arXiv subjects

J. I. Katz

Publications and source records attributed to J. I. Katz.

At least 37 records · Page 2Linked to original sources

arXiv2022

Precession and Jitter in FRB 180916B

Recent CHIME/FRB observations of the periodic repeating FRB 180916B have produced a homogeneous sample of 44 bursts. These permit a redetermination of the modulation period and phase window, in agreement with earlier results. If the periodicity results from the precession of an accretion disc, in analogy with those of Her X-1, SS 433, and many other superorbital periods, the width of the observable phase window indicates that the disc axis jitters by an angle of about 0.14 of the inclination angle, similar to the ratio of 0.14 in the well-observed jittering jet source SS 433.

astro-ph.HE↗

arXiv2022

The Absence of Periodicity in Repeating FRB

Popular Fast Radio Burst models involve rotating magnetized neutron stars, yet no rotational periodicities have been found. Small datasets exclude exact periodicity in FRB 121102. Recent observations of over 1500 bursts from each of FRB 121102 and FRB 20201124A also have not found periodicity. Periodograms of events with cosine-distributed random offsets as large as $\pm 0.6 P$ from a strict period $P$ would still reveal the underlying periodicity. The sensitivity of periodograms of long data series, such as bursts observed on multiple days, to slow frequency drifts is mitigated by considering individual observing sessions, and results are shown for FRB 121102. Models of repeating FRB without intrinsic periodicity are considered, as are models of apparently non-repeating FRB.

astro-ph.HE↗

arXiv2022

The Environment and Constraints on the Mass of FRB 190520B

Recent observations of FRB 20190520B have revealed rapid fluctuation of its Dispersion Measure within apparently fixed bounds, as well as a reversal of its Rotation Measure. The fluctuations of Dispersion Measure are uncorrelated with the intervals between bursts, setting upper bounds $\sim 10\,$s on any characteristic time scale of the dispersing region; it must be very compact. Measurements of the full dependence of the dispersive time delay on frequency may determine the actual electron density and the size of this region. It is possible to set a lower bound on the mass of the FRB source from constraints on the size of the dispersing region and its time scale of variation. Comparison of the variations of DM and RM leads to an estimate of the magnetic field $\sim 500\,μ$G.

astro-ph.HE↗

arXiv2022

GLEAM-X J16279.5-523504.3 as a White Dwarf Pulsar

The low frequency radio source GLEAM-X J162759.5$-$523504.3 emits pulsed coherent polarized emission like that of radio pulsars. Yet its period of 18.18 min (1091 s) is hundreds of times longer than those of confirmed radio pulsars, and if it is a neutron star its mean radiated power exceeds the upper limit on its spin-down power by more than an order of magnitude. This may be explained if it is a white dwarf pulsar, with a moment of inertia several orders of magnitude greater than those of neutron stars. The Lorentz factor of the emitting charge bunches may be bounded from below by the widths of the temporal substructure of their radiation. If the emission is curvature radiation, the radius of curvature may be estimated from the Lorentz factor and the frequencies of emission; it is consistent with a white dwarf's inner magnetosphere but not a neutron star's.

astro-ph.SR↗

arXiv2022

The Sources of Apparently Non-Repeating FRB

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 more frequent weaker but detectable repetitive outbursts in apparent non-repeaters resembles the distribution of SGR outbursts, with a large gap between giant outbursts and lesser outbursts. This suggests mini-SGR as sources, more energetic than SGR 1935$+$2154 associated with FRB 200428 but less energetic than SGR 1806$-$20 that had no associated FRB. Their largest radio outbursts would, at cosmological distances, be apparently non-repeating FRB and their X-ray and gamma-ray outbursts would be undetectable. The large gap between the strongest outburst of FRB 200428 and its lesser outbursts resembles the gamma-ray properties of individual well-observed SGR; at twenty times its actual distance, FRB 200428 would have been an apparent non-repeater.

astro-ph.HE↗

arXiv2021

Painting Asteroids for Planetary Defense

Asteroidal impact threats to the Earth will be predicted a century or more in advance. Changing an asteroid's albedo changes the force of Solar radiation on it, and hence its orbit. Albedo may be changed by applying a thin ($\sim 0.1\,μ$) reflective coat of alkali metal, dispensed as vapor by an orbiting spacecraft. A complete coat reduces the effective Solar gravity, changing the orbital period. A Tunguska-class (50 m diameter) asteroid in a nominal orbit with perihelion 1 AU and aphelion 3 AU ($a = 2\,$AU, $e = 0.5$) may be displaced along its path by $\sim 1000\,$km in 100 years, sufficient to avoid impact in a populated area, by application of one kg of lithium or sodium metal over its entire surface. Alternatively, coating one hemisphere of an asteroid in an elliptical orbit may produce a Solar radiation torque, analogous to but distinct from the Yarkovsky effect, displacing it by an Earth radius in $\sim 200$ years. The time required scales as the square root of the asteroid's diameter (the 1/6 power of its mass) because the displacement increases quadratically with time, making it possible to prevent the catastrophic impact of a km-sized asteroid with a minimal mass.

astro-ph.EP↗

arXiv2021

FRB 190520B -- A FRB in a Supernova Remnant?

