187 research outputs found
X-ray discovery of a dwarf-galaxy galaxy collision
We report the discovery of a probable dwarf galaxy colliding with NGC 1232.
This collision is visible only in the X-ray spectral band, and it is creating a
region of shocked gas with a temperature of 5.8 MK covering an impact area 7.25
kpc in diameter. The X-ray luminosity is 3.7 x1038ergs s-1. The long lifetime
of this gas against radiative and adiabatic cooling should permit the use of
the luminous afterglow from such collisions to be used as a way of estimating
their importance in galaxy evolution.Comment: 5 Pages, Published in ApJ 770, 17, 201
Chandra observations of the pulsar PSR B1929+10 and its environment
We report on two Chandra observations of the 3-Myr pulsar B1929+10, which
reveal a faint compact (~9"x5") nebula elongated in the direction perpendicular
to the pulsar's proper motion, two patchy wings, and a possible short (~3") jet
emerging from the pulsar. In addition, we detect a tail extending up to at
least 4' in the direction opposite to the pulsar's proper motion, aligned with
the 15'-long tail detected in ROSAT and XMM-Newton observations. The overall
morphology of the nebula suggests that the shocked pulsar wind is confined by
the ram pressure due to the pulsar's supersonic speed. The shape of the compact
nebula in the immediate vicinity of the pulsar seems to be consistent with the
current MHD models. However, since these models do not account yet for the
change of the flow velocity at larger distances from the pulsar, they are not
able to constrain the extent of the long pulsar tail. The luminosity of the
whole nebula as seen by Chandra is ~10^30 ergs/s in the 0.3-8 keV band, for the
distance of 361 pc. Using the Chandra and XMM-Newton data, we found that the
pulsar spectrum is comprised of non-thermal (magnetospheric) and thermal
components. The non-thermal component can be described by a power-law model
with photon index ~1.7 and luminosity 1.7x10^30 ergs/s in the 0.3-10 keV band.
The blackbody fit for the thermal component, which presumably emerges from hot
polar caps, gives the temperature kT~0.3 keV and projected emitting area 3x10^3
m^2, corresponding to the bolometric luminosity ~(1-2)x10^30 ergs/s.Comment: 14 pages, 12 figures and 2 tables; accepted by ApJ; version with
low-resolution figure
X-ray emission from J1446-4701, J1311-3430 and other black widow pulsars
We present the results of detailed X-ray analysis of two black-widow pulsars
(BWPs), J1446-4701 and J1311-3430. PSR J1446-4701 is a BWP with orbital
parameters near the median values of the sample of known BWPs. Its X-ray
emission detected by is well characterized by a soft power-law
(PL) spectrum (photon index ), and it shows no significant
orbital modulations. In view of a lack of radio eclipses and an optical
non-detection, the system most likely has a low orbital inclination. PSR
J1311-3430 is an extreme BWP with a very compact orbit and the lowest minimum
mass companion. Our data confirm the hard, ,
emission seen in previous observations. Through phase-restricted spectral
analysis, we found a hint () of spectral hardening around
pulsar inferior conjunction. We also provide a uniform analysis of the 12 BWPs
observed with and compare their X-ray properties. Pulsars with soft,
, emission seem to have lower than average X-ray and -ray
luminosities. We do not, however, see any other prominent correlation between
the pulsar's X-ray emission characteristics and any of its other properties.
The contribution of the intra-binary shock to the total X-ray emission, if any,
is not discernible in this sample of pulsars with shallow observations.Comment: 15 pages, 10 figures, accepted by Ap
X-ray Source Population in the Elliptical Galaxy NGC 720 with Chandra
With a Chandra ACIS-S3 observation, we detect 42 X-ray point sources in the
elliptical galaxy NGC 720, including a possible central source. Most of these
sources will be low-mass X-ray binaries (LMXBs), and 12 are located within 2"
of globular cluster candidates. We investigate both the hardness ratios and
combined spectra of the sources. They exhibit a distribution of X-ray colors
similar to those seen in other early-type galaxies. We find that there is a
population of highly absorbed sources located at large distances from the
center of the galaxy. The overall spatial distribution of sources is consistent
with the ellipticity and position angle of the galaxy, but the sources appear
to form several arcs. NGC 720 contains nine ultraluminous sources (L_x >= 10^39
ergs/s). This number is more than have previously been detected in an
early-type galaxy but similar to the number seen in the Antennae merger system.
