- ID:
- ivo://CDS.VizieR/J/MNRAS/474/4937
- Title:
- Interplanetary scintillation at 162 and 1400MHz
- Short Name:
- J/MNRAS/474/4937
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the first astrophysical application of the technique of wide-field interplanetary scintillation (IPS) with the Murchison Widefield Array (MWA). This powerful technique allows us to identify and measure sub-arcsecond compact components in low-frequency radio sources across large areas of sky without the need for long-baseline interferometry or ionospheric calibration. We present the results of a 5-min observation of a 30x30deg^2^ MWA field at 162MHz with 0.5s time resolution. Of the 2550 continuum sources detected in this field, 302 (12 per cent) show rapid fluctuations caused by IPS. We find that at least 32 per cent of bright low-frequency radio sources contain a sub-arcsecond compact component that contributes over 40 per cent of the total flux density. Perhaps surprisingly, peaked-spectrum radio sources are the dominant population among the strongly scintillating, low-frequency sources in our sample. While gamma-ray active galactic nuclei are generally compact, flat-spectrum radio sources at higher frequencies (162MHz), the properties of many of the Fermi blazars in our field are consistent with a compact component embedded within more extended low-frequency emission. The detection of a known pulsar in our field shows that the wide-field IPS technique is at the threshold of sensitivity needed to detect new pulsars using image plane analysis, and scaling the current MWA sensitivity to that expected for SKA-low implies that large IPS-based pulsar searches will be feasible with SKA. Calibration strategies for the SKA require a better knowledge of the space density of compact sources at low radio frequencies, which IPS observations can now provide.
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- ID:
- ivo://CDS.VizieR/J/MNRAS/473/2965
- Title:
- Interplanetary scintillation at 79 and 158MHz
- Short Name:
- J/MNRAS/473/2965
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first dedicated observations of Interplanetary Scintillation (IPS) with the Murchison Widefield Array. We have developed a synthesis imaging technique, tailored to the properties of modern 'large-N' low-frequency radio telescopes. This allows us to image the variability on IPS time-scales across 900deg^2^ simultaneously. We show that for our observations, a sampling rate of just 2Hz is sufficient to resolve the IPS signature of most sources. We develop tests to ensure that IPS variability is separated from ionospheric or instrumental variability. We validate our results by comparison with existing catalogues of IPS sources, and near-contemporaneous observations by other IPS facilities. Using just 5 min of data, we produce catalogues at both 79 and 158MHz, each containing over 350 scintillating sources. At the field centre, we detect approximately one scintillating source per square degree, with a minimum scintillating flux density at 158MHz of 110mJy, corresponding to a compact flux density of approximately 400mJy. Each of these sources is a known radio source, however only a minority were previously known to contain sub-arcsecond components. We discuss our findings and the prospects they hold for future astrophysical and heliospheric studies.
- ID:
- ivo://CDS.VizieR/J/A+A/403/555
- Title:
- Interplanetary Scintillation Pushchino Survey
- Short Name:
- J/A+A/403/555
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Interplanetary scintillating (IPS) radio sources from the Pushchino Survey (PS) in the area of 0.11sr have been cross-identified with objects from the 7C and FIRST catalogues. We have obtained improved positions of IPS radio sources, which are necessary for their optical identification. The data on sizes and morphology provided by the FIRST catalogue have shown that more than 50% of IPS radio sources are single and compact (<3") at {nu}=1400MHz. Most of them belong to the class of compact steep spectrum radio sources. About 15% of IPS radio sources are single partially resolved FIRST objects (sizes of 3"-9") and another 11% are double radio sources with compact components. The remaining 22% have larger sizes and, as a rule, a more complex structure too. Because IPS sources certainly contain an appreciable part of their radiation at low frequencies (100MHz) in very compact (~0.1") components and have steep spectra, we hope that a significant part of the Pushchino Survey objects are very probable candidates for steep spectrum quasars.
