arXiv subjects

J. I. Katz

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

At least 55 records · Page 3Linked to original sources

arXiv2020

Are Fast Radio Bursts Made By Neutron Stars?

Popular models of repeating Fast Radio Bursts (and perhaps of all Fast Radio Bursts) involve neutron stars because of their high rotational or magnetostatic energy densities. These models take one of two forms: giant but rare pulsar-like pulses like those of Rotating RAdio Transients and outbursts like those of Soft Gamma Repeaters. Here I collate the evidence, recently strengthened, against these models, including the absence of Galactic micro-FRB, and attribute the 16 day periodicity of FRB 180916.J0158+65 to the precession of a jet produced by a massive black hole's accretion disc.

astro-ph.HE↗

arXiv2019

FRB Energetics and Sources

Repeating and apparently non-repeating fast radio bursts (FRB) differ by orders of magnitude in duty factors, energy and rotation measure. Extensive monitoring of apparently non-repeating FRB has failed to find any repetitions. This suggests the two types differ qualitatively, rather than in repetition rate, and are produced by distinct kinds of sources. The absence of periodicity in repeating FRB argues that they are not produced by neutron stars. They may originate in dilute relativistic jets produced by low luminosity black hole accretion. Non-repeating FRB may be produced by catastrophic events such as the collapse of an accreting magnetic neutron star to a black hole or of an accreting magnetic white dwarf to a neutron star, during which a disappearing magnetic moment radiates dipole radiation that accelerates electrons in nearby matter. If they are emitted by collimated beams of relativistic particles or charge "bunches" with Lorentz factor $γ$, their radiation is collimated into a solid angle $\sim γ^{-2}$ sterad, reducing the energy requirement. If powered by magnetic reconnection, a pulse of length $Δt$ may draw on the magnetic energy in a volume $\sim γ^4 (c Δt)^3$, although only a fraction $\sim 1/γ^2$ of this may be dissipated without decollimation.

astro-ph.HE↗

arXiv2019

Evidence against non-gravitational acceleration of 1I/2017 U1 `Oumuamua

Micheli, et al. (2018) reported that a seven-parameter fit to the orbit of 1I/2017 U1 `Oumuamua indicated a non-gravitational acceleration in the anti-Solar direction, and attributed it to recoil from comet-like outgassing. The implied gas to dust ratio is at least 100 times greater than that of known Solar System comets. The reported collapse of the scatter of nearly contemporaneous coordinate residuals upon inclusion of the non-gravitational term in the orbital fits is difficult to understand. There are grounds for skepticism.

astro-ph.EP↗

arXiv2019

Emissivity of Ammonia Ice

Bodies in the outer Solar System may consist of, or be covered by, solid ammonia. Their temperature depends on its emissivity. We calculate that emissivity as a function of frequency, angle and polarization and convolve it with a Planck function to obtain its integrated emissivity.

astro-ph.EP↗

arXiv2019

Long Term Trends in Atmospheric Pressure and its Variance

We use the Global Historical Climatology Network--daily database to calculate trends in sea-level atmospheric pressures, their variance and the variance of their day-to-day differences in nine regions of the world. Changes in pressure reflect the addition of water vapor to the warming atmosphere and changes in circulation patterns. Pressure gradients drive fronts and storm systems, and pressure differences, a meteorological parameter distinct from temperature and precipitation, are a proxy for storminess. In eight of nine regions the mean sea level pressure decreased at a rate significant at the $2σ$ (95\% confidence) level if correlations between stations are small, but this nominal assumption is uncertain. We find lower bounds on the characteristic time scale of change of the sea level pressure variance and its differences between consecutive days. Depending on assumptions about the uncertainties of the mean values of trends averaged over many ($> 1000$ in some regions) stations, these lower bounds on the time scales of change of the variances range from $\sim 100$ to several thousand years. Trends in the variance of day-to-day pressure differences are negative and nominally significant in six of nine regions. Nominally significant trends in the pressure variances themselves are positive in three regions and negative in one.

physics.ao-ph↗

arXiv2018

Coherent Plasma-Curvature Radiation in FRB

Curvature radiation is a natural candidate for the emission mechanism of FRB. However, FRB spectra have structure with $Δν/ν\sim \text{0.03--0.2}$, inconsistent with the very smooth spectrum of curvature radiation. Although this spectral structure might be attributed to chromatic scintillation or lensing, in four FRB high spectral resolution data indicate scintillation decorrelation bandwidths much narrower than the observed $\sim \text{30--300}$ MHz spectral structure. Some of the observed structure may be intrinsic to the radiation mechanism. I suggest that the observed spectral structure reflects the spatial structure of a clumpy radiating charge distribution, and that the characteristic curvature radiation frequency may be much higher than the observed frequencies. In this coupled plasma-curvature radiation process the radiated spectra are the product of the spectra of the plasma wave and that of incoherent curvature radiation. The argument applies to all coherent radiation processes, including those that produce pulsar nanoshots. The implied FRB "clump" charges are large, and produce electrostatic potentials that suggest electron Lorentz factors $\gtrsim 10^2$. The result applies generally to coherently radiating sources.

astro-ph.HE↗

arXiv2018

Fast Radio Bursts

More than a decade after their discovery, astronomical Fast Radio Bursts remain enigmatic. They are known to occur at "cosmological" distances, implying large energy and radiated power, extraordinarily high brightness and coherent emission. Yet their source objects, the means by which energy is released and their radiation processes remain unknown. This review is organized around these unanswered questions.

astro-ph.HE↗

arXiv2018

Why is Interstellar Object 1I/2017 U1 (`Oumuamua) Rocky, Tumbling and Very Prolate?

