101 research outputs found
NuSTAR Observations of G11.2–0.3
We present in this paper the hard X-ray view of the pulsar wind nebula in G11.2−0.3 and its central pulsar powered pulsar J1811−1925 as seen by NuSTAR. We complement the data with Chandra for a more complete picture and confirm the existence of a hard, power-law component in the shell with photon index Γ = 2.1 ± 0.1, which we attribute to synchrotron emission. Our imaging observations of the shell show a slightly smaller radius at higher energies, consistent with Chandra results, and we find shrinkage as a function of increased energy along the jet direction, indicating that the electron outflow in the PWN may be simpler than that seen in other young PWNe. Combining NuSTAR with INTEGRAL, we find that the pulsar spectrum can be fit by a power law with Γ = 1.32 ± 0.07 up to 300 keV without evidence of curvature
Protease activity in the medium of larch (Larix spec.) embryogenic suspension cultures and medium-protein stabilization by compatible solutes
The stability of recombinant, secreted protein in the medium of transgenic plant cell cultures heavily determines the resulting protein yield, which is a crucial factor for every production system. In order to gain more knowledge about the feasability of rapidly growing larch (Larix sp.) embrogenic cell cultures as a possible expression system for recombinant proteins, spent cell culture medium was characterized in this study. An accumulation of endogenous proteins could be observed in the medium of larch embrogenic suspension cultures which reached up to 1750 μg per g fresh weight. In contrast, low protease activity accumulated within a typical 14-day culture period in the medium. This activity was up to 20 times lower than the protease activity in two callus-derived suspension cultures of tobacco (genotype R1 and BY-2) which were measured in parallel. To asses the stability of foreign proteins, medium aliquots were spiked with Immunoglobulin G (IgG) and the amount of protein degradation was determined after 23 h of incubation by SDS-PAGE. The loss of IgG was comparable in three different larch genotypes, resulting in a mean loss of 18 % during the incubation time. This loss could remarkably be diminished by the addition of ectoin derivatives, known to be protein-protective „compatible solutes“ of bacterial origin. The most effective one was hydroxyectoin which resulted in a 76 % reduction of the observed IgG degradation. The stabilization of proteins in plant cell culture medium by compatible solutes is shown here for the first time. The possible mechanism of the stabilizing effect is discussed
The Giant Flare of December 27, 2004 from SGR 1806-20
The giant flare of December 27, 2004 from SGR 1806-20 represents one of the
most extraordinary events captured in over three decades of monitoring the
gamma-ray sky. One measure of the intensity of the main peak is its effect on
X- and gamma-ray instruments. RHESSI, an instrument designed to study the
brightest solar flares, was completely saturated for ~0.5 s following the start
of the main peak. A fortuitous alignment of SGR 1806-20 near the Sun at the
time of the giant flare, however, allowed RHESSI a unique view of the giant
flare event, including the precursor, the main peak decay, and the pulsed tail.
