1,018 research outputs found
The NuSTAR View of the Seyfert 2 Galaxy NGC 4388
We present analysis of NuSTAR X-ray observations in the 3-79 keV energy band
of the Seyfert 2 galaxy NGC 4388, taken in 2013. The broadband sensitivity of
NuSTAR, covering the Fe K line and Compton reflection hump, enables
tight constraints to be placed on reflection features in AGN X-ray spectra,
thereby providing insight into the geometry of the circumnuclear material. In
this observation, we found the X-ray spectrum of NGC 4388 to be well described
by a moderately absorbed power law with non-relativistic reflection. We fit the
spectrum with phenomenological reflection models and a physical torus model,
and find the source to be absorbed by Compton-thin material (N cm) with a very weak Compton reflection hump
(R 0.09) and an exceptionally large Fe K line (EW eV) for a source with weak or no reflection. Calculations
using a thin-shell approximation for the expected Fe K EW indicate that
an Fe K line originating from Compton-thin material presents a possible
explanation.Comment: 5 pages, 2 figures. Accepted for publication in Ap
Constraining the fraction of Compton-thick AGN in the Universe by modelling the diffuse X-ray background spectrum
This paper investigates what constraints can be placed on the fraction of
Compton-thick (CT) AGN in the Universe from the modeling of the spectrum of the
diffuse X-ray background (XRB). We present a model for the synthesis of the XRB
that uses as input a library of AGN X-ray spectra generated by the Monte Carlo
simulations described by Brightman & Nandra. This is essential to account for
the Compton scattering of X-ray photons in a dense medium and the impact of
that process on the spectra of obscured AGN. We identify a small number of
input parameters to the XRB synthesis code which encapsulate the minimum level
of uncertainty in reconstructing the XRB spectrum. These are the power-law
index and high energy cutoff of the intrinsic X-ray spectra of AGN, the level
of the reflection component in AGN spectra and the fraction of CT AGN in the
Universe. We then map the volume of the space allowed to these parameters by
current observations of the XRB spectrum in the range 3-100 keV. One of the
least constrained parameters is the fraction of CT AGN. Statistically
acceptable fits to the XRB spectrum at the 68% confidence level can be obtained
for CT fractions in the range 5-50%. This is because of degeneracies among
input parameters to the XRB synthesis code and uncertainties in the modeling of
AGN spectra (e.g. reflection). The most promising route for constraining the
fraction of CT AGN in the Universe is via the direct detection of those sources
in high energy (>10keV) surveys. It is shown that the observed fraction of CT
sources identified in the SWIFT/BAT survey, limits the intrinsic fraction of CT
AGN, at least at low redshift, to 10-20% (68% confidence level). We also make
predictions on the number density of CT sources that current and future X-ray
missions are expected to discover. Testing those predictions will constrain the
intrinsic fraction of CT AGN as a function of redshift.Comment: To appear in A&
A statistical relation between the X-ray spectral index and Eddington ratio of active galactic nuclei in deep surveys
We present an investigation into how well the properties of the accretion flow on to a supermassive black hole may be coupled to those of the overlying hot corona. To do so, we specifically measure the characteristic spectral index, Γ, of a power-law energy distribution, over an energy range of 2–10 keV, for X-ray selected, broad-lined radio-quiet active galactic nuclei (AGN) up to z ∼ 2 in Cosmic Evolution Survey (COSMOS) and Extended Chandra Deep Field South (E-CDF-S). We test the previously reported dependence between Γ and black hole mass, full width at half-maximum (FWHM) and Eddington ratio using a sample of AGN covering a broad range in these parameters based on both the Mg II and Hα emission lines with the later afforded by recent near-infrared spectroscopic observations using Subaru/Fibre Multi Object Spectrograph. We calculate the Eddington ratios, λ_(Edd), for sources where a bolometric luminosity (L_(Bol)) has been presented in the literature, based on spectral energy distribution fitting, or, for sources where these data do not exist, we calculate L_(Bol) using a bolometric correction to the X-ray luminosity, derived from a relationship between the bolometric correction and L_X/L_(3000). From a sample of 69 X-ray bright sources (>250 counts), where Γ can be measured with greatest precision, with an estimate of L_(Bol), we find a statistically significant correlation between Γ and λ_(Edd), which is highly significant with a chance probability of 