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NASA NTRS1988

Voyager and IUE observations of 3C 273 - Detection of possible Lyman continuum absorption in a nearby (z = 0.158) quasar

Results of near-simultaneous IUE and Voyager ultraviolet spectrometer (UVS) observations of 3C 273, obtained during the period of 1985 late July-early August are reported. The UVS data show a significant drop in flux for observed wavelengths below 1060 A. This may be due to Lyman continuum absorption in the rest frame of 3C 273. If so, then the lack of associated Lyman-alpha absorption severely constrains the properties of the absorbing medium. The most plausible explanation may therefore be that the edge is due to absorption in an accretion disk within the nucleus of 3C 273. Alternatively, models in which the drop in flux is due to a turnover in the underlying continuum cannot be excluded; this interpretation raises serious questions concerning the total energy budget in the broad-line regions. In either case, there can be no reddening of the source of continuum emission other than that due to the Galaxy.

Reichert, G. A.↗
NASA NTRS1988

The contribution to the gamma-ray background from a superposition of 3C 273-like jet sources

Recent theories suggest that quasar jets may produce the gamma-ray emission observed in sources such as 3C 273. One of these theories is tested to see if it is consistent with observations of the gamma-ray background. Quasar jets are taken as the source of this radiation, each with the spectrum of the nearby quasar 3C 273, and with an evolution in time based on a model for the observed gamma-rays of 3C 273. In that model, a plasma jet interacts with the ambient intergalactic gas to produce (from nuclear collisions) secondary electrons which lead to isotropic bremsstrahlung gamma-rays, and ultimately to a double radio source. It is shown that the gamma-ray background can be modeled in general as a superposition of such discrete sources of various redshifts. The results are consistent with the observed background intensity and spectral form; of course, there are uncertain and adjustable parameters.

Sadun, Alberto C.↗
NASA NTRS1989

The miniblazar in 3C 273

The compact core of 3C 273 has been studied for over two years using optical photometry and accurate polarimetry. A wealth of polarization behavior, including variable polarization, observed at a level of under 1 percent is described. The results indicate that 3C 273 harbors a weak continuum component having all the characteristic properties of blazars. It is predicted that other compact radio sources with low optical polarization will also be found to harbor miniblazars. The detection of variable polarization in 3C 273 strengthens the link between superluminal motion at radio wavelengths and blazar activity at optical wavelengths.

Impey, C. D.↗
NASA NTRS1990

Growth of improved quality 3C-SiC films on 6H-SiC substrates

Previously reported chemical vapor deposition of 3C-SiC on 6H-SiC has resulted in films with a high density of double positioning boundaries (DPBs). It is found that growth on as-grow faces of 6H-SiC crystals can yield films that are largely free of DPBs. The (111) 3C-SiC films, up to 12 microns thick, were evaluated by optical and electron microscopy and low-temperature photoluminescence (LTPL). The LTPL spectra of the films were similar to those of high quality Lely-grown 3C-SiC.

Powell, J. A.↗
NASA NTRS1990

The peculiar hydrogen cloud in the Virgo Cluster and 3C 273

It is shown that the nearest bright extragalactic object to the peculiar hydrogen cloud recently discovered in the Virgo Cluster by Giovanelli and Haynes is the bright QSO 3C 273. Further, it is pointed out that the jet in 3C 273 points in almost the same direction as the major axis of the cloud. Despite the redshift difference, possible physical connections between the cloud and 3C 273 are explored.

Arp, H. C.↗
NASA NTRS1992

TeV gamma rays from 3C 279 - A possible probe of origin and intergalactic infrared radiation fields

The gamma-ray spectrum of 3C 279 during 1991 June exhibited a near-perfect power law between 50 MeV and over 5 GeV with a differential spectral index of -(2.02 +/- 0.07). If extrapolated, the gamma-ray spectrum of 3C 279 should be easily detectable with first-generation air Cerenkov detectors operating above about 0.3 TeV provided there is no intergalactic absorption. However, by using model-dependent lower and upper limits for the extragalactic infrared background radiation field, a sharp cutoff of the 3C 279 spectrum is predicted at between about 0.1 and about 1 TeV. The sensitivity of present air Cerenkov detectors is good enough to measure such a cutoff, which would provide the first opportunity to obtain a measurement of the extragalactic background infrared radiation field.

