According to the Fermi Large Area Telescope Second Source Catalog (2FGL), about one-third of the gamma -ray sources listed have no assigned counterparts at lower energies. Many statistical methods ...have been developed to find proper counterparts for these sources. We explore the sky area covered at low radio frequency by the Westerbork in the Southern Hemisphere (WISH) survey to search for blazar-like associations among the unidentified gamma -ray sources (UGSs) listed in the 2FGL. Searching the WISH and NRAO Very Large Array Sky Survey radio surveys within the positional uncertainty regions of the 2FGL UGSs, we select as gamma -ray blazar candidates the radio sources characterized by flat radio spectra between 352 MHz and 1400 MHz. We propose new gamma -ray blazar associations for eight UGSs and we also discuss their spectral properties at low radio frequencies. We compare the radio flux density distribution of the low radio frequency gamma -ray blazar candidates with that of gamma -ray blazars associated with other methods. We find significant differences between these distributions. Finally, we discuss the results of this association method and its possible applicability to other regions of the sky and future radio surveys.
Context.Many of the extragalactic sources detected in γ rays at TeV energies are BL Lac objects. In particular, they belong to the subclass of “high frequency peaked BL Lacs” (HBLs), as their ...spectral energy distributions exhibit a first peak in the X-ray band. At a closer look, their X-ray spectra appear to be generally curved into a log-parabolic shape. In a previous investigation of Mrk 421, two correlations were found between the spectral parameters. One involves the height Sp increasing with the position Ep of the first peak; this was interpreted as a signature of synchrotron emission from relativistic electrons. The other involves the curvature parameter b decreasing as Ep increases; this points toward statistical/stochastic acceleration processes for the emitting electrons. Aims.We analyse X-ray spectra of several TeV HBLs to pinpoint their behaviours in the $E_{\rm p}-S_{\rm p}$ and $E_{\rm p}-b$ planes and to compare them with Mrk 421. Methods.We perfom X-ray spectral analyses of a sample of 15 BL Lacs. We report the whole set of observations obtained with the BeppoSAX, XMM-Newton and Swift satellites between 29/06/96 and 07/04/07. We focus on five sources (PKS 0548-322, 1H 1426+418, Mrk 501, 1ES 1959+650, PKS 2155-304) whose X-ray observations warrant detailed searching of correlations or trends. Results.Within our database, we find that four out of five sources, namely PKS 0548-322, 1H 1426+418, Mrk 501 and 1ES 1959+650, follow similar trends as Mrk 421 in the $E_{\rm p}-S_{\rm p}$ plane, while PKS 2155-304 differs. As for the $E_{\rm p}-b$ plane, all TeV HBLs follow a similar behaviour. Conclusions.The trends exhibited by Mrk 421 appear to be shared by several TeV HBLs, such as to warrant discussing predictions from the X-ray spectral evolution to that of TeV emissions.
We report the results of our exploratory program carried out with the southern Astrophysical Research telescope aimed at associating counterparts and establishing the nature of the Fermi Unidentified ...gamma -ray Sources (UGSs). We selected the optical counterparts of six UGSs from the Fermi catalog on the basis of our recently discovered tight connection between infrared and gamma -ray emission found for the gamma -ray blazars detected by the Wide-Field Infrared Survey Explorer in its all-sky survey. We perform for the first time a spectroscopic study of the low-energy counterparts of the Fermi UGSs, in the optical band, confirming the blazar-like nature of the whole sample. We also present new spectroscopic observations of six active galaxies of uncertain type associated with Fermi sources which appear to be BL Lac objects. Finally, we report the spectra collected for six known gamma -ray blazars belonging to the Roma BZCAT that were obtained to establish their nature or better estimate their redshifts. Two interesting cases of high redshift and extremely luminous BL Lac objects (z > or =, slanted 1.18 and z > or =, slanted 1.02, based on the detection of Mg II intervening systems) are also discussed.
We present the analysis of nine radio sources belonging to the Third Cambridge Revised catalog (3CR) observed with Chandra during Cycle 20 in the redshift range between 1.5 and 2.5. This study ...completes the 3CR Chandra Snapshot Survey thus guaranteeing the X-ray coverage of all 3CR sources identified to date. This sample lists two compact steep spectrum sources, four radio galaxies, and three quasars. We detected X-ray emission from all nuclei, with the only exception of 3C 326.1 and 3C 454.1 and from radio lobes in six out of nine sources at a level of confidence larger than ∼5 . We measured X-ray fluxes and luminosities for all nuclei and lobes in the soft (0.5-1 keV), medium (1-2 keV), and hard (2-7 keV) X-ray bands. Since the discovered X-ray extended emission is spatially coincident with the radio structure in all cases, its origin could be due to inverse Compton (IC) scattering of the cosmic microwave background (CMB) occurring in radio lobes.
