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At least 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

Simultaneous Planck, Swift, and Fermi Observations of X-Ray and gamma-Ray Selected Blazars

We present simultaneous Planck, Swift, Fermi, and ground-based data for 105 blazars belonging to three samples with flux limits in the soft X-ray, hard X-ray, and -ray bands, and we compare our results to those of a companion paper presenting simultaneous Planck and multi-frequency observations of 104 radio-loud northern active galactic nuclei selected at radio frequencies. While we confirm several previous results, our unique data set has allowed us to demonstrate that the selection method strongly influences the results, producing biases that cannot be ignored. Almost all the BL Lac objects have been detected by Fermi Large Area Telescope (LAT), whereas 30 to 40% of the flat-spectrum radio quasars (FSRQs) in the radio, soft X-ray, and hard X-ray selected samples are still below the gamma ray detection limit even after integrating 27 months of Fermi-LAT data. The radio to sub-millimetre spectral slope of blazars is quite flat, with [alpha] approximately 0 up to about 70 GHz, above which it steepens to [alpha] approximately -0.65. BL Lacs have significantly flatter spectra than FSRQs at higher frequencies. The distribution of the rest-frame synchrotron peak frequency (v(sup IC) (sub (PEAK)), ranges from 10(sup 21) to 10(sup 22) HZ. The distribution of the rest-frame synchrotron peak frequency (v(sup s)(sub peak)) in the spectral energy distribution (SED) of FSRQs is the same in all the blazar samples with (v(sup s)(sub peak) = 10(sup 13:1 plus or minus 0.1) Hz, while the mean inverse-Compton peak frequency,(v(sup IC)(sub peak) ranges from 10(sup 21) to 10(sup 22) Hz. The distributions of v(sup S)(sub peak) and of v(sup IC)(sub peak) of BL Lacs are much broader and are shifted to higher energies than those of FSRQs; their shapes strongly depend on the selection method. The Compton dominance of blazars ranges from less than 0.2 to nearly 100, with only FSRQs reaching values larger than about 3. Its distribution is broad and depends strongly on the selection method, with gamma-ray selected blazars peaking at approximately 7 or more, and radio-selected blazars at values close to 1, thus implying that the common assumption that the blazar power budget is largely dominated by high-energy emission is a selection effect. A comparison of our multi-frequency data with theoretical predictions shows that simple homogeneous SSC models cannot explain the simultaneous SEDs of most of the gamma-ray detected blazars in all samples. The SED of the blazars that were not detected by Fermi-LAT may instead be consistent with SSC emission. Our data challenge the correlation between bolometric luminosity and v(sup S)(sub peak) predicted by the blazar sequence.

Giommi, P.↗
NASA NTRS2012

Simultaneous Planck, Swift, and Fermi Observations of X-ray and Gamma-ray Selected Blazars

We present simultaneous Planck, Swift, Fermi, and ground-based data for 105 blazars belonging to three samples with flux limits in the soft X-ray, hard X-ray, and gamma-ray bands, with additional 5 GHz flux-density limits to ensure a good probability of a Planck detection. We compare our results to those of a companion paper presenting simultaneous Planck and multi-frequency observations of 104 radio-loud northern active galactic nuclei selected at radio frequencies. While we confirm several previous results, our unique data set allows us to demonstrate that the selection method strongly influences the results, producing biases that cannot be ignored. Almost all the BL Lac objects have been detected by the Fermi Large Area Telescope (LAT), whereas 30% to 40% of the flat-spectrum radio quasars (FSRQs) in the radio, soft X-ray, and hard X-ray selected samples are still below the gamma-ray detection limit even after integrating 27 months of Fermi-LAT data. The radio to sub-millimetre spectral slope of blazars is quite flat, with (alpha) approx 0 up to about 70GHz, above which it steepens to (alpha) approx -0.65. The BL Lacs have significantly flatter spectra than FSRQs at higher frequencies. The distribution of the rest-frame synchrotron peak frequency (nu(sup s)(sub peak)) in the spectral energy distribution (SED) of FSRQs is the same in all the blazar samples with (nu(sup s)(sub peak)) = 10(exp 13.1 +/- 0.1) Hz, while the mean inverse Compton peak frequency, (nu(sup IC)(sub peak)), ranges from 10(exp 21) to 10(exp 22) Hz. The distributions of nu(sup s)(sub peak) and nu(sup IC)(sub peak) of BL Lacs are much broader and are shifted to higher energies than those of FSRQs; their shapes strongly depend on the selection method. The Compton dominance of blazars. defined as the ratio of the inverse Compton to synchrotron peak luminosities, ranges from less than 0.2 to nearly 100, with only FSRQs reaching values larger than about 3. Its distribution is broad and depends strongly on the selection method, with gamma-ray selected blazars peaking at approx 7 or more, and radio-selected blazars at values close to 1, thus implying that the common assumption that the blazar power budget is largely dominated by high-energy emission is a selection effect. A comparison of our multi-frequency data with theoretical predictions shows that simple homogeneous SSC models cannot explain the simultaneous SEDs of most of the gamma-ray detected blazars in all samples. The SED of the blazars that were not detected by Fermi~LAT may instead be consistent with SSC emission. Our data challenge the correlation between bolometric luminosity and nu(sup s)(sub peak) predicted by the blazar sequence.

