scholarly journals A LOFAR census of non-recycled pulsars: extending to frequencies below 80 MHz

2020 ◽  
Vol 635 ◽  
pp. A75 ◽  
Author(s):  
A. V. Bilous ◽  
L. Bondonneau ◽  
V. I. Kondratiev ◽  
J.-M. Grießmeier ◽  
G. Theureau ◽  
...  
Keyword(s):  
Flux Density ◽  
Low Frequency ◽  
Spectral Indices ◽  
Low Frequencies ◽  
Density Measurements ◽  
High Band

We present the results from the low-frequency (40–78 MHz) extension of the first pulsar census of non-recycled pulsars carried out with the LOw-Frequency ARray (LOFAR). We used the low-band antennas of the LOFAR core stations to observe 87 pulsars out of 158 that had been previously detected using high-band antennas. We present flux densities and flux-calibrated profiles for the 43 pulsars we detected. Of this sample, 17 have not, to our knowledge, previously been detected at such low frequencies. Here we recalculate the spectral indices using the new low-frequency flux density measurements from the LOFAR census and discuss the prospects of studying pulsars at very low frequencies using current and upcoming facilities, such as the New Extension in Nançay Upgrading LOFAR (NenuFAR).

scholarly journals Superluminal Motion in CTA 102

1989 ◽  
Vol 134 ◽  
pp. 529-530
Author(s):  
Ann E. Wehrle
Keyword(s):  
Flux Density ◽  
High Speed ◽  
Low Frequency ◽  
Precise Determination ◽  
Flux Variation ◽  
Low Frequencies ◽  
Superluminal Motion ◽  
Low Frequency Variability ◽  
Expansion Speed

Sholomitskii (1965) discovered that the flux density of the quasar CTA 102 varies at low frequencies on a timescale of a few months. Low-frequency variability can be explained by “superluminal flux variation” (Romney et al. 1984): If the intrinsic brightness of a component moving in a relativistically beamed source varies by only a few percent, the observer sees its flux density change by a much larger factor δ3-α when the optically thin blob moves almost directly toward the observer. Such a relativistically beamed source is likely to exhibit superluminal motion if studied with sufficient resolution and sensitivity. Superluminal motion in CTA 102 was discovered by Bååth (1987) who concluded on the basis of maps made at three epochs at a frequency of 932 MHz that two components were separating at a rate of 0.65 milliarcseconds (mas) per year. Using a redshift z = 1.037 and H0 = 100 km s−1 Mpc−1, q0 = 0.5, this expansion speed corresponds to (18 ± 4)h−1c. The extraordinarily high speed led us to make VLBI images of the source at a higher frequency in order to increase the resolution and make a more precise determination of the speed.

scholarly journals Spectral Index - Redshift Relation for Radio Galaxies and Quasars

1996 ◽  
Vol 175 ◽  
pp. 569-570
Author(s):  
R.D. Dagkesamanskii
Keyword(s):  
Flux Density ◽  
Spectral Index ◽  
Low Frequency ◽  
Radio Galaxies ◽  
Cosmological Evolution ◽  
Radio Sources ◽  
Spectral Indices ◽  
Extragalactic Radio Sources

Cosmological evolution of synchrotron spectra of the powerful extragalactic radio sources was studied by many authors. Some indications of such an evolution had been found firstly by analysis of ‘spectral index - flux density’ (α – S) relation for the sample of relatively strong radio sources. Later Gopal-Krishna and Steppe extended the analysis to weaker sources and found that the slope of αmed(S) curve changes dramatically at intermediate flux densities. Gopal-Krishna and Steppe pointed out that the maxima of the αmed(S) curve and of differential source counts are at almost the same flux density ranges (see, Fig. 2). It has to be noticed that the all mentioned results were obtained using the low-frequency spectral indices and on the basis of low frequency samples.

scholarly journals A low frequency study of linear polarization in radio galaxies

2020 ◽  
Author(s):  
V H Mahatma ◽  
M J Hardcastle ◽  
J Harwood ◽  
S P O’Sullivan ◽  
G Heald ◽  
...  
Keyword(s):  
Flux Density ◽  
Angular Size ◽  
Low Frequency ◽  
Radio Galaxies ◽  
Low Frequencies ◽  
Sky Survey ◽  
Linearly Polarized ◽  
Low Mass ◽  
The Magnetic Field ◽  
Cent Detection

