[show abstract][hide abstract] ABSTRACT: (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.
The Astrophysical Journal 12/2012; 763(2). · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: Isolated compact groups of galaxies (CGs) present a range of dynamical
states, group velocity dispersions, and galaxy morphologies with which to study
galaxy evolution, particularly the properties of gas both within the galaxies
and in the intragroup medium. As part of a large, multiwavelength examination
of CGs, we present an archival study of diffuse X-ray emission in a subset of
nine Hickson compact groups observed with the Chandra X-ray Observatory. We
find that seven of the groups in our sample exhibit detectable diffuse
emission. However, unlike large-scale emission in galaxy clusters, the diffuse
features in the majority of the detected groups are linked to the individual
galaxies, in the form of both plumes and halos likely as a result of star
formation or AGN activity, as well as in emission from tidal features. Unlike
previous studies from earlier X-ray missions, HCGs 31, 42, 59, and 92 are found
to be consistent with the Lx-T relationship from clusters within the errors,
while HCGs 16 and 31 are consistent with the cluster Lx-sigma relation, though
this is likely coincidental given that the hot gas in these two systems is
largely due to star formation. We find that Lx increases with decreasing group
HI to dynamical-mass ratio with tentative evidence for a dependance in X-ray
luminosity on HI morphology whereby systems with intragroup HI indicative of
strong interactions are considerably more X-ray luminous than passively
evolving groups. We also find a gap in the Lx of groups as a function of the
total group specific star formation rate. Our findings suggest that the hot gas
in these groups is not in hydrostatic equilibrium and these systems are not
low-mass analogs of rich groups or clusters, with the possible exception of HCG
The Astrophysical Journal 12/2012; 763(2). · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: XPHOT is an IDL implementation of a non-parametric method for estimating
the apparent and intrinsic broad-band fluxes and absorbing X-ray column
densities of weak X-ray sources. XPHOT is intended for faint sources
with greater than ˜5-7 counts but fewer than 100-300 counts where
parametric spectral fitting methods will be superior. This method is
similar to the long-standing use of color-magnitude diagrams in optical
and infrared astronomy, with X-ray median energy replacing color index
and X-ray source counts replacing magnitude. Though XPHOT was calibrated
for thermal spectra characteristic of stars in young stellar clusters,
recalibration should be possible for some other classes of faint X-ray
sources such as extragalactic active galactic nuclei.
[show abstract][hide abstract] ABSTRACT: Giant HII regions represent the dominant model of star formation (SF) in
the Galaxy, and the Cepheus Loop is an excellent nearby prototype for
giant, asymmetric HII bubbles. We propose a Spitzer/IRAC mosaic of the
rich and compact principal ionizing cluster Be59 and its parental cloud.
These Spitzer data in conjunction with our X-ray, archival IR, and
follow-up optical data will allow us: 1) to search for and characterize
a suspected older generation of stars that could have both carved the
Cepheus Loop and induced the formation of Be59, and 2) to quantify
recent and current SF in Be59 and numerous cloudlets and pillars. This
study will test an important model for the morphology and evolution of
asymmetric bubbles and advance our understanding of the effect of SF
that is layered in time and space on the SF rate in giant Galactic
[show abstract][hide abstract] ABSTRACT: We analyze the long-term (rest-frame 3-30 yr) X-Ray variability of eleven
broad absorption line (BAL) quasars, mainly to constrain the variation
properties of the X-Ray absorbing shielding gas that is thought to play a
critical role in BAL wind launching. Our BAL quasar sample has coverage with
multiple X-ray observatories including Chandra, XMM-Newton, BeppoSAX, ASCA,
ROSAT, and Einstein; 3-11 observations are available for each source. For seven
of the eleven sources we have obtained and analyzed new Chandra observations
suitable for searching for any strong X-ray variability. We find highly
significant X-Ray variability in three sources (PG 1001+054, PG 1004+130, and
PG 2112+059). The maximum observed amplitude of the 2-8 keV variability is a
factor of $3.8\pm 1.3$, $1.5\pm 0.2$, and $9.9\pm 2.3$ for PG 1001+054, PG
1004+130, and PG 2112+059, respectively, and these sources show detectable
variability on rest-frame timescales down to 5.8, 1.4, and 0.5 yr. For PG
1004+130 and PG 2112+059 we also find significant X-Ray spectral variability
associated with the flux variability. Considering our sample as a whole, we do
not find that BAL quasars exhibit exceptional long-term X-Ray variability when
compared to the quasar population in general. We do not find evidence for
common strong changes in the shielding gas owing to physical rearrangement or
accretion-disk rotation, although some changes are found; this has implications
for modeling observed ultraviolet BAL variability. Finally, we report for the
first time an X-Ray detection of the highly polarized and well-studied BAL
quasar IRAS 14026+4341 in its new Chandra observation.