6.59× 10^(−8). A statistically significant correlation between Γ and the FWHM of the optical lines is confirmed, but at lower significance than with λ_(Edd) indicating that λ_(Edd) is the key parameter driving conditions in the corona. Linear regression analysis reveals that Γ = (0.32 ± 0.05) log_(10)λ_(Edd) + (2.27 ± 0.06) and Γ = (−0.69 ± 0.11) log_(10)(FWHM/km s^(−1)) + (4.44 ± 0.42). Our results on Γ–λ_(Edd) are in very good agreement with previous results. While the Γ–λ_(Edd) relationship means that X-ray spectroscopy may be used to estimate black hole accretion rate, considerable dispersion in the correlation does not make this viable for single sources, however could be valuable for large X-ray spectral samples, such as those to be produced by eROSITA
Suzaku Confirms NGC~3660 is an Unabsorbed Seyfert 2
An enigmatic group of objects, unabsorbed Seyfert 2s may have intrinsically
weak broad line regions, obscuration in the line of sight to the BLR but not to
the X-ray corona, or so much obscuration that the X-ray continuum is completely
suppressed and the observed spectrum is actually scattered into the line of
sight from nearby material. NGC 3660 has been shown to have weak broad
optical/near infrared lines, no obscuration in the soft X-ray band, and no
indication of "changing look" behavior. The only previous hard X-ray detection
of this source by Beppo-SAX seemed to indicate that the source might harbor a
heavily obscured nucleus. However, our analysis of a long-look Suzaku
observation of this source shows that this is not the case, and that this
source has a typical power law X-ray continuum with normal reflection and no
obscuration. We conclude that NGC 3660 is confirmed to have no unidentified
obscuration and that the anomolously high Beppo-SAX measurement must be due to
source confusion or similar, being inconsistent with our Suzaku measurements as
well as non-detections from Swift-BAT and RXTE.Comment: Accepted to PAS
Searching for the Donor Stars of ULX Pulsars
We report on our search for the optical counterparts of two ultraluminous
X-ray pulsars with known orbital periods, M82 X-2 and NGC 5907 X-1, in new and
archival HST observations, in an effort to characterize the donor stars in
these systems. We detect five near-infrared sources consistent with the
position of M82 X-2 that are too bright to be single stars. We also detect
seven sources in the WFC3/UVIS F336W image whose photometry matches that of
10-15 M stars turning off the main sequence. Such stars have densities
consistent with the properties of the donor star of M82 X-2 as inferred from
X-ray timing analysis, although it is also possible that the donor is a lower
mass star below our detection limit or that there is a significant contribution
from the accretion disc to the optical emission. We detect three candidate
counterparts to NGC 5907 X-1 in the near-infrared. All of these are too bright
to be the donor star of the ULX, which based on its orbital period is a red
giant. The high background at the location of NGC 5907 X-1 precludes us from
detecting this expected donor star. The recently discovered NGC 5907 ULX-2 also
falls within the field of view of the near-infrared imaging; we detect four
sources in the error circle, with photometry that matches AGB stars. The star
suggested to be the counterpart of NGC 5907 ULX-2 by Pintore et al. (2018)
falls outside our 2- error circle.Comment: 10 pages, 3 figures, accepted for publication in Ap
From Structure to Purpose: Green and Social Narratives, and the Shifting Morality of Islamic Finance in Kuala Lumpur
Background: The anthropology of sustainability documents and interprets diverse visions of sustainable and liveable futures. Islamic scholars and financiers are now debating the distinctive contribution of Islamic finance to global sustainability. While mainstream global finance has only recently begun to pay explicit attention to social and environmental sustainability, Islamic economics has always emphasised the need to benefit society, the community, and the environment. Objectives: We ask what has been the influence of the emergence of green and social finance upon Islamic finance in Malaysia, the global centre of Islamic finance. Methods: The study is based on collaborative, co-productive ethnography and autoethnography, and textual analysis of working documents of the Securities Commission Malaysia, focusing on how environmental requirements are expressed in new financial products, known as green sukuks, or green Islamic bonds. Results and conclusions: We have found that much of the moral debate in Islamic finance has revolved around the distribution of financial risk: when investors share the risk of failure, they can participate in society rather than merely exploiting social relations, yet the emergence of ‘green’ Islamic finance appears to shift the centre of moral gravity away from risk structuring towards technical criteria of sustainability, replicating the growth-oriented anthropocentric managerialism of mainstream finance