Abstract Radio galaxies are linearly polarized – an important property that allows us to infer the properties of the magnetic field of the source and its environment. However at low frequencies, Faraday rotation substantially depolarizes the emission, meaning that comparatively few polarized radio galaxies are known at low frequencies. Using the LOFAR Two Metre Sky Survey at 150 MHz and at 20 arcsec resolution, we select 342 radio galaxies brighter than 50 mJy and larger than 100 arcsec in angular size, of which 67 are polarized (18 per cent detection fraction). These are predominantly Fanaroff Riley type II (FR-II) sources. The detection fraction increases with total flux density, and exceeds 50 per cent for sources brighter than 1 Jy. We compare the sources in our sample detected by LOFAR to those also detected in NVSS at 1400 MHz, and find that our selection bias toward bright radio galaxies drives a tendency for sources depolarized between 1400 and 150 MHz to have flatter spectra over that frequency range than those that remain polarized at 150 MHz. By comparing observed rotation measures with an analytic model we find that we are preferentially sensitive to sources in low mass environments. We also infer that sources with one polarized hotspot are inclined by a small angle to the line of sight, while sources with hotspots in both lobes lie in the plane of the sky. We conclude that low frequency polarization in radio galaxies is related to a combination of environment, flux density and jet orientation.

scholarly journals Spectral Analysis of Four Recycled Pulsars

1992 ◽  
Vol 128 ◽  
pp. 150-153
Author(s):  
R. S. Foster ◽  
L. Fairhead ◽  
D. C. Backer
Keyword(s):  
Spectral Analysis ◽  
Flux Density ◽  
Frequency Component ◽  
Component Model ◽  
Spectral Indices ◽  
Density Measurements ◽  
Pulse Component ◽  
Dispersion Measures ◽  
Analytic Models ◽  
Better Than

AbstractFlux density measurements of four recycled pulsars, PSR 1620-26, PSR 1821-24, PSR 1855+09, and PSR 1937+21, have been made to determine their spectral indices in the range between 425 MHz to 3 GHz. The four objects are shown to have indices that range from –1.3 to –2.6. The luminosities of these four pulsars are spread over nearly three orders of magnitude. An analytic pulse component model is developed for each object. Individual components are allowed to have different spectral indices and hence different component ratios as a function of frequency. Component separations are evaluated as a function of frequency. The analytic models are used to determine dispersion measures with a precision better than 0.01 pc cm–3 for each object. The intrinsic pulse widths of each of these objects is less than ~4 percent of their respective pulse periods.

Pulsar Radio Spectra

1996 ◽  
Vol 160 ◽  
pp. 271-277 ◽  
Author(s):  
Valerij M. Malofeev
Keyword(s):  
Flux Density ◽  
Spectral Indices ◽  
Pulsar Radio ◽  
Density Measurements ◽  
Energy Maximum

AbstractA review of simultaneous and compiled spectra is presented, and a catalog of radio spectra for 340 pulsars reported. Pulsars with flux density measurements at three and more frequencies are included. Statistics of spectral indices and frequencies of the energy maximum and the break are presented, as well as the correlations with other pulsar parameters. The classification of 127 rich pulsar spectra has been made. Three main types of spectra are identified.

scholarly journals Low-frequency Flux Density Measurements and Pulsars with GHz-peaked Spectra

2021 ◽  
Vol 923 (2) ◽  
pp. 211
Author(s):  
J. Kijak ◽  
R. Basu ◽  
W. Lewandowski ◽  
K. Rożko
Keyword(s):  
Flux Density ◽  
High Frequency ◽  
Supernova Remnant ◽  
Low Frequency ◽  
Physical Parameters ◽  
Absorption Model ◽  
Pulsar Wind Nebulae ◽  
Entire Sample ◽  
Density Measurements ◽  
Pulsar Wind

Abstract We have estimated flux densities of several pulsars from radio interferometric observations mainly at 325 MHz using the Giant Metrewave Radio Telescope. The new observations allowed us to update the spectral nature of the observed pulsars, and in six sources we identified relatively high frequency turnovers, which can be classified as new GHz-peaked spectrum (GPS) pulsars. For such objects the turnover in the spectrum is most likely caused by absorption in the immediate vicinity of the pulsar (or in the interstellar medium). We modeled the turnover spectra using the thermal free–free absorption model and the physical parameters obtained from the fits enabled us to identify the environments that could potentially be responsible for the observed absorption, such as pulsar wind nebulae, supernova remnant nebulae or H ii regions. The discovery of 6 new GPS pulsars brings the total number of such objects to 33 and we discuss the properties of the entire sample.

A thermoelectric device for ophthalmic heat flux density measurements: results of piloting in healthy individuals

2019 ◽  
Vol 80 (3) ◽  
pp. 45-51
Author(s):  
L. Anatychuk ◽  
N. Pasyechnikova ◽  
V. Naumenko ◽  
O. Zadorozhnyy ◽  
R. Kobylianskyi ◽  
...  
Keyword(s):  
Heat Flux ◽  
Flux Density ◽  
Heat Flux Density ◽  
Thermoelectric Device ◽  
Healthy Individuals ◽  
Density Measurements
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