813 research outputs found
Letter from McHenry County Sheriff regarding Treatment of Prisoners by the Minot Police Department, July 1918
Letter from McHenry County Sheriff J.A. Wik to Attorney General Langer regarding the treatment of prisoners in Minot, North Dakota, dated July 18, 1918. Wik writes that he has interviewed the prisoners about their treatment at the hands of the Minot Police Department but none of the prisoners cooperated.https://commons.und.edu/langer-papers/1294/thumbnail.jp
Liftable vector fields over corank one multigerms
In this paper, a systematic method is given to construct all liftable vector
fields over an analytic multigerm of
corank at most one admitting a one-parameter stable unfolding.Comment: 34 pages. In ver. 2, several careless mistakes for calculations in
Section 6 were correcte
XMM-Newton Observation of the Northwest Radio Relic Region in Abell 3667
Abell 3667 is the archetype of a merging cluster with radio relics. The NW
radio relic is the brightest cluster relic or halo known, and is believed to be
due to a strong merger shock. We have observed the NW relic for 40 ksec of net
XMM time. We observe a global decline of temperature across the relic from 6 to
1 keV, similar to the Suzaku results. Our new observations reveal a sharp
change of both temperature and surface brightness near the position of the
relic. The increased X-ray emission on the relic can be equivalently well
described by either a thermal or nonthermal spectral model. The parameters of
the thermal model are consistent with a Mach number M~2 shock and a shock speed
of ~1200 km s^-1. The energy content of the relativistic particles in the radio
relic can be explained if they are (re)-accelerated by the shock with an
efficiency of ~0.2%. Comparing the limit on the inverse Compton X-ray emission
with the measured radio synchrotron emission, we set a lower limit to the
magnetic field in the relic of 3 muG. If the emission from the relic is
non-thermal, this lower limit is in fact the required magnetic field.Comment: 11 pages, ApJ in pres
On the absence of radio halos in clusters with double relics
Pairs of radio relics are believed to form during cluster mergers, and are
best observed when the merger occurs in the plane of the sky. Mergers can also
produce radio halos, through complex processes likely linked to turbulent
re-acceleration of cosmic-ray electrons. However, only some clusters with
double relics also show a radio halo. Here, we present a novel method to derive
upper limits on the radio halo emission, and analyse archival X-ray Chandra
data, as well as galaxy velocity dispersions and lensing data, in order to
understand the key parameter that switches on radio halo emission. We place
upper limits on the halo power below the
correlation for some clusters, confirming that clusters with double relics have
different radio properties. Computing X-ray morphological indicators, we find
that clusters with double relics are associated with the most disturbed
clusters. We also investigate the role of different mass-ratios and
time-since-merger. Data do not indicate that the merger mass ratio has an
impact on the presence or absence of radio halos (the null hypothesis that the
clusters belong to the same group cannot be rejected). However, the data
suggests that the absence of radio halos could be associated with early and
late mergers, but the sample is too small to perform a statistical test. Our
study is limited by the small number of clusters with double relics. Future
surveys with LOFAR, ASKAP, MeerKat and SKA will provide larger samples to
better address this issue.Comment: 12 pages, 7 figures, MNRAS accepte
Supermodel Analysis of the Hard X-Ray Excess in the Coma Cluster
The Supermodel provides an accurate description of the thermal contribution
by the hot intracluster plasma which is crucial for the analysis of the hard
excess. In this paper the thermal emissivity in the Coma cluster is derived
starting from the intracluster gas temperature and density profiles obtained by
the Supermodel analysis of X-ray observables: the XMM-Newton temperature
profile and the Rosat brightness distribution. The Supermodel analysis of the
BeppoSAX/PDS hard X-ray spectrum confirms our previous results, namely an
excess at the c.l. of ~4.8sigma and a nonthermal flux of 1.30+-0.40x 10^-11 erg
cm^-2 s^-1 in the energy range 20-80 keV. A recent joint XMM-Newton/Suzaku
analysis reports an upper limit of ~6x10^-12 erg cm^-2 s^-1 in the energy range
20-80 keV for the nonthermal flux with an average gas temperature of 8.45+-0.06
keV, and an excess of nonthermal radiation at a confidence level above 4sigma,
without including systematic effects, for an average XMM-Newton temperature of
8.2 keV in the Suzaku/HXD-PIN FOV, in agreement with our earlier PDS analysis.
Here we present a further evidence of the compatibility between the Suzaku and
BeppoSAX spectra, obtained by our Supermodel analysis of the PDS data, when the
smaller size of the HXD-PIN FOV and the two different average temperatures
derived by XMM-Newton and by the joint XMM-Newton/Suzaku analysis are taken
into account. The consistency of the PDS and HXD-PIN spectra reaffirms the
presence of a nonthermal component in the hard X-ray spectrum of the Coma
cluster. The Supermodel analysis of the PDS data reports an excess at c.l.
above 4sigma also for the higher average temperature of 8.45 keV thanks to the
PDS FOV considerably greater than the HXD-PIN FOV.Comment: 18 pages, 7 figures, accepted for publication in Ap
Dark matter line emission constraints from NuSTAR observations of the Bullet Cluster
Line emission from dark matter is well motivated for some candidates e.g.
sterile neutrinos. We present the first search for dark matter line emission in
the 3-80keV range in a pointed observation of the Bullet Cluster with NuSTAR.
We do not detect any significant line emission and instead we derive upper
limits (95% CL) on the flux, and interpret these constraints in the context of
sterile neutrinos and more generic dark matter candidates. NuSTAR does not have
the sensitivity to constrain the recently claimed line detection at 3.5keV, but
improves on the constraints for energies of 10-25keV.Comment: 7 pages, 5 figures, submitted to Ap
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