17,296 research outputs found
A TiO study of the black-hole binary GRO J0422+32 in a very low state
We present 53 simultaneous photometric (I band) and spectroscopic (6900-9500
Angstroms) observations of J0422+32, taken during December 1997. From these we
determine that J0422+32 was in its lowest state yet observed, at
I=20.44+/-0.08. Using relative spectrophotometry, we show that it is possible
to correct very accurately for telluric absorption. Following this, we use the
TiO bands at 7055 Angstroms and 7589 Angstroms for a radial velocity study and
thereby obtain a semi-amplitude of 378+/-16kms-1, which yields
f(M)=1.191+/-0.021M_solar and q=9.0+2.2-2.7, consistent with previous
observations. We further demonstrate that this little explored method is very
powerful for such systems. We also determine a new orbital ephemeris of
HJD=2450274.4156+/-0.0009 + 0.2121600+/-0.0000002E.
We see some evidence for an ellipsoidal modulation, from which we determine
the orbital inclination of J0422+32 to be less than 45 degrees. We therefore
calculate a minimum mass for the primary of 2.22M_solar, consistent with a
black hole, but not necessarily the super-massive one proposed by Beekman et al
(1997). We obtain an M4-5 spectral type for the secondary star and determine
that the secondary contributes 38+/-2% of the flux that we observe from
J0422+32 over the range 6950-8400 Angstroms. From this we calculate the
distance to the system to be 1.39+/-0.15kpc.Comment: (1) Department of Physics, Keele University, Keele, Staffordshire,
ST5 5BG (2) Department of Astrophysics, Nuclear Physics Laboratory, Keble
Road, Oxfo rd, OX1 3RH Accepted, to appear in MNRAS 8 pages, 5 figure
X-ray sources and their optical counterparts in the globular cluster M 22
Using XMM-Newton EPIC imaging data, we have detected 50 low-luminosity X-ray
sources in the field of view of M 22, where 5 +/- 3 of these sources are likely
to be related to the cluster. Using differential optical photometry, we have
identified probable counterparts to those sources belonging to the cluster.
Using X-ray spectroscopic and timing studies, supported by the optical colours,
we propose that the most central X-ray sources in the cluster are cataclysmic
variables, millisecond pulsars, active binaries and a blue straggler. We also
identify a cluster of galaxies behind this globular cluster.Comment: 11 pages, 7 figures, accepted for publication in A&
Investigating slim disk solutions for HLX-1 in ESO 243-49
The hyper luminous X-ray source HLX-1 in the galaxy ESO 243-49, currently the
best intermediate mass black hole candidate, displays spectral transitions
similar to those observed in Galactic black hole binaries, but with a
luminosity 100-1000 times higher. We investigated the X-ray properties of this
unique source fitting multi-epoch data collected by Swift, XMM-Newton & Chandra
with a disk model computing spectra for a wide range of sub- and
super-Eddington accretion rates assuming a non-spinning black hole and a
face-on disk (i = 0 deg). Under these assumptions we find that the black hole
in HLX-1 is in the intermediate mass range (~2 x 10^4 M_odot) and the accretion
flow is in the sub-Eddington regime. The disk radiation efficiency is eta =
0.11 +/-0.03. We also show that the source does follow the L_X ~ T^4 relation
for our mass estimate. At the outburst peaks, the source radiates near the
Eddington limit. The accretion rate then stays constant around 4 x 10^(-4)
M_odot yr^(-1) for several days and then decreases exponentially. Such
"plateaus" in the accretion rate could be evidence that enhanced mass transfer
rate is the driving outburst mechanism in HLX-1. We also report on the new
outburst observed in August 2011 by the Swift-X-ray Telescope. The time of this
new outburst further strengthens the ~1 year recurrence timescale.Comment: 24 pages, 10 figures, accepted for publication in Ap
Optical variability of the accretion disk around the intermediate mass black hole ESO 243-49 HLX-1 during the 2012 outburst
We present dedicated quasi-simultaneous X-ray (Swift) and optical (Very Large
Telescope (VLT), V- and R-band) observations of the intermediate mass black
hole candidate ESO 243-49 HLX-1 before and during the 2012 outburst. We show
that the V-band magnitudes vary with time, thus proving that a portion of the
observed emission originates in the accretion disk. Using the first quiescent
optical observations of HLX-1, we show that the stellar population surrounding
HLX-1 is fainter than V~25.1 and R~24.2. We show that the optical emission may
increase before the X-ray emission consistent with the scenario proposed by
