We discuss the relationship between a standard Shakura & Sunyaev accretion disc model and the big blue bump (BBB) observed in Type 1 active galactic nuclei. Given the similarity between the BBB and ...the predicted disc spectrum, we propose a new method to estimate black hole masses which relies on the modelling of both optical and UV data with a Shakura & Sunyaev disc spectrum. We apply this method to a sample of 23 radio-loud narrow-line Seyfert 1 (RL-NLS1) galaxies, using data from Wide-field Infrared Survey Explorer, SDSS and GALEX. Our black hole mass estimates are at least a factor of ∼6 above previous results based on single epoch virial methods, while the Eddington ratios are correspondingly lower. Hence, the black hole masses of RL-NLS1 galaxies are typically above 108 M, in agreement with the typical black hole mass of blazars.
QSFit: automatic analysis of optical AGN spectra Calderone, G; Nicastro, L; Ghisellini, G ...
Monthly Notices of the Royal Astronomical Society,
12/2017, Letnik:
472, Številka:
4
Journal Article
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Abstract
We present QSFit (Quasar Spectral Fitting package), a new software package to automatically perform the analysis of active galactic nuclei (AGNs) optical spectra. The software provides ...luminosity estimates for the AGN continuum, the Balmer continuum, both optical and ultraviolet iron blended complex, host galaxy and emission lines, as well as width, velocity offset and equivalent width of 20 emission lines. Improving on a number of previous studies on AGN spectral analysis, QSFit fits all the components simultaneously, using an AGN continuum model which extends over the entire available spectrum, and is thus a probe of the actual AGN continuum whose estimates are scarcely influenced by localized features (e.g. emission lines) in the spectrum. We used QSFit to analyse 71 251 optical spectra of Type 1 AGN at z < 2 (obtained by the Sloan Digital Sky Survey, SDSS) and to produce a publicly available catalogue of AGN spectral properties. Such catalogue
allowed us (for the first time) to estimate the AGN continuum slope and the Balmer continuum luminosity on a very large sample, and to show that there is no evident correlation between these quantities the redshift. All data in the catalogue, the plots with best-fitting model and residuals, and the idl code we used to perform the analysis, are available on a dedicated website. The whole fitting process is customizable for specific needs, and can be extended to analyse
spectra from other data sources. The ultimate purpose of QSFit is to allow astronomers to run standardized recipes to analyse the AGN data, in a simple, replicable and shareable way.
ABSTRACT
Driven by the imminent need to rapidly process and classify millions of AGN spectra drawn from next generation astronomical facilities, we present a spectral fitting routine for Type 2 AGN ...spectra optimized for high volume processing, using the quasar spectral fitting library (qsfit). We analyse an optically selected sample of 813 luminous Type 2 AGN spectra at z < 0.83 from the Sloan Digital Sky Survey (SDSS) to qualify its performance. We report a median narrow line H α/H β Balmer decrement of 4.5 ± 0.8, alluding to the presence of dust in the narrow line region (NLR). We publish a specialized qsfit fitting routine for high signal-to-noise ratio spectra and general fitting routine for double peaked Type 2 AGN spectra applied on a subsample of 45 spectra from our parent sample. We report a median red and blue peak velocity separation of 390 ± 60 kms−1. No trend is found for red or blue peaks to exhibit systematically different luminosity or ionization properties. Emission line diagnostics show that the double peaks in all sources are illuminated by an AGN-powered ionizing continuum. Finally, we examine the morphology of host galaxies of our double peaked sample. We find double peaked Type 2 AGN reside in merging systems at a comparable frequency to single peaked AGN. This suggests that the double peaked AGN phenomenon is likely to have a bi-conical outflow origin in the majority of cases. We publicly release the code used for spectral analysis and produced catalogues used in this work.
Summary EGFR overexpression in salivary gland carcinomas provides the rational for the investigation of anti-EGFR treatments in recurrent and/or metastatic salivary gland cancers (RMSGCs). The ...activity of cetuximab in terms of clinical benefit rate (CBR) defined as the occurrence of objective response (CR or PR) or stable disease (SD) for ⩾6 months was investigated. From April to December 2005, 30 patients 23 adenoid cystic carcinoma (ACC) and 7 non-ACC were treated with cetuximab at 400 mg/m2 /week followed by 250 mg/m2 /week until progression, major toxicity or voluntary discontinuation. EGFR expression and gene status were retrospectively analyzed by immunocytochemistry and fluorescence in situ hybridization, respectively. A median of 14 courses of cetuximab (range 5–54) were infused. Skin toxicity was the main adverse event. Cetuximab provides a CBR in 50% (95% CL, 31 to 69%) of cases. None tumor sample showed EGFR gene amplification and an increased EGFR copy number was observed in 12% of samples, all ACC. Skin rash ⩾G2, EGFR overexpression and EGFR copy number were not statistically correlated to CB. In RMSGCs further evaluations of EGFR targeting agents are advisable and should take place by appropriate tumor biological selection, differentiating ACC from non-ACC.
