Recent observations of fast radio bursts (FRBs) indicate a perplexing, inconsistent picture. We propose a unified scenario to interpret diverse FRBs observed. A regular pulsar, otherwise unnoticeable ...at a cosmological distance, may produce a bright FRB if its magnetosphere is suddenly "combed" by a nearby, strong plasma stream toward the anti-stream direction. If the Earth is to the night side of the stream, the combed magnetic sheath would sweep across the direction of Earth and make a detectable FRB. The stream could be an AGN flare, a GRB or supernova blastwave, a tidal disruption event, or even a stellar flare. Since it is the energy flux received by the pulsar rather than the luminosity of the stream origin that defines the properties of the FRB, this model predicts a variety of counterparts of FRBs, including a possible connection between FRB 150418 and an AGN flare, a possible connection between FRB 131104 and a weak GRB, a steady radio nebula associated with the repeating FRB 121102, and probably no bright counterparts for some FRBs.
We estimate the upper limit redshifts of known fast radio bursts (FRBs) using the dispersion measure (DM)-redshift (z) relation and derive the upper limit peak luminosity Lp and energy E of FRBs ...within the observational band. The average z upper limits range from 0.17 to 3.10, the average Lp upper limits range from 1.24 × 1042 erg s−1 to 7.80 × 1044 erg s−1, and the average E upper limits range from 6.91 × 1039 erg to 1.94 × 1042 erg. FRB 160102 with DM = 2596.1 0.3 pc cm−3 likely has a redshift greater than 3. Assuming that its intrinsic DM contribution from the host and FRB source is DMhost + DMscr ∼ 100 pc cm−3, such an FRB can be detected up to z ∼ 3.6 by Parkes and the Five-hundred-meter Aperture Spherical radio Telescope (FAST) under ideal conditions up to z ∼ 10.4. Assuming the existence of FRBs that are detectable at z ∼ 15 by sensitive telescopes such as FAST, the upper limit DM for FRB searches may be set to ∼9000 pc cm−3. For single-dish telescopes, those with a larger aperture tend to detect more FRBs than those with a smaller aperture if the FRB luminosity function index L is steeper than 2, and vice versa. In any case, large-aperture telescopes such as FAST are more capable of detecting high-z FRBs, even though most of FRBs detected by them are still from relatively low redshifts.
ABSTRACT The discoveries of GW150914, GW151226, and LVT151012 suggest that double black hole (BH-BH) mergers are common in the universe. If at least one of the two merging black holes (BHs) carries a ...certain amount of charge, possibly retained by a rotating magnetosphere, the inspiral of a BH-BH system would drive a global magnetic dipole normal to the orbital plane. The rapidly evolving magnetic moment during the merging process would drive a Poynting flux with an increasing wind power. The magnetospheric activities during the final phase of the merger would make a fast radio burst (FRB) if the BH charge can be as large as a factor of q ˆ ∼ ( 10 − 9 - 10 − 8 ) of the critical charge Qc of the BH. At large radii, dissipation of the Poynting flux energy in the outflow would power a short-duration high-energy transient, which would appear as a detectable short-duration gamma-ray burst (GRB) if the charge can be as large as q ˆ ∼ ( 10 − 5 - 10 − 4 ) . The putative short GRB coincident with GW150914 recorded by Fermi GBM may be interpreted with this model. Future joint GW/GRB/FRB searches would lead to a measurement or place a constraint on the charges carried by isolate BHs.
The origin of fast radio bursts (FRBs) remains mysterious. Recently, the only repeating FRB source, FRB 121102, was reported to possess an extremely large and variable rotation measure (RM). The ...inferred magnetic field strength in the burst environment is comparable to that in the vicinity of the supermassive black hole Sagittarius A* of our Galaxy. Here, we show that all of the observational properties of FRB 121102 (including the high RM and its evolution, the high linear polarization degree, an invariant polarization angle across each burst and other properties previously known) can be interpreted within the "cosmic comb" model, which invokes a neutron star with typical spin and magnetic field parameters whose magnetosphere is repeatedly and marginally combed by a variable outflow from a nearby low-luminosity accreting supermassive black hole in the host galaxy. We propose three falsifiable predictions (periodic "on/off" states, and periodic/correlated variation of RM and polarization angle) of the model and discuss other FRBs within the context of the cosmic comb model as well as the challenges encountered by other repeating FRB models in light of the new observations.
Double neutron star mergers are strong sources of gravitational waves. The upcoming advanced gravitational wave detectors are expected to make the first detection of gravitational wave bursts (GWBs) ...associated with these sources. Proposed electromagnetic counterparts of a GWB include a short gamma-ray burst, an optical macronova, and a long-lasting radio afterglow. Here we suggest that at least some GWBs could be followed by an early afterglow lasting for thousands of seconds, if the post-merger product is a highly magnetized, rapidly rotating, massive neutron star rather than a black hole. This afterglow is powered by dissipation of a proto-magnetar wind. The X-ray flux is estimated to be as bright as (10 super(?8)-10 super(?7)) erg s super(-1) cm super(?2). The optical flux is subject to large uncertainties but could be as bright as 17th magnitude in R band. We provide observational hints of such a scenario, and discuss the challenge and strategy to detect these signals.