Stecker, F. W.↗
NASA NTRS1993

EGRET detection of high-energy gamma radiation from the OVV quasar 3C 454.3

High-energy gamma radiation has been observed from the optically violent variable quasar 3C 454.3 (PKS 2251 + 158) by the Energetic Gamma-Ray Experiment Telescope on the Compton Observatory. During the 1992 January-February observation, the emission showed a power-law photon spectrum with an exponent of -2.18 +/- 0.08. The flux density (greater than 100 MeV) was observed to vary within the range (0.4-1.4) x 10 exp -6 photon/sq cm s on a time scale of less than a week. Lower sensitivity observations during 1992 April and May also detected emission within that range, but with lower statistical significance. An earlier low-sensitivity exposure during 1991 August gave a 95 percent confidence upper limit of 0.26 x 10 exp 6 photon/sq cm s. The similarity of the gamma-ray emission of 3C 454.3 to that of 3C 279 parallels the similarity of these two objects at lower frequencies.

Hartman, R. C.↗
NASA NTRS1993

High-resolution radio observations of the supernova remnant 3C 391 - Possible breakout morphology

We present radio observations of the bright compact SNR 3C 391 (G31.9+0.0) made with the VLA2 at 6 arcsec resolution. The remnant's morphology suggests expansion into a medium with a very strong density gradient. We interpret radio and X-ray morphologies as evidence for a breakout of the expanding material into a region of abruptly lower density. The CO survey of Sanders et al. (1986), though not fully sampled, shows the presence of molecular gas at the position of the remnant, with a radial velocity of 90-110 km/s similar to the highest velocity absorption features seen in H I toward 3C 391. This gas may thus be near the remnant, though direct evidence of interaction is lacking. More detailed CO observations, and searches for evidence of shocked molecular gas such as 2.12 micron emission from H2, might confirm or refute the tantalizing possibility that 3C 391 is interacting with an observable molecular cloud.

Reynolds, Stephen P.↗
NASA NTRS1993

The ROSAT spectrum of 3C 351 - A warm absorber in an X-ray-'quiet' quasar?

3C 351 is one of the most X-ray-quiet radio quasars (alpha(ox) about 1.6). We have observed 3C 351 with the ROSAT position sensitive proportional counter (PSPC) and find a complex X-ray spectrum which is not well reproduced by a power law plus low-energy cut-off model. Soft excess, partial covering, and 'warm absorber' models can all produce acceptable fits, although only the warm absorber model gives typical values for the high-energy continuum slope. The alpha(ox) measured by using quasi-simultaneous ROSAT, MMT, and HST observations is in the range 1.5-1.6, significantly above the average of 1.37 for a complete sample of 33 3CR quasars. If the soft excess or partial covering models are correct, 3C 351 appears X-ray-quiet in the PSPC band because it has an extremely steep or flat intrinsic high-energy spectral slope. However, if the warm absorber model is correct, the quasar is intrinsically X-ray-quiet; the normalization of the intrinsic (unabsorbed) X-ray emission is unusually low relative to the optical luminosity. We investigate the properties of our warm absorber model in some detail. The apparently complicated behavior of the fit parameters may be understood by considering the effects of changing absorbing column and ionization parameter on intrinsic power-law-spectra of different slopes.

Fiore, Fabrizio↗
NASA NTRS1994

The multifrequency spectral evolution of blazar 3C 345

The blazar 3C 345 underwent a 2.5 mag optical outburst between 1990 November and 1991 May. We have obtained 10 nearly simultaneous multifrequency spectra during the course of the outburst in order to study the multifrequency spectral variations of 3C 345 as a function of time. Although our observations were not sampled frequently enough to completely resolve the variations in every frequency band, the general rise and decline of the outburst were seen in the UV through radio with differing rise times. Simulations of an electron distribution injected into a tangled magnetic field show a relationship between frequency and characteristic timescale that was also observed in the radio variations of 3C 345. The two X-ray observations made during the monitoring period showed no evidence of variability. The multifrequency spectrum was modeled with two major components: a relativistic jet and a relativistic thermal accretion disk. Models calculated for each spectrum indicate that the outburst can be explained in terms of these models by varying the high-energy cutoff of the injected electron distribution in the jet model, while also varying the mass accretion rate in the disk model. There is marginal evidence that the inferred accretion rate varies with the jet luminosity.

Webb, J. R.↗
NASA NTRS1994

Ultraviolet observations of the gamma-ray blazer 3C 279 following the gamma-ray flare of 1991 June

Ultraviolet observations of the gamma-ray balzar 3C 279 were carried out in 1991 July with the International Ultraviolet Explorer (IUE) satellite, 28 days after the outburst of intense gamma-ray emission detected from this source with the high-energy Energetic Gamma Ray Experiment Telescope (EGRET) instrument aboard the Compton Gamma-Ray Observatory. IUE observations were conducted over the wavelength range 1200-3200 A (5-10 eV) and are compared with archival UV measurements spanning the period 1988-1991. This set of observations was analyzed with a uniform, standardized data-reduction procedure. No significant variability in the UV spectrum of 3C 279 is noted over timescales of hours, though variations at the 3 sigma level or higher exist on longer timescales of months to years. The UV observations which most closely bracket the gamma-ray flare detected by EGRET show approximately 3 sigma differences in flux and spectral index, consistent with (but not definitive proof of) variations in the UV flux period of the gamma-ray flare. Statistically marginal evidence for a monotonic correlation is found between UV spectral index and the emission observed from 3C 279, in that a harder spectrum is associated with increased UV flux.

