15510685
X-ray properties of the quasar He 0450-2958
We present an XMM-Newton EPIC observation of HE 0450-2958, which may be a "naked" quasar as suggested by Magain and coworkers. The XMM-Newton EPIC spectra show a substantial soft X-ray excess and a steep photon index, as well as marginal evidence for a weak Fe K alpha line. The X-ray absorption is consistent with the Galactic level. The 0.3-10 keV EPIC spectra can be fitted by a power-law plus blackbody model; however, the fit by a relativistically blurred photoionized disk reflection model is better. We estimate a black hole mass of 2(-1.3)(+7) x 10(7) M-circle dot from the X-ray variability. This broadly agrees with the value derived from the optical H beta line width. These results support a high-state Seyfert galaxy as the source. HE 0450-2958 shares properties with transitionary objects from ultraluminous infrared galaxies to quasars. We suggest that HE 0450-2958 is just in the beginning of an optical quasar window.
15715110
Suppressed star formation in circumnuclear regions in seyfert galaxies
Feedback from black hole activity is widely believed to play a key role in regulating star formation and black hole growth. A long-standing issue is the relation between star formation and the fueling of the supermassive black holes in active galactic nuclei (AGNs). We compile a sample of 57 Seyfert galaxies to tackle this issue. We estimate the surface densities of gas and star formation rates in circumnuclear regions (CNRs). Comparing them with the well-known Kennicutt-Schmidt (K-S) law, we find that the star formation rates (SFRs) in the CNRs of most Seyfert galaxies are suppressed in this sample. Feedback is suggested to explain the suppressed SFRs.
16433217
The afterglows of ultraluminous quasars
Quasars represent a brief phase in the life cycle of most massive galaxies, but the evolutionary connection between central black holes and their host galaxies remains unclear. While quasars are active and shining brighter than the Compton-limit luminosity, their radiation heats the surrounding medium to the Compton temperature, forming Compton spheres extending to the Stromgren radius of Fe26+/He2+. After the quasars shut off, their "afterglow" can be detected through three signatures: (1) an extended X-ray envelope, with a characteristic temperature of ~3 × 107 K, (2) Lyα and Lyβ lines and the K edge of Fe26+, and (3) nebulosity from hydrogen and helium recombination emission lines. We discuss the possibility of detecting these signatures using Chandra, the planned X-Ray Evolving Universe Spectroscopy mission, and ground-based optical telescopes. The luminosity and size of quasar afterglows can be used to constrain the lifetime of quasars.
119102309
Possible hard X-ray shortages in bursts from KS 1731-260 and 4U 1705-44
Aims. A hard X-ray shortage, implying the cooling of the corona, was observed during bursts of IGR J17473-272, 4U 1636-536, Aql X-1, and GS 1826-238. Apart from these four sources, we investigate here an atoll sample, in which the number of bursts for each source is larger than 5, to explore the possible additional hard X-ray shortage during Rossi X-ray timing explorer (RXTE) era. Methods. According to the source catalog that shows type-I bursts, we analyzed all the available pointing observations of these sources carried out by the RXTE proportional counter array. We grouped and combined the bursts according to their outburst states and searched for the possible hard X-ray shortage while bursting. Results. We found that the island states of KS 1731-260 and 4U 1705-44 show a hard X-ray shortage at significant levels of 4.5 and 4.7σ and a systematic time lag of 0.9 ± 2.1 s and 2.5 ± 2.0 s with respect to the soft X-rays, respectively. While in their banana branches and other sources, we did not find any consistent shortage.
17396076
INTEGRAL and RXTE/ASM observations on IGR J17098−3628
To probe further the possible nature of the unidentified source IGR J17098-3628, we have carried out a detailed analysis of its long-term time variability as monitored by RXTE/ASM, and of its hard X-ray properties as observed by INTEGRAL. INTEGRAL has monitored this sky region over years and significantly detected IGR J17098-3628 only when the source was in this dubbed active state. In particular, at $\ge$ 20 keV, IBIS/ISGRI caught an outburst in March 2005, lasting for $\sim$5 days with detection significance of 73$\sigma$ (20-40 keV) and with the emission at $ $20 keV) outburst by $\sim$2 days. This resembles the behavior of X-ray novae like XN 1124-683, hence it further suggests a LMXB nature for IGR J17098-3628. While the quality of the ASM data prevents us from drawing any definite conclusions, these discoveries are important clues that, coupled with future observations, will help to resolve the as yet unknown nature of IGR J17098-3628.
