The optimization of G.729 speech codec and implementation on the S3C2440

Geng, Wang; Zhang, Yongjie

doi:10.1109/iceceng.2011.6057461

Cited by 3 publications

(3 citation statements)

References 4 publications

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“…Kraemer) to generate a dataset with a cumulative effective exposure time of 147.82 ks (Table 1). These observations were then reprocessed and analyzed using CIAO 4.11 and CALDB 4.8.2 to enable subpixel analysis (Tsunemi et al 2001;Wang et al 2011). Each individual observation was inspected for high background flares (≥3σ) and all were deemed acceptable.…”

Section: Observations and Analysismentioning

confidence: 99%

Chandra Observations of NGC 7212: Large-scale Extended Hard X-Ray Emission

Jones

Fabbiano

Elvis

et al. 2020

ApJ

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Recent observations of nearby Compton thick (CT) active galactic nuclei (AGNs) with Chandra have resolved hard (> 3 keV) X-ray emission extending out from the central supermassive black hole to kiloparsec scales, challenging the long-held belief that the characteristic hard X-ray continuum and fluorescent Fe K lines originate in the inner ∼parsec due to the excitation of obscuring material. In this paper we present the results of the most recent Chandra ACIS-S observations of NGC 7212, a CT AGN in a compact group of interacting galaxies, with a total effective exposure of ∼150 ks. We find ∼20% of the observed emission is found outside of the central kiloparsec, with ∼17% associated with the soft X-rays, and ∼3% with hard X-ray continuum and Fe K line. This emission is extended both along the ionization cone and in the cross-cone direction up to ∼3.8 kpc scales. The spectrum of NGC 7212 is best represented by a mixture of thermal and photoionization models that indicate the presence of complex gas interactions. These observations are consistent with what is observed in other CT AGN (e.g., ESO 428−G014, NGC 1068), providing further evidence that this may be a common phenomenon. High-resolution observations of extended CT AGN provide an especially valuable environment for understanding how AGN feedback impacts host galaxies on galactic scales.

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Section: Observations and Analysismentioning

confidence: 99%

Chandra Observations of NGC 7212: Large-scale Extended Hard X-Ray Emission

Jones

Fabbiano

Elvis

et al. 2020

ApJ

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“…Thus, in our comparisons, the profile of PKS 2126-528 conveniently illustrates how a pile-up of the order of 10% modifies the PSF in the first 2 . At larger radii, the pile-up has no effects (see e.g., NGC 4151, Wang et al 2011). The small discrepancy between the profiles of PKS 2126-5128 and those of the simulated PSF could be due to changes of the Chandra-PSF since the time the source was observed.…”

Section: Surface-brightness Profilesmentioning

confidence: 96%

Chandra imaging of the ~kpc extended outflow in 1H 0419-577

Gesu

Costantini

Piconcelli

et al. 2017

A&A

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The Seyfert 1 galaxy 1H 0419-577 hosts a ∼kpc extended outflow that is evident in the [O iii] image and that is also detected as a warm absorber in the UV/X-ray spectrum. Here, we analyze a ∼30 ks Chandra-ACIS X-ray image, with the aim of resolving the diffuse extranuclear X-ray emission and of investigating its relationship with the galactic outflow. Thanks to its sub-arcsecond spatial resolution, Chandra resolves the circumnuclear X-ray emission, which extends up to a projected distance of at least ∼16 kpc from the center. The morphology of the diffuse X-ray emission is spherically symmetrical. We could not recover a morphological resemblance between the soft X-ray emission and the ionization bicone that is traced by the [O iii] outflow. Our spectral analysis indicates that one of the possible explanations for the extended emission is thermal emission from a low-density (n H ∼ 10 −3 cm −3 ) hot plasma (T e ∼ 0.22 keV). If this is the case, we may be witnessing the cooling of a shock-heated wind bubble. In this scenario, the [O iii] emission line and the X-ray/UV absorption lines may trace cooler clumps that are entrained in the hot outflow. Alternatively, the extended emission could be to due to a blend of emission lines from a photoionized gas component having a hydrogen column density of N H ∼ 2.1×10 22 cm −2 and an ionization parameter of log ξ ∼ 1.3. Because the source is viewed almost edge-on we argue that the photoionized gas nebula must be distributed mostly along the polar directions, outside our line of sight. In this geometry, the X-ray/UV warm absorber must trace a different gas component, physically disconnected from the emitting gas, and located closer to the equatorial plane.

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“…The origin of N-rich quasars is generally attributed to unusually high metallicities (e.g., Z > 5Z ⊙ ; Dietrich et al 2003;Nagao et al 2006). The high metallicities could result from either extreme global enrichment in the cores of giant elliptical galaxies (Hamann & Ferland 1993, but see Friaca & Terlevich 1998;Romano et al 2002 for arguments against this) or local enrichment in the central part of the quasar (Collin & Zahn 1999;Wang et al 2011).…”

Section: Introductionmentioning

confidence: 99%

A Candidate Tidal Disruption Event in a Quasar at z = 2.359 from Abundance Ratio Variability

Liu

Dittmann

Shen

et al. 2018

ApJ

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A small fraction of quasars show an unusually high nitrogen-to-carbon ratio (N/C) in their spectra. These "nitrogen-rich" (N-rich) quasars are a long-standing puzzle because their interstellar medium implies stellar populations with abnormally high metallicities. It has recently been proposed that N-rich quasars may result from tidal disruption events (TDEs) of stars by supermassive black holes. The rapid enhancement of nitrogen and the depletion of carbon due to the carbon-nitrogen-oxygen cycle in supersolar mass stars could naturally produce high N/C. However, the TDE hypothesis predicts that the N/C should change with time, which has never hitherto been observed. Here we report the discovery of the first N-rich quasar with rapid N/C variability that could be caused by a TDE. Two spectra separated by 1.7 years (rest-frame) show that the N III] λ1750/C III] λ1909 intensity ratio decayed by ∼ 86%±14% (1σ). Optical (rest-frame UV) lightcurve and X-ray observations are qualitatively consistent with the TDE hypothesis; though, the time baseline falls short of a definitive proof. Putting the single-object discovery into context, statistical analyses of the ∼ 80 known N-rich quasars with high-quality archival spectra show evidence (at a 5σ significance level) of a decrease in N/C on timescales of > 1 year (rest-frame) and a constant level of ionization (indicated by the C III] λ1909/C IV λ1549 intensity ratio). If confirmed, our results demonstrate the method of identifying TDE candidates in quasars via abundance ratio variability, opening a new window of TDE observations at high redshift (z > 2) with upcoming large-scale time-domain spectroscopic surveys. 1 The BLR gas mass is luminosity dependent and is likely higher in luminous quasars (Baldwin et al. 2003a).

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The optimization of G.729 speech codec and implementation on the S3C2440

Cited by 3 publications

References 4 publications

Chandra Observations of NGC 7212: Large-scale Extended Hard X-Ray Emission

Chandra Observations of NGC 7212: Large-scale Extended Hard X-Ray Emission

Chandra imaging of the ~kpc extended outflow in 1H 0419-577

A Candidate Tidal Disruption Event in a Quasar at z = 2.359 from Abundance Ratio Variability

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