23,923 research outputs found
A deep Chandra observation of the cluster environment of the z=1.786 radio galaxy 3C294
We report the results from a 200 ks Chandra observation of the z=1.786 radio
galaxy 3C294 and its cluster environment, increasing by tenfold our earlier
observation. The diffuse emission, extending about 100 kpc around the nucleus,
has a roughly hourglass shape in the N-S direction with surprisingly sharp
edges to the N and S. The spectrum of the diffuse emission is well fitted by
either a thermal model of temperature 3.5 keV and abundance <0.9 solar
(2-sigma), or a power-law with photon index 2.3. If the emission is due to hot
gas then the sharp edges mean that it is probably not in hydrostatic
equilibrium. Much of the emission is plausibly due to inverse Compton
scattering of the Cosmic Microwave Background (CMB) by nonthermal electrons
produced earlier by the radio source. The required relativistic electrons would
be of much lower energy and older than those responsible for the present radio
lobes. This could account for the lack of detailed spatial correspondence
between the X-rays and the radio emission, the axis of which is at a position
angle of about 45 deg. Hot gas would still be required to confine the
relativistic plasma; the situation could parallel that of the radio bubbles
seen as holes in nearby clusters, except that in 3C294 the bubbles are bright
in X-rays owing to the extreme power in the source and the sixty fold increase
in the energy density of the CMB. The X-ray spectrum of the radio nucleus is
hard, showing a reflection spectrum and iron line. The source is therefore an
obscured radio-loud quasar.Comment: In press (MNRAS), 10 pages, 12 figures (2 colour
VLT near-infrared spectra of hard serendipitous Chandra sources
We present near-infrared long-slit spectra of eight optically-dim X-ray
sources obtained with ISAAC on the Very Large Telescope. Six of the sources
have hard X-ray emission with a significant fraction of the counts emerging
above 2 keV. All were discovered serendipitously in the fields of three nearby
galaxy clusters observed with Chandra, and identified through near-infrared
imaging. The X-ray fluxes lie close to the break in the source counts. Two of
the sources show narrow emission lines, and a third has a broad line. One of
the narrow line-emitting sources has a clear redshift identification at z=2.18,
while the other has a tentative determination based on the highest redshift
detection of He I 10830 at z=1.26. The remainder have featureless spectra to
deep limiting equivalent widths of 20--60 angstroms and line flux approx= 5 x
10^{-17} erg/s/cm^2 in the K-band. High-quality J, H and Ks--band images of the
sources were combined with archival optical detections or limits to estimate a
photometric redshift for six. Two sources show complex double morphology. The
hard sources have spectral count ratios consistent with heavily obscured AGN,
while the host galaxy emits much of the optical and near-infrared flux. The
most likely explanation for the featureless continua is that the line photons
are being scattered or destroyed by optically-thick gas and associated dust
with large covering fractions.Comment: Replaced in response to problems with the PDF version of Fig 4 at
arxiv.org, but not at the mirror sites (lanl.gov, soton.ac.uk). No content
change
Recommended from our members
Petrography and bulk composition of Miller Range 05035: a new lunar VLT gabbro
Miller Range (MIL) 05035 is a crystalline lunar mare gabbroic meteorite collected in Antarctica in 2005 [1]. It is an important new sample in the lunar meteorite (LM) collection as it is only one of ~8 to be classified as basaltic in nature. MIL 05035 is coarsely grained with large pyroxene grains ( 8mm) subophitically enclosing plagioclase grains ( 6mm), and accessory ilmenite, spinel, silica and sulphide phases
Extended X-ray emission around four 3C quasars at 0.55<z<0.75 observed with Chandra
We report on the detection of a soft spatially-extended component of X-ray
emission around four intermediate-redshift 3C quasars observed with Chandra:
3C254, 3C263, 3C275.1 and 3C281. The bolometric luminosity of this emission
ranges over 0.3-1.6 times 10^{44}erg/s, and extends to lengthscales of over 350
kpc at the redshift of the quasar. The X-rays are most likely thermal emission
from the intracluster medium of a cluster of galaxies around each quasar, which
provides the working surface for the powerful radio lobes. Some X-ray emission
is also seen to be associated with the radio plasma.Comment: 8 pages, 4 panelled figures, MNRAS in pres
Atomic Gas in Debris Discs
We have conducted a search for optical circumstellar absorption lines in the
spectra of 16 debris disc host stars. None of the stars in our sample showed
signs of emission line activity in either H, Ca II or Na I,
confirming their more evolved nature. Four stars were found to exhibit narrow
absorption features near the cores of the photospheric Ca II and Na I D lines
(when Na I D data were available). We analyse the characteristics of these
spectral features to determine whether they are of circumstellar or
interstellar origins. The strongest evidence for circumstellar gas is seen in
the spectrum of HD110058, which is known to host a debris disc observed close
to edge-on. This is consistent with a recent ALMA detection of molecular gas in
this debris disc, which shows many similarities to the Pictoris system.Comment: Accepted 13/12/2016. Received 2/12/2016; Deposited on 22/11/2016. -
13 Pages, 9 Figures - MNRAS Advance Access published December 15, 201
Universal trapping scaling on the unstable manifold for a collisionless electrostatic mode
An amplitude equation for an unstable mode in a collisionless plasma is
derived from the dynamics on the two-dimensional unstable manifold of the
equilibrium. The mode amplitude decouples from the phase due to the
spatial homogeneity of the equilibrium, and the resulting one-dimensional
dynamics is analyzed using an expansion in . As the linear growth rate
vanishes, the expansion coefficients diverge; a rescaling
of the mode amplitude absorbs these
singularities and reveals that the mode electric field exhibits trapping
scaling as . The dynamics for
depends only on the phase where is the derivative of the dielectric as
.Comment: 11 pages (Latex/RevTex), 2 figures available in hard copy from the
Author ([email protected]); paper accepted by Physical Review
Letter
- …