The ratio L_ULX/L_B for NGC 720 is more than double the ratio for the S0 galaxy
NGC 1553 and a factor of seven higher than for the elliptical galaxy NGC 4697,
although uncertainties in the distance and the source spectral properties could
bring these ratios into agreement. The X-ray source luminosity function is also
nearly as flat as those seen in disk and merger systems. The large number of
ULXs in NGC 720 and its relatively flat XLF may provide evidence against the
association of all ULXs with young stars. We also see a possible high
luminosity break in the luminosity function at 2x10^39 h_50^-2 ergs/s.Comment: 28 pages, 7 figures, accepted for publication in Ap
Chandra X-ray Observations of Newly Discovered, z ~ 1 Clusters from the Red-Sequence Cluster Survey
Observational studies of cluster evolution over moderate redshift ranges (to
z ~ 1) are a powerful tool for constraining cosmological parameters, yet a
comprehensive knowledge of the properties of these clusters has been hitherto
unattained. Using a highly efficient optical selection technique, the
Red-Sequence Cluster Survey (RCS) has unearthed a large sample of high redshift
cluster candidates. All six of the clusters from this sample which have been
observed with the Chandra X-Ray Observatory were detected in the X-ray. These
Chandra follow-up observations (0.64 < z < 1.0) indicate that the clusters are
systematically less luminous than their similarly rich, X-ray selected
counterparts at lower redshifts, though they are consistent with standard Lx-Tx
relationships. Comparisons with X-ray selected samples suggest that the
discrepancy may be due in part to systematic differences in the spatial
structure of the X-ray emitting gas. Our initial results from Chandra follow-up
observations of six RCS clusters are presented, including beta model parameters
and spectral information.Comment: 8 pages, 4 figures. To appear in Advances in Space Research.
Presented at the 35th COSPAR Scientific Assembly, Paris, France, 18-25 July
2004 - Scientific Commission E1.2: Clusters of Galaxies: New Insights from
XMM-Newton, Chandra and INTEGRA
Supernova Remnant 1987A: The Latest Report from the Chandra X-Ray Observatory
We continue monitoring supernova remnant (SNR) 1987A with the {\it Chandra
X-ray Observatory}. As of 2004 January, bright X-ray spots in the northwest and
the southwest are now evident in addition to the bright eastern ring. The
overall X-ray spectrum, Since 2002 December, can be described by a planar shock
with an electron temperature of 2.1 keV. The soft X-ray flux is now 8
10 ergs cm s, which is about five times higher
than four years ago. This flux increase rate is consistent with our prediction
based on an exponential density distribution along the radius of the SNR
between the H{\small II} region and the inner ring. We still have no direct
evidence of a central point source, and place an upper limit of = 1.3
10 ergs s on the 310 keV band X-ray luminosity.Comment: 9 pages, AdSpR in pres
Investigating the X-ray enhancements of highly radio-loud quasars at z > 4
We have investigated the jet-linked \mbox{X-ray} emission from highly
radio-loud quasars (HRLQs; ) at high redshift. We studied the X-ray
properties of 15 HRLQs at , using new {\it Chandra} observations for six
objects and archival {\it XMM-Newton} and {\it Swift} observations for the
other nine. We focused on testing the apparent enhancement of jet-linked
\mbox{X-ray} emission from HRLQs at . Utilizing an enlarged (24 objects)
optically flux-limited sample with complete X-ray coverage, we confirmed that
HRLQs at have enhanced X-ray emission relative to that of HRLQs at
1--2 with matched UV/optical and radio luminosity, at a
\mbox{4.0--4.6}~ level; the X-ray enhancements are confirmed
considering both two-point spectral indices and inspection of broad-band
spectral energy distributions. The typical factor of enhancement is revised to
, which is smaller than but consistent with previous
results. A fractional IC/CMB model can still explain our results at high
redshift, which puts tighter constraints on the fraction of IC/CMB X-rays at
lower redshifts, assuming the physical properties of quasar jets do not have a
strong redshift dependence. A dominant IC/CMB model is inconsistent with our
data.Comment: 25 pages, 12 figures, Accepted for publication in MNRA
Stellar Clusters in the NGC 6334 Star Forming Complex
The full stellar population of NGC 6334, one of the most spectacular regions
of massive star formation in the nearby Galaxy, have not been well-sampled in
past studies. We analyze here a mosaic of two Chandra X-ray Observatory images
of the region using sensitive data analysis methods, giving a list of 1607
faint X-ray sources with arcsecond positions and approximate line-of-sight
absorption. About 95 percent of these are expected to be cluster members, most
lower mass pre-main sequence stars. Extrapolating to low X-ray levels, the
total stellar population is estimated to be 20-30,000 pre-main sequence stars.
