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NASA NTRS2002

The Relationship Between X-Rays and Relativistic Jets

We present recent multiwaveband observations centered on X-ray monitoring of blazars and the radio galaxy 3C 120 with the RXTE satellite, In 3C 120, we observed four X-ray dips, each followed by ejections of superluminal radio knots down the jet. This behavior, similar to that of the microquasar GRS 1915+105, is interpreted as infall of a piece of the inner accretion disk causing ejection of energy into the relativistic jet. The X-ray emission from the quasars PKS 1510-089, 3C 279, and 3C 273 is highly variable on timescales as short as approximately 1 day. Over 2 years, X-ray flares in PKS 1510-089 occurred about 2 weeks after radio outbursts, which can be explained by light-travel delays. In 3C 279 the X-ray and optical variations are usually well correlated, with very little, if any, time delay. We conclude that the X-ray and optical emission from blazars occurs near the radio core rather than close to the black hole.

Marscher, A. P.↗
NASA NTRS1971

The small-scale structure of radio galaxies and quasi-stellar sources at 3.8 centimeters.

Observation of fringes from 31 compact radio sources, including eight known or suspected galaxies and 20 known or suspected QSSs, by using the Goldstack interferometer at lambda = 3.8 cm (d/lambda = 10 to the 8th power). Fringe visibility curves were obtained for nine sources showing structure on a scale of .001 sec of arc, and simple models are fitted to the data. Results for 3C 273 and 3C 279 are compared with data taken by Knight et al. (1971) at an earlier epoch. The apparent changes in brightness distribution of 3C 273 and 3C 279 are difficult to explain.

Cohen, M. H.↗
NASA NTRS1978

A high declination search at 8 GHz for compact radio sources

With the Haystack-NRAO interferometer (baseline length of 20 million wavelengths at 3.8 cm) 37 sources were observed whose declinations were above 50 deg. Seven of these sources have compact cores with diameters smaller than 5 milliarcsec and with correlated flux densities greater than about 0.5 Jy; the remaining sources have no cores with flux densities above about 0.3 Jy, the sensitivity limit of the interferometer. Two of the sources with detected compact cores, 4C 67.05 and 3C 418, were also observed with longer-baseline interferometers; the diameter of the core of 4C 67.05 was estimated to be smaller than 1 milliarcsec and that of 3C 418 to be smaller than 0.4 milliarcsec. All diameter estimates were based on an assumed circular Gaussian distribution of radio brightness and refer to the contour with brightness density e to the -1/2 power times that of the center. Positions for the detected sources were also obtained from the interferometric data, the uncertainty in these coordinate estimates ranging from 0.04 to 0.6 arcsec. The compact core detected in 3C 390.3 was found to lie near the center of this extended (approximately 4 arcmin in diameter) double radio source and to be coincident to within 1 arcsec with an N galaxy previously identified with 3C 390.3.

Wittels, J. J.↗
NASA NTRS1985

The hydrogen line spectra of narrow-line radio galaxies

The results of the first detection of Ly-alpha in a narrow-line radio galaxy are reported. Nearly simultaneous optical and UV observations of 3C 192 and 3C 223 allow the measurement of both Balmer and Lyman decrements. These line ratios are approximate functions of the interstellar reddening and of a parameter which is proportional to the amount of H I collisional excitation present. The reddening of 3C 192 is slightly larger than that due to the Galaxy, although 3C 223 may have a larger value. Both galaxies have intrinsic Balmer and Lyman decrements which are significantly steeper than case B, suggesting that the gas is photoionized by a fairly hard X-ray continuum. The deduced values of L-alpha/H-beta and H-alpha/H-beta compare favorably with predictions of recent models.

Ferland, G. J.↗
NASA NTRS1988

Ultraviolet and optical spectra of broadline radio galaxies

Near-simultaneous ultraviolet and optical spectra of three broadline radio galaxies (3C 382, 3C 445, and PKS 2349-014) have been obtained, and the emission lines of Ly-alpha, H-beta, and H-alpha have been deconvolved into narrow and broad components; published fluxes for 3C 390.3 are also included in this study. Although the broad Ly-alpha/H-beta ratios in these objects cover a large range (1.2-22.3), there is no evidence that these ratios are intrinsically different from those of Seyfert 1 galaxies or quasars. Thus, in general, the higher H-alpha/H-beta ratios in these broadline radio galaxies cannot entirely be due to additional reddening of the broadline region. However, in the specific case of 3C 445, there is evidence that the nonstellar continuum and broadline region are highly reddened.