- ID:
- ivo://CDS.VizieR/J/A+A/421/455
- Title:
- Interplanetary Scintillation Pushchino Survey II
- Short Name:
- J/A+A/421/455
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of optical identification of 248 interplanetary scintillating (IPS) radio sources from the Pushchino Survey (PS) in the area of 0.11sr with the center at RA=10h28m, DE=+41{deg}. All 260 counterparts of IPS radio sources from the 7C and FIRST catalogues, which had been found in Paper I (Cat. <J/A+A/403/555>), were considered. We used USNO-B1.0 catalogue (limiting magnitude m_R_~21) for the optical identification and searched the literature to find optical data for fainter objects. Photometric and spectroscopic observations were conducted on the 1m and 6m telescopes of SAO RAS. Optical magnitudes or deep limits for 22 objects and redshifts for 26 ones have been obtained. In total, we collected optical data for 116 (68 with redshift) counterparts of the PS radio sources. For the subsample of the PS quasars (41 objects) the redshift distribution was compared to those of several other samples of quasars (BRL, 3CRR, MQS, B3-VLA, 7CRS I-III and PKS 0.25Jy) which have complete or nearly complete redshift information.
- ID:
- ivo://CDS.VizieR/J/MNRAS/229/589
- Title:
- Interplanetary Scintillation Survey at 81.5 MHz
- Short Name:
- J/MNRAS/229/589
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A catalog of 1789 radio sources which exhibit interplanetary scintillation (IPS) at 81.5 MHz is presented. The angular diameters of scintillating components in the range 0.2-2 arcsec are listed together with values of the scintillating flux density at a solar elongation of 90 deg. IPS selects those sources which are highly compact, such as pulsars and some unusual extragalactic sources, or those in which energy is being released from active beams in the outer lobes of intrinsically powerful radio galaxies and quasars. The survey was made with the 3.6-hectare array at Cambridge and covers the area of sky between declinations -10 deg and +83 deg at all values of right ascension. The array was operated as a north-south phase-switching interferometer observing sources near meridian transit. Sixteen declination beams were produced covering the observed declination range. The half-power width of a declination beam is 5.5 sec(52.16-DEC) degrees, where DEC is the declination of peak beam response. The half-power beam width in right ascension is 107 sec(delta) s for a source at declination delta. The faintest sources in the catalogue have scintillating flux densities of about 0.3 Jy rms at a solar elongation of 90 deg, and total flux densities of about 5 Jy at 81.5 MHz. The sensitivity of the survey is not uniform over the sky, being determined largely by the galactic background emission. The flux density corresponding to one source per beam area in this survey is about 2.3 Jy at 81.5 MHz so that confusion errors are likely to be significant for total flux density S <= 20 Jy.
- ID:
- ivo://CDS.VizieR/J/ApJS/165/439
- Title:
- Interstellar scintillation at 2 and 8GHz
- Short Name:
- J/ApJS/165/439
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- From 1979 to 1996 the Green Bank Interferometer was used by the Naval Research Laboratory to monitor the flux density from 146 compact radio sources at frequencies near 2 and 8GHz. We filter the light curves to separate intrinsic variations on times of a year or more from more rapid interstellar scintillation (ISS) on times of 550 days. Whereas the intrinsic variation at 2GHz is similar to that at 8GHz (although diminished in amplitude), the ISS variation is much stronger at 2 than at 8GHz. We characterize the ISS variation by an rms amplitude and a timescale and examine the statistics of these parameters for the 121 sources with significant ISS at 2GHz. We model the scintillations using the NE2001 Galactic electron model assuming the sources are brightness-limited.
- ID:
- ivo://CDS.VizieR/J/A+AS/132/211
- Title:
- Interstellar SiO sources
- Short Name:
- J/A+AS/132/211
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of a survey of SiO emission using the 15-m SEST and the 20-m Onsala telescope are presented in two tables. The sample contains altogether 369 objects including 270 H2O masers, 19 OH masers and 62 IRAS sources with colours typical for ultracompact HII regions. The remaining target sources consist of dust continuum peaks a CS emission peak near H2O masers (12) and Herbig-Haro objects (6). The entries are arranged according to increasing right ascension.