The Astrophysical Journal 09/2012; 759(1). · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: In the cores of some clusters of galaxies the hot intracluster plasma is dense enough that it should cool radiatively in the cluster's lifetime, leading to continuous 'cooling flows' of gas sinking towards the cluster centre, yet no such cooling flow has been observed. The low observed star-formation rates and cool gas masses for these 'cool-core' clusters suggest that much of the cooling must be offset by feedback to prevent the formation of a runaway cooling flow. Here we report X-ray, optical and infrared observations of the galaxy cluster SPT-CLJ2344-4243 (ref. 11) at redshift z = 0.596. These observations reveal an exceptionally luminous (8.2 × 10(45) erg s(-1)) galaxy cluster that hosts an extremely strong cooling flow (around 3,820 solar masses a year). Further, the central galaxy in this cluster appears to be experiencing a massive starburst (formation of around 740 solar masses a year), which suggests that the feedback source responsible for preventing runaway cooling in nearby cool-core clusters may not yet be fully established in SPT-CLJ2344-4243. This large star-formation rate implies that a significant fraction of the stars in the central galaxy of this cluster may form through accretion of the intracluster medium, rather than (as is currently thought) assembling entirely via mergers.
[show abstract][hide abstract] ABSTRACT: In the cores of some galaxy clusters the hot intracluster plasma is dense
enough that it should cool radiatively in the cluster's lifetime, leading to
continuous "cooling flows" of gas sinking towards the cluster center, yet no
such cooling flow has been observed. The low observed star formation rates and
cool gas masses for these "cool core" clusters suggest that much of the cooling
must be offset by astrophysical feedback to prevent the formation of a runaway
cooling flow. Here we report X-ray, optical, and infrared observations of the
galaxy cluster SPT-CLJ2344-4243 at z = 0.596. These observations reveal an
exceptionally luminous (L_2-10 keV = 8.2 x 10^45 erg/s) galaxy cluster which
hosts an extremely strong cooling flow (dM/dt = 3820 +/- 530 Msun/yr). Further,
the central galaxy in this cluster appears to be experiencing a massive
starburst (740 +/- 160 Msun/yr), which suggests that the feedback source
responsible for preventing runaway cooling in nearby cool core clusters may not
yet be fully established in SPT-CLJ2344-4243. This large star formation rate
implies that a significant fraction of the stars in the central galaxy of this
cluster may form via accretion of the intracluster medium, rather than the
current picture of central galaxies assembling entirely via mergers.
[show abstract][hide abstract] ABSTRACT: Rich young stellar clusters produce HII regions whose expansion into the
nearby molecular cloud is thought to trigger the formation of new stars.
However, the importance of this mode of star formation is uncertain. This
investigation seeks to quantify triggered star formation (TSF) in IC 1396A
(a.k.a., the Elephant Trunk Nebula), a bright rimmed cloud (BRC) on the
periphery of the nearby giant HII region IC 1396 produced by the Trumpler 37
cluster. X-ray selection of young stars from Chandra X-ray Observatory data is
combined with existing optical and infrared surveys to give a more complete
census of the TSF population. Over 250 young stars in and around IC 1396A are
identified; this doubles the previously known population. A spatio-temporal
gradient of stars from the IC 1396A cloud toward the primary ionizing star HD
206267 is found. We argue that the TSF mechanism in IC 1396A is the
radiation-driven implosion process persisting over several million years.