Crenshaw, D. Michael↗
NASA NTRS1993

An Interlaminar Tensile Strength Specimen

This paper describes a technique to determine interlaminar tensile strength, sigma(sub 3c), of a fiber reinforced composite material using a curved beam. The specimen was a unidirectional curved beam, bent 90 deg, with straight arms. Attached to each arm was a hinged loading mechanism that was held by the grips of a tension testing machine. Geometry effects of the specimen, including the effects of loading arm length, inner radius, thickness, and width, were studied. The data sets fell into two categories: low strength corresponding to a macroscopic flaw related failure and high strength corresponding to a microscopic flaw related failure. From the data available, the specimen width and loading arm length had little effect on sigma(sub 3c). The inner radius was not expected to have a significant effect on sigma(sub 3c), but this conclusion could not be confirmed because of differences in laminate quality for each curve geometry. The thicker specimens had the lowest value of sigma(sub 3c) because of poor laminate quality.

Martin, Roderick H.↗
NASA NTRS2000

Beamed and Unbeamed X-Ray Emission in FR1 Radio Galaxies

The research exploited ROSAT's sensitivity, together with its spatial and spectral resolution, to separate X-ray emission components in the sources. Prior to ROSAT, the dominant X-ray emission mechanism in radio galaxies as a class was unclear, with correlations between the X-ray and radio emission used on one hand to argue for a nuclear origin for the X-rays, and on the other hand for a thermal origin. Our observations (normally between 10 and 25 ks in length) routinely detected the target sources, and demonstrated that both resolved (thermal) and unresolved X-ray emission are typically present. Highlights of our work included two of the first detections of high-power radio galaxies at high redshift, 3C 280 and 3C 220.1. When combined with the work of two other groups, we find that of the 38 radio galaxies at z > 0.6 in the 3CRR sample, 12 were observed in ROSAT pointed observations and 9 were detected with the four most significant detections exhibiting source extent, including 3C 280 and 3C 220.1. Moreover, we discovered extended emission around five 3CRR quasars at redshift greater than about 0.4, one of which is at z > 0.6. Unification predicts that the X-ray environments of powerful radio galaxies and quasars should be similar, and our results show that powerful radio sources are finding some of the highest-redshift X-ray clusters known to date, pointing to deep gravitational potential wells early in the Universe.

Worrall, Diana M.↗
NASA NTRS2000

Constraints on Particles and Fields from X-Ray Data

We review emission processes for the handful of extragalactic radio sources which produce X-rays from hotspots and knots in radio jets. In almost all cases, the emitting feature shows a large gradient in radio brightness, indicative of the presence of a strong shock. Since both thermal and synchrotron self Compton models face severe difficulties (except for the hotspots of Cygnus A and 3C 295), the most likely explanation is the presence of gamma = 10(exp 7) electrons producing X-ray synchrotron emission. The major problems remaining are why so few features have been detected so far and why has no optical emission been detected in some cases. While a somewhat unique situation exists for 3C 390.3, serious problems remain for Pictor A, 3C 120, and the quasar jets in 3C 273 and PKS 0637.