Giommi, P.↗
NASA NTRS2000

The Far-Infrared Emission of Radio Loud and Radio Quiet Quasars

Continuum observations at radio, millimeter, infrared and soft X-ray energies are presented for a sample of 22 quasars, consisting of flat and steep spectrum radio loud, radio intermediate and radio quiet objects. The primary observational distinctions, among the different kinds of quasars in the radio and IR energy domains are studied using large observational datasets provided by ISOPHOT on board the Infrared Space Observatory, by the IRAM interferometer, by the sub-millimetre array SCUBA on JCMT, and by the European Southern Observatory (ESO) facilities IRAC1 on the 2.2 m telescope and SEST. The spectral energy distributions of all quasars from radio to IR energies are analyzed and modeled with non-thermal and thermal spectral components. The dominant mechanism emitting in the far/mid-IR is thermal dust emission in all quasars, with the exception of flat spectrum radio loud quasars for which the presence of thermal IR emission remains rather uncertain, since it is difficult to separate it from the bright non-thermal component. The dust is predominantly heated by the optical/ultraviolet radiation emitted from the external components of the AGN. A starburst contributes to the IR emission at different levels, but always less than the AGN (<= 27%). The distribution of temperatures, sizes, masses, and luminosities of the emitting dust are independent of the quasar type.

Polletta, M.↗
DOE OSTI2026

Discovery of a nearby radio relic in the low-mass, merging cluster Abell 4067

Shock waves generated during cluster mergers offer a powerful probe of how large-scale structure grows and evolves in the Universe. As part of the MeerKAT-South Pole Telescope (SPT) survey, we report the discovery of a single arc-like radio relic in the galaxy cluster Abell 4067 ($z=0.099$), one of the lowest-mass clusters known to host such a structure. MeerKAT UHF-band (0.58–1.09 GHz) observations reveal a relic with a largest linear size of $\sim 1.48\pm 0.02$ Mpc, located at a projected distance of 0.95 Mpc from the cluster centre. XMM–Newton X-ray data show that the relic’s position and orientation relative to the intracluster medium (ICM) elongation are consistent with a merger-driven shock-wave scenario. The relic has an estimated radio power of $3.10\pm 0.03\times 10^{24}$ W Hz$^{-1}$ at 150 MHz. When placed in the $P_{150\, \mathrm{MHz}}$–$M_{500}$ scaling relation, the Abell 4067 relic appears less luminous compared to relics in more massive clusters, suggesting an association with weak merger shocks. This finding supports the idea that relics in low-mass clusters may form through less energetic merger events, leading to weak merger shocks. The latter is supported by the absence of a detectable central radio halo in Abell 4067, which reinforces the idea that luminous radio haloes are not a universal outcome of cluster mergers and highlights the role of cluster mass, merger energetics, and evolutionary stage in shaping diffuse radio emission in the ICM.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