Bonnell, Jerry T.↗
NASA NTRS1994

The 1993 multiwavelength campaign on 3C 279: The radio to gamma-ray energy distribution inlow state

Simultaneous observations of 3C 279 at radio, millimeter, near-infrared, optical, ultraviolet (with IUE) and X-ray (with ROSAT) wavelengths were obtained in 1992 December-1993 January, during a three week pointing at the source by the Compton Gamma Ray Observatory. The blazar was in a quiescent or 'low' state during this period. Comparing the multiwavelength energy distribution to that from 1991 June, when 3C 279 was in its brightest recorded gamma-ray state, we find the following: (1) 3C 279 faded dramatically at all frequencies above 10(exp 14) Hz, while the flux variations at low frequencies (radio to millimeter wavelengths) were minor. (2) The near-infrared-optical-ultraviolet spectral shape was softer (steeper) in the quiescent state, and the X-ray spectra also appear softer, although the spectral indix measured by ROSAT refer to a lower energy band than that measured earlier with Ginga. (3) The ratio of the gamma-ray luminosity to that across all other frequencies decreased from a value of approximately equal to 10 in the flaring state to a value approximately equal to 1 in the quiescent state. These findings imply that the production of gamma-rays is closely related to the optical-ultraviolet continuum, in agreement with models where gamma-rays are produced through inverse Compton (IC) scattering by relativistic electrons emitting the synchrotron continuum. The observed nonlinear relation between the synchrotron and IC requires both a change in the electron spectrum and an associated change in the seed photons.

Maraschi, L.↗
NASA NTRS1997

Contemporaneous IUE, EUVE, and High-Energy Observations of 3C 273

We present the results of our 1994 January and 1995 January observations of the quasar 3C 273 obtained with the International Ultraviolet Explorer (IUE) and the Extreme-Ultraviolet Explorer (EUVE). These observations were part of a large multiwavelength campaign to observe 3C 273 from radio through gamma-rays. Our 1995 January photometric observations with the EUVE Lexan/B Deep Survey (DS) instrument indicate strong evidence for variability, at a 99% confidence level, during the 12 day observing period. We have utilized ROSAT PSPC soft X-ray power-law models to correlate with EUVE count rates. Besides variations in the normalization level between both observations, our EUV count rates are consistent with a simple power-law model with spectral index alpha approx. 1.77 (F(sub upsilon) proportional to upsilon(sup -alpha) that can be extrapolated from the soft X-rays to the EUV range. The active galactic nucleus 3C 273 is an important blazar to study because in our picture it reveals the presence of both disk and relativistic beam spectral contributions.

Ramos, E.↗
NASA NTRS2000

Finite-Element Modeling of 3C-SiC Membranes

Finite-element modeling (FEM) of 3C-SiC thin-film membranes on Si substrates was used to determine the residual stress and center deflection with applied pressure. The anisotropic, three-dimensional model includes the entire 3C-SiC membrane and Si substrate with appropriate material properties and boundary conditions. Residual stress due to the thermal-expansion-coefficient mismatch between the3C-SiC film and Si substrate was included in the model. Both before-and after-etching, residual stresses were calculated. In-plane membrane stress and normal deflection with applied pressure were also calculated. FEM results predict a tensile residual stress fo 259 MPa in the 3C-SiC membrane before etching. This decreases to 247 MPa after etching the substrate below the membrane. The residual stress experimentally measured on sample made at Case Western Reserve University was 280 MPa on post-etched membranes. This is excellent agreement when an additional 30-40 MPa of residual stress to account for lattice mismatch is added to the FEM results.

DeAnna, R. G.↗
NASA NTRS2001

Multi-Epoch Multiwavelength Spectra and Models for Blazar 3C 279

Of the blazars detected by EGRET in GeV gamma-rays, 3C 279 is not only the best-observed by EGRET, but also one of the best-monitored at lower frequencies. We have assembled eleven spectra, from GHz radio through GeV gamma-rays, from the time intervals of EGRET observations. Although some of the data have appeared in previous publications, most are new, including data taken during the high states in early 1999 and early 2000. All of the spectra show substantial gamma-ray contribution to the total luminosity of the object; in a high state, the gamma-ray luminosity dominates over that at all other frequencies by a factor of more than 10. There is no clear pattern of time correlation; different bands do not always rise and fall together, even in the optical, X-ray, and gamma-ray bands. The spectra are modeled using a leptonic jet, with combined synchrotron self-Compton + external Compton gamma-ray production. Spectral variability of 3C 279 is consistent with variations of the bulk Lorentz factor of the jet, accompanied by changes in the spectral shape of the electron distribution. Our modeling results are consistent with the UV spectrum of 3C 279 being dominated by accretion disk radiation during times of low gamma-ray intensity.