Analysis of the X-ray luminosity and initial mass functions indicates that >140
stars down to 0.1 Msun were formed by TSF. Considering other BRCs in the IC
1396 HII region, we estimate the TSF contribution for the entire HII region
exceeds 14-25% today, and may be higher over the lifetime of the HII region.
Such triggering on the periphery of HII regions may be a significant mode of
star formation in the Galaxy.
Monthly Notices of the Royal Astronomical Society 08/2012; 426(4). · 5.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: We present 35 ks Chandra ACIS observations of the 42 Myr old radio pulsar PSR
B1451-68. A point source is detected 0.32" +/- 0.73" from the expected radio
pulsar position. It has ~200 counts in the 0.3-8 keV energy range. We identify
this point source as the X-ray counterpart of the radio pulsar. PSR B1451-68 is
located close to a 2MASS point source, for which we derive 7% as the upper
limit on the flux contribution to the measured pulsar X-ray flux. The pulsar
spectrum can be described by either a power-law model with photon index
Gamma=2.4 (+0.4/-0.3) and a unrealistically high absorbing column density N(H)=
(2.5 (+1.2/-1.3)) * 10^(21) cm^-2, or by a combination of a kT=0.35
(+0.12/-0.07) keV blackbody and a Gamma = 1.4 +/- 0.5 power-law component for
N(H)[DM]= 2.6 * 10^(20) cm^-2, estimated from the pulsar dispersion measure. At
the parallactic, Lutz-Kelker bias corrected distance of 480 pc, the non-thermal
X-ray luminosities in the 0.3-8 keV energy band are either Lx(nonth)= (11.3 +/-
1.7) * 10^(29) erg/s or Lx(nonth)= (5.9 (+4.9/-5.0)) * 10^(29) erg/s,
respectively. This corresponds to non-thermal X-ray efficiencies of either
eta(nonth)= Lx(nonth) / (dE/dt) ~ 0.005 or 0.003, respectively.
The Astrophysical Journal 02/2012; 749(2). · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: Taking advantage of the high sensitivity of the Chandra Advanced CCD Imaging
Spectrometer, we have conducted a snap-shot survey of pulsars previously
undetected in X-rays. We detected 12 pulsars and established deep flux limits
for 11 pulsars. Using these new results, we revisit the relationship between
the X-ray luminosity, L_psr_x, and spin-down power, Edot. We find that the
obtained limits further increase the extremely large spread in the non-thermal
X-ray efficiencies, eta_psr_x=L_psr_x/Edot, with some of them being now below
1e-5. Such a spread cannot be explained by poorly known distances or by beaming
of pulsar radiation. We also find evidence of a break in the dependence of
L_psr_x on Edot, such that pulsars become more X-ray efficient at Edot<~
1e34-1e35 erg/s. We examine the relationship between the gamma-ray luminosity,
L_psr_g, and Edot, which exhibits a smaller scatter compared to that in X-rays.
This confirms that the very large spread in the X-ray efficiencies cannot be
explained just by beaming because the gamma-ray emission is generally expected
to be beamed stronger than the X-ray emission. Intriguingly, there is also an
indication of a break in the L_psr_g(Edot) dependence at Edot~1e35 erg/s, with
lower-Edot pulsars becoming less gamma-ray efficient. We also examine the
distance-independent L_psr_f/L_psr_x ratio as a function of Edot for a sample
of gamma-ray pulsars observed by Chandra and find that it peaks at Edot~1e35
erg/s, showing that the breaks cannot originate from poorly measured distances.
We discuss the implications of our findings for existing models of
magnetospheric emission and venues for further exploration.