The Third Fermi Large Area Telescope Catalog of Gamma-Ray Pulsars

We present 294 pulsars found in GeV data from the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope. Another 33 millisecond pulsars (MSPs) discovered in deep radio searches of LAT sources will likely reveal pulsations once phase-connected rotation ephemerides are achieved. A further dozen optical and/or X-ray binary systems colocated with LAT sources also likely harbor gamma-ray MSPs. This catalog thus reports roughly 340 gamma-ray pulsars and candidates, 10% of all known pulsars, compared to ≤11 known before Fermi. Half of the gamma-ray pulsars are young. Of these, the half that are undetected in radio have a broader Galactic latitude distribution than the young radio-loud pulsars. The others are MSPs, with six undetected in radio. Overall, ≥236 are bright enough above 50 MeV to fit the pulse profile, the energy spectrum, or both. For the common two-peaked profiles, the gamma-ray peak closest to the magnetic pole crossing generally has a softer spectrum. The spectral energy distributions tend to narrow as the spindown power $\dot{E}$ decreases to its observed minimum near 10 33 erg s -1 , approaching the shape for synchrotron radiation from monoenergetic electrons. We calculate gamma-ray luminosities when distances are available. Our all-sky gamma-ray sensitivity map is useful for population syntheses. The electronic catalog version provides gamma-ray pulsar ephemerides, properties, and fit results to guide and be compared with modeling results.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1975

SAS-2 High energy gamma-ray observations of the Vela pulsar

The second Small Astronomy Satellite high-energy (35 MeV) gamma-ray telescope detected pulsed gamma-ray emission at the radio period from PSR 0833-45, the Vela pulsar, as well as an unpulsed flux from the Vela region. The pulsed emission consists of two peaks, one following the radio peak by about 13 msec, and the other 0.4 period after the first. The luminosity of the pulsed emission above 100 MeV from Vela is about 0.1 that of the pulsar NP0532 in the Crab nebula, whereas the pulsed emission from Vela at optical wavelengths is less than 0.0004 that from the Crab. The relatively high intensity of the pulsed gamma-ray emission and the double peak structure, compared to the single pulse in the radio emission, suggests that the high energy gamma-ray pulsar emission may be produced under different conditions from those found at lower energies.

Thompson, D. J.↗
NASA NTRS1979

Voyager spacecraft radio observations of Jupiter: Initial cruise results

Jupiter's low-frequency radio emission were detected by the planetary radio astronomy instruments onboard the two Voyager spacecraft. The emission is surprisingly similar in morphology but opposite in polarization to the high-frequency Jovian radio noise that were observed with ground-based telescopes for more than two decades. Several possible explanations for the behavior of the low-frequency emission are examined, but none of them is completely satisfactory.

Kaiser, M. L.↗
NASA NTRS1982

Fiducial reference for the Hipparcos reference system

Means of determining the Hipparcos satellite instrumental system rotation and for tying Hipparcos system coordinates to a fundamental coordinate system are discussed. Observational characteristics requirements for radio sources and stars, for a Hipparcos-Space Telescope reference tie are given. Rotation of the Hipparcos system with respect to the extragalactic system can be derived from observations of the relative radial positions and motions of selected Hipparcos stars and quasi-stellar objects.

Hemenway, D.↗
NASA NTRS1982

Observations of Paschen alpha in the broad-line radio galaxy 3C 445

P alpha line flux measurements of the broad-line radio galaxy 3C 445 made at the NASA IR Telescope Facility in September 1981 are discussed. Broad-band measurements were obtained at H of 1.65 micron and K of 2.2 microns. A line flux of P alpha was found at 3.4 times 10 to the -13th ergs/sq cm sec. No discernable variation was detectable regarding measurements made in 1976. Substantial reddening was concluded to exist, although the H gamma lines observed were not due to reddening. The total H alpha luminosity was determined to be 4 x 10 to the 43rd ergs/sec. Steep Balmer line decrements are concluded to be due to interposed dust.