We investigated the rest-frame spectral lags of two complete samples of bright long (50) and short (6) gamma-ray bursts (GRB) detected by Swift. We analysed the Swift/Burst Alert Telescope data ...through a discrete cross-correlation function fitted with an asymmetric Gaussian function to estimate the lag and the associated uncertainty. We find that half of the long GRBs have a positive lag and half a lag consistent with zero. All short GRBs have lags consistent with zero. The distributions of the spectral lags for short and long GRBs have different average values. Limited by the small number of short GRBs, we cannot exclude at more than 2s significance level that the two distributions of lags are drawn from the same parent population. If we consider the entire sample of long GRBs, we do not find evidence for a lag-luminosity correlation, rather the lag-luminosity plane appears filled on the left-hand side, thus suggesting that the lag-luminosity correlation could be a boundary. Short GRBs are consistent with the long ones in the lag-luminosity plane.
We compare the prompt intrinsic spectral properties of a sample of short gamma-ray bursts (GRBs) with the first 0.3 s (rest frame) of long GRBs observed by Fermi/GBM (Gamma Burst Monitor). We find ...that short GRBs and the first part of long GRBs lie on the same E
p–E
iso correlation, that is parallel to the relation for the time-averaged spectra of long GRBs. Moreover, they are indistinguishable in the E
p–L
iso plane. This suggests that the emission mechanism is the same for short and for the beginning of long events, and both short and long GRBs are very similar phenomena, occurring on different time-scales. If the central engine of a long GRB would stop after ∼0.3 × (1 + z) s, the resulting event would be spectrally indistinguishable from a short GRB.
Abstract
B2 0954+25A, detected by the Fermi satellite, is a blazar with interesting observational properties: it has been observed to transit from a jet-dominated to a disc-dominated state; its radio ...spectrum appears flat at all observing frequencies (down to 74 MHz); optically, the Hβ; line profile is asymmetric. The flatness of the radio spectrum suggests that the isotropic emission from radio lobes is very weak, despite the large size of its jet (≳500 kpc). Its broad-band spectral energy distribution is surprisingly similar to that of the prototypical γ-ray, radio-loud, type 1 narrow-line Seyfert (γ-NLS1) galaxy PMN J0948+0022. In this work, we revisit the mass estimates of B2 0954+25A considering only the symmetric component of the Hβ; line and find (1-3) × 108 M⊙. In light of our composite analysis, we propose to classify the source as a transition object between the classes of flat spectrum radio quasars and γ-NLS1 galaxies. A comparison with two members of each class (3C 273 and PMN J0948+0022) is discussed.
We present the analysis of the extraordinarily bright gamma-ray burst (GRB) 130427A under the hypothesis that the GRB central engine is an accretion-powered magnetar. In this framework, initially ...proposed to explain GRBs with precursor activity, the prompt emission is produced by accretion of matter on to a newly born magnetar, and the observed power is related to the accretion rate. The emission is eventually halted if the centrifugal forces are able to pause accretion. We show that the X-ray and optical afterglow is well explained as the forward shock emission with a jet break plus a contribution from the spin-down of the magnetar. Our modelling does not require any contribution from the reverse shock, that may still influence the afterglow light curve at radio and mm frequencies, or in the optical at early times. We derive the magnetic field (B ∼ 1016 G) and the spin period (P ∼ 20 ms) of the magnetar and obtain an independent estimate of the minimum luminosity for accretion. This minimum luminosity results well below the prompt emission luminosity of GRB 130427A, providing a strong consistency check for the scenario where the entire prompt emission is the result of continuous accretion on to the magnetar. This is in agreement with the relatively long spin period of the magnetar. GRB 130427A was a well-monitored GRB showing a very standard behaviour and, thus, is a well-suited benchmark to show that an accretion-powered magnetar gives a unique view of the properties of long GRBs.
A fuel processor, which incorporates a catalytic autothermal reformer (ATR), a sulfur trap, and a water–gas-shift (WGS) bed engineered to thermally integrate the ATR and WGS processes for improved ...thermal efficiency, was developed and tested with natural gas as a hydrogen generator for fuel cell applications. In this study, the fuel processor was successfully run over 2300
h of continuous operation at 3.1–16.0
kWth input energy capacities. Test results obtained from characterizing the ATR performance show that the reformer achieved over 40%
H
2
(dry basis) in the ATR reformate and 96–99.9% methane conversion over the entire test duration. The methane reforming efficiency reached over 90% at 16.0
kWth input energy level (or equivalent to 29
L/min fuel processing rate), but decreased with decreasing fuel processing rate. The oxygen-to-fuel molar ratio and the fuel processing rate were found to be the key operating parameters in determining the ATR bed temperature, the methane conversion, and the methane reforming efficiency.
The recent detection of γ-ray emission from four radio-loud narrow-line Seyfert 1 galaxies suggests that the engine driving the active galactic nuclei (AGN) activity of these objects shares some ...similarities with that of blazars, namely the presence of a γ-ray emitting, variable jet of plasma closely aligned to the line of sight. In this work we analyse the γ-ray light curves of the four radio-loud narrow-line Seyfert 1 galaxies for which high-energy γ-ray emission has been discovered by Fermi/LAT, in order to study their variability. We find significant flux variability in all the sources. This allows us to exclude a starburst origin of the γ-ray photons and confirms the presence of a relativistic jet. Furthermore, we estimate the minimum e-folding variability time-scale (3-30 d) and infer an upper limit for the size of the emitting region (0.2-2 pc, assuming a relativistic Doppler factor δ= 10 and a jet aperture of θ= 0.1 rad).
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