53,429 research outputs found
A search for energy-dependence of the Kes 73/1E 1841-045 morphology in GeV
While the Kes 73/1E 1841-045 system had been confirmed as an extended GeV
source, whether its morphology depends on the photon energy or not deserves our
further investigation. Adopting data collected by Fermi Large Area Telescope
(LAT) again, we look into the extensions of this source in three energy bands
individually: 0.3-1 GeV, 1-3 GeV and 3-200 GeV. We find that the 0.3-1 GeV
morphology is point-like and is quite different from those in the other two
bands, although we cannot robustly reject a unified morphology for the whole
LAT band.Comment: Approved for publication in PoS as a proceeding of the 7th
International Fermi Symposium (IFS2017
Tip-sample interactions in atomic force microscopy: I. Modulating adhesion between silicon nitride and glass
An adhesive interaction between a silicon nitride AFM tip and glass substrate in water is described. This adhesion is in the range 5-40 nN, of which a large component is likely to be due to hydrogen bonding between the silanol groups on both surfaces. The interaction can be modulated by a variety of buffers commonly used in biochemical and biological research, including sodium phosphate, tris(hydroxymethyl)aminomethane, glycine, and N-2-hydroxyethyl-piperazine N'-2-ethanesulfonic acid. Using these buffers it appears that there are effects of ion concentration, ion type and pH on the measured adhesion. Of the conditions examined, phosphate was most effective at reducing adhesion and could be used at concentrations as low as 10 mM at neutral pH. The results demonstrate that the chemical interactions between tip and sample can be modulated, and provide a basis for designing conditions for imaging and manipulating biological molecules and structures
Fermi Large Area Telescope Observations of the Fast-dimming Crab Nebula in 60-600 MeV
Context: The Crab pulsar and its nebula are the origin of relativistic
electrons which can be observed through their synchrotron and inverse Compton
emission. The transition between synchrotron-dominated and
inverse-Compton-dominated emissions takes place at eV. Aims: The
short-term (weeks to months) flux variability of the synchrotron emission from
the most energetic electrons is investigated with data from ten years of
observations with the Fermi Large Area Telescope (LAT) in the energy range from
60 MeV to 600 MeV. Methods: The off-pulse light-curve has been reconstructed
from phase-resolved data. The corresponding histogram of flux measurements is
used to identify distributions of flux-states and the statistical significance
of a lower-flux component is estimated with dedicated simulations of mock
light-curves. The energy spectra for different flux states are reconstructed.
Results: We confirm the presence of flaring-states which follow a log-normal
flux distribution. Additionally, we discover a low-flux state where the flux
drops to as low as 18.4% of the intermediate-state average flux and stays there
for several weeks. The transition time is observed to be as short as 2 days.
The energy spectrum during the low-flux state resembles the extrapolation of
the inverse-Compton spectrum measured at energies beyond several GeV energy,
implying that the high-energy part of the synchrotron emission is dramatically
depressed. Conclusions: The low-flux state found here and the transition time
of at most 10 days indicate that the bulk (%) of the synchrotron emission
above eV originates in a compact volume with apparent angular size of
. We tentatively infer that
the so-called inner knot feature is the origin of the bulk of the -ray
emission.Comment: Accepted by A&A on 05.05.2020; Original version submitted on
19.09.201
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