- ID:
- ivo://CDS.VizieR/J/ApJS/197/24
- Title:
- Chandra large-scale extragalactic jets. I.
- Short Name:
- J/ApJS/197/24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we report the first stages of an investigation into the X-ray properties of extragalactic jets (XJET project). Our approach is to subject all sources for which X-ray emission has been detected by Chandra to uniform reduction procedures. Using Chandra archival data for 106 such sources, we measure X-ray fluxes in three bands and compare these to radio fluxes. We discuss the sample, the reduction methods, and present first results for the ratio of X-ray to radio flux for jet knots and hotspots. In particular, we apply statistical tests to various distributions of key observational parameters to evaluate differences between the different classes of sources.
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- ID:
- ivo://CDS.VizieR/J/ApJ/740/87
- Title:
- Chandra observations of radio transients
- Short Name:
- J/ApJ/740/87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a 50ks Chandra/ACIS-I X-ray observation of the Bower et al. (2007ApJ...666..346B) Very Large Array archival field. The observations reach a limiting sensitivity of ~10^-4^counts/s, corresponding to a flux of a few times 10^-15^erg/s/cm^2^ for the models we explore. The Chandra observations were undertaken to search for X-ray counterparts to the eight transient sources without optical counterparts, and the two transient sources with optical counterparts seen by Bower et al. Neither of the sources with optical counterparts was detected in X-rays. One of the eight optical non-detections is associated with a marginal (2.4{sigma}) X-ray detection in our Chandra image. A second optically undetected Bower et al. transient may be associated with a z=1.29 X-ray-detected quasar or its host galaxy, or alternatively is undetected in X-rays and is a chance association with the nearby X-ray source. The X-ray flux upper limits, and the one marginal detection, are consistent with the interpretation of Ofek et al. (2010ApJ...711..517O) that the optically undetected radio transients are flares from isolated old Galactic neutron stars. The marginal X-ray detection has a hardness ratio that implies a temperature too high for a simple one-temperature neutron star model, but plausible multi-component fits are not excluded, and in any case the marginal X-ray detection may be due to cosmic rays or particle background. The X-ray flux upper limits are also consistent with flare star progenitors at >~1kpc (which would require the radio luminosity of the transient to be unusually high for such an object) or less extreme flares from brown dwarfs at distances of around 100pc.
- ID:
- ivo://CDS.VizieR/J/ApJ/615/897
- Title:
- Chandra X-Ray sources in the {gamma} Cyg Field
- Short Name:
- J/ApJ/615/897
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In search of the counterpart to the brightest unidentified gamma-ray source, 3EG J2020+4017 (2CG 078+2), we report on new X-ray and radio observations of the {gamma} Cygni field with the Chandra X-Ray Observatory and with the Green Bank Telescope (GBT). We also report on reanalysis of archival ROSAT data.
- ID:
- ivo://CDS.VizieR/J/AJ/150/81
- Title:
- CHANG-ES. IV. VLA D-configuration observations
- Short Name:
- J/AJ/150/81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first part of the observations made for the Continuum Halos in Nearby Galaxies, an EVLA Survey (CHANG-ES) project. The aim of the CHANG-ES project is to study and characterize the nature of radio halos, their prevalence as well as their magnetic fields, and the cosmic rays illuminating these fields. This paper reports observations with the compact D configuration of the Karl G. Jansky Very Large Array (VLA) for the sample of 35 nearby edge-on galaxies of CHANG-ES. With the new wide bandwidth capabilities of the VLA, an unprecedented sensitivity was achieved for all polarization products. The beam resolution is an average of 9.6" and 36" with noise levels reaching approximately 6 and 30{mu}Jy/beam for C- and L-bands, respectively (robust weighting). We present intensity maps in these two frequency bands (C and L), with different weightings, as well as spectral index maps, polarization maps, and new measurements of star formation rates (SFRs). The data products described herein are available to the public in the CHANG-ES data release available at http://www.queensu.ca/changes. We also present evidence of a trend among galaxies with larger halos having higher SFR surface density, and we show, for the first time, a radio continuum image of the median galaxy, taking advantage of the collective signal-to-noise ratio of 30 of our galaxies. This image shows clearly that a "typical" spiral galaxy is surrounded by a halo of magnetic fields and cosmic rays.