The recently discovered first interstellar object 1I/2017 U1 (`Oumuamua) has brightness that varies by a factor of 10, a range greater than that of any Solar System asteroid, a spectrum characteristic of Type D asteroids, and no evidence of evaporating volatiles, contrary to expectation for exo-Oort clouds. This object was the first example of the proposed "Jurads", objects depleted in volatiles and ejected from planetary systems during the post-main sequence evolution of their parent star. I suggest that heating by the star's giant stage fluidized a precursor cometary object as volatiles escaped, causing it to assume the Jacobi ellipsoidal shape of a self-gravitating incompressible liquid. The collision that produced the inferred tumbling motion must have occurred thousands of years after the formation of 1I/2017 U1 `Oumuamua. Jacobi ellipsoids have a unique relation among rotation rate, density and axial ratio. The inferred axial ratio $\gtrapprox 5$ implies a lower bound on the density of 1.6 g/cm$^3$, excluding an icy interior unless it is almost entirely frozen CO$_2$. This object is the first Jurad to be discovered and may be related to accreting objects that pollute white dwarf atmospheres and may make Soft Gamma Repeaters.

astro-ph.EP↗

arXiv2017

FRB 121102 Burst Pairs

The repeating FRB 121102 emitted a pair of discrete bursts separated by 37 ms and another pair, 131 days later, separated by 34 ms, during observations that detected FRB at a mean rate of $2 \times 10^{-4}$/s. Here I assume that these events are separate bursts rather than multiple peaks from longer single bursts and consider their implications. They then are inconsistent with Poissonian statistics. The measured intervals constrain any possible periodic modulation underlying the highly episodic emission. If more such short intervals are measured a period may be determined or periodicity may be excluded. Sources of narrow wandering beams predict pairs (or higher multiples) of bursts closely spaced in time compared to the mean event rate.

astro-ph.HE↗

arXiv2017

FRB Strength Distribution Challenges the Cosmological Principle

The distribution of FRB fluxes and fluences is characterized by a few very bright events and a deficiency of fainter events compared to expectations for a homogeneous space-filling distribution. I define a metric to quantify this, and apply it to the 17 presently known Parkes FRB, products of a comparatively homogeneous search. With 98\% confidence we reject the hypothesis of a homogeneous distribution in Euclidean space. Possible explanations include a reduction of fainter events by cosmological redshifts or evolution or a cosmologically local concentration of events. The former is opposed by the small value of the one known FRB redshift. The latter contradicts the Cosmological Principle, but may be explained if the brighter FRB originate in the Local Supercluster.

astro-ph.HE↗

arXiv2017

Changing World Extreme Temperature Statistics

We use the Global Historical Climatology Network--daily database to calculate a nonparametric statistic that describes the rate at which all-time daily high and low temperature records have been set in nine geographic regions (continents or major portions of continents) during periods mostly from the mid-20th Century to the present. This statistic was defined in our earlier work on temperature records in the 48 contiguous United States. In contrast to this earlier work, we find that in every region except North America all-time high records were set at a rate significantly (at least $3σ$) higher than in the null hypothesis of a stationary climate. Except in Antarctica, all-time low records were set at a rate significantly lower than in the null hypothesis. In Europe, North Africa and North Asia the rate of setting new all-time highs increased suddenly in the 1990's, suggesting a change in regional climate regime; in most other regions there was a steadier increase.

physics.ao-ph↗

arXiv2017

Can Dips of Boyajian's Star be Explained by Circumsolar Rings?

Could the dips of "Boyajian's Star" (KIC 8462852) have been caused by matter in our Solar System? The interval between periods of deep dips is nearly twice the orbital period of the Kepler satellite. I consider heliocentric obscuring rings in the outer Solar System that graze the line of sight to the star once per orbit of Kepler. The hypothesis predicts that future dips may be observed from Earth during windows separated by a year, although their detailed structure depends on the distribution of particles along the ring. Dips observed at terrestrial sites separated by > 1000 km in a direction perpendicular to the Earth's orbital motion may be uncorrelated.

astro-ph.EP↗

arXiv2017

FRB as Products of Accretion Disc Funnels

The repeating FRB 121102, the only FRB with an accurately determined position, is associated with a variable persistent radio source consistent with a low luminosity active galactic nucleus. I suggest that FRB originate in the accretion disc funnels of intermediate mass black holes. Narrowly collimated radiation is emitted along the wandering instantaneous angular momentum axis of accreted matter. We observe this emission as a fast radio burst when it sweeps across the direction to the observer. This model constrains the mass of the black hole to values below those of galactic nuclei. It predicts, in contrast to neutron star (pulsar or SGR) models, that repeating FRB will not be periodic and will be co-located with persistent but variable radio sources resulting from the off-axis emission. The model is analogous, on smaller spatial, lower mass and accretion rate and shorter temporal scales, to AGN making double radio sources, with FRB corresponding to blazars in which the jets point toward us.

astro-ph.HE↗

arXiv2017

Do FRB Mark Dark Core Collapse?

