Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userRBSC-NVSS Sample. I. Radio and Optical Identifications of a Complete Sample of 1500 Bright X-ray Sources
122
0
0.0
(
0
)
Authors
F. E. Bauer
Ask ChatGPT about the research
No Arabic abstract
We cross-identified the ROSAT Bright Source Catalog (RBSC) and the NRAO VLA Sky Survey (NVSS) to construct the RBSC-NVSS sample of the brightest X-ray sources (>= 0.1 counts/s or ~1E-12 ergs/cm/cm/s in the 0.1-2.4 keV band) that are also radio sources (S >= 2.5 mJy at 1.4 GHz) in the 7.8 sr of extragalactic sky with |b| > 15 degrees. and delta > -40 degrees. The sky density of NVSS sources is low enough that they can be reliably identified with RBSC sources having average rms positional uncertainties = 10 arcsec. We used the more accurate radio positions to make reliable X-ray/radio/optical identifications down to the POSS plate limits. We obtained optical spectra for many of the bright identifications lacking published redshifts. The resulting X-ray/radio sample is unique in its size (N ~ 1500 objects), composition (a mixture of nearly normal galaxies, Seyfert galaxies, quasars, and clusters), and low average redshift (<z> ~ 0.1).
rate research
Read More
We present high sensitivity polarimetric observations in 6 bands covering the 5.5-38 GHz range of a complete sample of 53 compact extragalactic radio sources brighter than 200 mJy at 20 GHz. The observations, carried out with the Australia Telescope Compact Array (ATCA), achieved a 91% detection rate (at 5 sigma). Within this frequency range the spectra of about 95% of sources are well fitted by double power laws, both in total intensity and in polarisation, but the spectral shapes are generally different in the two cases. Most sources were classified as either steep- or peaked-spectrum but less than 50% have the same classification in total and in polarised intensity. No significant trends of the polarisation degree with flux density or with frequency were found. The mean variability index in total intensity of steep-spectrum sources increases with frequency for a 4-5 year lag, while no significant trend shows up for the other sources and for the 8 year lag. In polarisation, the variability index, that could be computed only for the 8 year lag, is substantially higher than in total intensity and has no significant frequency dependence.
We present a carefully selected sub-sample of Swift Long Gamma-ray Bursts (GRBs), that is complete in redshift. The sample is constructed by considering only bursts with favorable observing conditions for ground-based follow-up searches, that are bright in the 15-150 keV Swift/BAT band, i.e. with 1-s peak photon fluxes in excess to 2.6 ph s^-1 cm^-2. The sample is composed by 58 bursts, 52 of them with redshift for a completeness level of 90%, while another two have a redshift constraint, reaching a completeness level of 95%. For only three bursts we have no constraint on the redshift. The high level of redshift completeness allows us for the first time to constrain the GRB luminosity function and its evolution with cosmic times in a unbiased way. We find that strong evolution in luminosity (d_l=2.3pm 0.6) or in density (d_d=1.7pm 0.5) is required in order to account for the observations. The derived redshift distribution in the two scenarios are consistent with each other, in spite of their different intrinsic redshift distribution. This calls for other indicators to distinguish among different evolution models. Complete samples are at the base of any population studies. In future works we will use this unique sample of Swift bright GRBs to study the properties of the population of long GRBs.
Starting from the Swift sample we define a complete sub-sample of 58 bright long Gamma Ray Bursts (GRB), 55 of them (95%) with a redshift determination, in order to characterize their properties. Our sample (BAT6) allows us to study the properties of the long GRB population and their evolution with cosmic time. We focus in particular on the GRB luminosity function, on the spectral-energy correlations of their prompt emission, on the nature of dark bursts, on possible correlations between the prompt and the X-ray afterglow properties, and on the dust extinction.
We present the X-ray properties of a sample of 17 radio sources observed with the Chandra X-ray Observatory as part of a project aimed at studying the X-ray emission from their radio jets. In this paper, we concentrate on the X-ray properties of the unresolved cores. The sample includes 16 quasars (11 core-dominated and 5 lobe-dominated) in the redshift range z=0.30--1.96, and one low-power radio-galaxy at z=0.064. No diffuse X-ray emission is present around the cores of the quasars, except for the nearby low-power galaxy that has diffuse emission on a scale and with a luminosity consistent with other FRIs. No high-amplitude, short-term variability is detected within the relatively short Chandra exposures. However, 1510-089 shows low-amplitude flux changes with a timescale of $sim$25 minutes. The X-ray spectra of the quasar cores are generally well described by a single power law model with Galactic absorption. However, in six quasars we find soft X-ray excess emission below 1.6 keV. Interestingly, we detect an Fe K-shell emission line, consistent with fluorescent Kalpha emission from cold Iron, in one lobe- and two core-dominated sources. The average X-ray photon index for the quasars in the sample is Gamma=1.66 and dispersion, sigma=0.23. The average spectral slope for our sample is flatter than the slope found for radio-quiet quasars and for radio-loud AGNs with larger jet orientations; this indicates that beaming affects the X-ray emission from the cores in our sample of quasars.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
