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Perley, R. A.

Publications and source records attributed to Perley, R. A..

11 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Discovery of a Luminous Radio Transient 460 pc from the Central Supermassive Black Hole in Cygnus A

We report the appearance of a new radio source at a projected offset of 460 pc from the nucleus of Cygnus A. The flux density of the source (which we designate Cygnus A-2) rose from an upper limit of <0.5 mJy in 1989 to 4 mJy in 2016 ( ν = 8.5 GHz), but is currently not varying by more than a few percent per year. The radio luminosity of the source is comparable to the most luminous known supernovae, it is compact in Very Long Baseline Array observations down to a scale of 4 pc, and it is coincident with a near-infrared point source seen in pre-existing adaptive optics and HST observations. The most likely interpretation of this source is that it represents a secondary supermassive black hole in a close orbit around the Cygnus A primary, though an exotic supernova model cannot be ruled out. The gravitational influence of a secondary SMBH at this location may have played an important role in triggering the rapid accretion that has powered the Cygnus A radio jet over the past 10{sup 7} years.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Radio-loud and radio-quiet QSOs

We discuss 6 GHz JVLA observations covering a volume-limited sample of 178 low-redshift (0.2 5 mJy beam{sup −1} (log(L)≳24). The radio luminosity function of optically selected QSOs and the extended radio emission associated with RLQs are both inconsistent with simple “unified” models that invoke relativistic beaming from randomly oriented QSOs to explain the difference between RLQs and RQQs. Some intrinsic property of the AGNs or their host galaxies must also determine whether or not a QSO appears radio-loud.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Absolute calibration of the radio astronomy flux density scale at 22 TO 43 GHz using Planck

The Planck mission detected thousands of extragalactic radio sources at frequencies from 28 to 857 GHz. Planck's calibration is absolute (in the sense that it is based on the satellite’s annual motion around the Sun and the temperature of the cosmic microwave background), and its beams are well characterized at sub-percent levels. Thus, Planck's flux density measurements of compact sources are absolute in the same sense. We have made coordinated Very Large Array (VLA) and Australia Telescope Compact Array (ATCA) observations of 65 strong, unresolved Planck sources in order to transfer Planck's calibration to ground-based instruments at 22, 28, and 43 GHz. The results are compared to microwave flux density scales currently based on planetary observations. Despite the scatter introduced by the variability of many of the sources, the flux density scales are determined to 1%–2% accuracy. At 28 GHz, the flux density scale used by the VLA runs 2%–3% ± 1.0% below Planck values with an uncertainty of ±1.0%; at 43 GHz, the discrepancy increases to 5%–6% ± 1.4% for both ATCA and the VLA.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

CONNECTING GRBs AND ULIRGs: A SENSITIVE, UNBIASED SURVEY FOR RADIO EMISSION FROM GAMMA-RAY BURST HOST GALAXIES AT 0 < z < 2.5

Luminous infrared galaxies and submillimeter galaxies contribute significantly to stellar mass assembly and provide an important test of the connection between the gamma-ray burst (GRB) rate and that of overall cosmic star formation. We present sensitive 3 GHz radio observations using the Karl G. Jansky Very Large Array of 32 uniformly selected GRB host galaxies spanning a redshift range from 0 < z < 2.5, providing the first fully dust- and sample-unbiased measurement of the fraction of GRBs originating from the universe's most bolometrically luminous galaxies. Four galaxies are detected, with inferred radio star formation rates (SFRs) ranging between 50 and 300 M {sub ☉} yr{sup –1}. Three of the four detections correspond to events consistent with being optically obscured 'dark' bursts. Our overall detection fraction implies that between 9% and 23% of GRBs between 0.5 < z < 2.5 occur in galaxies with S {sub 3GHz} > 10 μJy, corresponding to SFR > 50 M {sub ☉} yr{sup –1} at z ∼ 1 or >250 M {sub ☉} yr{sup –1} at z ∼ 2. Similar galaxies contribute approximately 10%-30% of all cosmic star formation, so our results are consistent with a GRB rate that is not strongly biased with respect to the total SFR of a galaxy. However, all four radio-detected hosts have stellar masses significantly lower than IR/submillimeter-selected field galaxies of similar luminosities. We suggest that the GRB rate may be suppressed in metal-rich environments but independently enhanced in intense starbursts, producing a strong efficiency dependence on mass but little net dependence on bulk galaxy SFR.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

INTEGRATED POLARIZATION PROPERTIES OF 3C48, 3C138, 3C147, AND 3C286

We present the integrated polarization properties of the four compact radio sources 3C48, 3C138, 3C147, and 3C286, from 1 to 50 GHz, over a 30 yr time frame spanning 1982-2012. Using the polarized emission of Mars, we have determined that the position angle of the linearly polarized emission of 3C286 rises from 33 Degree-Sign at 8 GHz to 36 Degree-Sign at 45 GHz. There is no evidence for a change in the position angle over time. Using these values, the position angles of the integrated polarized emission from the other three sources are determined as a function of frequency and time. The fractional polarization of 3C286 is found to be slowly rising, at all frequencies, at a rate of {approx}0.015% yr{sup -1}. The fractional polarizations of 3C48, 3C138, and 3C147 are all slowly variable, with the variations correlated with changes in the total flux densities of these sources.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