The X-ray sources show a complicated spatial pattern with about 10 distinct
star clusters. The heavily-obscured clusters are mostly associated with
previously known far-infrared sources and radio HII regions. The
lightly-obscured clusters are mostly newly identified in the X-ray images.
Dozens of likely OB stars are found, both in clusters and dispersed throughout
the region, suggesting that star formation in the complex has proceeded over
millions of years. A number of extraordinarily heavily absorbed X-ray sources
are associated with the active regions of star formation.Comment: To appear in the Astronomical Journal. A version with high-quality
figures appears at http://www.astro.psu.edu/users/edf/NGC6334.pd
An X-ray and Multiwavelength Survey of Highly Radio-Loud Quasars at z > 4: Jet-Linked Emission in the Brightest Radio Beacons of the Early Universe
(Abridged) We present a systematic study of the X-ray and multiwavelength
properties of a sample of 17 highly radio-loud quasars (HRLQs) at z > 4 with
sensitive X-ray coverage from new Chandra and archival Chandra, XMM-Newton, and
Swift observations. Eight of the new and archival observations are reported in
this work for the first time. New Chandra observations of two moderately
radio-loud and highly optically luminous quasars at z > 4 are also reported.
Our HRLQ sample represents the top ~5% of radio-loud quasars in terms of radio
loudness. We found that our HRLQs have an X-ray emission enhancement over HRLQs
at lower redshifts (by a typical factor of ~3), and this effect, after
controlling for several factors which may introduce biases, has been solidly
estimated to be significant at the 3-4 sigma level. HRLQs at z=3-4 are also
found to have a similar X-ray emission enhancement over z < 3 HRLQs, which
supports further the robustness of our results. We discuss models for the X-ray
enhancement's origin including a fractional contribution from inverse Compton
scattering of cosmic microwave background photons. No strong correlations are
found between the relative X-ray brightness and optical/UV emission-line
rest-frame equivalent widths (REWs) for radio-loud quasars. However, the line
REWs are positively correlated with radio loudness, which suggests that
relativistic jets make a negligible contribution to the optical/UV continua of
these HRLQs (contrary to the case where the emission lines are diluted by the
relativistically boosted continuum). Our HRLQs are generally consistent with
the known anti-correlation between radio loudness and X-ray power-law photon
index. We also found that the two moderately radio-loud quasars appear to have
the hardest X-ray spectra among our objects, suggesting that intrinsic X-ray
absorption (N_H~10^23 cm^-2) may be present.Comment: ApJ in press; 9 figures, 13 table
The Small-scale Structure of N103B - Nature of Nuture?
We present new results from a 40.8 ks Chandra ACIS observation of the young
supernova remnant (SNR) N103B located in the Large Magellanic Cloud. The high
resolution Chandra image reveals structure at the sub-arcsecond level,
including several bright knots and filaments. Narrow-band imaging and spatially
resolved spectroscopy reveal dramatic spectral variations in this remnant as
well. In this paper we discuss whether these variations are due to
inhomogeneities in the surrounding environment or were generated in the
explosion which created the SNR.Comment: 6 pages, 5 figures, in "X-rays at Sharp Focus: Chandra Science
Symposium", July 16-18, 200
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