FRB 190520B, a repeating FRB near-twin of FRB 121102, was discovered \citep{N21} to have a dispersion measure excess over the intergalactic and Galactic contributions of about 900 pc-cm$^{-3}$, attributable to its host galaxy or near-source environment. This excess varies on a time scale of $\sim 30\,$y and might be explained by a supernova remnant no more than a few decades old. A magnetic field in equipartition with the remnant's expansion would be ${\cal O}(1\,\text{G})$. I suggest the use of baseband data to measure very large rotation measures.

astro-ph.HE↗

arXiv2021

Dodgeball -- Can a Satellite Avoid Being Hit by Debris?

Can a satellite dodge a collision with untracked orbiting debris? Can a satellite dodge collision with a tracked object, making only the avoidance manœuvers actually required to avoid collision, despite the uncertainties of predicted conjunctions? Satellite-borne radar may distinguish actual collision threats from the much greater number of near misses because an object on a collision course has constant bearing, which may be determined by interferometric detection of the radar return. A large constellation of such radars may enable the determination of the ephemerides of all cm-sized debris in LEO.

astro-ph.EP↗

arXiv2021

Testing Models of Periodically Modulated FRB Activity

The activity of the repeating FRB 20180916B is periodically modulated with a period of 16.3 days, and FRB 121102 may be similarly modulated with a period of about 160 days. In some models of this modulation the period derivative is insensitive to the uncertain parameters; these models can be tested by measurement of or bounds on the derivative. In other models values of the uncertain parameters can be constrained. Periodic modulation of aperiodic bursting activity may result from emission by a narrow beam wandering within a cone or funnel along the axis of a precessing disc, such as the accretion discs in X-ray binaries. The production of FRB 200428 by a neutron star that is neither accreting nor in a binary then shows universality: coherent emission may occur in a wide range of environments.

astro-ph.HE↗

arXiv2021

When Outliers Are Different

When does the presence of an outlier in some measured property indicate that the outlying object differs qualitatively, rather than quantitatively, from other members of its apparent class? Historical examples include the many types of supernovæ and short {\it vs.\/} long Gamma Ray Bursts. There may be only one parameter and one outlier, so that principal component analyses are inapplicable. A qualitative difference implies that some parameter has a characteristic scale, and hence its distribution cannot be a power law (that can have no such scale). If the distribution is a power law the objects differ only quantitatively. The applicability of a power law to an empirical distribution may be tested by comparing the most extreme member to its next-most extreme. The probability distribution of their ratio is calculated, and compared to data for stars, radio and X-ray sources, and the fluxes, fluences and rotation measures of Fast Radio Bursts. It is found with high statistical significance that the giant outburst of soft gamma repeater SGR 1806-20 differed qualitatively from its lesser outbursts and FRB 200428 differed qualitatively from other FRB (by location in the Galaxy), but that in some supernova remnant models of rotation measure FRB 121102 is not, statistically significantly, an outlier.

astro-ph.HE↗

arXiv2021

A FRB in a Globular Cluster: Why Is This Neutron Star Different From (Almost) All Other Neutron Stars?

Most Fast Radio Burst (FRB) models are built from comparatively common astronomical objects: neutron stars, black holes and supernova remnants. Yet FRB sources are rare, and most of these objects, found in the Galaxy, do not make FRB. Special and rare circumstances may be required for these common objects to be sources of FRB. The recent discovery of a repeating FRB in a globular cluster belonging to the galaxy M81 suggests a model involving a neutron star and a close binary companion, likely a white dwarf; both neutron stars and close binaries are superabundant in globular clusters. Magnetic interaction is a plausible, though unproven, mechanism of acceleration of relativistic particles that may radiate coherently as FRB. Double neutron star binaries cannot be the observed long-lived repeating FRB sources, but might make much shorter lived sources, and perhaps non-repeating FRB.

