7 research outputs found
Discovery of a z=4.93, X-ray selected quasar by the Chandra Multiwavelength Project (ChamP)
We present X-ray and optical observations of CXOMP J213945.0-234655, a high
redshift (z=4.93) quasar discovered through the Chandra Multiwavelength Project
(ChaMP). This object is the most distant X-ray selected quasar published, with
an X-ray luminosity of L(X)=5.9x10^44 erg/s (measured in the 0.3-2.5 keV band
and corrected for Galactic absorption). CXOMP J213945.0-234655 is a g' dropout
object (>26.2), with r'=22.87 and i'=21.36. The rest-frame X-ray to optical
flux ratio is similar to quasars at lower redshifts and slightly X-ray bright
relative to z>4 optically-selected quasars observed with Chandra. The ChaMP is
beginning to acquire significant numbers of high redshift quasars to
investigate the unobscured X-ray luminosity function out to z~5.Comment: Published in ApJ Letters; 4 pages; 3 figures;
http://hea-www.harvard.edu/CHAMP
Chandra Observations of the QSO Pair Q2345+007: Binary Quasar or Massive Dark Lens?
The components of the wide (7.3") separation quasar pair Q2345+007A,B
(z=2.15) have the most strikingly similar optical spectra seen to date (Steidel
& Sargent 1991) yet no detected lensing mass, making this system the best
candidate known for a massive (1e14 Msun) dark matter lens system. Here we
present results from a 65ksec Chandra observation designed to investigate
whether it is a binary quasar or a gravitational lens. We find no X-ray
evidence for a lensing cluster to a (0.5-2keV) flux limit of 2e-15 cgs, which
is consistent with lensing only for a reduced baryon fraction. Using the
Chandra X-ray observations of the quasars themselves, together with new and
published optical measurements, we use the observed emission properties of the
quasars for further tests between the lens and binary hypotheses. Assuming
similar line-of-sight absorption to the images, we find that their X-ray
continuum slopes are inconsistent (Gamma_A=2.30 and Gamma_B=0.83) as are their
X-ray to optical flux ratios. The probability that B suffers absorption
sufficient to account for these spectral differences is negligible. We present
new optical evidence that the flux ratio of the pair is variable, so the
time-delay in a lens scenario could cause some of the discrepancies. However,
adequately large variations in overall spectral energy distribution are rare in
individual QSOs. All new evidence here weighs strongly toward the binary
interpretation. Q2345+007 thus may represent the highest redshift example known
of interaction-triggered but as-yet unmerged luminous AGN.Comment: 15 pages, Latex, emulateapj style, including 3 tables and 5 figures.
Accepted Feb 1, 2002 for publication in ApJ Main Journal. See also
http://hea-www.harvard.edu/~pgreen/Papers.htm
CfA3: 185 Type Ia Supernova Light Curves from the CfA
We present multi-band photometry of 185 type-Ia supernovae (SN Ia), with over
11500 observations. These were acquired between 2001 and 2008 at the F. L.
Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics (CfA).
This sample contains the largest number of homogeneously-observed and reduced
nearby SN Ia (z < 0.08) published to date. It more than doubles the nearby
sample, bringing SN Ia cosmology to the point where systematic uncertainties
dominate. Our natural system photometry has a precision of 0.02 mag or better
in BVRIr'i' and roughly 0.04 mag in U for points brighter than 17.5 mag. We
also estimate a systematic uncertainty of 0.03 mag in our SN Ia standard system
BVRIr'i' photometry and 0.07 mag for U. Comparisons of our standard system
photometry with published SN Ia light curves and comparison stars, where
available for the same SN, reveal agreement at the level of a few hundredths
mag in most cases. We find that 1991bg-like SN Ia are sufficiently distinct
from other SN Ia in their color and light-curve-shape/luminosity relation that
they should be treated separately in light-curve/distance fitter training
samples. The CfA3 sample will contribute to the development of better
light-curve/distance fitters, particularly in the few dozen cases where
near-infrared photometry has been obtained and, together, can help disentangle
host-galaxy reddening from intrinsic supernova color, reducing the systematic
uncertainty in SN Ia distances due to dust.Comment: Accepted to the Astrophysical Journal. Minor changes from last
version. Light curves, comparison star photometry, and passband tables are
available at http://www.cfa.harvard.edu/supernova/CfA3
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Discovery of a z = 4.93, X-Ray-selected Quasar by the Chandra Multiwavelength Project (ChaMP)
We present X-ray and optical observations of CXOMP J213945.0-234655, a high-redshift (z = 4.93) quasar discovered through the Chandra Multiwavelength Project (ChaMP). This object is the most distant X-ray-selected quasar published, with a rest-frame X-ray luminosity of LX = 5.9 Ă 1044 ergs s-1 (measured in the 0.3-2.5 keV band and corrected for Galactic absorption). CXOMP J213945.0-234655 is a g' dropout object (>26.2), with r' = 22.87 and i' = 21.36. The rest-frame X-ray-to-optical flux ratio is similar to quasars at lower redshifts and slightly X-ray bright relative to z > 4 optically selected quasars observed with Chandra. The ChaMP is beginning to acquire significant numbers of high-redshift quasars to investigate the X-ray luminosity function out to z ~ 5.Astronom
Characterizing the profiles of patients with acute concussion versus prolonged post-concussion symptoms in Ontario
Abstract Identifying vulnerability factors for developing persisting concussion symptoms is imperative for determining which patients may require specialized treatment. Using cross-sectional questionnaire data from an Ontario-wide observational concussion study, we compared patients with acute concussion (â€â14 days) and prolonged post-concussion symptoms (PPCS) (â„â90 days) on four factors of interest: sex, history of mental health disorders, history of headaches/migraines, and past concussions. Differences in profile between the two groups were also explored. 110 patients with acute concussion and 96 patients with PPCS were included in our study. The groups did not differ on the four factors of interest. Interestingly, both groups had greater proportions of females (acute concussion: 61.1% F; PPCS: 66.3% F). Patient profiles, however, differed wherein patients with PPCS were significantly older, more symptomatic, more likely to have been injured in a transportation-related incident, and more likely to live outside a Metropolitan city. These novel risk factors for persisting concussion symptoms require replication and highlight the need to re-evaluate previously identified risk factors as more and more concussions occur in non-athletes and different risk factors may be at play