The Astrophysical Journal Supplement Series 02/2012; 201(2). · 16.24 Impact Factor
[show abstract][hide abstract] ABSTRACT: We report the discovery of 12 new fossil groups of galaxies, systems dominated by a single giant elliptical galaxy and cluster-scale gravitational potential, but lacking the population of bright galaxies typically seen in galaxy clusters. These fossil groups (FGs), selected from the maxBCG optical cluster catalog, were detected in snapshot observations with the Chandra X-ray Observatory. We detail the highly successful selection method, with an 80% success rate in identifying 12 FGs from our target sample of 15 candidates. For 11 of the systems, we determine the X-ray luminosity, temperature, and hydrostatic mass, which do not deviate significantly from expectations for normal systems, spanning a range typical of rich groups and poor clusters of galaxies. A small number of detected FGs are morphologically irregular, possibly due to past mergers, interaction of the intra-group medium (IGM) with a central AGN, or superposition of multiple massive halos. Two-thirds of the X-ray-detected FGs exhibit X-ray emission associated with the central BCG, although we are unable to distinguish between AGN and extended thermal galaxy emission using the current data. This sample, a large increase in the number of known FGs, will be invaluable for future planned observations to determine FG temperature, gas density, metal abundance, and mass distributions, and to compare to normal (non-fossil) systems. Finally, the presence of a population of galaxy-poor systems may bias mass function determinations that measure richness from galaxy counts. When used to constrain power spectrum normalization and Ω m , these biased mass functions may in turn bias these results.
The Astrophysical Journal 01/2012; 747(2). · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: We summarize the results of the late‐time Chandra observations of the X‐ray afterglow of the Swift‐discovered GRB 060729. These Chandra observations have been the latest X‐ray detections of an afterglow even, up to 21 month after the trigger. The last two Chandra observations in December 2007 and May 2008 suggest a break at about a year after the burst, implying a jet half‐opening angle of about 14 degrees, if interpreted as a jet break. As an alternative this break may have a spectral origin. In that case no jet break was observed and the half‐opening angle is larger than 15 degrees for a wind medium. Comparing the X‐ray afterglow of GRB 060729 with other bright X‐ray afterglows we discuss why the afterglow of GRB 060729 was such an exceptionally long‐lasting event. The detection by Chandra in May 2008 was the latest detection of an X‐ray afterglow at cosmological distance ever.
[show abstract][hide abstract] ABSTRACT: The Chandra Carina Complex Project (CCCP) is a 1.42deg2^ survey, at an assumed distance of 2.3kpc, of the Great Nebula in Carina with the Imaging array of the Advanced CCD Imaging Spectrometer (ACIS-I) on the Chandra X-ray Observatory, and is described in Townsley et al. (2011ApJS..194....1T). The Very Large Project (VLP) data were acquired over nine months, from 2008 February 12 through 2008 October 15 and were completed with Chandra archive ObsID 6402 (Trumpler 16, in 2006 Aug 30), ObsID 4495 (Trumpler 14, in 2004 Sep 21), and ObsID 6578 (Treasure Chest Cluster, in 2006 Apr 16). (3 data files).
[show abstract][hide abstract] ABSTRACT: The CCCP observations and their analysis are described in detail by
Townsley et al. (2011ApJS..194....1T) and Broos et al. (2011, Cat.
J/ApJS/194/2). Twenty-two overlapping pointings with the Chandra
Advanced CCD Imaging Spectrometer (ACIS), each subtending 17'x17', were
observed. They cover a 1.4deg2^ region. The X-ray data are aligned to
the Two Micron All Sky Survey (2MASS)/Hipparcos frame and, in most
cases, source positions have accuracies better than 0.5". Infrared
counterparts are found by positional coincidences with 2MASS, VLT HAWK-I
(Preibisch et al. 2011, Cat. J/ApJS/194/10), and other published
(3 data files).
[show abstract][hide abstract] ABSTRACT: We present a 1.42deg2^ mosaic of diffuse X-ray emission in the Great Nebula in Carina from the Chandra X-ray Observatory Advanced CCD Imaging Spectrometer camera. After removing >14000 X-ray point sources from the field, we smooth the remaining unresolved emission, tessellate it into segments of similar apparent surface brightness, and perform X-ray spectral fitting on those tessellates to infer the intrinsic properties of the X-ray-emitting plasma. By modeling faint resolved point sources, we estimate the contribution to the extended X-ray emission from unresolved point sources and show that the vast majority of Carina's unresolved X-ray emission is truly diffuse. Line-like correlated residuals in the X-ray spectral fits suggest that substantial X-ray emission is generated by charge exchange at the interfaces between Carina's hot, rarefied plasma and its many cold neutral pillars, ridges, and clumps. (2 data files).
