Chance coincidences and the so-called redshift systems in the absorption spectrum of PKS 0237-23

It is shown that the number of redshift systems based on Civ doublets, proposed by Borosonet al. (1978) in the absorption spectrum of the quasar PKS 0237-23, is insignificantly different from that that would be expected from chance coincidences. Consequently, these systems and theirz-values appear to be devoid of any physical significance.     

The redshift distribution of quasar absorption lines and its origin

We have made statistical analyses of current data on the absorption line redshifts of quasars. All our results, including the distribution of relative velocities and the power-spectrum of the redshift distribution of absorption systems, are in favour of the cosmological hypothesis of the origin of the quasar absorption lines. We point out that the peaks in the relative velocity distribution are no compelling evidence for the rival, intrinsic hypothesis because they can be well explained by the model of density perturbation in the early universe [10].     

On the time evolution of quasar luminosity and redshift distribution

The possibility to predict the redshift distribution on the basis of certain assumptions about the time-dependence of quasar luminosity is discussed. It is found that for a certain general class of models that resembles the spinar model for quasars only specific combinations of parameters give rise to acceptable results. Further consequences are discussed.     

New perspective about the existence of a supermassive black hole in a quasar with double redshift systems

Research of several years has confirmed the general aspect that the most acceptable model in quasars' nuclei is a rotating Kerr black hole.Assuming the Kerr type potential given by the equation:

Variability in the southern blazars PKS 1921-293 and PKS 2155-152

We report results of 1435 MHz rapid variability observations of the southern extragalactic sources PKS 1921-293 and PKS 2155-152. Both objects displayed variability in their flux densities on timescales of the order of one and two weeks, respectively. A brief discussion on the origin of this variability is presented, with a comparison of different models that could account for the observations.Fellow of CONICET.     

Deconvolution of quasar images from point-spread function: Application to 3C 273, PKS 2135+147, and PKS 0812+020

The photometric structure of the resolved quasars 3C 273, PKS 2135+147, and PKS 0812+020 has been restored by an effective deconvolution procedure from observed photographic profiles and PFSs given by Wyckoffet al. (1981). Three well-defined components have been found in quasars: (1) the central point-like source, containing about 75% of the total light, (2) an intermediate region of about 10 kpc radius, whose luminosity seems to depend on the quasar's absolute luminosity, and (3) an external region with dimensions and behaviour of the brightness profile typical of giant elliptical and cD galaxies. The apperance of the photographic images of quasars with underlying nebulosities is discussed on the grounds of reliable extended PFSs and distances. An extensive discussion is devoted to the numerical aspects of deconvolution, which belongs to the class of ill-posed inverse problems. The regularization method, which avoids the numerical instabilities arising in such problems as well in the estimation of many nonlinear parameters is also described.     

On variations in the fine-structure constant and stellar pollution of quasar absorption systems

At redshifts   z _abs≲ 2  , quasar absorption-line constraints on space–time variations in the fine-structure constant, α, rely on the comparison of Mg  ii and Fe  ii transition wavelengths. One potentially important uncertainty is the relative abundance of Mg isotopes in the absorbers, which, if different from solar, can cause spurious shifts in the measured wavelengths and, therefore, α. Here we explore chemical evolution models with enhanced populations of intermediate-mass (IM) stars, which, in their asymptotic giant branch phase, are thought to be the dominant factories for heavy Mg isotopes at the low metallicities typical of quasar absorption systems. By design, these models partially explain recent Keck/HIRES evidence for a smaller α in   z _abs < 2  absorption clouds than on Earth. However, such models also overproduce N, violating observed abundance trends in high- z _abs damped Lyman-α (DLA) systems. Our results do not support the recent claim of Ashenfelter et al. that similar models of IM-enhanced initial mass functions (IMFs) may simultaneously explain the HIRES varying-α data and DLA N abundances. We explore the effect of the IM-enhanced model on Si, Al and P abundances, finding it to be much less pronounced than for N. We also show that the ¹³C/¹²C ratio, as measured in absorption systems, could constitute a future diagnostic of non-standard models of the high-redshift IMF.     