Harris, D. E.↗
NASA NTRS2000

Continued RXTE Observations of Three Blazars

This project continued (during Cycle 3 of the RXTE mission) weekly observations of the quasars PKS 1510-089 and 3C 454.3 and the BL Lac object OJ 287. The data were analyzed by the PI and his graduate student. In the middle of Cycle 3, the PI changed the mode of observation of 3C 454.3, based on a report from another astronomer that observations with the Rosat satellite had found a strong confusing X-ray source about 45 arcmin away. The RXTE observations, in which the flux was measured while pointing directly at 3C 454.3 and then 15' from 3C 454.3, in the direction away from the confusing source. The flux decreased considerably, and so it appears that nearly all the X-ray flux measured by RXTE comes from the confusing source rather than the quasar. OJ 287 was detected only at one epoch of the Cycle 3 observations. This corresponded to a particularly quiet period for this source, when its flux at other wavebands was also low. From the single epoch of detection, no conclusions can be drawn concerning the general nature of the X-ray emission from this object. In contrast to the other two sources, the results of the observations of PKS 1510-089, when combined with data from cycles 3 and 4, are very interesting. The RXTE (2.4-20 keV) abd 14.5 GHz University of Michigan Radio Astronomy Observatory (UMRAO) light curves through the end of RXTE Cycle 4 are shown for PKS 1510-089. Visual inspection reveals an obvious correlation between the X-ray and 14.5 GHz light curves. While this is as expected in the SSC model in a source with simultaneous mm-wave (the photons thought to be scattered to X-ray energies) and cm-wave variations, the X-ray spectrum is flat ("energy" spectral index alpha = 0.2-0.5, where F (sub v) proportional to v (sup - alpha)) compared with the mm-wave synchrotron spectrum (alpha approximately equal to 0.8). The PI is currently engaged in theoretical work to determine whether this is possible for an SSC model.

Marscher, Alan P.↗
NASA NTRS2011

New Insights on the Accretion Disk-Winds Connection in Radio-Loud AGNs from Suzaku

From the spectral analysis of long Suzaku observations of five radio-loud AGNs we have been able to discover the presence of ultra-fast outflows with velocities ,,approx.0.1 c in three of them, namely 3C III, 3C 120 and 3C 390.3. They are consistent with being accretion disk winds/outflows. We also performed a follow-up on 3C III to monitor its outflow on approx.7 days time-scales and detected an anti-correlated variability of a possible relativistic emission line with respect to blue-shifted Fe K features, following a flux increase. This provides the first direct evidence for an accretion disc-wind connection in an AGN. The mass outflow rate of these outflows can be comparable to the accretion rate and their mechanical power can correspond to a significant fraction of the bolometric luminosity and is comparable to their typical jet power. Therefore, they can possibly play a significant role in the expected feedback from AGNs and can give us further clues on the relation between the accretion disk and the formation of winds/jets.

Tombesi, F.↗
NASA NTRS1972

Physical associations between quasi-stellar objects and galaxies.

Evaluation of evidence pertaining to apparent associations between galaxies and quasi-stellar objects. It is shown that for the five 3C QSOs which lie very close to bright galaxies the QSO-galaxy angular separations are inversely proportional to the redshifts of the galaxies. This lends additional support to the association hypothesis. However, an analysis of an essentially disjoint sample of QSOs identified from the Parkes radio catalog, and fainter galaxies in the catalog of Zwicky and his associates, reveals no statistically significant tendency toward pairing of QSOs and galaxies. The results can be explained in one of two ways. One is that, despite the evidence to the contrary, the 3C results are due to chance. The other is that real associations in the second sample are masked by selection effects. It is shown that several selectional biases do indeed discriminate against the detection of QSO-galaxy pairs, especially for fainter objects. Finally, on the assumption that the 3C QSO-galaxy associations are real, the relationship of QSOs to galaxies is discussed.

Burbidge, G. R.↗
NASA NTRS1976

High-resolution radio observations of three supernova remnants

The paper presents and discusses radio observations of three supernova remnants (G21.5-0.9, G29.7-0.3, and 3C 391) made at 3.7 and 11.1 centimeters. The supernova remnant G21.5-0.9 has an elliptical brightness distribution and is similar to the Crab Nebula as well as 3C 58 in appearance and spectrum. The two remnants G29.7-0.3 and 3C 391 both show a broken shell structure typical of most galactic supernova remnants.

Becker, R. H.↗
NASA NTRS1978

Preliminary results of linear polarization measurements at 99 GHz

The results of the first linear polarization measurements of extrasolar radio sources at a frequency above 35 GHz are presented. For the quasars 3C 273 and 3C 345, the observed position angles are in accord with the predictions of Inoue, and the measurements are consistent with the suggestion that the compact components responsible for the high-frequency emission are affected by high degrees of internal Faraday depolarization. For the radio galaxy 3C 274 (Virgo A) the observed position angle and degree of polarization are consistent with the model of Hobbs and Waak.