17406200
EVOLUTION OF GASEOUS DISK VISCOSITY DRIVEN BY SUPERNOVA EXPLOSIONS IN STAR-FORMING GALAXIES AT HIGH REDSHIFT
Motivated by Genzel et al.'s observations of high-redshift star-forming galaxies, containing clumpy and turbulent rings or disks, we build a set of equations describing the dynamical evolution of gaseous disks with inclusion of star formation and its feedback. Transport of angular momentum is due to "turbulent" viscosity induced by supernova explosions in the star formation region. Analytical solutions of the equations are found for the initial cases of a gaseous ring and the integrated form for a gaseous disk, respectively. For a ring with enough low viscosity, it evolves in a slow process of gaseous diffusion and star formation near the initial radius. For a high viscosity, the ring rapidly diffuses in the early phase. The diffusion drives the ring into a region with a low viscosity and starts the second phase undergoing pile-up of gas at a radius following the decreased viscosity torque. The third is a sharply decreasing phase because of star formation consumption of gas and efficient transportation of gas inward forming a stellar disk. We apply the model to two z similar to 2 galaxies BX 482 and BzK 6004, and find that they are undergoing a decline in their star formation activity.
110785158
Measurement of wakefields generated in accelerator test structures using the SLC
Research is underway at SLAC to develop accelerator structures for the next generation linear collider. An important feature of the design is a detuning of the dipole moddes -of the cells to suppress the long-range transverse wakefield bptwo orders of magnitude. This paper describes a facility, called ASSET, that will be incorporated into the SLAC Linear Collider (SLC) to test the long-range wakefield suppression and also to measure the other components of the wakefields generated in accelerator test structures. _- 1 INTRGDUCTION The-designs being considered at SLAC for the Next Linear Collider (NLC) employ multi-bunch operation in a high acceleration -gradient X-band linac. The limitations in this _ __ approach come in part from the transverse and longitudinal wakefields generated in the accelerator structures of the linac. A particularly troublesome problem is the long-range transverse wakefield, -which if not controlled, will produce a large growth in the transverse motion of the bunches. The .currently favored cure for this problem is to detune the dipole mode frequencies of the cells of the structures so the sum of the wakefields generated in each structure decohere (l). Since a two orders of magnitude reduction is required, and the theoretical calculations of the suppression (2) have some uncertainty, it is important that the performance of the structures be verified before they are produced for use in an accelerator. Thus far, measurements of the wakefield suppression have been made on short-length detuned structures at Argonne's Advanced Accelerator Test Facility (3). Although the results look promising, this facility currently does not have the measurement precision required for the NLC structures being developed, nor the capability of measuring the wakefields beyond a few ns compared to the few hundred ns needed. In the future, the plan is to do the measurements at SLAC with a dedicated facility called the Accelerator Structure SETup or ASSET (4). It exploits the "asset" of the-SLC in its capability to independently inject two low emittance bunches (electrons and positrons) into the linac with individual control of the bunch timing and intensity. The layout for. ASSET. is shown in figure 1. It is divided into two sect*3 that.will take the place of the first two 3
117940041
Measurement of top quark–antiquark pair production in association with a W or Z boson in pp collisions at $$\sqrt{s} = 8$$s=8$$\,\text {TeV}$$TeV
A measurement of the cross section for the production of top quark–antiquark pairs ($${\mathrm {t}}\overline{{\mathrm {t}}}$$tt¯) in association with a vector boson V (W or Z) in proton-proton collisions at $$\sqrt{s} = 8$$s=8$$\,\text {TeV}$$TeV is presented. The results are based on a dataset corresponding to an integrated luminosity of 19.5 fb$$^{-1}$$-1 recorded with the CMS detector at the LHC. The measurement is performed in three leptonic (e and $$\upmu $$μ) channels: a same-sign dilepton analysis targeting $${\mathrm {t}}\overline{{\mathrm {t}}} \mathrm {W} $$tt¯W events, and trilepton and four-lepton analyses designed for $${\mathrm {t}}\overline{{\mathrm {t}}} {\mathrm {Z}} $$tt¯Z events. In the same-sign dilepton channel, the $${\mathrm {t}}\overline{{\mathrm {t}}} \mathrm {W} $$tt¯W cross section is measured as $$\sigma _{{\mathrm {t}}\overline{{\mathrm {t}}} \mathrm {W}} = 170 ^{+90}_{-80}\,\text {(stat)} \pm 70\,\text {(syst)} \, \text {fb} $$σtt¯W=170-80+90(stat)±70(syst)fb, corresponding to a significance of 1.6 standard deviations over the background-only hypothesis. Combining the trilepton and four-lepton channels, a direct measurement of the $${\mathrm {t}}\overline{{\mathrm {t}}} {\mathrm {Z}} $$tt¯Z cross section, $$\sigma _{{\mathrm {t}}\overline{{\mathrm {t}}} {\mathrm {Z}}} = 200 ^{+80}_{-70}\,\text {(stat)} ^{+40}_{-30}\,\text {(syst)} \mathrm{fb}^{-1} $$σtt¯Z=200-70+80(stat)-30+40(syst)fb-1, is obtained with a significance of 3.1 standard deviations. The measured cross sections are compatible with standard model predictions within their experimental uncertainties. The inclusive $${\mathrm {t}}\overline{{\mathrm {t}}} {\mathrm {V}} $$tt¯V process is observed with a significance of 3.7 standard deviations from the combination of all three leptonic channels.