[show abstract][hide abstract] ABSTRACT: Very few old radio pulsars are detected in X-rays. These objects are in general very faint due to their cold surfaces and relatively low spin-down powers. Yet, old radio pulsars appear to convert their spin-down energy more efficiently into X-ray emission than their younger relatives. It is unclear how much of this X-ray emission can be attributed to thermally emitting, hot polar caps or to magnetospheric emission. The evolution of NS magnetospheres with age and the polar cap heating mechanism are both interesting for the entire NS population, but can be particularly well studied in the case of old X-ray detected radio pulsars. Here, we present recent Chandra observations of the 4.25e7 yrs old radio pulsar PSR B1451-68. The spectrum of the found X-ray source can be described by a power law with photon index ˜ 2.7. Its isotropic luminosity is L_X ˜ 1.7e30 d^2_450pc erg/s (0.3 keV to 8keV), which corresponds to a high X-ray efficiency of 8e-3. We discuss the influence of a nearby star on the detected X-ray emission.
[show abstract][hide abstract] ABSTRACT: We present a 1.42 deg2 mosaic of diffuse X-ray emission in the Great Nebula in Carina from the Chandra X-ray Observatory Advanced CCD Imaging Spectrometer camera. After removing >14,000 X-ray point sources from the field, we smooth the remaining unresolved emission, tessellate it into segments of similar apparent surface brightness, and perform X-ray spectral fitting on those tessellates to infer the intrinsic properties of the X-ray-emitting plasma. By modeling faint resolved point sources, we estimate the contribution to the extended X-ray emission from unresolved point sources and show that the vast majority of Carina's unresolved X-ray emission is truly diffuse. Line-like correlated residuals in the X-ray spectral fits suggest that substantial X-ray emission is generated by charge exchange at the interfaces between Carina's hot, rarefied plasma and its many cold neutral pillars, ridges, and clumps.
The Astrophysical Journal Supplement Series 04/2011; 194(1):15. · 16.24 Impact Factor
[show abstract][hide abstract] ABSTRACT: We present a catalog of ~14,000 X-ray sources observed by the ACIS instrument on the Chandra X-ray Observatory within a 1.42 deg2 survey of the Great Nebula in Carina, known as the Chandra Carina Complex Project (CCCP). This study appears in a special issue devoted to the CCCP. Here, we describe the data reduction and analysis procedures performed on the X-ray observations, including calibration and cleaning of the X-ray event data, point-source detection, and source extraction. The catalog appears to be complete across most of the field to an absorption-corrected total-band luminosity of ~1030.7 erg s–1 for a typical low-mass pre-main-sequence star. Counterparts to the X-ray sources are identified in a variety of visual, near-infrared, and mid-infrared surveys. The X-ray and infrared source properties presented here form the basis of many CCCP studies of the young stellar populations in Carina.
The Astrophysical Journal Supplement Series 04/2011; 194(1):2. · 16.24 Impact Factor
[show abstract][hide abstract] ABSTRACT: LS 5039 is a high-mass binary with a period of 4 days, containing a compact
object and an O star, one of the few high-mass binaries detected in gamma-rays.
Our Chandra ACIS observation of LS 5039 provided a high-significance (~10sigma)
detection of extended emission clearly visible for up to 1' from the point
source. The spectrum of this emission can be described by an absorbed power-law
model with photon index Gamma=1.9pm0.3, somewhat softer than the point source
spectrum Gamma=1.44pm0.07, with the same absorption, N_H=(6.4pm0.6)e21 /cm2.
The observed 0.5-8 keV flux of the extended emission is 8.8e-14 erg/s/cm2, or
5% of the point source flux; the latter is a factor of ~2 lower than the lowest
flux detected so far. Fainter extended emission with comparable flux and a
softer (Gamma~3) spectrum is detected at even greater radii (up to 2'). Two
possible interpretations of the extended emission are a dust scattering halo
and a synchrotron nebula powered by energetic particles escaping the binary. We
discuss both of these scenarios and favor the nebula interpretation, although
some dust contribution is possible. We have also found transient sources
located within a narrow stripe south of LS 5039. We discuss the likelihood of
these sources to be related to LS 5039.
The Astrophysical Journal 03/2011; 735. · 6.73 Impact Factor