In our previous analysis we investigated the large-scale environment of two samples of radio galaxies (RGs) in the local universe (i.e., with redshifts zsrc ≤ 0.15), classified as FR I and FR II on ...the basis of their radio morphology. The analysis was carried out using (i) extremely homogeneous catalogs and (ii) a new method, known as cosmological overdensity, to investigate their large-scale environments. We concluded that, independently of the shape of their radio extended structure, RGs inhabit galaxy-rich large-scale environments with similar characteristics and richness. In the present work, we first highlight additional advantages of our procedure, which does not suffer cosmological biases and/or artifacts, and then we carry out an additional statistical test to strengthen our previous results. We also investigate properties of RG environments using those of the cosmological neighbors. We find that large-scale environments of both FR Is and FR IIs are remarkably similar and independent of the properties of central RG. Finally, we highlight the importance of comparing radio sources in the same redshift bins to obtain a complete overview of their large-scale environments.
ABSTRACT
Giant radio galaxies (GRGs), with extended structures reaching hundreds of kpc, are among the most spectacular examples of ejection of relativistic plasma from supermassive black holes. In ...this work, third of a series, we present Low-Frequency Array (LOFAR) images at 144 MHz, collected in the framework of the LOFAR Two-metre Sky Survey Data Release 2 (LoTSS DR2), for nine sources extracted from our sample of hard X-ray-selected GRGs (HXGRGs, i.e. from INTEGRAL/Imager on-Board the INTEGRAL Satellite and Swift/Burst Alert Telescope catalogues at >20 keV). Thanks to the resolution and sensitivity of LoTSS, we could probe the complex morphology of these GRGs, unveiling cases with diffuse (Mpc-scale) remnant emission, presence of faint off-axis wings, or a misaligned inner jet. In particular, for one source (B2 1144+35B), we could clearly detect a ∼300 kpc wide off-axis emission, in addition to an inner jet whose orientation is not aligned with the lobes axis. For another source (J1153.9+5848), a structure consistent with jet precession was revealed, appearing as an X-shaped morphology with relic lobes having an extension larger than the present ones, and with a different axis orientation. From an environment analysis, we found two sources showing an overdensity of cosmological neighbours, and a correspondent association with a galaxy cluster from catalogues. Finally, a comparison with radio-selected GRGs from LoTSS DR1 suggested that, on average, HXGRGs can grow to larger extents. These results highlight the importance of deep low-frequency observations to probe the evolution of radio galaxies, and ultimately estimate the duty cycle of their jets.
Abstract
We present new Karl G. Jansky Very Large Array (VLA, 1.5 GHz) radio data for the giant elliptical galaxy IC 4296, supported by archival radio, X-ray (Chandra, and XMM–Newton) and optical ...(SOAR, and HST) observations. The galaxy hosts powerful radio jets piercing through the inner hot X-ray emitting atmosphere, depositing most of the energy into the ambient intracluster medium (ICM). Whereas the radio surface brightness of the A configuration image is consistent with a Fanaroff–Riley Class I system, the D configuration image shows two bright, relative to the central region, large (${\sim } 160\, \rm {kpc}$ diameter), well-defined lobes, previously reported by Killeen et al., at a projected distance $r\gtrsim 230\, \rm {kpc}$. The XMM–Newton image reveals an X-ray cavity associated with one of the radio lobes. The total enthalpy of the radio lobes is ${\sim }7\times 10^{59}\, \rm {erg}$ and the mechanical power output of the jets is ${\sim } 10^{44}\, \rm {erg\, s}^{-1}$. The jets are mildly curved and possibly rebrightened by the relative motion of the galaxy and the ICM. The lobes display sharp edges, suggesting the presence of bow shocks, which would indicate that they are expanding supersonically. The central entropy and cooling time of the X-ray gas are unusually low and the nucleus hosts a warm Hα + $\rm{N\,{\small II}}$ nebula and a cold molecular CO disc. Because most of the energy of the jets is deposited far from the nucleus, the atmosphere of the galaxy continues to cool, apparently feeding the central supermassive black hole and powering the jet activity.
