J. J. Broderick

Millimeter-Wave Signature of Strange Matter Stars

One of the most important questions in the study of compact objects is the nature of pulsars, including whether they consist of neutron star matter or strange quark matter (SQM). However, few mechanisms for distinguishing between these two possibilities have been proposed. The purpose of this Letter is to show that a strange star (one made of SQM) will have a vibratory mode with an oscillation frequency of approximately 250 GHz (millimeter wave). This mode corresponds to motion of the center of the expected crust of normal matter relative to the center of the strange quark core, without distortion of either. Radiation from currents generated in the crust at the mode frequency would be an SQM signature. We also consider effects of stellar rotation, estimate power emission and signal-to-noise ratio, and discuss briefly the particularly important, but unsolved, question of possible mechanisms for exciting the mode.

18 centimeter VLBI observations of the quasar NRAO 140 during and after a low-frequency outburst

VLBI and spectra observations have been used to identify the specific site of a low-frequency outburst in the quasar NRAO 140. The properties of the low-frequency variability in the quasar are compared with the predictions of several models. The refractive scintillation model alone does not account for the sources properties. 32 references.

Observations of Intense 100-MICRON Objects at 3.5 Millimeter Wave-Length

Measurements have been made at 85 GHz of 12 objects identified by Hoffman, Frederick, and Emery as sources of 100- mu emission in excess of 10/sup -22/ W cm/sup -2/ Hz/sup -1/. In an attempt to detect the lo ngwavelength tail of the far-infrared spectral component, the observed 3.5-mm flux densities for each of the sources are compared with that expected from an extrapolation of the radio spectrum from lower frequencies: No unequivocal evidence is found for the presence of any contribution to the 85-GHz flux attributable to the presence of a high-frequency component. This result not only restricts a large class of models in which the 100- mu emission arises from nonthermal processes but it also requires that if the infrared radiation is due to thermal emission from dust grains then the temperature of those grains must exceed 20 deg K. Finally a plot of 100- mu fiux density versus 3.5-mm flux density suggests a separation of the sources into two classes that may be quite distinct. (auth)

Interstellar Broadening of Compact Low Galactic Latitude Radio Sources

Scattering of radio waves off inhomogeneities in electron density in the interstellar medium can produce an apparent broadening in the angular diameter of an intrinsically compact background radio source. The magnitude and distribution of this effect at low galactic latitudes (|b|<5 ) is not well known, although several cases suggest substantial broadening in certain directions, such as the Cygnus X region (Anderson et a_l. 1972), and the galactic center (Davies, Walsh, and Booth 1976). Large scattering in the plane is consistent with the scintillation properties of pulsars seen through substantial thicknesses (~ 1 kpc) of the galactic disk.

Superluminal Motion in NRAO 140 and a Possible Future Method for Constraining Ho and qo

NRAO 140 is a quasar (z = 1.258) which is among only 3 or 4 such objects (and the one with the highest z) which were detected at X-ray energies prior to the operation of the Einstein Observatory (Marscher et al. 1979). We obtained contemporaneous X-ray and radio VLBI observations of the source in early 1980, to determine whether Compton scattering within the radio source is the primary X-ray emission mechanism (Marscher and Broderick 1981b). Instead, we found that the radio parameters predicted more than 103 times more X-ray flux than was observed. Since the Compton calculation is independent of distance, and since the troublesome component was partially resolved (and hence not a high-brightness-temperature emitter), we found that relativistic motion aimed nearly directly toward the observer with Lorentz factor exceeding 4, needed to be invoked in order to bring the predicted Compton flux down to the observed level (Marscher and Broderick 1981a, b). Since relativistic motion is also the preferred explanation for the apparent superluminal expansion seen in some compact radio sources (e.g., M. Cohen, this volume; Marscher and Scott 1980; Kellermann and Pauliny-Toth 1981), we predicted that the compact components in NRAO 140 should appear to separate at a speed exceeding about 4c.