55 research outputs found
Investigating model dependencies for obscured Active Galactic Nuclei: a case study of NGC 3982
X-ray spectroscopy of heavily obscured Active Galactic Nuclei (AGN) offers a
unique opportunity to study the circum-nuclear environment of accreting
supermassive black holes (SMBHs). However, individual models describing the
obscurer have unique parameter spaces that give distinct parameter posterior
distributions when fit to the same data. To assess the impact of model-specific
parameter dependencies, we present a case study of the nearby heavily obscured
low-luminosity AGN NGC 3982, which has a variety of column density estimations
reported in the literature. We fit the same broadband XMM-Newton + NuSTAR
spectra of the source with five unique obscuration models and generate
posterior parameter distributions for each. By using global parameter
exploration, we traverse the full prior-defined parameter space to accurately
reproduce complex posterior shapes and inter-parameter degeneracies. The unique
model posteriors for the line-of-sight column density are broadly consistent,
predicting Compton-thick at the
3 confidence level. The posterior median intrinsic X-ray luminosity in
the 2-10 keV band however was found to differ substantially, with values in the
range log ergs = 40.9-42.1 for the individual
models. We additionally show that the posterior distributions for each model
occupy unique regions of their respective multi-dimensional parameters spaces,
and how such differences can propagate into the inferred properties of the
central engine. We conclude by showcasing the improvement in parameter
inference attainable with the High Energy X-ray Probe (HEX-P) with a uniquely
broad simultaneous and high-sensitivity bandpass of 0.2-80 keV.Comment: 26 pages, 6+6 figures (text+appendix), 1 table. Accepted for
publication in Ap
A comprehensive X-ray view of the active nucleus in NGC 4258
(Abridged) We present a detailed broadband X-ray spectrum of NGC 4258, with
the goal of precisely measuring the coronal luminosity and accretion flow
properties of the AGN, and track any possible variation across two decades of
observations. We collect archival XMM-Newton, Chandra, Swift/BAT and NuSTAR
spectroscopic observations spanning 15 years, and fit them with a suite of
state of the art models, including a warped disk model which is suspected to
provide the well known obscuration observed in the X-rays. We complement this
information with archival results from the literature. Clear spectral
variability is observed among the different epochs. The obscuring column
density shows possibly periodic fluctuations on a timescale of 10 years, while
the intrinsic luminosity displays a long term decrease of a factor of three in
a time span of 15 years (from erg s
in the early 2000s, to erg s
in 2016). The average absorption-corrected X-ray luminosity
, combined with archival determinations of the bolometric
luminosity, implies a bolometric correction , intriguingly
typical for Seyferts powered by accretion through geometrically thin,
radiatively efficient disks. Moreover, the X-ray photon index is
consistent with the typical value of the broader AGN population. However, the
accretion rate in Eddington units is very low, well within the expected RIAF
regime. Our results suggest that NGC 4258 is a genuinely low-luminosity Seyfert
II, with no strong indications in its X-ray emission for a hot, RIAF-like
accretion flow.Comment: Accepted for publication in A&A. 14 pages, 6 figures, 3 table
Comments on “Ochratoxin A: In utero Exposure in Mice Induces Adducts in Testicular DNA. Toxins 2010, 2, 1428–1444”—Mis-Citation of Rat Literature to Justify a Hypothetical Role for Ochratoxin A in Testicular Cancer
A manuscript in the journal recently cited experimental rat data from two manuscripts to support plausibility of a thesis that ochratoxin A might be a cause of human testicular cancer. I believe that there is no experimental evidence that ochratoxin A produces testicular cancer in rats or mice
Accretion Disc Evolution in GRO J1655-40 and LMC X-3 with Relativistic and Non-Relativistic Disc Models
Black hole X-ray binaries are ideal environments to study the accretion
phenomena in strong gravitational potentials. These systems undergo dramatic
accretion state transitions and analysis of the X-ray spectra is used to probe
the properties of the accretion disc and its evolution. In this work, we
present a systematic investigation of 1800 spectra obtained by RXTE PCA
observations of GRO J1655-40 and LMC X-3 to explore the nature of the accretion
disc via non-relativistic and relativistic disc models describing the thermal
emission in black-hole X-ray binaries. We demonstrate that the non-relativistic
modelling throughout an outburst with the phenomenological multi-colour disc
model DISKBB yields significantly lower and often unphysical inner disc radii
and correspondingly higher (50-60\%) disc temperatures compared to its
relativistic counterparts KYNBB and KERRBB. We obtained the dimensionless spin
parameters of and for GRO
J1655-40 with KERRBB and KYNBB, respectively. We report a spin value of
for LMC X-3 using the updated black hole mass of 6.98
. Both measurements are consistent with the previous studies.