Introduction: rethinking the frontier in Amazonia and Siberia: extractive economies, indigenous politics and social transformations
none3siThe adage that anthropology is comparative if it is anything at all has been tested in recent years to great effect, particularly on the theme of the body (Gregor & Tuzin 2001; Lambeck & Strathern 1998), and with greater confidence than a decade previously (Holy 1987). The body provides a useful starting point for cross-cultural comparison because there can at some level be said to be a common factor: the physically existing, universal human body. While this apparent universality and constancy of the body may be questioned in the light of ethnographic evidence, and the body can be politicised in differing ways, when politics and history themselves are made into the points of comparison a new and somewhat different challenge is set. To compare frontiers, as the theatres in which cultural difference is played out, constitutes a doubly comparative scenario, as each case being compared involves the meeting of social groups and their own mutual comparison as an exploration of mutual similarity and difference. The comparison of frontiers thus involves the comparison of sets of political relationships, as the variable ways in which subjects relate to others.openBrightman, Marc; GROTTI, VANESSA; Ulturgasheva, OlgaBrightman, Marc; GROTTI, VANESSA; Ulturgasheva, Olg
Evidence for a Variable Ultrafast Outflow in the Newly Discovered Ultraluminous Pulsar NGC 300 ULX-1
Ultraluminous pulsars are a definite proof that persistent super-Eddington
accretion occurs in nature. They support the scenario according to which most
Ultraluminous X-ray Sources (ULXs) are super-Eddington accretors of stellar
mass rather than sub-Eddington intermediate mass black holes. An important
prediction of theories of supercritical accretion is the existence of powerful
outflows of moderately ionized gas at mildly relativistic speeds. In practice,
the spectral resolution of X-ray gratings such as RGS onboard XMM-Newton is
required to resolve their observational signatures in ULXs. Using RGS, outflows
have been discovered in the spectra of 3 ULXs (none of which are currently
known to be pulsars). Most recently, the fourth ultraluminous pulsar was
discovered in NGC 300. Here we report detection of an ultrafast outflow (UFO)
in the X-ray spectrum of the object, with a significance of more than
3{\sigma}, during one of the two simultaneous observations of the source by
XMM-Newton and NuSTAR in December 2016. The outflow has a projected velocity of
65000 km/s (0.22c) and a high ionisation factor with a log value of 3.9. This
is the first direct evidence for a UFO in a neutron star ULX and also the first
time that this its evidence in a ULX spectrum is seen in both soft and hard
X-ray data simultaneously. We find no evidence of the UFO during the other
observation of the object, which could be explained by either clumpy nature of
the absorber or a slight change in our viewing angle of the accretion flow.Comment: 10 pages, 4 figures. Accepted to MNRA
Spectral Changes in the Hyperluminous Pulsar in NGC 5907 as a Function of Super-Orbital Phase
We present broad-band, multi-epoch X-ray spectroscopy of the pulsating
ultra-luminous X-ray source (ULX) in NGC 5907. Simultaneous XMM-Newton and
NuSTAR data from 2014 are best described by a multi-color black-body model with
a temperature gradient as a function of accretion disk radius significantly
flatter than expected for a standard thin accretion disk (T(r) ~ r^{-p}, with
p=0.608^{+0.014}_{-0.012}). Additionally, we detect a hard power-law tail at
energies above 10 keV, which we interpret as being due to Comptonization. We
compare this observation to archival XMM-Newton, Chandra, and NuSTAR data from
2003, 2012, and 2013, and investigate possible spectral changes as a function
of phase over the 78d super-orbital period of this source. We find that
observations taken around phases 0.3-0.4 show very similar temperature
profiles, even though the observed flux varies significantly, while one
observation taken around phase 0 has a significantly steeper profile. We
discuss these findings in light of the recent discovery that the compact object
is a neutron star and show that precession of the accretion disk or the neutron
star can self-consistently explain most observed phenomena.Comment: 7 pages, 5 figures, submitted to ApJ; comments welcom
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