Rudy, R. J.↗
NASA NTRS1988

The ultraviolet spectrum of RX Puppis

The UV spectrum of the peculiar star RX Puppis has afforded symbiotic star investigators a wealth of information for unraveling its mysteries. RX Pup and R Aqr, both being of the D-type variety, are now better understood as result of an extended coverage of observations at different wavelengths including radio observations using the VLA. These stars present challenges to the understanding of the symbiotic phenomenon and clues to other astrophysical phenomena like jets. Resolution of the question whether RX Pup has a jet system and an associated system of rings/extended disk or, alternatively, a colliding winds region will be resolved by high resolution radio observations or future observations using the Hubble Space Telescope.

Kafatos, M.↗
NASA NTRS1990

CO excitation in four IR luminous galaxies

The correlation between the CO and far infrared luminosities of spiral galaxies is well established. The luminosity ration, L sub FIR/L sub CO in IR luminous active galaxies is, however, systematically five to ten times higher than in ordinary spirals and molecular clouds in our Galaxy. Furthermore, the masses of molecular hydrogen in luminous galaxies are large, M (H2) approx. equals 10(exp 10) solar magnitude, which indicates the observed luminosity ratios are due to an excess of infrared output, rather than a deficiency of molecular gas. These large amounts of molecular gas may fuel luminous galaxies through either star formation or nuclear activity. This interpretation rests on applying the M (H2)/L sub CO ratio calibrated in our Galaxy to galaxies with strikingly different luminosity ratios. But are the physical conditions of the molecular gas different in galaxies with different luminosity ratios. And, if so, does the proportionality between CO and H2 also vary among galaxies. To investigate these questions researchers observed CO (2 to 1) and (1 to 0) emission from four luminous galaxies with the Institute for Radio Astronomy in the Millimeter range (IRAM) 30 m telescope. Researchers conclude that most of the CO emission from these Arp 193, Arp 220, and Mrk 231 arises in regions with moderate ambient densities similar to the clouds in the Milky Way molecular ring. The emission is neither from dense hot cloud cores nor from the cold low density gas characteristic of the envelopes of dark clouds.

Radford, Simon J. E.↗
NASA NTRS1990

CS in nearby galaxies: Distribution, kinematics, and multilevel studies

As a result of observations at the Institute for Radio Astronomy in the Millimeter Range (IRAM) 30-m telescope, maps of the distribution of the J = 2-1 transition of CS toward the galaxies IC 342 and NGC 253 are presented. The distribution of the CS emission from NGC 253 is consistent with the CO 1-0 line. The distribution of the CS emission from IC 342, however, resembles more that seen in the CO 3-2 line. For the first time, the detection of the isotopic substitution C-34S is reported toward an external galaxy: The C-34S 2-1 line has been detected toward NGC 253 and M 82 and the C-34S line has been detected tentatively toward M 82. Also for the first time, extragalactic CS has been observed in the 3-2 (toward NGC 253, IC 342 and M 82) and 5-4 (NGC 253 and IC 342) transitions.

Mauersberger, R.↗
NASA NTRS1990

Spatial variation of the physical conditions of molecular gas in galaxies

Multi-line studies of CO-12, CO-13, C-18O, HCN, and HCO(+) at 3 mm, 1.3 mm, and 0.8 mm using the Institute for Radio Astronomy in the Millimeter range (IRAM) 30 m telescope, with the IRAM superconductor insulator superconductor (SIS) receivers and the Max Planck Institute for External Physics (MPE) 350 GHz SIS receiver, show that the densities and temperatures of molecular gas in external galaxies change significantly with position. CO-12 measures the densities and temperature of diffuse interclump molecular gas, but not the bulk of the molecular gas. Simple one-component models, with or without external heating, cannot account for the weakness of the CO-12 J = 3 to 2 line relative to J = 2 to 1 and J = 1 to 0. CO-12 does not trace the bulk of the molecular gas, and optical depth effects obviate a straightforward interpretation of CO-12 data. Instead, researchers turned to the optically thin CO isotopes and other molecular species. Isotopic CO lines measure the bulk of the molecular gas, and HCN and HCO(+) pick out denser regions. Researchers find a warm ridge of gas in IC 342 (Eckart et al. 1989), denser gas in the starburst nucleus of IC 342, and a possible hot-spot in NGC 2903. In IC 342, NGC 2146, and NGC 6764, the CO-13 J = 2 to 1 line is subthermally populated, implying gas densities less than or equal to 10(exp 4) cm(-3).