Are some neutron stars produced without a supernova, without ejecting mass in a remnant? Theoretical calculations of core collapse in massive stars often predict this. The observation of the repeating FRB 121102, whose dispersion measure has not changed over several years, suggests that dark core collapses are not just failures of computer codes, but may be real. The existence of one repeating FRB with unchanging dispersion measure is not conclusive, but within a decade hundreds or thousands of FRB are expected to be discovered, likely including scores of repeaters, permitting useful statistical inferences. A na\"ıve supernova remnant model predicts observable decline in dispersion measure for 100 years after its formation. If an upper limit on the decline of 2 pc/cm$^3$-y is set for five repeating FRB, then the na\"ıve model with nominal parameters is rejected at the 95\% level of confidence. This may indicate dark neutron star formation without a supernova or supernova remnant. This hypothesis may also be tested with LSST data that would show, if present, a supernova at an interferometric FRB position if it occurred within the LSST epoch.

astro-ph.HE↗

arXiv2017

FRB as Pulsar Lightning

There are striking phenomenological similarities between Fast Radio Bursts and lightning in the Earth's and planetary atmospheres. Both have very low duty factors, $\lesssim 10^{-8}$--$10^{-5}$ for FRB and (very roughly) $\sim 10^{-4}$ for the main return strokes in an active thundercloud. Lightning occurs in an electrified insulating atmosphere when a conducting path is created by and permits current flow. FRB may occur in neutron star magnetospheres whose plasma is believed to be divided by vacuum gaps. Vacuum is a perfect insulator unless electric fields are sufficient for electron-positron pair production by curvature radiation, a high-energy analogue of electrostatic breakdown in an insulating gas. FRB may be "electrars" powered by the release of stored electrostatic energy, counterparts to Soft Gamma Repeaters powered by the release of stored magnetostatic energy (magnetars). This frees pulsar FRB models from the constraint that their power not exceed the instantaneous spin-down power. Energetic constraints imply that the sources of more energetic FRB have shorter spin-down lifetimes, perhaps shorter than the three years over which FRB 121102 has been observed to repeat.

astro-ph.HE↗

arXiv2017

Reply to Burridge & Linden: Hot water may freeze sooner than cold

In a recent paper in Scientific Reports, Burridge \& Linden misinterpret the Mpemba effect as a statement about the rate of cooling of liquid water, when it is in fact a statement about the rate of freezing of water. Debunking an obviously absurd claim about cooling, they miss the significant effect, its only quantitative experimental study and a theoretical argument that explains the effect and predicts that it occurs only for "hard" water (water with significant dissolved Mg and Ca bicarbonates). This prediction remains to be tested.

physics.pop-ph↗

arXiv2017

Trends in U. S. Storminess 1949--2009

We use an extensive NOAA database of hourly precipitation data from 5995 stations in the 48 contiguous United States over the period 1949--2009 to investigate possible trends in the frequency and severity of extreme weather events, defined as periods of intense precipitation. The frequency and intensity of these events are quantified by a dimensionless storminess, defined as the variance of the hourly rainfall at a site normalized by the square of the mean rainfall at that site. For 1722 stations with sufficient data, we compute the rate of change of the logarithm of the storminess at each station and set bounds on its mean (over stations) trend; use of the logarithms weights trends at calm stations equally to those at stormy stations and enhances the statistical power of the mean. These results are confirmed by reversing the order of averaging: first computing, for each year, the mean (over stations) logarithm of the storminess, and then fitting to its trend. We set $2σ$ upper bounds of 0.001/y (doubling or halving time scales $> 1000$ y) on any trend, increasing or decreasing.

physics.ao-ph↗

arXiv2017

Changing U.S. Extreme Temperature Statistics

The rise in global mean temperature is an incomplete description of warming. For many purposes, including agriculture and human life, temperature extremes may be more important than temperature means and changes in local extremes may be more important than mean global changes. We define a nonparametric statistic to describe extreme temperature behavior by quantifying the frequency of local daily all-time highs and lows, normalized by their frequency in the null hypothesis of no climate change. We average this metric over 1218 weather stations in the 48 contiguous United States, and find significantly fewer all-time lows than for the null hypothesis of unchanging climate. Record highs, by contrast, exhibit no significant trend. The metric is evaluated by Monte Carlo simulation for stationary and warming temperature distributions, permitting comparison of the statistics of historic temperature records with those of modeled behavior.

physics.ao-ph↗