Lasota et al. (2011) in which the regular outbursts could be related to the
passage at periastron of a star circling the intermediate mass black hole in an
eccentric orbit, which triggers mass transfer into a quasi-permanent accretion
disk around the black hole. Further, if there is indeed a delay in the X-ray
emission we estimate the mass-transfer delivery radius to be ~1e11 cm.Comment: 9 pages, 2 figures, accepted for publication in ApJ
Role of Protected Block Curriculum in Surgical Education
A protected block curriculum for surgical resident training began at the Medical College of Wisconsin in 2005. The curriculum has evolved with time as educational emphasis has changed. However, the concept of having resident learners relieved of clinical duty to focus on learning has not changed. Separate protected block curriculums are held for PGY1 and PGY 2 during which residents have no clinical responsibilities. These periods are defined at the beginning of each academic year and are distributed to all faculties. The systematic design, implementation, and evaluation of the protected block curriculum (PBC) Model provides an educationally grounded model for training surgical residents consistent with accreditation council for graduate medical education (ACGME) competency mandates. Resident evaluations consistently support the use of our PBC as a method to attain and practice skill sets in a nonthreatening environment. Faculty benefits are able to evaluate residents’ knowledge, skills, and attitudes in a nonclinical setting and engage residents as individuals. The format extended into the PGY3–5 years of training as it evolved. Over more than a decade of using PBC, we have performed a number of analyses on the program and even determined a cost for the program. The program continues to be adjusted to new technology and curriculum initiatives
XMM-Newton X-ray and optical observations of the globular clusters M 55 and NGC 3201
We have observed two low concentration Galactic globular clusters with the
X-ray observatory XMM-Newton. We detect 47 faint X-ray sources in the direction
of M 55 and 62 in the field of view of NGC 3201. Using the statistical Log
N-Log S relationship of extragalactic sources derived from XMM-Newton Lockman
Hole observations, to estimate the background source population, we estimate
that very few of the sources (1.5+/-1.0) in the field of view of M 55 actually
belong to the cluster. These sources are located in the centre of the cluster
as we expect if the cluster has undergone mass segregation. NGC 3201 has
approximately 15 related sources, which are centrally located but are not
constrained to lie within the half mass radius. The sources belonging to this
cluster can lie up to 5 core radii from the centre of the cluster which could
imply that this cluster has been perturbed. Using X-ray (and optical, in the
case of M 55) colours, spectral and timing analysis (where possible) and
comparing these observations to previous X-ray observations, we find evidence
for sources in each cluster that could be cataclysmic variables, active
binaries, millisecond pulsars and possible evidence for a quiescent low mass
X-ray binary with a neutron star primary, even though we do not expect any such
objects in either of the clusters, due to their low central concentrations. The
majority of the other sources are background sources, such as AGN.Comment: 12 pages, 7 figures, accepted to be published in A&
Opening access to administrative data for evaluating public services: the case of the Justice Data Lab
As government administrative data sets are increasingly made available for new (non-administrative) purposes, there is a need to improve access to such resources for voluntary and community organizations, social enterprises and private businesses for statistical analysis and evaluation purposes. The Justice Data Lab set up by the Ministry of Justice in the UK presents an innovative case of how administrative data can be linked to other data held by organizations delivering public services. The establishment of a unit within a secure setting holding evaluation and statistical expertise has enabled providers of programmes aimed at reducing re-offending to obtain evidence on how the impact of their interventions differs from that of a matched comparison group. This article explores the development of the Justice Data Lab, the methodological and other challenges faced, and the experiences of user organizations. The article draws out implications for future development of Data Labs and the use of administrative data for the evaluation of public services
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