- ID:
- ivo://CDS.VizieR/J/A+A/305/960
- Title:
- Interstellar S isotopes
- Short Name:
- J/A+A/305/960
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A ^12^C^32^S, ^13^C^32^S, ^12^C^34^S, and ^12^C^33^S J=2-1 line survey has been made to study interstellar ^32^S/^34^S and ^34^S/^33^S ratios from the galactic disk. The four CS isotopomers were detected in 20 star forming regions with galactocentric distances between 3 and 9kpc. From a comparison of line velocities, the C^33^S J=2-1 rest frequency is ~250kHz below the value given in the Lovas (1992) catalog. Taking ^12^C/^13^C ratios from Wilson & Rood (1994) and assuming equal ^12^C^32^S and ^13^C^32^S excitation temperatures and beam filling factors, ^12^C^32^S opacities are in the range 3 to 15; average ^32^S/^34^S and ^34^S/^33^S isotope ratios are 24.4+/-5.0 and 6.27+/-1.01, respectively. While no systematic variation in the ^34^S/^33^S isotope ratio is found, the ^32^S/^34^S ratio increases with galactocentric distance when accounting for the ^12^C/^13^C gradient of the galactic disk. A fit to the unweighted data yields ^32^S/^34^S=3.3+/-0.5(D_GC_/kpc)+4.1+/-3.1 with a correlation coefficient of 0.84. Since the interstellar sulfur (S) isotopes are synthesized by oxygen burning in massive stars, consequences for nucleosynthesis and models of chemical evolution are briefly discussed.
- ID:
- ivo://CDS.VizieR/J/ApJS/241/2
- Title:
- Ionization profiles of 8 Galactic H II regions
- Short Name:
- J/ApJS/241/2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using Green Bank Telescope radio recombination line (RRL) data, we analyze the role of leaking radiation from HII regions in maintaining the ionization of the interstellar medium (ISM). We observed a sample of eight Galactic HII regions of various sizes, morphologies, and luminosities. For each region, the hydrogen RRL intensity decreases roughly as a power-law with the distance from the center of the region. This suggests that radiation leaking from the HII region is responsible for the majority of surrounding ionized gas producing RRL emission. Our results further indicate that the hydrogen RRL intensity appears to be fundamentally related to the HII region sizes traced by their photodissociation regions, such that physically smaller HII regions show a steeper decrease in intensity with an increasing distance from the region centers. As a result, giant HII regions may have a much larger effect in maintaining the ionization of the ISM. For six of the eight observed HII regions, we find a decrease in the ^4^He^+^/H^+^ abundance ratio with an increasing distance, indicating that He-ionizing photons are being absorbed within the ionization front of the HII region. There is enhanced carbon RRL emission toward directions with strong continuum background, suggesting that the carbon emission is amplified by stimulated emission.
- ID:
- ivo://CDS.VizieR/J/ApJ/756/72
- Title:
- IRAC identifications for 510 AEGIS20 radio sources
- Short Name:
- J/ApJ/756/72
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Infrared 3.6-8{mu}m images of the Extended Groth Strip yield plausible counterpart identifications for all but one of 510 radio sources in the AEGIS20 S(1.4GHz)>50{mu}Jy sample. This is the first such deep sample that has been effectively 100% identified. Achieving the same identification rate at R band would require observations reaching R_AB_>27. Spectroscopic redshifts are available for 46% of the sample and photometric redshifts for an additional 47%. Almost all of the sources with 3.6{mu}m AB magnitudes brighter than 19 have spectroscopic redshifts z<1.1, while fainter objects predominantly have photometric redshifts with 1<~z<~3. Unlike more powerful radio sources that are hosted by galaxies having large stellar masses within a relatively narrow range, the AEGIS20 counterparts have stellar masses spanning more than a factor of 10 at z~1. The sources are roughly 10%-15% starbursts at z<~0.5 and 20%-25% active galactic nuclei mostly at z>1 with the remainder of uncertain nature.