ACTIVE GALACTIC NUCLEUS AND STARBURST RADIO EMISSION FROM OPTICALLY SELECTED QUASI-STELLAR OBJECTS

We used the 1.4 GHz NVSS to study radio sources in two color-selected QSO samples: a volume-limited sample of 1313 QSOs defined by M{sub i} < -23 in the redshift range 0.2 < z < 0.45 and a magnitude-limited sample of 2471 QSOs with m{sub r} {<=} 18.5 and 1.8 < z < 2.5. About 10% were detected above the 2.4 mJy NVSS catalog limit and are powered primarily by active galactic nuclei (AGNs). The space density of the low-redshift QSOs evolves as {rho}{proportional_to}(1 + z){sup 6}. In both redshift ranges the flux-density distributions and luminosity functions of QSOs stronger than 2.4 mJy are power laws, with no features to suggest more than one kind of radio source. Extrapolating the power laws to lower luminosities predicts the remaining QSOs should be extremely radio quiet, but they are not. Most were detected statistically on the NVSS images with median peak flux densities S{sub p}(mJy beam{sup -1}) Almost-Equal-To 0.3 and 0.05 in the low- and high-redshift samples, corresponding to spectral luminosities log [L{sub 1.4GHz}(W Hz{sup -1})] Almost-Equal-To 22.7 and 24.1, respectively. We suggest that the faint radio sources are powered by star formation at rates M-dot{approx}20M{sub Circled-Dot-Operator }yr{sup -1} in the moderate luminosity (median (M{sub i}) Almost-Equal-To -23.4) low-redshift QSOs and M-dot{approx}500M{sub Circled-Dot-Operator }yr{sup -1} in the very luminous ((M{sub i}) Almost-Equal-To -27.5) high-redshift QSOs. Such luminous starbursts [(log (L{sub IR}/L{sub Sun })) {approx} 11.2 and 12.6, respectively] are consistent with ''quasar mode'' accretion in which cold gas flows fuel both AGN and starburst.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

AN ACCURATE FLUX DENSITY SCALE FROM 1 TO 50 GHz

We develop an absolute flux density scale for centimeter-wavelength astronomy by combining accurate flux density ratios determined by the Very Large Array between the planet Mars and a set of potential calibrators with the Rudy thermophysical emission model of Mars, adjusted to the absolute scale established by the Wilkinson Microwave Anisotropy Probe. The radio sources 3C123, 3C196, 3C286, and 3C295 are found to be varying at a level of less than {approx}5% per century at all frequencies between 1 and 50 GHz, and hence are suitable as flux density standards. We present polynomial expressions for their spectral flux densities, valid from 1 to 50 GHz, with absolute accuracy estimated at 1%-3% depending on frequency. Of the four sources, 3C286 is the most compact and has the flattest spectral index, making it the most suitable object on which to establish the spectral flux density scale. The sources 3C48, 3C138, 3C147, NGC 7027, NGC 6542, and MWC 349 show significant variability on various timescales. Polynomial coefficients for the spectral flux density are developed for 3C48, 3C138, and 3C147 for each of the 17 observation dates, spanning 1983-2012. The planets Venus, Uranus, and Neptune are included in our observations, and we derive their brightness temperatures over the same frequency range.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1996

The Astronomical Low-Frequency Array

An array of satellites is proposed to make astronomic observations in the low frequency range of a few tens of MHz down to roughly 100 kHz, a range that cannot be observed through the ionosphere. The array would be in a solar orbit to avoid radio interference from Earth and to simplify trajectory tracking and control.

low-frequency array radio astronomy microsats↗
NASA NTRS1991

Multifrequency radio observations of Cygnus A - Spectral aging in powerful radio galaxies

A detailed analysis of the radio spectrum across the lobes of Cygnus A is presented in order to critically test the synchroton spectral aging theory. The results are in good agreement with the jet model for powerful radio galaxies, involving particle acceleration at the hot spots and outflow into the radio lobes, with subsequent energy loss due to synchrotron radiation. The hot spot spectra are well represented by a spectral aging model involving continuous injection of relativistic particles. Both hot spots have spectral break frequencies around 10 GHz. An injection index of 0.5 is found for both hot spots, consistent with diffusive shock acceleration at a strong nonrelativistic shock in a Newtonian fluid. The LF hot spot emission spectrum falls below the injected power law. This effect is isolated to the hot spots, and is best explained by a low-energy cutoff in the particle distribution.

Carilli, C. L.↗
NASA NTRS1975

An anomaly in the flux of Cassiopeia A at 38 MHz

The secular decrease in the flux of the supernova remnant Cassiopeia A has been measured at many radio frequencies. Observations are reported which indicate that this flux decrease has halted at 38 MHz and that the flux is increasing at this frequency. This may indicate that a new era of activity has begun in this object.

Erickson, W. C.↗