1,516 research outputs found
High Energy Cosmic-ray Diffusion in Molecular Clouds: A Numerical Approach
The propagation of high-energy cosmic rays through giant molecular clouds
constitutes a fundamental process in astronomy and astrophysics. The diffusion
of cosmic-rays through these magnetically turbulent environments is often
studied through the use of energy-dependent diffusion coefficients, although
these are not always well motivated theoretically. Now, however, it is feasible
to perform detailed numerical simulations of the diffusion process
computationally. While the general problem depends upon both the field
structure and particle energy, the analysis may be greatly simplified by
dimensionless analysis. That is, for a specified purely turbulent field, the
analysis depends almost exclusively on a single parameter -- the ratio of the
maximum wavelength of the turbulent field cells to the particle gyration
radius. For turbulent magnetic fluctuations superimposed over an underlying
uniform magnetic field, particle diffusion depends on a second dimensionless
parameter that characterizes the ratio of the turbulent to uniform magnetic
field energy densities. We consider both of these possibilities and parametrize
our results to provide simple quantitative expressions that suitably
characterize the diffusion process within molecular cloud environments. Doing
so, we find that the simple scaling laws often invoked by the high-energy
astrophysics community to model cosmic-ray diffusion through such regions
appear to be fairly robust for the case of a uniform magnetic field with a
strong turbulent component, but are only valid up to TeV particle
energies for a purely turbulent field. These results have important
consequences for the analysis of cosmic-ray processes based on TeV emission
spectra associated with dense molecular clouds.Comment: Accepted for publication in The Astrophysical Journa
Broadband X-ray spectral analysis of the Seyfert 1 galaxy GRS 1734-292
We discuss the broadband X-ray spectrum of GRS 1734-292 obtained from
non-simultaneous XMM-Newton and NuSTAR observations, performed in 2009 and
2014, respectively. GRS1734-292 is a Seyfert 1 galaxy, located near the
Galactic plane at . The NuSTAR spectrum ( keV) is dominated by
a primary power-law continuum with and a high-energy
cutoff keV, one of the lowest measured by NuSTAR in a
Seyfert galaxy. Comptonization models show a temperature of the coronal plasma
of keV and an optical depth, assuming a slab
geometry, or a similar temperature and
assuming a spherical geometry. The 2009 XMM-Newton
spectrum is well described by a flatter intrinsic continuum
() and one absorption line due to Fe\textsc{XXV}
K produced by a warm absorber. Both data sets show a modest iron
K emission line at keV and the associated Compton reflection, due
to reprocessing from neutral circumnuclear material
Experiential Learning through Community Co-design in Interior Design Pedagogy
The profit‐driven tendency of interior design trends and styles today has developed in line with the decrease of social awareness in design. The majority of interior design students also decide to pursue interior design education for its marketable and profitable purposes rather than seeing interior design as a field of opportunity to contribute to the social welfare of their communities. Hence, the objective of this research is to implement community service through co‐design in interior design pedagogy. The article describes the learning and design methods used based on human‐centred design approaches of co‐design and analyses the resulting benefits from this approach. Findings reveal that the process of collective creativity and collaborative development with the community enables a direct experience of learning and fosters a deeper connection and understanding of users. They also promote novel multidisciplinary design innovations, accommodate the communitys potentials in the society and stimulate a reflexive impact, allowing students to reflect on their future role as interior designers in bringing positive changes to their community against the profit‐driven tendency of contemporary designers today
A growth-rate indicator for Compton-thick active galactic nuclei
Due to their heavily obscured central engines, the growth rate of
Compton-thick (CT) active galactic nuclei (AGN) is difficult to measure. A
statistically significant correlation between the Eddington ratio,
{\lambda}, and the X-ray power-law index, {\Gamma}, observed in
unobscured AGN offers an estimate of their growth rate from X-ray spectroscopy
(albeit with large scatter). However, since X-rays undergo reprocessing by
Compton scattering and photoelectric absorption when the line-of-sight to the
central engine is heavily obscured, the recovery of the intrinsic {\Gamma} is
challenging. Here we study a sample of local, predominantly Compton-thick
megamaser AGN, where the black hole mass, and thus Eddington luminosity, are
well known. We compile results on X-ray spectral fitting of these sources with
sensitive high-energy (E> 10 keV) NuSTAR data, where X-ray torus models which
take into account the reprocessing effects have been used to recover the
intrinsic {\Gamma} values and X-ray luminosities, L. With a simple
bolometric correction to L to calculate {\lambda}, we find a
statistically significant correlation between {\Gamma} and {\lambda} (p
= 0.007). A linear fit to the data yields {\Gamma} =
(0.410.18)log{\lambda}+(2.38 0.20), which is
statistically consistent with results for unobscured AGN. This result implies
that torus modeling successfully recovers the intrinsic AGN parameters. Since
the megamasers have low-mass black holes (M M)
and are highly inclined, our results extend the {\Gamma}-{\lambda}
relationship to lower masses and argue against strong orientation effects in
the corona, in support of AGN unification. Finally this result supports the use
of {\Gamma} as a growth-rate indicator for accreting black holes, even for
Compton-thick AGN.Comment: Accepted for publication in Ap
Computer Components and Systems
Contains reports on three research projects.United States Navy, Bureau of Ships (Contract NObsr 77603
NuSTAR and Suzaku X-ray Spectroscopy of NGC 4151: Evidence for Reflection from the Inner Accretion Disk
We present X-ray timing and spectral analyses of simultaneous 150 ks Nuclear
Spectroscopic Telescope Array (NuSTAR) and Suzaku X-ray observations of the
Seyfert 1.5 galaxy NGC 4151. We disentangle the continuum emission, absorption,
and reflection properties of the active galactic nucleus (AGN) by applying
inner accretion disk reflection and absorption-dominated models. With a
time-averaged spectral analysis, we find strong evidence for relativistic
reflection from the inner accretion disk. We find that relativistic emission
arises from a highly ionized inner accretion disk with a steep emissivity
profile, which suggests an intense, compact illuminating source. We find a
preliminary, near-maximal black hole spin a>0.9 accounting for statistical and
systematic modeling errors. We find a relatively moderate reflection fraction
with respect to predictions for the lamp post geometry, in which the
illuminating corona is modeled as a point source. Through a time-resolved
spectral analysis, we find that modest coronal and inner disk reflection flux
variation drives the spectral variability during the observations. We discuss
various physical scenarios for the inner disk reflection model, and we find
that a compact corona is consistent with the observed features.Comment: 20 pages, 12 figures, accepted for publication in Ap
Resolving the cosmic X-ray background with a next-generation high-energy X-ray observatory
The cosmic X-ray background (CXB), which peaks at an energy of ~30 keV, is
produced primarily by emission from accreting supermassive black holes (SMBHs).
The CXB therefore serves as a constraint on the integrated SMBH growth in the
Universe and the accretion physics and obscuration in active galactic nuclei
(AGNs). This paper gives an overview of recent progress in understanding the
high-energy (>~10 keV) X-ray emission from AGNs and the synthesis of the CXB,
with an emphasis on results from NASA's NuSTAR hard X-ray mission. We then
discuss remaining challenges and open questions regarding the nature of AGN
obscuration and AGN physics. Finally, we highlight the exciting opportunities
for a next-generation, high-resolution hard X-ray mission to achieve the
long-standing goal of resolving and characterizing the vast majority of the
accreting SMBHs that produce the CXB.Comment: Science White paper submitted to Astro2020 Decadal Survey; 5 pages, 3
figures, plus references and cover pag
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