The heating of the X-ray gas by the radiogas in the cluster PKS 0745-191

Calculations of the energy evolution of relativistic particles in a cluster of galaxies are presented. The heating of the X-ray gas by the radio gas in the cluster PKS 0745-191 is derived using Chandra X-ray data and VLA radio data. It is found that the heating is not sufficient for the radiation loss of the X-ray gas if the lower limit of energy in the power-law spectrum of relativistic electrons is set at 0.001 erg.     

The brightness temperature problem in extreme intra-day variable quasars: a model for PKS 0405-385

I re-examine the brightness temperature problem in PKS 0405-385, which is an extreme intra-day variable radio quasar with an inferred brightness temperature of  ∼5 × 10¹⁴ K  at 5 GHz, well above the Compton catastrophe limit of  ∼10¹¹ K  that is reached when the synchrotron photon energy density exceeds the energy density of the magnetic field. If one takes into account the uncertainty in the distance to the ionized clouds responsible for interstellar scintillation causing rapid intra-day variability in PKS 0405-385, it is possible that the brightness temperature could be as low as  ∼10¹³ K  at 5 GHz, or even lower. The radio spectrum can be fitted by optically thin emission from mono-energetic electrons, or an electron spectrum with a low-energy cut-off such that the critical frequency of the lowest energy electrons is above the radio frequencies of interest. If one observes optically thin emission along a long narrow emission region, the average energy density in the emission region can be many orders of magnitude lower than calculated from the observed intensity if one assumed a spherical emission region. I discuss the physical conditions in the emission region and find that the Compton catastrophe can then be avoided using a reasonable Doppler factor. I also show that MeV to 100-GeV gamma-ray emission at observable flux levels should be expected from extreme intra-day variable sources such as PKS 0405-385.     

The quasar epoch and the stellar ages of early-type galaxies

We investigate the hypothesis that quasars formed together with the stellar populations of early-type galaxies. This hypothesis – in conjunction with the stellar ages of early-type galaxies from population synthesis models, the relation of black hole mass to bulge velocity dispersion, and the velocity dispersion distribution of spheroids from the Sloan Digital Sky Survey – completely determines the cosmic accretion history of supermassive black holes and the redshift evolution of the characteristic luminosity. On the other hand, the precise shape of the luminosity function of quasars depends on the light curve of quasars and – in the optical, but not so much in X-rays – on the covering factor of the dust surrounding the active nucleus. We find a plausible set of assumptions for which the coeval formation of supermassive black holes and elliptical galaxies is in good agreement with the observed B -band and X-ray luminosity functions of quasars.     

Interstellar Scintillation and Annual Cycles in the BL Lac Source PKS 1519-273

We have measured annual cycles in the time scales of the rapid, intra-day variability of the total and circularly polarized flux density, of the unusual BL Lac source PKS 1519–273 at 4.8 and 8.6 GHz. This data was collected at the ATCA over the last seven years, and establishes unequivocally interstellar scintillation as the principal mechanism responsible for this cm-wavelength intra-day variability.     

星系团PKS 0745-191中射电气体与X射线气体的相互作用

利用星系团PKS 0745—191中心区域的Chandra数据,研究了在中心星系的西边且沿着射电结构而分布的一团明亮X射线气体的性质,发现这团气体是低温而高密的;另由射电观测计算发现射电气体在中心星系的西边压强梯度要大于东边,这说明那团 X射线冷气体与射电气体之间存在相互作用．该冷气体可能是由射电浮力泡从中心星系带出;或者是外围冷气体受到了射电气体的支撑及扰动而形成．进一步,假设气体处在压强重力平衡状态,计算了中心区域的X射线气体的体积占有率为b=0．69±0．28,并且讨论了射电气体所包含的相对论性粒子的性质以及射电气体膨胀对冷流的影响．     

Hadronuclear interpretation of the possible neutrino emission from PKS B1424-418,GB6 J1040+0617 and PKS 1502+106

In addition to neutrino event IceCube-170922A which is observed to be associated with a γ-ray flare from blazar TXS 0506+056,there are also several neutrino eve...     

