Search

Fast radio bursts (FRBs) are highly energetic radio pulses from cosmological origins. Despite an abundance of detections, their nature remains elusive. At least a subset of FRBs is expected to repeat, as the volumetric FRB rate surpasses that of any known cataclysmic event, which has been confirmed by observations. One of the proposed mechanisms to generate repeating FRBs is supergiant pulses from young and highly spinning neutron stars (NSs), in which case FRBs could inherit the periodicity of their parent NS. Here we examine the consequences of such a population of periodic fast radio bursts (PFRBs). We calculate the rate and lifetime of PFRB progenitors, and find that each newly born highly spinning NS has to emit a number of detectable bursts during its active lifetime of yr, after which it becomes too dim and crosses a PFRB “death line” analogous to the pulsar one. We propose several tests of this hypothesis. First, the period of PFRBs would increase over time, and their luminosity would decrease, due to the NS spin-down. Second, PFRBs may show modest amounts of rotation measure, given the lack of expelled matter from the pulsar, as opposed to the magnetar-sourced FRBs proposed to explain the first repeater FRB 121102. As an example, we study whether the second confirmed repeater (FRB 180814) is a PFRB, given the preference for an inter-pulse separation of 13 ms within its sub-bursts. We show that, if confirmed, this period would place FRB 180814 in a different category as FRB 121102. We develop tests that would identify—and characterize—the prospective population of PFRBs. [ABSTRACT FROM AUTHOR]

The possibility of fast radio burst (FRB) emission being suppressed at low frequencies, resulting in a cutoff of the average rest-frame spectrum, has been raised as an explanation for the lack of detections at meter wavelengths. We examine propagation effects that could cause this suppression, and find that a low-frequency spectral cutoff may be generic regardless of the specific FRB emission mechanism. We then illustrate the effects of a low-frequency spectral cutoff on the statistics of FRBs, given a cosmological source population. The observed FRB rate peaks at a specific frequency under a variety of assumptions. Observations at lower frequencies are more sensitive to high-redshift events than observations above the maximal-rate frequency, and therefore result in more sharply broken fluence distributions. Our results suggest that the absence of low-frequency FRBs, and the differences between the Parkes and the Australian Square Kilometre Array FRB samples, can be fully explained by suppressed low-frequency FRB emission. [ABSTRACT FROM AUTHOR]

Over 80% of the cosmic baryon density is likely to be distributed in the diffuse, ≳104 K circumgalactic and intergalactic medium (CGM and IGM, respectively). We demonstrate that the dispersion measures (DMs) of samples of localized fast radio bursts (FRBs) can be used to measure the distribution of baryons between the CGM and IGM. We propose to separate the CGM and IGM contributions to FRB DMs by including redshift and mass measurements of intervening galaxies. Using simulated samples of FRB sight lines through intervening galaxy halos and an illustrative model for the CGM, and including realistic observational uncertainties, we show that small samples (O(101)–O(102)) of localized FRBs are sensitive to the presence of CGM gas. The fractions of baryons in the CGM and IGM can be accurately estimated with a few tens of FRBs at z < 1, with uncertainties of ∼10% with N = 10 FRBs that decline as N−1/2. The characteristic radial density profiles of CGM halos may also be possible to constrain with larger FRB samples. The required samples of localized FRBs are expected to be assembled in the coming few years by instruments such as the Australian Square Kilometre Array Pathfinder, the Deep Synoptic Array, MeerKAT, UTMOST-2D, and the Very Large Array. [ABSTRACT FROM AUTHOR]

We present detailed submillimeter- through centimeter-wave observations of the extraordinary extragalactic transient AT2018cow. The apparent characteristics—the high radio luminosity, the rise and long-lived emission plateau at millimeter bands, and the sub-relativistic velocity—have no precedent. A basic interpretation of the data suggests coupled to a fast but sub-relativistic () shock in a dense () medium. We find that the X-ray emission is not naturally explained by an extension of the radio-submm synchrotron spectrum, nor by inverse Compton scattering of the dominant blackbody UV/optical/IR photons by energetic electrons within the forward shock. By , the X-ray emission shows spectral softening and erratic inter-day variability. Taken together, we are led to invoke an additional source of X-ray emission: the central engine of the event. Regardless of the nature of this central engine, this source heralds a new class of energetic transients shocking a dense medium, which at early times are most readily observed at millimeter wavelengths. [ABSTRACT FROM AUTHOR]

We use data on extreme radio scintillation to demonstrate that this phenomenon is associated with hot stars in the solar neighborhood. The ionized gas responsible for the scattering is found at distances up to from the host star, and on average must comprise ∼105 distinct structures per star. We detect azimuthal velocities of the plasma, relative to the host star, up to , consistent with warm gas expanding at the sound speed. The circumstellar plasma structures that we infer are similar in several respects to the cometary knots seen in the Helix and in other planetary nebulae. There the ionized gas appears as a skin around tiny molecular clumps. Our analysis suggests that molecular clumps are ubiquitous circumstellar features, unrelated to the evolutionary state of the star. The total mass in such clumps is comparable to the stellar mass. [ABSTRACT FROM AUTHOR]