- ID:
- ivo://CDS.VizieR/J/ApJ/833/248
- Title:
- Chemical properties of red MSX sources (RMSs)
- Short Name:
- J/ApJ/833/248
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Red Midcourse Space Experiment (MSX) Sources (RMSs) are regarded as excellent candidates of massive star-forming regions. In order to characterize the chemical properties of massive star formation, we made a systematic study of 87 RMSs in the southern sky, using archival data taken from the Atacama Pathfinder Experiment Telescope Large Area Survey of the Galaxy (ATLASGAL), the Australia Telescope Compact Array, and the Millimetre Astronomy Legacy Team Survey at 90GHz (MALT90). According to previous multiwavelength observations, our sample could be divided into two groups: massive young stellar objects and HII regions. Combined with the MALT90 data, we calculated the column densities of N_2_H^+^, C_2_H, HC_3_N, and HNC and found that they are not much different from previous studies made in other massive star-forming regions. However, their abundances are relatively low compared to infrared dark clouds (IRDCs). The abundances of N_2_H^+^ and HNC in our sample are at least 1mag lower than those found in IRDCs, indicating chemical depletions in the relatively hot gas. Besides, the fractional abundances of N_2_H^+^, C_2_H, and HC_3_N seem to decrease as a function of their Lyman continuum fluxes (N_L_), indicating that these molecules could be destroyed by UV photons when HII regions have formed inside. We also find that the C_2_H abundance decreases faster than HC_3_N with respect to N_L_. The abundance of HNC has a tight correlation with that of N_2_H^+^, indicating that it may be also preferentially formed in cold gas. We regard our RMSs as being in a relatively late evolutionary stage of massive star formation.
- ID:
- ivo://CDS.VizieR/J/A+A/658/A6
- Title:
- 3C293 high and low resolution maps
- Short Name:
- J/A+A/658/A6
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Active galactic nuclei (AGNs) show episodic activity, which can be evident in galaxies that exhibit restarted radio jets. These restarted jets can interact with their environment, leaving signatures on the radio spectral energy distribution. Tracing these signatures is a powerful way to explore the life of radio galaxies. This requires resolved spectral index measurements over a broad frequency range including low frequencies. We present such a study for the radio galaxy 3C293, which has long been thought to be a restarted galaxy on the basis of its radio morphology. Using the International LOFAR telescope (ILT) we probed spatial scales as fine as ~0.2-arcsec at 144MHz, and to constrain the spectrum we combined these data with Multi-Element Radio Linked Interferometer Network (MERLIN) and Very Large Array (VLA) archival data at frequencies up to 8.4GHz that have a comparable resolution. In the inner lobes (~2kpc), we detect the presence of a spectral turnover that peaks at ~225MHz and is most likely caused by free-free absorption from the rich surrounding medium. We confirm that these inner lobes are part of a jet-dominated young radio source (spectral age ~0.17Myr), which is strongly interacting with the rich int <0.27Myr. The outer lobes (extending up to ~100kpc) have a spectral index of ~0.6-0.8 from 144-4850MHz with a remarkably uniform spatial distribution and only mild spectral curvature. We propose that intermittent fuelling and jet flow disruptions are powering the mechanisms that keep the spectral index in the outer lobes from steepening and maintain the spatial uniformity of the spectral index. Overall, it appears that 3C293 has gone through multiple (two to three) epochs of activity. This study adds 3C293 to the new sub-group of restarted galaxies with short interruption time periods. This is the first time a spatially resolved study has been performed that simultaneously studies a young source as well as the older outer lobes at such low frequencies. This illustrates the potential of the International LOFAR telescope to expand such studies to a larger sample of radio galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJS/255/5