If at least one of the members of a compact binary coalescence is charged, the inspiral of the two members would generate a Poynting flux with an increasing power, giving rise to a brief ...electromagnetic counterpart temporally associated with the chirp signal of the merger (with possibly a small temporal offset), which we term as the charged compact binary coalescence (cCBC) signal. We develop a general theory of cCBC for any mass and amount of charge for each member. Neutron stars (NSs), as spinning magnets, are guaranteed to be charged, so the cCBC signal should accompany all NS mergers. The cCBC signal is clean in a black hole (BH)-NS merger with a small mass ratio ( ), in which the NS plunges into the BH as a whole, and its luminosity/energy can reach that of a fast radio burst if the NS is Crab-like. The strength of the cCBC signal in Extreme Mass Ratio Inspiral Systems is also estimated.
The first gravitational wave (GW) - gamma-ray burst (GRB) association, GW170817/GRB 170817A, had an offset in time, with the GRB trigger time delayed by ~1.7 s with respect to the merger time of the ...GW signal. We generally discuss the astrophysical origin of the delay time, Δ t, of GW-GRB associations within the context of compact binary coalescence (CBC) - short GRB (sGRB) associations and GW burst - long GRB (lGRB) associations. In general, the delay time should include three terms, the time to launch a clean (relativistic) jet, Δ t jet; the time for the jet to break out from the surrounding medium, Δ t bo; and the time for the jet to reach the energy dissipation and GRB emission site, Δ t GRB. For CBC-sGRB associations, Δtjet and Δ t bo are correlated, and the final delay can be from 10 ms to a few seconds. For GWB-lGRB associations, Δ t jet and Δ t bo are independent. The latter is at least ~10 s, so that Δ t of these associations is at least this long. For certain jet launching mechanisms of lGRBs, Δ t can be minutes or even hours long due to the extended engine waiting time to launch a jet. We discuss the cases of GW170817/GRB 170817A and GW150914/GW150914-GBM within this theoretical framework and suggest that the delay times of future GW/GRB associations will shed light into the jet launching mechanisms of GRBs.
We provide a comprehensive review of major developments in our understanding of gamma-ray bursts, with particular focus on the discoveries made within the last fifteen years when their true nature ...was uncovered. We describe the observational properties of photons from the radio to 100s GeV bands, both in the prompt emission and the afterglow phases. Mechanisms for the generation of these photons in GRBs are discussed and confronted with observations to shed light on the physical properties of these explosions, their progenitor stars and the surrounding medium. After presenting observational evidence that a powerful, collimated, jet moving at close to the speed of light is produced in these explosions, we describe our current understanding regarding the generation, acceleration, and dissipation of the jet. We discuss mounting observational evidence that long duration GRBs are produced when massive stars die, and that at least some short duration bursts are associated with old, roughly solar mass, compact stars. The question of whether a black-hole or a strongly magnetized, rapidly rotating neutron star is produced in these explosions is also discussed. We provide a brief summary of what we have learned about relativistic collisionless shocks and particle acceleration from GRB afterglow studies, and discuss the current understanding of radiation mechanism during the prompt emission phase. We discuss theoretical predictions of possible high-energy neutrino emission from GRBs and the current observational constraints. Finally, we discuss how these explosions may be used to study cosmology, e.g. star formation, metal enrichment, reionization history, as well as the formation of first stars and galaxies in the universe.
Abstract
Recently, one fast radio burst (FRB), FRB 200428, was detected from the Galactic magnetar soft gamma-ray repeater (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 broader widths and lower flux densities due to the smaller Doppler factor involved. We derive two “closure relations” to judge whether a long, less luminous radio burst could be an SRB. The 2.2 s, 308 Jy ms, ∼111 MHz radio burst detected from SGR J1935+2154 by the BSA/LPI radio telescope may be such an SRB. The ∼2 ms, 60 mJy ms faint burst detected by the Five-hundred-meter Aperture Spherical radio Telescope from the same source could be also an SRB if the corresponding FRB has a narrow spectrum. If the FRB beam is narrow, there should be many more SRBs than FRBs from Galactic magnetars. The lack of detection of abundant SRBs from magnetars would disfavor the hypothesis that all SGR–bursts are associated with narrow-beam FRBs.
Small‐molecule‐based second near‐infrared (NIR‐II) activatable fluorescent probes can potentially provide a high target‐to‐background ratio and deep tissue penetration. However, most of the reported ...NIR‐II activatable small‐molecule probes exhibit poor versatility owing to the lack of a general and stable optically tunable group. In this study, we designed NIRII‐HDs, a novel dye scaffold optimized for NIR‐II probe development. In particular, dye NIRII‐HD5 showed the best optical properties such as proper pKa value, excellent stability, and high NIR‐II brightness, which can be beneficial for in vivo imaging with high contrast. To demonstrate the applicability of the NIRII‐HD5 dye, we designed three target‐activatable NIR‐II probes for ROS, thiols, and enzymes. Using these novel probes, we not only realized reliable NIR‐II imaging of different diseases in mouse models but also evaluated the redox potential of liver tissue during a liver injury in vivo with high fidelity.
A series of O‐HD‐like dyes (NIRII‐HDs) with bright and stable NIR‐II emission together with proper pKa is reported. By decorating the tunable hydroxyl group, the novel NIR‐II dye NIRII‐HD5 can serve as an effective platform to design various activatable NIR‐II probes for reliable in vivo bioimaging with high contrast.
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