Since RHESSI was saturated during the main peak, we augment these observations
with Wind and RHESSI particle detector data in order to reconstruct the main
peak as well. Here we present detailed spectral analysis and evolution of the
giant flare. We report the novel detection of a relatively soft fast peak just
milliseconds before the main peak, whose timescale and sizescale indicate a
magnetospheric origin. We present the novel detection of emission extending up
to 17 MeV immediately following the main peak, perhaps revealing a
highly-extended corona driven by the hyper-Eddington luminosities. The spectral
evolution and pulse evolution during the tail are presented, demonstrating
significant magnetospheric twist and evolution during this phase. Blackbody
radii are derived for every stage of the flare, which show remarkable agreement
despite the range of luminosities and temperatures covered. Finally, we place
significant upper limits on afterglow emission in the hundreds of seconds
following the giant flare.Comment: 32 pages, 14 figures, submitted to Ap
NuSTAR Observations of G11.2–0.3
We present in this paper the hard X-ray view of the pulsar wind nebula in G11.2−0.3 and its central pulsar powered pulsar J1811−1925 as seen by NuSTAR. We complement the data with Chandra for a more complete picture and confirm the existence of a hard, power-law component in the shell with photon index Γ = 2.1 ± 0.1, which we attribute to synchrotron emission. Our imaging observations of the shell show a slightly smaller radius at higher energies, consistent with Chandra results, and we find shrinkage as a function of increased energy along the jet direction, indicating that the electron outflow in the PWN may be simpler than that seen in other young PWNe. Combining NuSTAR with INTEGRAL, we find that the pulsar spectrum can be fit by a power law with Γ = 1.32 ± 0.07 up to 300 keV without evidence of curvature
Modeling Aerial Gamma-Ray Backgrounds using Non-negative Matrix Factorization
Airborne gamma-ray surveys are useful for many applications, ranging from
geology and mining to public health and nuclear security. In all these
contexts, the ability to decompose a measured spectrum into a linear
combination of background source terms can provide useful insights into the
data and lead to improvements over techniques that use spectral energy windows.
Multiple methods for the linear decomposition of spectra exist but are subject
to various drawbacks, such as allowing negative photon fluxes or requiring
detailed Monte Carlo modeling. We propose using Non-negative Matrix
Factorization (NMF) as a data-driven approach to spectral decomposition. Using
aerial surveys that include flights over water, we demonstrate that the
mathematical approach of NMF finds physically relevant structure in aerial
gamma-ray background, namely that measured spectra can be expressed as the sum
of nearby terrestrial emission, distant terrestrial emission, and radon and
cosmic emission. These NMF background components are compared to the background
components obtained using Noise-Adjusted Singular Value Decomposition (NASVD),
which contain negative photon fluxes and thus do not represent emission spectra
in as straightforward a way. Finally, we comment on potential areas of research
that are enabled by NMF decompositions, such as new approaches to spectral
anomaly detection and data fusion.Comment: 14 pages, 12 figures, accepted for publication in IEEE Transactions
on Nuclear Scienc
Broadband X-ray Imaging and Spectroscopy of the Crab Nebula and Pulsar with NuSTAR
We present broadband (3 -- 78 keV) NuSTAR X-ray imaging and spectroscopy of
the Crab nebula and pulsar. We show that while the phase-averaged and spatially
integrated nebula + pulsar spectrum is a power-law in this energy band,
spatially resolved spectroscopy of the nebula finds a break at 9 keV in
the spectral photon index of the torus structure with a steepening
characterized by . We also confirm a previously reported
steepening in the pulsed spectrum, and quantify it with a broken power-law with
break energy at 12 keV and . We present spectral
maps of the inner 100\as\ of the remnant and measure the size of the nebula as
a function of energy in seven bands. These results find that the rate of
shrinkage with energy of the torus size can be fitted by a power-law with an
index of , consistent with the predictions of Kennel
and Coroniti (1984). The change in size is more rapid in the NW direction,
coinciding with the counter-jet where we find the index to be a factor of two
larger. NuSTAR observed the Crab during the latter part of a -ray
flare, but found no increase in flux in the 3 - 78 keV energy band
A Spatially Resolved Study of the Synchrotron Emission and Titanium in Tycho's Supernova Remnant with NuSTAR
We report results from deep observations (~750 ks) of Tycho's supernova