Jackson, James M.↗
NASA NTRS1992

High-resolution imaging of QSO 2305 + 187 (= 4C 18.68)

Optical imaging of QSO 2305 + 187 with resolution ranging from 0.1 to 1.0 arcsec in continuum and line emission is presented. The data are from FOCAM and the HR Cam of the Canada-France-Hawaii Telescope, and the Wide Field Camera of the Hubble Space Telescope. These are compared with previously published optical and radio images. The QSO host galaxy has the basic properties of an elliptical, but has significant irregularities, and tidal tails which indicate an ongoing gravitational interaction with a close companion.

Hutchings, J. B.↗
NASA NTRS1995

KAO and AAT observations of the Galactic Center filaments

We have used the Kuiper Airborne Observatory (KAO) and the Anglo-Australian Telescope (AAT) to investigate the nature of the filamentary radio emission from the Galactic center region. KAO observations of the FIR line and continuum emission from the radio peak G0.095+0.012 and the E2 thermal radio filament northeast of the Galactic center can be produced by numerous nearby stars with T(sub eff) approx. 35,000 K; these can account for both the FIR luminosity and the excitation of the gas. Much of the FIR continuum and most of the strong (Si II) (34.8 micron) line emission are probably produced in the ionized gas of the filament. The FIR (O III) 52 and 88 micron lines imply an electron density of a few hundred; when compared with the radio emission measure, this implies the filament is roughly tubular or somewhat flattened in the plane of the sky. The (O III) and (S III) lines show higher excitation associated with the filament, and suggest that exciting stars may be located within the filaments and/or southeast of the E2 filament. AAT observations in the near infrared (NIR) in fact reveal a nearby cluster of hot stars southeast of the E2 filament. Additional hot stars, not identifiable from their NIR spectra, are likely to be present. These stars and those in the cluster can plausibly produce the observed radio and FIR emission in the region. The morphology of the filament is not explained by existing information however.

Erickson, Edwin F.↗
NASA NTRS2004

VLA Imaging of Protoplanetary Environments

We summarize progress on our program to use high angular resolution observations at millimeter wavelengths to probe the structure of protoplanetary disks in nearby star forming regions. The primary facilities for this work are the Very Large Array (VLA) of the National Radio Astronomy Observatories (NRAO), and the recently upgraded Australia Telescope Compact Array (ATCA) that now allows access to exciting targets in the far southern sky. We are improving our capabilities to interpret these observations with radiative transfer modeling. Many recent highlights of our program were presented in an invited review. Below we summarize major accomplishments of the past year.

Wilner, David J.↗
NASA NTRS2013

Reflection-dominated Nuclear X-Ray Emission in the Early-Type Galaxy ESO 565 G019

We present the discovery of a reflection-dominated active galactic nucleus (AGN) in the early-type radio-quietgalaxy ESO 565G019 with Suzaku and SwiftBurst Alert Telescope. The source X-ray spectrum below 10 keVis characteristic of other Compton-thick (CT) AGNs, clearly showing an inverted continuum and prodigiousfluorescence iron emission above 3 keV. A Compton shoulder to the neutral Fe K line also appears to be present.There is evidence for long-term hard X-ray flux variability that we associate with changes in the intrinsic AGNpower law. More of such reflection-dominated AGNs should be uncovered in the near future with the increasedsensitivity of ongoing and new hard X-ray surveys. ESO 565G019 is hosted in an early-type galaxy whosemorphology has been variously classified as either type E or type S0. Only about 20 bona fide CT-AGNs have been identified in the local universe so far, and all exist in host galaxies with late Hubble types (S0 or later). CT columns of nuclear obscuring gas are uncommon in early-type galaxies in the local universe, so confirmation of the exact morphological class of ESO 565G019 is important. Infrared photometry also shows the presence of largequantities of cool dust in the host, indicative of significant ongoing star formation. ESO 565G019 may be the firstidentified local example of minor-merger-driven CT-AGN growth in an early-type host, or may be the result ofinteraction with its neighboring galaxy ESO 565G018 in a wide pair.

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