- ID:
- ivo://CDS.VizieR/J/A+A/370/468
- Title:
- Variability of gamma-ray sources
- Short Name:
- J/A+A/370/468
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of 40 low-latitude unidentified 3EG gamma-ray sources which were found to be not positionally coincident with any known class of potential gamma-ray emitters in the Galaxy (Romero et al., 1999A&A...348..868R). We have performed a variability analysis which reveals that many of these 40 sources are variable. These sources have, in addition, a steep mean value of the gamma-ray spectral index, <{Gamma}>=2.41+/-0.2, which, combined with the high level of variability, seems to rule out a pulsar origin. The positional coincidences with uncatalogued candidates to supernova remnants were also studied. Only 7 sources in the sample are spatially coincident with these candidates, a result that is shown to be consistent with the expected level of pure chance association. A complementary search for weak radio counterparts was also conducted and the results are presented as an extensive table containing all significant point-like radio sources within the 40 EGRET fields. We argue that in order to produce the high variability, steep gamma-ray spectra, and absence of strong radio counterparts observed in some of the gamma-ray sources of our sample, a new class of objects should be postulated, and we analyze a viable candidate.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/137/5022
- Title:
- Variability of radio-bright BL Lac objects
- Short Name:
- J/AJ/137/5022
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Radio-bright BL Lacertae objects (BLOs) are typically very variable and exhibit prominent flaring. We use a sample of 24 BLOs, regularly monitored at Metsahovi Radio Observatory, to get a clear idea of their flaring behavior in the radio domain and to find possible commonalities in their variability patterns. Our goal was to compare the results given by computational timescales and the observed variability parameters determined directly from the flux curves. Also, we wanted to find out if the BLO flares adhere to the generalized shock model, which gives a schematic explanation for the physical process giving rise to the variability. We use long-term monitoring data from 4.8, 8, 14.5, 22, 37, 90, and 230GHz, obtained mainly from the University of Michigan and Metsahovi Radio Observatories. The structure function, discrete correlation function, and Lomb-Scargle periodogram timescales, calculated in a previous study, are analyzed in more detail. Also, we determine flare durations, rise and decay times, and absolute and relative peak fluxes from the monitoring data.
- ID:
- ivo://CDS.VizieR/J/ApJ/742/49
- Title:
- Variable and transient radio sources in FIRST
- Short Name:
- J/ApJ/742/49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A comprehensive search for variable and transient radio sources has been conducted using ~55000 snapshot images of the Faint Images of the Radio Sky at Twenty-cm survey (Cat. VIII/90). We present an analysis leading to the discovery of 1627 variable and transient objects down to mJy levels over a wide range of timescales (a few minutes to years). Variations observed range from 20% to a factor of 25. Multi-wavelength matching for counterparts reveals the diverse classes of objects exhibiting variability, ranging from nearby stars and pulsars to galaxies and distant quasars. Interestingly, more than half of the objects in the sample have either no classified counterparts or no corresponding sources at any other wavelength and require multi-wavelength follow-up observations. We discuss these classes of variables and speculate on the identity of objects that lack multi-wavelength counterparts.
- ID:
- ivo://CDS.VizieR/J/ApJ/737/45
- Title:
- Variable 1.4GHz radio sources from NVSS and FIRST
- Short Name:
- J/ApJ/737/45
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We augment the two widest/deepest 1.4GHz radio surveys, the NRAO VLA Sky Survey (NVSS) and the Faint Images of the Radio Sky at Twenty centimeters (FIRST), with the mean epoch in which each source was observed. We use these catalogs to search for unresolved sources that vary between the FIRST and NVSS epochs. We find 43 variable sources (0.1% of the sources) that vary by more than 4{sigma}, and we construct the mean structure function of these objects. This enables us to explore radio variability on timescales between several months and about five years. We find that, on these timescales, the mean structure function of the variable sources is consistent with a flat structure function. A plausible explanation to these observations is that a large fraction of the variability at 1.4GHz is induced by scintillations in the interstellar medium, rather than by intrinsic variability. Finally, for a subsample of the variables for which the redshift is available, we do not find strong evidence for a correlation between the variability amplitude and the source redshift.
- ID:
- ivo://CDS.VizieR/J/ApJ/622/187
- Title:
- Velocity of eight RASSCALS galaxy groups
- Short Name:
- J/ApJ/622/187
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the distribution of gas pressure and entropy in eight groups of galaxies belonging to the ROSAT All-Sky Survey/Center for Astrophysics Loose Systems (RASSCALS, Cat. <J/ApJ/534/114>). We use archival and proprietary XMM-Newton observations, supplementing the X-ray data with redshifts derived from the literature; we also list 125 new redshifts measured with the Gemini North telescope.