The Periodicity Analysis of Radio Flux Variability of PKS 1510-089 with the Period04 Method

We have collected the 37 GHz radio data of PKS 1510-089 from 1990 to 2005, and obtained its long-term light curve after making data processing. From the light curve we can find that the activity in PKS 1510-089 is very strong. In this paper, the Period04 method is used for the first time to analyze the light periodicity of PKS 1510-089. The result indicates that its radio emission at 37 GHz has the periods of (1.87±0.13) yr and (0.87±0.07) yr. This result is consistent with the results obtained by Xie et al. in 2004, 2005, 2008, and Wu et al. in 2005 with other methods of data analysis.     

PKS2250-41 and the Role of Jet Cloud Interactions in Powerful Radio Galaxies

We have studied the effects of the interaction between the radio jet and the ambient gas in the powerful radio galaxy PKS2250-41 (z = 0.31). Our results show that the gas has been accelerated, compressed, heated and collisionally ionized by the shock. This study helps us to understand the processes which determine the observed properties of many high redshift radio galaxies. This revised version was published online in July 2006 with corrections to the Cover Date.     

Interaction between the X-ray gas and radio gas in the galaxy cluster PKS 0745-191

By analyzing the Chandra data of the central region of the galaxy cluster PKS 0745-191, the properties of a patch of bright X-ray gas distributed along the radio structure in the west of the central galaxy are investigated. This gas is found to be cooler and denser than the ambient gas. According to the calculation based on radio observations, the pressure gradient of the radio gas in the west is greater than that in the east. It means that there is interaction between that patch of cool X-ray gas and the radio gas. The cool gas is either formed by outer cool gas supported and disturbed by the radio gas, or is brought out from the central galaxy by radio buoyant bubbles. Assuming that the gas is in pressure-gravity balance, the volume filling factor of the X-ray gas in the central region is calculated to be b = 0.69 ± 0.28, and the properties of the relativistic particles in the radio gas, as well as the expansion effect of the radio gas on the cooling flow, are discussed.     

Probing the mass and anisotropy of the Milky Way gaseous halo: sight-lines toward Mrk 421 and PKS 2155-304

We recently found that the halo of the Milky Way contains a large reservoir of warm-hot gas that accounts for large fraction of the missing baryons from the Galaxy. The average physical properties of this circumgalactic medium (CGM) are determined by combining average absorption and emission measurements along several extragalactic sightlines. However, there is a wide distribution of both, the halo emission measure and the O?vii column density, suggesting that the Galactic warm-hot gaseous halo is anisotropic. We present Suzaku observations of fields close to two sightlines along which we have precise O?vii absorption measurements with Chandra. The column densities along these two sightlines are similar within errors, but we find that the emission measures are different: 0.0025±0.0006 cm^?6?pc near the Mrk 421 direction and 0.0042±0.0008 cm^?6?pc close to the PKS 2155-304 sightline. Therefore the densities and pathlengths in the two directions must be different, providing a suggestive evidence that the warm-hot gas in the CGM of the Milky Way is not distributed uniformly. However, the formal errors on derived parameters are too large to make such a claim. In the Mrk 421 direction we derive the density of \(1.6^{+2.6}_{-0.8} \times 10^{-4}~\mbox{cm}^{-3}\) and pathlength of \(334^{+685}_{-274}~\mbox{kpc}\) . In the PKS 2155-304 direction we measure the gas density of \(3.6^{+4.5}_{-1.8} \times10^{-4}~\mbox{cm}^{-3}\) and path-length of \(109^{+200}_{-82}~\mbox{kpc}\) . Thus the density and pathlength along these sightlines are consistent with each other within errors. The average density and pathlength of the two sightlines are similar to the global averages, so the halo mass is still huge, over 10 billion solar masses. With more such studies, we will be able to better characterize the CGM anisotropy and measure its mass more accurately. We can then compare the observational results with theoretical models and investigate if/how the CGM structure is related to the larger scale environment of the Milky Way. We also show that the Galactic disk makes insignificant contribution to the observed O?vii absorption; a similar conclusion was also reached by Henley and Shelton (2013) about the emission measure. We further argue that any density inhomogeneity in the warm-hot gas, be it from clumping, from the disk, or from a non-constant density gradient, would strengthen our result in that the Galactic halo path-length and the mass would become larger than what we estimate here. As such, our results are conservative and robust.