remnant (SNR) with NuSTAR. Using these data, we produce narrow-band images over
several energy bands to identify the regions producing the hardest X-rays and
to search for radioactive decay line emission from 44Ti. We find that the
hardest (>10 keV) X-rays are concentrated in the southwest of Tycho, where
recent Chandra observations have revealed high emissivity "stripes" associated
with particles accelerated to the knee of the cosmic-ray spectrum. We do not
find evidence of 44Ti, and we set limits on its presence and distribution
within the SNR. These limits correspond to a upper-limit 44Ti mass of M44 <
2.4x10^-4 M_sun for a distance of 2.3 kpc. We perform spatially resolved
spectroscopic analysis of sixty-six regions across Tycho. We map the best-fit
rolloff frequency of the hard X-ray spectra, and we compare these results to
measurements of the shock expansion and ambient density. We find that the
highest energy electrons are accelerated at the lowest densities and in the
fastest shocks, with a steep dependence of the roll-off frequency with shock
velocity. Such a dependence is predicted by models where the maximum energy of
accelerated electrons is limited by the age of the SNR rather than by
synchrotron losses, but this scenario requires far lower magnetic field
strengths than those derived from observations in Tycho. One way to reconcile
these discrepant findings is through shock obliquity effects, and future
observational work is necessary to explore the role of obliquity in the
particle acceleration process.Comment: 12 pages, 12 figures, ApJ in pres
The Hard X-Ray View of the Young Supernova Remnant G1.9+0.3
NuSTAR observed G1.9+0.3, the youngest known supernova remnant in the Milky
Way, for 350 ks and detected emission up to 30 keV. The remnant's X-ray
morphology does not change significantly across the energy range from 3 to 20
keV. A combined fit between NuSTAR and CHANDRA shows that the spectrum steepens
with energy. The spectral shape can be well fitted with synchrotron emission
from a power-law electron energy distribution with an exponential cutoff with
no additional features. It can also be described by a purely phenomenological
model such as a broken power-law or a power-law with an exponential cutoff,
though these descriptions lack physical motivation. Using a fixed radio flux at
1 GHz of 1.17 Jy for the synchrotron model, we get a column density of N = cm, a spectral index of
, and a roll-off frequency of Hz. This can be explained by particle
acceleration, to a maximum energy set by the finite remnant age, in a magnetic
field of about 10 G, for which our roll-off implies a maximum energy of
about 100 TeV for both electrons and ions. Much higher magnetic-field strengths
would produce an electron spectrum that was cut off by radiative losses, giving
a much higher roll-off frequency that is independent of magnetic-field
strength. In this case, ions could be accelerated to much higher energies. A
search for Ti emission in the 67.9 keV line results in an upper limit of
assuming a line width of 4.0 keV (1 sigma).Comment: 9 pages, 6 figures, accepted Ap
NuSTAR study of Hard X-Ray Morphology and Spectroscopy of PWN G21.5-0.9
We present NuSTAR high energy X-ray observations of the pulsar wind nebula
(PWN)/supernova remnant G21.5-0.9. We detect integrated emission from the
nebula up to ~40 keV, and resolve individual spatial features over a broad
X-ray band for the first time. The morphology seen by NuSTAR agrees well with
that seen by XMM-Newton and Chandra below 10 keV. At high energies NuSTAR
clearly detects non-thermal emission up to ~20 keV that extends along the
eastern and northern rim of the supernova shell. The broadband images clearly
demonstrate that X-ray emission from the North Spur and Eastern Limb results
predominantly from non-thermal processes. We detect a break in the spatially
integrated X-ray spectrum at ~9 keV that cannot be reproduced by current SED
models, implying either a more complex electron injection spectrum or an
additional process such as diffusion compared to what has been considered in
previous work. We use spatially resolved maps to derive an energy-dependent
cooling length scale, with . We find
this to be inconsistent with the model for the morphological evolution with
energy described by Kennel & Coroniti (1984). This value, along with the
observed steepening in power-law index between radio and X-ray, can be
quantitatively explained as an energy-loss spectral break in the simple scaling
model of Reynolds (2009), assuming particle advection dominates over diffusion.
This interpretation requires a substantial departure from spherical
magnetohydrodynamic (MHD), magnetic-flux-conserving outflow, most plausibly in
the form of turbulent magnetic-field amplification.Comment: 13 pages, 8 figures, 1 table, Accepted for publication in the
Astrophysical Journa
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