BLAZAR SPECTRAL PROPERTIES AT 74 MHz Massaro, F; Giroletti, M; Paggi, A ...
The Astrophysical journal. Supplement series,
10/2013, Letnik:
208, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Blazars are the most extreme class of active galactic nuclei. Despite a previous investigation at 102 MHz for a small sample of BL Lac objects and our recent analysis of blazars detected in the ...Westerbork Northern Sky Survey, a systematic study of the blazar spectral properties at frequencies below 100 MHz has been never carried out. In this paper, we present the first analysis of the radio spectral behavior of blazars based on the recent Very Large Array Low-frequency Sky Survey (VLSS) at 74 MHz. We search for blazar counterparts in the VLSS catalog, confirming that they are detected at 74 MHz. We then show that blazars present radio-flat spectra (i.e., radio spectral indices of ~0.5) when evaluated, which also about an order of magnitude in frequency lower than previous analyses. Finally, we discuss the implications of our findings in the context of the blazars-radio galaxies connection since the low-frequency radio data provide a new diagnostic tool to verify the expectations of the unification scenario for radio-loud active galaxies.
We present arcsecond-resolution data in the radio, IR, optical, and X-ray for 4C+19.44 (=PKS 1354+195), the longest and straightest quasar jet with deep X-ray observations. We report results from ...radio images with half to one arcsecond angular resolution at three frequencies, plus Hubble Space Telescope and Spitzer data. The Chandra data allow us to measure the X-ray spectral index in 10 distinct regions along the 18″ jet and compare with the radio index. The radio and X-ray spectral indices of the jet regions are consistent with a value of throughout the jet, to within uncertainties. The X-ray jet structure to the south extends beyond the prominent radio jet and connects to the southern radio lobe, and there is extended X-ray emission, both in the direction of the unseen counter-jet, and also coincident with the northern radio lobe. This jet is remarkable because its straight appearance over a large distance allows the geometry factors to be taken as fixed along the jet. Using the model of inverse Compton scattering of the cosmic microwave background (iC/CMB) by relativistic electrons, we find that the magnetic field strengths and Doppler factors are relatively constant along the jet. If instead the X-rays are synchrotron emission, they must arise from a population of electrons distinct from the particles producing the radio synchrotron spectrum.
PURPOSE: We sought to determine the effects of a communication process that was designed to encourage the use of advanced supportive technology when it is of benefit, but to limit its burdens when it ...is ineffective. We compared usual care with a proactive, multidisciplinary method of communicating that prospectively identified for patients and families the criteria that would determine whether a care plan was effective at meeting the goals of the patient. This process allowed caregivers to be informed of patient preferences about continued advanced supportive technology when its continuation would result in a compromised functional outcome or death.
MATERIALS AND METHODS: We performed a before-and-after study in 530 adult medical patients who were consecutively admitted to a university tertiary care hospital for intensive care. Multidisciplinary meetings were held within 72 hours of critical care admission. Patients, families, and the critical care team discussed the care plan and the patients’ goals and expectations for the outcome of critical care. Clinical “milestones” indicative of recovery were identified with time frames for their occurrence. Follow-up meetings were held to discuss palliative care options when continued advanced supportive technology was not achieving the patient’s goals. We measured length of stay, mortality, and provider team and family consensus in 134 patients before the intensive communication intervention and in 396 patients after the intervention.
RESULTS: Intensive communication significantly reduced the median length of stay from 4 days (interquartile range, 2 to 11 days) to 3 days (2 to 6 days,
P = 0.01 by survival analysis). This reduction remained significant after adjustment for acute physiology and chronic health evaluation (APACHE) 3 score risk ratio (RR) = 0.81; 95% confidence interval (CI), 0.66 to 0.99;
P = 0.04). Subgroup analysis revealed that this reduction occurred in our target group, patients with acuity scores in the highest quartile who died (RR = 0.60; 95% CI, 0.38 to 0.92;
P = 0.02). The intervention, which allowed dying patients earlier access to palliative care, was not associated with increased mortality.
CONCLUSIONS: Intensive communication was associated with a reduction in critical care use by patients who died. Our multidisciplinary process targeted advanced supportive technology to patients who survived and allowed the earlier withdrawal of advanced supportive technology when it was ineffective.
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