- Title:
- CHIME/Pulsar 400-800MHz obs. of ATNF pulsars
- Short Name:
- J/ApJS/255/5
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We present the design, implementation, and performance of the digital pulsar observing system constructed for the Canadian Hydrogen Intensity Mapping Experiment (CHIME). Using accelerated computing, this system processes independent, digitally steered beams formed by the CHIME correlator to simultaneously observe up to 10 radio pulsars and transient sources. Each of these independent streams is processed by the CHIME/Pulsar back-end system, which can coherently dedisperse, in real time, up to dispersion measure values of 2500pc/cm^3^. The tracking beams and real-time analysis system are autonomously controlled by a priority-based algorithm that schedules both known sources and positions of interest for observation with observing cadences as rapid as 1 day. Given the distribution of known pulsars and radio-transient sources and the dynamic scheduling, the CHIME/Pulsar system can monitor 400-500 positions once per sidereal day and observe most sources with declinations greater than -20{deg} once every ~4 weeks. We also discuss the extensive science program enabled through the current modes of data acquisition for CHIME/Pulsar that centers on timing and searching experiments.
- ID:
- ivo://CDS.VizieR/J/ApJS/155/149
- Title:
- CH_3_OH 7_0_-6_1_ A^+^ maser sources
- Short Name:
- J/ApJS/155/149
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a Very Large Array survey of 44 massive star-forming regions in the 44GHz 7_0_-6_1_ A^+^ methanol transition; 37 fields showed maser emission. Thirty-one sources were also observed in the 23GHz 9_2_-10_1_ A^+^ methanol line; two fields showed maser emission.
- ID:
- ivo://CDS.VizieR/J/A+A/563/A68
- Title:
- CH_3_OH and H_2_O Galactic center masers
- Short Name:
- J/A+A/563/A68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of star formation in the central molecular zone (CMZ) of our Galaxy through the association of three star formation indicators: 6.7GHz CH_3_OH masers, 22GHz H_2_O masers, and enhanced 4.5{mu}m emission ('green') sources. We explore how star formation in the CMZ (|l|<1.3{deg}, |b|<10') compares with that of the Galactic disk (6{deg}>l>345{deg}, |b|<2{deg}). Using an automated algorithm, we search for green sources toward 6.7GHz CH_3_OH masers detected in the Parkes Methanol Multibeam Survey. We combine these results with lists of 22GHz H_2_O masers, including our Mopra survey of the CMZ. We find that the correlation of CH_3_OH masers with green sources is a function of Galactic latitude, with a minimum close to b=0 and increasing with |b| (toward the central part of the Galaxy, 6{deg}>l>345{deg}, |b|<2{deg}). We find no significant difference between the correlation rate of CH_3_OH masers with green sources in the CMZ and the disk. This suggests that although the physical conditions of the gas are different in the CMZ from that of the Galactic disk, once gravitational instability sets in at sufficiently high densities, signatures of star formation appear to be similar in both regions. Moreover, the detection of green sources, even at the distance of the Galactic center, shows that our technique can easily identify the early stages of star formation, especially in low-extinction regions of the Galaxy. Through the association of H_2_O and CH_3_OH masers, we identify 15 star-forming sites in the CMZ. We find a higher correlation rate of coincident H_2_O and CH_3_OH masers within the CMZ compared to the Galactic disk, indicating a difference in the maser evolutionary sequence for star-forming cores in these two regions.
- ID:
- ivo://CDS.VizieR/J/other/RAA/10.67
- Title:
- CH_3_OH maser sources
- Short Name:
- J/other/RAA/10.6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the 13.7m telescope of the Purple Mountain Observatory (PMO), a survey of the J=1-0 lines of CO and its isotopes was carried out on 98 methanol maser sources in January 2008. Eighty-five sources have infrared counterparts within one arcmin.