astro-ph.HE↗

arXiv2021

Apparatus for Measuring Strength in Biaxial Compression

Most measurements of compressive strength of ductile materials have involved Hopkinson-Kolsky bars or Taylor anvils placing samples in uniaxial compression. In these geometries strain is limited by the tendency of the sample to petal, in analogy to necking in uniaxial tension. Estimation of strength for any other form of the stress tensor requires assuming a shape for the yield surface; because data exist only for uniaxial compression these assumptions are untested. In an imploding spherical shell compression is biaxial, the plastic strain may not be small and the material behavior may be nonlinear as a result of work hardening and heating by plastic work. We propose to measure the strengths of materials in biaxial compression,both quasistatically and dynamically, using the compression of thin spherical shells. We suggest surrounding the shell with an annulus filled with a mixture of H$_2$ and Cl$_2$ gases whose volumetric detonation is initiated by a flash of blue and near-ultraviolet light. Less promising approaches are described in appendices.

physics.ins-det↗

arXiv2021

Fermi at Trinity

Enrico Fermi estimated the yield of the Trinity test to be about 10 kilotons by dropping small pieces of paper and observing their motion in the blast wave. This is about 40% of the radiochemically derived value of $25 \pm 2$ kilotons that necessarily includes thermal and nuclear radiation that do not contribute to the blast. Although this story is classic, there appears to be no account of how he related his observation to the yield. This note attempts to reconstruct how he might have done so.

physics.hist-ph↗

arXiv2021

`Oumuamua is not Artificial

I summarize evidence against the hypothesis that `Oumuamua is the artificial creation of an advanced civilization. An appendix discusses the flaws and inconsistencies of the "Breakthrough" proposal for laser acceleration of spacecraft to semi-relativistic speeds. Reality is much more challenging, and interesting.

physics.pop-ph↗

arXiv2021

Arrokoth's Necklace

Flyby images of (486958) Arrokoth (Ultima Thule, 2014 MU$_{69}$) show a comparatively bright "necklace" in the neck, or cleft between its two lobes, in contrast to its generally low albedo. We suggest that the necklace may be the result of thermally controlled ice deposition. The necklace is found in the most (orbitally averaged) shaded part of its surface. It may consist of clean, high albedo, ice condensed from vapor sublimed by dirty, low albedo, ice elsewhere; clean ice accumulates where the maximum temperatures are the lowest. Ammonia and propane have the necessary mesovolatile vapor pressure. Surrounding gas in the proto-Solar System would facilitate redeposition of molecules sublimed by warmer parts of the surface into the cleft, as well as smoothing the surface and explaining, by hydrodynamic drag, Arrokoth's slow (compared to its breakup rate) rotation. Alternatively, a layer of hoarfrost thick enough ($\gtrsim 0.1\,μ$) to have a high albedo could have formed more recently.

astro-ph.EP↗

arXiv2020

The Environment of FRB 121102 and Possible Relation to SGR/PSR J1745-2900

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".

astro-ph.HE↗

arXiv2020

The FRB-SGR Connection

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 Lorentz factors $\gtrapprox 100$. Coulomb repulsion implies that the electrons making up these bunches may have yet larger Lorentz factors, limited by their incoherent curvature radiation. These electrons also Compton scatter the soft gamma-rays of the SGR. In FRB 200428 the power radiated coherently at radio frequencies exceeded that of Compton scattering, but in more luminous SGR outbursts Compton scattering dominates, precluding the acceleration of energetic electrons. This explains the absence of a FRB associated with the giant 27 December 2004 outburst of SGR 1806$-$20. SGR with luminosity $\gtrsim 10^{42}$ ergs/s do not emit FRB, while those of lesser luminosity can do so. "Superbursts" like FRB 200428 are produced when narrowly collimated FRB are aligned with the line of sight; they are unusual, but not rare, and "cosmological" FRB may be superbursts.

astro-ph.HE↗

arXiv2020

Searching for Galactic Micro-FRB with Lunar Scattering

Does the Galaxy contain sources of micro-FRB, lower energy events resembling the known FRB but detectable only at Galactic distances? The answer to this question is essential to determining the nature of FRB sources. At typical ($10$ kpc) Galactic distances a burst would be about 117 dB brighter than at a "cosmological" ($z = 1$) distance. The radiation of Galactic micro-FRB, if they exist, could be detected after Lunar reflection, or an upper bound on their rate set, by a modest (20 m at 1.4 GHz) radio telescope staring at the Moon. It would have all-sky sensitivity. The delay between detection of direct (by STARE2 or dipoles) and Lunar-scattered radiation would restrict a burst's position to a narrow arc.

astro-ph.HE↗