Hartman, R. C.↗
NASA NTRS2007

The Remarkable X-ray Spectrum of the Broad-Line Radio Galaxy 3C 445

The nearby (z=0.057) radio-loud source 3C 445, optically classified as a Broad-Line Radio Galaxy, exhibits an X-ray spectrum strongly reminiscent of an obscured AGN, suggesting we are seeing this source at a relatively large angle from the radio jet. Here we present an archival 15 ks XMM-Newton observation of 3C 445 which confirms the remarkable complexity of its X-ray emission. The X-ray emission is described by a power law continuum with GAMMA approximately equal to 1.4, absorbed by several layers of cold gas, plus strong cold reflection. A narrow, unresolved Fe Kalpha emission line is detected, confirming previous findings, with EW approximately equal to 400 eV. A soft excess is present below 2 keV over the extrapolation of the hard X-ray power law, which we model with a power law with the same photon index and absorbed by a column density N(sub H)5 approximately equal to 10(sup 20) cm(sup -2) in excess to Galactic. Remarkably, a host of emission lines are present below 2 keV, confirming previous indications from ASCA, due to H- and He-like O, Mg, and Si. The detection of two features at 0.74 and 0.87 keV, identified with OVII and OVIII Radiative Recombination Continuum features, suggest an origin of the lines from a photoionized gas, with properties very similar to radio-quiet obscured AGN. Two different ionized media, or a single stratified medium, are required to fit the soft X-ray data satisfactorily. The similarity of the X-ray spectrum of 3C 445 to Seyferts underscores that the central engines of radio-loud and radio-quiet AGN similarly host both cold and warm gas.

Sambruna, R. M.↗
NASA NTRS2008

Gamma-Ray Emision from the Broad-Line Radio Galaxy 3C 111

The broad-line radio galaxy 3C 111 has been suggested as the counterpart of the Gamma-ray source 3EGJ0416+3650. While 3C 111 meets most of the criteria for a high-probability identification, like a bright fla t-spectrum radio core and a blazarlike broadband SED, in the Third EG RET Catalog, the large positional offset of about 1.5 degrees put 3C1 11 outside the 99% probability region for 3EG J0416+3650, making this association questionable. We present a re-analysis of all available data for 3C111 from the EGRET archives, resulting in probable detection of high-energy Gamma-ray emission above 1000MeV from a position clo se to the nominal position of 3C 111, in two separate viewing periods (VPs), at a 3sigma level in each. A new source, GROJ0426+3747, appea rs to be present nearby, seen only in the >1000MeV data. For >100MeV, the data are in agreement with only one source (at the original cata log position) accounting for most of the EGRET-detected emission of 3 EGJ0416+3650. A follow-up Swift UVOT/XRT observation reveals one mode rately bright X-ray source in the error box of 3EGJ0416+3650, but bec ause of the large EGRET position uncertainty, it is not certain that the X-ray and Gamma-ray sources are associated. A Swift observation of GROJ0426+3747 detected no X.ray source nearby.

Hartman, Robert C.↗
NASA NTRS2007

The Trails of Superluminal Jet Components in 3C 111

The parsec-scale radio jet of the broad-line radio galaxy 3C 111 has been monitored since 1995 as part of the 2cm Survey and MOJAVE monitoring observations conducted with the VLBA. Here, we present results from 18 epochs of VLBA observations of 3C 111 and from 18 years of radio flux density monitoring observations conducted at the University of Michigan. A major radio flux-density outburst of 3C 111 occurred in 1996 and was followed by a particularly bright plasma ejection associated with a superluminal jet component. This major event allows us to study a variety of processes associated with outbursts of radio-loud AGN in much greater detail than possible in other cases: the primary perturbation gives rise to the formation of a forward and a backward-shock, which both evolve in characteristically different ways and allow us to draw conclusions about the workflow of jet-production events; the expansion, acceleration and recollimation of the ejected jet plasma in an environment with steep pressure and density gradients are revealed; trailing components are formed in the wake of the primary perturbation as a result of Kelvin- Helmholtz instabilities from the interaction of the jet with the external medium. The jet-medium interaction is further scrutinized by the linear-polarization signature of jet components traveling along the jet and passing a region of steep pressure/density gradients.

Kadler, M.↗