest extraordinary brightness temperature, a coherent emission mechanism is required. In relativistic shocks, it is well known that coherent electromagnetic waves are excited by synchrotron maser instability (SMI) in the shock transition (Hoshino & Arons 1991). Recently, the SMI is used for the model of FRBs (e.g., Lyubarsky 2014; Plotnikov & Sironi 2019; Metzger et al. 2019) and attracts much of attention in astrophysics. In this study, by performing 2D PIC simulation of ion-electron shocks, we will demonstrate that large-amplitude precursor waves are indeed excited by the SMI. Especially for relatively high magnetization, the wave amplitude is significantly amplified and exceeds that in pair plasmas due to a positive feedback process associated with ion-electron coupling. Based on the simulation results, we will discuss the applicability of the SMI for FRBs in this talk.
Feb. 19 (Fri)
Chair: Koutarou Kyutoku
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Suta Tanaka
Laboratory Experiment of Induced Compton Scattering: Initial Results
Induced Compton scattering is an interaction between bright radiation-field and rarefied plasma (electons). The very process is considered to be important around pulsars and fast radio burst. However, we still do not know which kind of signatures can be left behind the observed radio signals when the scattering has occurred. In December 2020, we conducted a laboratory experiment of induced Compton scattering in order to find the signature of induced Compton scatteing in the scattered spectrum. Here, we will show the preliminary results of the experiment and discuss them.
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Ryuichi Takahashi
Statistical modelling of the cosmological dispersion measure
We investigated the basic statistics of the cosmological dispersion measure (DM)— such as its mean, variance, probability distribution, angular power spectrum and correlation function—using the state-of-the-art hydrodynamic simulations, IllustrisTNG300, for the fast radio burst (FRB) cosmology. To model the DM statistics, we first measured the free-electron abundance and the power spectrum of its spatial fluctuations. The free-electron power spectrum turns out to be consistent with the dark matter power spectrum at large scales, but it is strongly damped at small scales (~1Mpc) owing to the stellar and active galactic nucleus feedback. The free-electron power spectrum is well modelled using a scale-dependent bias factor (the ratio of its fluctuation amplitude to that of the dark matter). We provide analytical fitting functions for the free-electron abundance and its bias factor. We next constructed mock sky maps of the DM by performing standard ray-tracing simulations with the TNG300 data. The DM statistics are calculated analytically from the fitting functions of the free-electron distribution, which agree well with the simulation results measured from the mock maps. We also obtained the probability distribution of source redshift for a given DM, which helps in identifying the host galaxies of FRBs from the measured DMs. The angular two-point correlation function of DM is described by a simple power-law function of angular separation, which will be confirmed by future observations when thousands of FRBs are available. This talk is based on our recent paper posted on arXiv (2010.01560).
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Tomoki Wada
Binary model for FRB121102
Some repeating FRBs have periodicity. For example, FRB180916 shows a 16-day periodicity, and the periodicity is explained by the binary comb model (Ioka & Zhang 2020). A period of 159 days has been reported for FRB 121102. In this talk, I will show that the binary model can explain this period of FRB 121102, and discuss the expected parameter regions of the binary.
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Kazumi Kashiyama
A "rotation-powered" model for repeating fast radio bursts
We revisit the rotation-powered neutron star (NS) model for fast radio burst (FRB) in which FRBs are produced in a cone of the open magnetic fields. We newly consider the possibility that the spindown power can be accumulated over time, e.g., in closed magnetic loops in the polar cap, and a release of the accumulated energy, e.g., by the interchange reconnection between a closed loop and a open field line, is the trigger of FRB. We construct a framework to constrain such models based on the energetic and geometrical conditions irrespective of the emission mechanism, and apply it to FRBs with known redshift. We show that the rotation-powered scenarios for repeating FRB are still possible for young NSs, including non magnetars. If the typical waiting time is determined by the rotation-power accumulation time in the polar region, (i) the timing of FRB 200428 ~ month after the onset of the outbursts of SGR 1935+2154 and the released energy in the X-ray flare can be consistently explained. Assuming the same FRB emission efficiency as FRB 200428, (ii) the progenitor NS of FRB 121102 is implied to be a ~10-100 yr old SLSN remnant (iii) while the progenitor NS of FRB 180916.J0158+65 be a ~100 yr old typical magnetar.
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Kunihito Ioka
Fast Radio Burst Breakouts from Magnetar Burst Fireballs
The recent discovery of a Mega-Jansky radio burst occurring simultaneously with short X-ray bursts from the Galactic magnetar (strongly magnetized neutron star (NS)) SGR 1935+2154 is a smoking gun for the hypothesis that some cosmological fast radio bursts (FRBs) arise from magnetar bursts. We argue that the X-ray bursts with high temperature T>30 keV entail an electron-positron (e+-) outflow from a trapped-expanding fireball, polluting the NS magnetosphere before the FRB emission. The e+- outflow is opaque to FRB photons, and is strongly Compton-dragged by the X-ray bursts. Nevertheless, the FRB photons can break out of the e+- outflow with radiation forces if the FRB emission radius is larger than a few tens of NS radii. A FRB is choked if the FRB is weaker or the X-ray bursts are stronger, possibly explaining why there are no FRBs with giant flares and no detectable X-ray bursts with weak FRBs. We also speculate that the e+- outflow may be inevitable for FRBs, solving the problem of why the FRBs occur only with high-T X-ray bursts. The breakout physics is important for constraining the emission mechanism and electromagnetic counterparts to future FRBs.