544 research outputs found
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
Letters to the Editor
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66389/1/j.1600-0447.1989.tb03017.x.pd
The Swift BAT Perspective on Non-thermal Emission in HIFLUGCS Galaxy Clusters
The search for diffuse non-thermal, inverse Compton (IC) emission from galaxy
clusters at hard X-ray energies has been underway for many years, with most
detections being either of low significance or controversial. In this work, we
investigate 14-195 keV spectra from the Swift Burst Alert Telescope (BAT)
all-sky survey for evidence of non-thermal excess emission above the
exponentially decreasing tail of thermal emission in the flux-limited HIFLUGCS
sample. To account for the thermal contribution at BAT energies, XMM-Newton
EPIC spectra are extracted from coincident spatial regions so that both thermal
and non-thermal spectral components can be determined simultaneously. We find
marginally significant IC components in six clusters, though after closer
inspection and consideration of systematic errors we are unable to claim a
clear detection in any of them. The spectra of all clusters are also summed to
enhance a cumulative non-thermal signal not quite detectable in individual
clusters. After constructing a model based on single-temperature fits to the
XMM-Newton data alone, we see no significant excess emission above that
predicted by the thermal model determined at soft energies. This result also
holds for the summed spectra of various subgroups, except for the subsample of
clusters with diffuse radio emission. For clusters hosting a diffuse radio
halo, a relic, or a mini-halo, non-thermal emission is initially detected at
the \sim5-sigma confidence level - driven by clusters with mini-halos - but
modeling and systematic uncertainties ultimately degrade this significance. In
individual clusters, the non-thermal pressure of relativistic electrons is
limited to \sim10% of the thermal electron pressure, with stricter limits for
the more massive clusters, indicating that these electrons are likely not
dynamically important in the central regions of clusters.Comment: 25 pages, 15 figures; some figure and table numbering differs from
published ApJ version: please see that for superior formattin
Hard X-ray Properties of the Merging Cluster Abell 3667 as Observed with Suzaku
Wide-band Suzaku data on the merging cluster Abell 3667 were examined for
hard X-ray emission in excess to the known thermal component. Suzaku detected
X-ray signals in the wide energy band from 0.5 to 40 keV. The hard X-ray (> 10
keV) flux observed by the HXD around the cluster center cannot be explained by
a simple extension of the thermal emission with average temperature of ~7 keV.
The emission is most likely an emission from a very hot (kT > 13.2 keV) thermal
component around the cluster center, produced via a strong heating process in
the merger. In the north-west radio relic, no signature of non-thermal emission
was observed. Using the HXD, the overall upper-limit flux within a 34'x34'
field-of-view around the relic is derived to be 5.3e-12 erg s-1 cm-2 in the
10-40 keV band, after subtracting the ICM contribution estimated using the XIS
or the XMM-Newton spectra. Directly on the relic region, the upper limit is
further tightened by the XIS data to be less than 7.3e-13 erg s-1 cm-2, when
converted into the 10--40 keV band. The latter value suggest that the average
magnetic field within the relic is higher than 1.6 uG. The non-thermal pressure
due to magnetic fields and relativistic electrons may be as large as ~20% of
the thermal pressure in the region.Comment: 18 pages, 13 figures, to be appeared in PASJ 200
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
The NuSTAR, XMM-Newton, and Suzaku View of A3395 at the Intercluster Filament Interface
Galaxy clusters are the largest virialized objects in the universe. Their merger dynamics and their interactions with the cosmic filaments that connect them are important for our understanding of the formation of large-scale structure. In addition, cosmic filaments are thought to possess the missing baryons in the universe. Studying the interaction of galaxy clusters and filaments therefore has the potential to unveil the origin of the baryons and the physical processes that occur during merger stages of galaxy clusters. In this paper, we study the connection between A3395 and the intercluster filament with NuSTAR, XMM-Newton, and Suzaku data. Since the NuSTAR observation is moderately contaminated by scattered light, we present a novel technique developed for disentangling this background from the emission from the intracluster medium. We find that the interface of the cluster and the intercluster filament connecting A3395 and A3391 does not show any signs of heated plasma, as was previously thought. This interface has low temperature, high density, and low entropy, thus we suggest that the gas is cooling, being enhanced by the turbulent or tidal "weather"driven during the early stage of the merger. Furthermore, our temperature results from the NuSTAR data are in agreement with those from XMM-Newton and from joint NuSTAR and XMM-Newton analysis for a region with ∼25% scattered light contamination within 1σ. We show that the temperature constraint of the intracluster medium is valid even when the data are contaminated up to ∼25% for ∼5 keV cluster emission
GRB 000418: A Hidden Jet Revealed?
We report on optical, near-infrared and centimeter radio observations of
GRB000418 which allow us to follow the evolution of the afterglow from 2 to 200
days after the gamma-ray burst. In modeling these broad-band data, we find that
an isotropic explosion in a constant density medium is unable to simultaneously
fit both the radio and optical data. However, a jet-like outflow with an
opening angle of 10-20 degress provides a good description of the data. The
evidence in favor of a jet interpretation is based on the behavior of the radio
light curves, since the expected jet break is masked at optical wavelengths by
the light of the host galaxy. We also find evidence for extinction, presumably
arising from within the host galaxy, with A(V)=0.4 mag, and host flux densities
of F_R=1.1 uJy and F_K=1.7 uJy. These values supercede previous work on this
burst due to the availability of a broad-band data set allowing a global
fitting approach. A model in which the GRB explodes into a wind-stratified
circumburst medium cannot be ruled out by these data. However, in examining a
sample of other bursts (e.g. GRB990510, GRB000301C) we favor the jet
interpretation for GRB000418.Comment: ApJ, submitte
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
A Hard X-ray Study of the Normal Star-Forming Galaxy M83 with NuSTAR
We present results from sensitive, multi-epoch NuSTAR observations of the
late-type star-forming galaxy M83 (d=4.6 Mpc), which is the first investigation
to spatially resolve the hard (E>10 keV) X-ray emission of this galaxy. The
nuclear region and ~ 20 off-nuclear point sources, including a previously
discovered ultraluminous X-ray (ULX) source, are detected in our NuSTAR
observations. The X-ray hardnesses and luminosities of the majority of the
point sources are consistent with hard X-ray sources resolved in the starburst
galaxy NGC 253. We infer that the hard X-ray emission is most likely dominated
by intermediate accretion state black hole binaries and neutron star low-mass
X-ray binaries (Z-sources). We construct the X-ray binary luminosity function
(XLF) in the NuSTAR band for an extragalactic environment for the first time.
The M83 XLF has a steeper XLF than the X-ray binary XLF in NGC 253, consistent
with previous measurements by Chandra at softer X-ray energies. The NuSTAR
integrated galaxy spectrum of M83 drops quickly above 10 keV, which is also
seen in the starburst galaxies NGC253, NGC 3310 and NGC 3256. The NuSTAR
observations constrain any AGN to be either highly obscured or to have an
extremely low luminosity of 10 erg/s (10-30 keV), implying it
is emitting at a very low Eddington ratio. An X-ray point source consistent
with the location of the nuclear star cluster with an X-ray luminosity of a few
times 10 erg/s may be a low-luminosity AGN but is more consistent with
being an X-ray binary.Comment: Accepted for publication in ApJ (25 pages, 17 figures
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