2136388
Are Seyfert 2 galaxies without polarized broad emission lines more obscured
New XMM-Newton data of seven Seyfert 2 galaxies with optical spectropolarimetric observations are presented. An analysis of the 0.5–10 keV spectra shows that four Seyfert 2 galaxies with polarized broad lines (PBLs) are absorbed by NH<1024 cm−2, while two of three Seyfert 2 galaxies without PBLs show evidence of Compton-thick obscuration, supporting the conclusion that Seyfert 2 galaxies without PBLs are more obscured than those with PBLs. Adding the measured obscuration indicators (NH, T ratio, and Fe Kα line EW) of six luminous AGNs to our previous sample improves the significance level of the difference in absorption from 92.3% to 96.3% for NH, 99.1% to 99.4% for T ratio, and 95.3% to 97.4% for Fe Kα line EW. The present results support and enhance the suggestions that the absence of PBLs in Seyfert 2 galaxies can be explained by larger viewing angles of the line of sight to the putative dusty torus, which leads to the obscuration of the broad-line scattering screen, as expected in the unification model.
118461506
UM 625 Revisited: Multiwavelength Study of a Seyfert 1 Galaxy with a Low-mass Black Hole
UM 625, previously identified as a narrow-line active galactic nucleus (AGN), actually exhibits broad H alpha and H beta lines whose width and luminosity indicate a low black hole (BH) mass of 1.6 x 10(6) M-circle dot. We present a detailed multiwavelength study of the nuclear and host galaxy properties of UM 625. Analysis of Chandra and XMM-Newton observations suggests that this system contains a heavily absorbed and intrinsically X-ray weak (alpha(ox) = -1.72) nucleus. Although not strong enough to qualify as radio loud, UM 625 does belong to a minority of low-mass AGNs detected in the radio. The broadband spectral energy distribution constrains the bolometric luminosity to L-bol approximate to (0.5-3) x 10(43) erg s(-1) and L-bol/L-Edd approximate to 0.02-0.15. A comprehensive analysis of Sloan Digital Sky Survey and Hubble Space Telescope images shows that UM 625 is a nearly face-on S0 galaxy with a prominent, relatively blue pseudobulge (Sersic index n = 1.60) that accounts for similar to 60% of the total light in the R band. The extended disk is featureless, but the central similar to 150-400 pc contains a conspicuous semi-ring of bright, blue star-forming knots, whose integrated ultraviolet luminosity suggests a star formation rate of similar to 0.3 M-(c) yr(-1). The mass of the central BH roughly agrees with the value predicted from its bulge velocity dispersion but is significantly lower than that expected from its bulge luminosity.
121941527
B∗ production in Z decays at LEP
Abstract The production of B ∗ mesons in Z decays has been measured at LEP with the L3 detector. A sample of Z → b b events was obtained by tagging muons in 1.6 million hadronic Z decays collected in 1991, 1992 and 1993. A signal with a peak value of E γ = 46.3 ± 1.9 (stat) MeV in the B rest frame energy spectrum was interpreted to come from the decay B ∗ → γB. The inclusive production ratio of B ∗ mesons relative to B mesons was determined from a fit to the spectrum to be N B ∗ (N B ∗ + N B ) = 0.76 ± 0.08 ± 0.06 , where the first error is statistical and the second is systematic.