Using our results, we highlight the importance of self-consistent modelling of
the thermal emission, especially when estimating the spin with the
continuum-fitting method which assumes the disc terminates at the innermost
stable circular orbit at all times.Comment: Accepted for publication in MNRAS, 23 pages 17 figure
An Iwasawa-Taniguchi Effect for Compton-thick Active Galactic Nuclei
We present the first study of an Iwasawa-Taniguchi/X-ray Baldwin effect for
Compton-thick active galactic nuclei (AGN). We report a statistically
significant anti-correlation between the rest-frame equivalent width (EW) of
the narrow core of the neutral Fe K fluorescence emission line,
ubiquitously observed in the reflection spectra of obscured AGN, and the
mid-infrared 12m continuum luminosity (taken as a proxy for the
bolometric AGN luminosity). Our sample consists of 72 Compton-thick AGN
selected from pointed and deep-field observations covering a redshift range of
. We employ a Monte Carlo-based fitting method, which returns
a Spearman's Rank correlation coefficient of , significant
to 98.7% confidence. The best fit found is , which is
consistent with multiple studies of the X-ray Baldwin effect for unobscured and
mildly obscured AGN. This is an unexpected result, as the Fe K line is
conventionally thought to originate from the same region as the underlying
reflection continuum, which together constitute the reflection spectrum. We
discuss the implications this could have if confirmed on larger samples,
including a systematic underestimation of the line of sight X-ray obscuring
column density and hence the intrinsic luminosities and growth rates for the
most luminous AGN.Comment: Accepted for publication in MNRAS. 58 pages (22 page manuscript; 13
figures + 26 page appendix; 66 figures). This version update combines the
manuscript and appendi
An Iwasawa-Taniguchi Effect for Compton-thick Active Galactic Nuclei
We present the first study of an Iwasawa–Taniguchi/‘X-ray Baldwin’ effect for Compton-thick active galactic nuclei (AGN). We report a statistically significant anticorrelation between the rest-frame equivalent width (EW) of the narrow core of the neutral Fe Kα fluorescence emission line, ubiquitously observed in the reflection spectra of obscured AGN, and the mid-infrared 12μm continuum luminosity (taken as a proxy for the bolometric AGN luminosity). Our sample consists of 72 Compton-thick AGN selected from pointed and deep-field observations covering a redshift range of z ∼ 0.0014−3.7. We employ a Monte Carlo-based fitting method, which returns a Spearman’s Rank correlation coefficient of ρ = − 0.28 ± 0.12, significant to 98.7 per cent confidence. The best-fitting found is
log(EW_(FeKα)) ∝ −0.08 ± 0.04log(L_(12μm)), which is consistent with multiple studies of the X-ray Baldwin effect for unobscured and mildly obscured AGN. This is an unexpected result, as the Fe Kα line is conventionally thought to originate from the same region as the underlying reflection continuum, which together constitute the reflection spectrum. We discuss the implications this could have if confirmed on larger samples, including a systematic underestimation of the line-of-sight X-ray obscuring column density and hence the intrinsic luminosities and growth rates for the most luminous AGN
Oncological Outcomes in Rats Given Nephrocarcinogenic Exposure to Dietary Ochratoxin A, Followed by the Tumour Promoter Sodium Barbital for Life: A Pilot Study
The potent experimental renal carcinogenesis of ochratoxin A (OTA) in male rats makes the dietary contaminant a potential factor in human oncology. We explored whether the tumour promoter sodium barbitate could shorten the otherwise long latency between exposure to toxin and tumourigenesis. Young rats, of a hybrid in which mononuclear leukaemia was rare, were given feed contaminated (5 ppm) with OTA for 36 weeks to initiate renal tumourigenesis. Some individuals were thereafter given sodium barbitate (500 ppm in drinking water) for life. Pathological outcomes were studied at or near the end of natural life. Renal tumours in males given barbitate became evident after latency of one year, but only slightly before those without barbitate. In contrast, female mammary tumourigenesis was advanced by at least 6 months synchronously in all rats given the OTA-barbitate regimen compared to tumourigenesis in controls. Diagnosis of malignant mammary angiosarcoma in a female given the OTA-barbitate regimen is a new finding in the rat. The long latency of OTA-induced renal tumourigenesis was not notably susceptible to accelerated promotion by barbitate, contrasting with an apparently marked effect of barbitate on development of mammary tumours
Evaluation of host-derived volatiles for trapping Culicoides biting midges (Diptera: Ceratopogonidae)
Culicoides biting midges (Diptera: Ceratopognidae) cause pain and distress through blood feeding, and transmit viruses that threaten both animal and human health worldwide. There are few effective tools for monitoring and control of biting midges, with semiochemical-based strategies offering the advantage of targeting host-seeking populations. In previous studies, we identified the host preference of multiple Culicoides species, including Culicoides impunctatus, as well as cattle-derived compounds that modulate the behavioral responses of C. nubeculosus under laboratory conditions. Here, we test the efficacy of these compounds, when released at different rates, in attracting C. impunctatus under field conditions in Southern Sweden. Traps releasing 1-octen-3-ol, decanal, phenol, 4-methylphenol or 3-propylphenol, when combined with carbon dioxide (CO2), captured significantly higher numbers of C. impunctatus compared to control traps baited with CO2 alone, with low release rates (0.1 mg h−1, 1 mg h−1) being generally more attractive. In contrast, traps releasing octanal or (E)-2-nonenal at 1 mg h−1 and 10 mg h−1 collected significantly lower numbers of C. impunctatus than control traps baited with CO2 only. Nonanal and 2-ethylhexanol did not affect the attraction of C. impunctatus when compared to CO2 alone at any of the release rates tested. The potential use of these semiochemicals as attractants and repellents for biting midge control is discussed
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