- ID:
- ivo://CDS.VizieR/J/AJ/133/2487
- Title:
- VERA 22GHz Fringe Search Survey
- Short Name:
- J/AJ/133/2487
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents results of a survey search for bright compact radio sources at 22GHz with the VERA radio interferometer. Each source from a list of 2494 objects was observed in one scan for 2 minutes. The purpose of this survey was to find compact extragalactic sources bright enough at 22GHz to be useful as phase calibrators. Observed sources were either (1) within 6{deg} of the Galactic plane, or (2) within 11{deg} of the Galactic center, or (3) within 2{deg} of known water masers. Among the observed sources, 549 were detected, including 180 extragalactic objects that were not previously observed with the very long baseline interferometry technique. Estimates of the correlated flux densities of the detected sources are presented. It was found that the probability of detecting a 200mJy source with 120s of integration time is 60%.
- ID:
- ivo://CDS.VizieR/J/MNRAS/360/340
- Title:
- Very Small Array. Flux density at 33GHz
- Short Name:
- J/MNRAS/360/340
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe the source subtraction strategy and observations for the extended Very Small Array (VSA), a cosmic microwave background interferometer operating at 33GHz. A total of 453 sources were monitored at 33GHz using a dedicated source subtraction baseline. 131 sources brighter than 20mJy were directly subtracted from the VSA visibility data. Some characteristics of the subtracted sources, such as spectra and variability, are discussed. The 33GHz source counts are estimated from a sample selected at 15GHz. The selection of VSA fields in order to avoid bright sources introduces a bias into the observed counts. This bias is corrected and the resulting source count is estimated to be complete in the flux-density range 20114mJy. The 33GHz source counts are used to calculate a correction to the VSA power spectrum for sources below the subtraction limit.
- ID:
- ivo://CDS.VizieR/J/MNRAS/341/1066
- Title:
- Very Small Array. II. CMB at 34GHz
- Short Name:
- J/MNRAS/341/1066
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have observed the cosmic microwave background (CMB) temperature fluctuations in eight fields covering three separated areas of sky with the Very Small Array at 34GHz. A total area of 101 square degrees has been imaged, with sensitivity on angular scales of 3.6{deg}-0.4{deg} (equivalent to angular multipoles l=150-900).
- ID:
- ivo://CDS.VizieR/J/A+A/453/911
- Title:
- VLA and IR observations of the S235A-B region
- Short Name:
- J/A+A/453/911
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on new aspects of the star-forming region S235AB revealed through high-resolution observations at radio and mid-infrared wavelengths. Using the Very Large Array, we carried out sensitive observations of S235AB in the cm continuum (6, 3.6, 1.3, and 0.7) and in the 22GHz water maser line. These were complemented with Spitzer Space Telescope Infrared Array Camera archive data to clarify the correspondence between radio and IR sources. We made also use of newly presented data from the Medicina water maser patrol, started in 1987, to study the variability of the water masers found in the region.
- ID:
- ivo://CDS.VizieR/J/A+A/640/A109
- Title:
- VLA and XMM-EPIX maps of M83
- Short Name:
- J/A+A/640/A109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Reconnection heating has been considered as a potential source of the heating of the interstellar medium. In some galaxies, significant polarised radio emission has been found between the spiral arms. This emission has a form of 'magnetic arms' that resembles the spiral structure of the galaxy. Reconnection effects could convert some of the energy of the turbulent magnetic field into the thermal energy of the surrounding medium, leaving more ordered magnetic fields, as is observed in the magnetic arms. Sensitive radio and X-ray data for the grand-design spiral galaxy M 83 are used for a detailed analysis of the possible interactions of magnetic fields with hot gas, including a search for signatures of gas heating by magnetic reconnection effects. Magnetic field strengths and energies derived from the radio emission are compared with the parameters of the hot gas calculated from the model fits to sensitive X-ray spectra of the hot gas emission. The available X-ray data allowed us to distinguish two thermal components in the halo of M 83. We found slightly higher average temperatures of the hot gas in the interarm regions, which results in higher energies per particle and is accompanied by a decrease in the energy density of the magnetic fields. The observed differences in the energy budget between the spiral arms and the interarm regions suggest that, similar to the case of another spiral galaxy NGC 6946, we may be observing hints for gas heating by magnetic reconnection effects in the interarm regions. These effects, which act more efficiently on the turbulent component of the magnetic field, are expected to be stronger in the spiral arms. However, with the present data it is only possible to trace them in the interarm regions, where the star formation and the resulting turbulence is low.
