E. M. Moore

Detection of AU-scale structure in molecular clouds

We have detected significant secular changes in the 4.83 GHz H 2 CO absorption line toward the compact extragalactic radio sources NRAO 150 and 3C 111 with the Very Large Array. In each case the absorption occurs within a molecular cloud in our Galaxy against the submilliarcsecond core or the background radio source. Because of relative motion between Earth and the cloud, the position of the line of sight through each cloud drifts by a transverse distance or ∼4 AU per year. The changes in absorption-line profile over a period of 2.05 yr are interpreted in terms of clumps of size ≤10 AU in the molecular cloud

EGRET observations of the 1993 March gamma-ray flare from PKS 0528+134

EGRET observation of PKS 0528 + 134 during the 1993 March flare in gamma-rays is presented here. During the flare gamma-rays were detected at a level approximately three times greater than the observed intensity in earlier observations. Spectra of the source during the flare, as well as during the nonflaring state are presented. The flux history of PKS 0528 + 134 as observed from the start of the Compton Gamma Ray Observatory (CGRO) mission up to the end of Phase 3 (1993 October) is given. Multiwavelength observations of PKS 0528 + 134 during the flare are also presented. A detailed relativistic SSC jet model agrees well with the 1993 March Multiwavelength spectrum; the data, however, are insufficient to discriminate between this and other emission models.

MULTIWAVEBAND OBSERVATIONS OF QUASARS WITH FLAT RADIO SPECTRA AND STRONG MILLIMETER-WAVE EMISSION

We present multiwaveband observations of a well-selected sample of 28 quasars and two radio galaxies with flat radio spectra and strong millimeter-wave emission (referred to here as FSRQs). The data are analyzed to determine the radio to infrared and X-ray to γ-ray properties of FSRQs and the relationships between them. Specifically, the synchrotron self-Compton (SSC) process is examined as a likely common radiation mechanism. For most sources, the broadband spectra are still incomplete, especially in the far-infrared and ultraviolet range. Therefore, precise analysis, such as model fitting of spectra, is not usually possible. To compensate partially for this, we have taken a statistical approach and examine the relationship between high- and low-energy emission by using the data set for the entire sample. We use very long baseline interferometry (VLBI) at 8.4 and 22 GHz—higher frequencies than those of previous surveys—in conjunction with nearly simultaneous radio to submillimeter-wave observations to determine the parameters of the synchrotron spectrum and to examine the compact angular structure of a subset of sources from our sample. These parameters are used to predict the SSC X-ray flux densities. Seven of 30 sources have predicted self-Compton X-ray flux densities well above the observed flux densities obtained with the ROSAT satellite unless one assumes that the radiating plasma experiences bulk relativistic motion directed toward the observers line of sight. Three of these seven sources are detected at γ-ray frequencies. Model spectra show that the X-rays are consistent with the first-order SSC process, with the simultaneous multiwaveband spectrum of the quasar 0836+710 obtained in 1992 March being very well fitted by SSC emission from a uniform, relativistically moving source. The γ-rays are not produced via second-order self-Compton scattering but rather by either first-order self-Compton scattering or some other process. A comparison of the ROSAT X-ray flux densities and those obtained earlier with the Einstein Observatory show that several FSRQs are X-ray variables on timescales of about a decade. Several sources that were observed more than once with ROSAT also show variability on timescales of 1-2 yr, with the X-ray variability in these cases often associated with millimeter-wave variability and lower VLBI core-to-jet flux ratios. Detections at γ-ray energies also appear to be related to increases in the radio to millimeter-wave flux densities. Statistical analysis shows that the millimeter-wave and X-ray luminosities for the sample are strongly correlated, with a linear regression slope ~0.65. The peak in the distribution of X-ray to millimeter spectral indices also indicates a strong connection between millimeter-wave and X-ray emission. Particularly interesting is a correlation between X-ray to millimeter spectral index and fraction of flux density contained in the VLBI core. This tendency toward higher X-ray fluxes from sources with stronger jet emission implies that the knots in the jet are prominent sources of X-rays.

Radio to γ-ray observations of 3C 454.3:1993–1995

Results from a multiwaveband study of the γ-ray-bright compact radio source 3C 454.3 are presented.