Engineering topics

Wandel, A.

Publications and source records attributed to Wandel, A..

6 records

NASA NTRS1989

On the ratio of the infrared-to-ultraviolet continuum to the X-rays in quasars and active galaxies

A sample of 122 quasars and Seyfert galaxies was analyzed and it was found that the NIR 7500 A rest frame luminosity is more linearly related to the X-ray luminosity than is the optical luminosity. It is also found that the mean spectral slope between 7500 and 4200 A in the rest frame monotonically flattens with luminosity over more than three orders of magnitude. The present results support models which attribute the IR and X-ray continua to linked nonthermal processes such as synchrotron self-Compton, while the blue-UV bump comes from a different source, such as an accretion disk.

Mushotzky, R. F.↗

NASA NTRS1988

Supernova remnants and the interstellar medium - Constraints from cosmic-ray acceleration

The reacceleration rate of cosmic rays by supernova (SN) remnants is calculated and expressed in terms of the parameters determining the cosmic ray model and the SN expansion. It is shown that the constraint on reacceleration derived from the B/C data leads to constraint on the expansion of SN remnants in the ISM and on the effective density of ISM. The effect of cloud evaporation is estimated and the expansion rate of supernova remnants, cosmic ray reacceleration, and the state of the ISM are solved for simultaneously. In the resulting self-consistent solution, SN remnants produce a reacceleration rate and an effective acceleration shock strength which is consistent with the values indicated by the cosmic ray data.

Wandel, A.↗

NASA NTRS1988

Multifrequency spectra of BL Lac objects

A program to obtain simultaneous multifrequency spectra of BL Lacertae objects that are known X-ray sources is discussed. The IUE spectra are generally featureless and well-fitted by power law models. For the faintest exposures, Gaussian extraction of the spectrum can greatly impove the signal-to-noise. Most program objects vary in the ultraviolet, although the time scales are not known because of limited observing time. The broadband spectra of BL Lacs exhibit a range of characteristics but the curvature is always downward and the shape is generally smooth. This can be interpreted as synchrotron emission from a relativistic jet; different jet models are possible, and each allows a range of values for the bulk velocity, magnetic field strength, and electron density. Synchrotron models are not required, however an accretion disk model also gives a good fit to the ultraviolet-through-X-ray continuum.

Urry, C. M.↗

NASA NTRS1987

Distributed reacceleration of cosmic rays

We develop a model in which cosmic rays, in addition to their initial acceleration by a strong shock, are continuously reaccelerated (e.g., by weak shocks) while propagating through the galaxy. The equations describing this acceleration scheme are solved analytically (approximating ionization losses by a cutoff) and numerically. Solutions for the spectra of primary and secondary cosmic rays are given in a closed analytic form, and they allow a rapid search in parameter space for viable propagation models with distributed reacceleration included. The observed boron-to-carbon ratio can be reproduced by the reacceleration theory over a range of escape parameters, some of them quite different from the standard "leaky box" model. It is also shown that even a very modest amount of reacceleration by strong shocks causes the boron-to carbon ratio to level off at sufficiently high energies, and this effect may be observed in the CRNE data. Several other curiosities in the data may be explained naturally if a modest amount of distributed reacceleration is invoked, including (a) the apparent truncation at low energy in the otherwise exponential pathlength distribution associated with the leaky box model, (b) the sub-iron isotopic anomalies and other effects noted by Silberberg et al., and (c) the discrepancy between the reported 10Be lifetime and the lifetime of cosmic rays in the dense strata of the galactic disk.

NASA Discipline Radiation Health↗

NASA NTRS1986

Observational determination of the masses of active galactic nuclei

The masses of 24 active galactic nuclei are determined on the basis of published observations, using data on both the X-ray variability and the width of the narrow forbidden lines of O III. The results are presented in tables and graphs, and it is found that the mass estimates based on the X-ray variability are in good agreement with the dynamic masses determined from the O III linewidth when reasonable values are selected for the radius of the region of X-ray origin and when a standard photoionization model is adopted for the line-emitting gas. The O III dynamic masses of Seyfert-2 nuclei are shown to be systematically lower than those predicted by the (delta t)/M(O III) correlation for Seyfert-1 nuclei.

Wandel, A.↗

NASA NTRS1985

Cosmic rays in the 10(16) to 10(19) eV range from pulsars

The flux is calculated of cosmic rays (CRs) produced by a distribution of pulsars that are: (1) born with rapid rotation rates, (2) slow down as they evolve, and (3) produce energetic nuclei with a characteristic energy proportional to their rotation rates. It is found that, for energy independent escape from the disk of the galaxy, the predicted spectrum will be essentially what is observed between approx 10 to the 16th power to 10 to the 19 power eV if the slow down law as inferred for radio pulsars can be extrapolated to young pulsars with shorter periods.

Wandel, A.↗