Climatology of midlatitude ionospheric disturbances from the Very Large Array Low-frequency Sky Survey

AbstractAbout one third of the gamma-ray sources detected by Fermi have still no firmly established counterpart at lower energies. Here we propose a new approach to find candidate counterparts for the unidentified gamma-ray sources (UGSs) based on the 325 MHz radio survey performed with Westerbork Synthesis Radio Telescope (WSRT) in the northern hemisphere. First we investigate the low-frequency radio properties of blazars, the largest known population of gamma-ray sources; then we search for sources with similar radio properties combining the information derived from the Westerbork Northern Sky Survey (WENSS) with those of the NRAO VLA Sky survey (NVSS). We present a list of candidate counterparts for 32 UGSs with at least one counterpart in the WENSS. We also performed an extensive research in literature to look for infrared and optical counterparts of the gamma-ray blazar candidates selected with the low-frequency radio observations to confirm their nature. On the basis of our multifrequency research we identify 23 new gamma-ray blazar candidates out of 32 UGSs investigated. I will also present the first analysis of very low frequency radio emission of blazars based on the recent Very Large Array Low-Frequency Sky Survey (VLSS) at 74 MHz. I show that blazars present radio flat spectra when evaluated at 74 MHz, about an order of magnitude in frequency lower than previous analyses. The implications of these findings in the contest of the blazars – radio galaxies connection will be discussed.

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VLSS redux: Software improvements applied to the Very Large Array Low-Frequency Sky Survey

Radio Science ◽

10.1029/2011rs004941 ◽

2012 ◽

Vol 47 (6) ◽

pp. n/a-n/a ◽

Cited By ~ 38

Author(s):

W. M. Lane ◽

W. D. Cotton ◽

J. F. Helmboldt ◽

N. E. Kassim

Keyword(s):

Low Frequency ◽

Large Array ◽

Very Large Array ◽

Sky Survey

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The Very Large Array Low-frequency Sky Survey Redux (VLSSr)

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stu256 ◽

2014 ◽

Vol 440 (1) ◽

pp. 327-338 ◽

Cited By ~ 128

Author(s):

W. M. Lane ◽

W. D. Cotton ◽

S. van Velzen ◽

T. E. Clarke ◽

N. E. Kassim ◽

...

Keyword(s):

Low Frequency ◽

Large Array ◽

Very Large Array ◽

Sky Survey

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Low frequency (74 MHz) radio continuum observations of the inner 13° × 7° of the Galactic center

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314001161 ◽

2013 ◽

Vol 9 (S303) ◽

pp. 464-466

Author(s):

M. Rickert ◽

F. Yusef-Zadeh ◽

C. Brogan

Keyword(s):

High Resolution ◽

Molecular Cloud ◽

Supernova Remnant ◽

Galactic Center ◽

Low Frequency ◽

Radio Continuum ◽

Large Array ◽

Very Large Array ◽

Image Displays ◽

Western Side

AbstractWe analyze a high resolution (114″ × 60″) 74 MHz image of the Galactic center taken with the Very Large Array (VLA). We have identified several absorption and emission features in this region, and we discuss preliminary results of two Galactic center sources: the Sgr D complex (G1.1–0.1) and the Galactic center lobe (GCL).The 74 MHz image displays the thermal and nonthermal components of Sgr D and we argue the Sgr D supernova remnant (SNR) is consistent with an interaction with a nearby molecular cloud and the location of the Sgr D Hii region on the near side of the Galactic center. The image also suggests that the emission from the eastern side of the GCL contains a mixture of both thermal and nonthermal sources, whereas the western side is primarily thermal.

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Drift-scan imaging of traveling ionospheric disturbances with the Very Large Array

Geophysical Research Letters ◽

10.1002/2014gl060951 ◽

2014 ◽

Vol 41 (14) ◽

pp. 4835-4843 ◽

Cited By ~ 6

Author(s):

J. F. Helmboldt

Keyword(s):

Ionospheric Disturbances ◽

Large Array ◽

Very Large Array ◽

Traveling Ionospheric Disturbances ◽

Drift Scan

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Finding Rare Quasars: VLA Snapshot Continuum Survey of FRI Quasar Candidates Selected from the LOFAR Two-Metre Sky Survey (LoTSS)

Galaxies ◽

10.3390/galaxies10010002 ◽

2021 ◽

Vol 10 (1) ◽

pp. 2

Author(s):

Gülay Gürkan ◽

Judith Croston ◽

Martin J. Hardcastle ◽

Vijay Mahatma ◽

Beatriz Mingo ◽

...

Keyword(s):

Low Frequency ◽

Stable Phase ◽

Galactic Centre ◽

Very Large Array ◽

Sky Survey ◽

Two Factors ◽

Radiative Power ◽

Galaxy Environment ◽

Systematic Selection ◽

Jet Power

The radiative and jet power in active galactic nuclei is generated by accretion of material on to supermassive galactic-centre black holes. For quasars, where the radiative power is by definition very high, objects with high radio luminosities form ∼10 per cent of the population, although it is not clear whether this is a stable phase. Traditionally, quasars with high radio luminosities have been thought to present jets with edge-brightened morphology (Fanaroff-Riley II−FR II) due to the limitations of previous radio surveys (i.e., FRIs were not observed as part of the quasar population). The LOw Frequency ARray (LOFAR) Two-metre Sky Survey (LoTSS) with its unprecedented sensitivity and resolution covering wide sky areas has enabled the first systematic selection and investigation of quasars with core-brightened morphology (Fanaroff-Riley I−FR). We carried out a Very Large Array (VLA) snapshot survey to reveal inner structures of jets in selected quasar candidates; 15 (25 per cent) out of 60 sources show clear inner jet structures that are diagnostic of FRI jets and 13 quasars (∼22 per cent) show extended structures similar to those of FRI jets. Black hole masses and Eddington ratios do not show a clear difference between FRI and FRII quasars. FRII quasars tend to have higher jet powers than FRI quasars. Our results show that the occurrence of FRI jets in powerful radiatively efficient systems is not common, probably mainly due to two factors: galaxy environment and jet power.

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