Hobbs, R. W.↗
NASA NTRS1980

X-ray variability in active galaxy nuclei and quasars in less than one day

Data obtained from the Einstein Observatory demonstrating variations in X-ray emission from the nuclei of active galaxies and quasars on time scales of hours rather than previously observed days or years is presented. Light curves obtained from the Einstein imaging proportional counter for the Seyfert 1 galaxy NGC 6814 and from the High Resolution Imager for the quasars OX 169 and 3C 273 are illustrated, and variations by factors greater than two on time scales less than 20,000 sec for the first two objects and by a factor of 10% on a time scale over 50,000 sec for 3C 273 are pointed out. The measurements are also used to determine that thermal bremsstrahlung cannot be the cause of the intensity decay in OX 169, and that, in the absence of relativistic effects, the efficiency for energy release in the matter involved in the emission of 3C 273 is at least 0.1.

Elvis, M.↗
NASA NTRS1983

Calculation of high-pressure phase transitions in solid N2 and the pressure dependence of intramolecular mode frequencies

A calculation that minimizes the energy of solid N2 with respect to a rhombohedral distortion of the Pm 3n structure shows that a low-temperature phase transition occurs into the R 3c calcite structure at P = 19.2 kbar with a volume change of 0.125 cu cm/mole. This transition agrees with recent Raman scattering measurements. Another transition from R 3c into R3(bar)m is predicted at P = 67.5 kbar, with a volume change of 0.1 cu cm/mole. The pressure dependence of the intramolecular mode frequencies for the R 3c structure are in reasonably good agreement with the two main branches observed experimentally.

Chandrasekharan, V.↗
NASA NTRS1985

Strong Lyman-alpha emission in three distant radio galaxies

Very strong, narrow Lyman alpha emission (equivalent width approximately 1000 angstroms) has been discovered in the redshifted ultraviolet spectra of three radio galaxies having z between 1.62 and 1.82. The three are 3C 256, 3C 239, and 3C 241. It is noted that Lyman alpha will probably be a very useful redshift and classification determinant in future spectroscopic surveys of active galaxies at still greater distances.

Spinrad, H.↗
NASA NTRS1992

The origin of the optical emission lines associated with extragalactic radio sources

The observed extended emission line regions (EELRs) associated with radio sources are investigated with the objective of determining the characteristics of the ionization mechanisms and the possible effect of star formation. The sources included in the sample are 3C 227, 3C 277.3, 3C 305, Cen A (NGC 5128), NGC 7385, PKS 0349-27, PKS 2152-69, and Minkowski's Object. It is shown that the emission-line ratios of the EELRs considered can be explained by models which account for the coupled effect of photoionization and shock acting at different degrees. It is also shown that the EELR ionization is not due to young stars. The main energy sources of the EELR are identified.

Viegas, S. M.↗
NASA NTRS1994

Gamma-ray bright quasars and BL Lacertae objects: EGRET data

The Compton Gamma-Ray Observatory (CGRO) Instruments, in particular, EGRET, have recently discovered new, gamma-ray bright active galactic nuclei (AGNs)(fluxes approximately 0.5-3 times as bright as 3C 273). Yet current sample sizes are modest (for example, EGRET as of 1993 January has detected 17 quasars and five BL Lac objects), and the sources probe only a small range in flux. Only by using a large, unbiased sample of AGNs can we answer key questions about source evolution, contributions to the gamma-ray background, and the different gamma-ray properties of quasars and BL Lac objects. Therefore, we need gamma-ray data on a much larger number of AGNs. We are currently pursuing two approaches toward remedying this situation: first, new (phase 2) OSSE, COMPTEL, and EGRET observations of X-ray selected AGNs predicted to be gamma-ray bright on simple assumptions; even an upper limit can set constraints on continuum models (e.g., pair production, synchrotron self-Compton); second, searches for radio-selected AGNs in wide-field EGRET data obtained during the pointings. For these AGN, we expect a large number of faint sources (i.e., mainly low signal-to-noise ratio detections and upper limits), a continuous progression down to the limiting EGRET sensitivity. Although special techniques must be employed to deal carefully with low-significance sources, the end product will be a much larger sample than currently available on which to base deductions about the gamma-ray properties of AGNs. Here we report the first results of this program. We find an upper limit for 3C 382 and demonstrate, using the 3C 382 field, how serendipitous blazars can systematically searched for in existing EGRET public (Phase 1) data. Preliminary results indicate that synchrotron self-Compton processes dominate.

Schachter, Jonathan↗