743 research outputs found
A near-IR variability study of the Galactic black hole: a red noise source with no detected periodicity
We present the results of near-infrared (2 and 3 microns) monitoring of Sgr
A*-IR with 1 min time sampling using the natural and laser guide star adaptive
optics (LGS AO) system at the Keck II telescope. Sgr A*-IR was observed
continuously for up to three hours on each of seven nights, between 2005 July
and 2007 August. Sgr A*-IR is detected at all times and is continuously
variable, with a median observed 2 micron flux density of 0.192 mJy,
corresponding to 16.3 magnitude at K'. These observations allow us to
investigate Nyquist sampled periods ranging from about 2 minutes to an hour.
Using Monte Carlo simulations, we find that the variability of Sgr A* in this
data set is consistent with models based on correlated noise with power spectra
having frequency dependent power law slopes between 2.0 to 3.0, consistent with
those reported for AGN light curves. Of particular interest are periods of ~20
min, corresponding to a quasi-periodic signal claimed based upon previous
near-infrared observations and interpreted as the orbit of a 'hot spot' at or
near the last stable orbit of a spinning black hole. We find no significant
periodicity at any time scale probed in these new observations for periodic
signals. This study is sensitive to periodic signals with amplitudes greater
than 20% of the maximum amplitude of the underlying red noise component for
light curves with duration greater than ~2 hours at a 98% confidence limit.Comment: 37 pages, 2 tables, 17 figures, accepted by Ap
Lifetime rates and types of subsequent child protection system contact following a first report of neglect: An age-stratified analysis
An estimated 1 in 3 U.S. children will be the subject of a child protective services (CPS) investigation during their lifetime, typically for allegations of neglect. Whether and how an initial report of neglect is addressed may place children on divergent trajectories for safety and stability throughout childhood. The purpose of this study is to track subsequent CPS contact among children born in California in 2000 who were first investigated by CPS for neglect allegations alone (no co-occurring abuse) and not permanently separated from their families of origin (i.e., not removed or reunified if removed). We estimated the rates of subsequent CPS referrals, substantiated maltreatment, placement in foster care, and allegations of physical and sexual abuse by age 18. We assessed how rates of subsequent contact varied by initial CPS response and age at first investigation. Supplemental analyses disaggregated data by race and ethnicity. Results indicate that 64% of children initially investigated for neglect alone were re-referred to CPS by age 18 and 16% experienced a subsequent removal; however, these estimates varied greatly by age. Four out of five (79% to 83%) of children initially investigated as infants had one or more subsequent CPS referrals during childhood. Children were not only re-referred for allegations of neglect; more than half of children re-referred were reported for allegations of physical or sexual abuse, indicating that abuse risk was either missed during the initial CPS investigation or escalated afterward. The failure to address maltreatment risks when children first present to the system is a complex problem with no easy solution. Our findings document that a majority of children initially referred for neglect experience future CPS involvement, often for allegations of physical or sexual abuse
An evolving hot spot orbiting around Sgr A*
Here we report on recent near-infrared observations of the Sgr A* counterpart
associated with the super-massive ~ 4x10^6 M_sun black hole at the Galactic
Center. We find that the May 2007 flare shows the highest sub-flare contrast
observed until now, as well as evidence for variations in the profile of
consecutive sub-flares. We modeled the flare profile variations according to
the elongation and change of the shape of a spot due to differential rotation
within the accretion disk.Comment: 7 pages, 5 figures, contribution for the conference "The Universe
under the Microscope" (AHAR 2008), to be published in Journal of Physics:
Conference Series by Institute of Physics Publishin
Rates of Emotional Disturbance Among Children in Foster Care: Comparing Federal Child Welfare Data and Medicaid Records in Two States
The purpose of this study is to estimate the rate of emotional disturbance (ED) among children in foster care and assess the validity of the national foster care census data (AFCARS) measure of ED. This study used linked child protection and Medicaid records from 2014 and 2015, for the states of California and Wisconsin, as well as data from AFCARS, a federal population census of children in foster care which states are mandated to contribute to. ED is defined by AFCARS and includes an array of mental and behavioral health diagnoses. According to AFCARS, 13% of CA children in foster care and 15% of WI children in foster care had an ED, whereas Medicaid claims produce rates of 45% and 48%, respectively. Rates of ED among children in congregate care were underestimated by 43?46 percentage points, with substantial proportions having diagnoses of disruptive behavioral disorders. Despite the AFCARS ED measure being cited in congressional testimonies and its wide use in research, results from this study suggest that the AFCARS ED estimates are an unreliable metric for use in research, policy, or practice
Madness decolonized?: Madness as transnational identity in Gail Hornstein’s Agnes’s Jacket
The US psychologist Gail Hornstein’s monograph Agnes’s Jacket: A Psychologist’s Search for the Meanings of Madness (2009) is an important intervention in the identity politics of the mad movement. Hornstein offers a resignified vision of mad identity that embroiders the central trope of an “anti-colonial” struggle to reclaim the experiential world “colonized” by psychiatry. A series of literal and figurative appeals make recourse to the inner world and (corresponding) cultural world of the mad, as well as to the ethno-symbolic cultural materials of dormant nationhood. This rhetoric is augmented by a model in which the mad comprise a diaspora without an origin, coalescing into a single transnational community. The mad are also depicted as persons displaced from their metaphorical homeland, the “inner” world “colonized” by the psychiatric regime. There are a number of difficulties with Hornstein’s rhetoric, however. Her “ethnicity-and-rights” response to the oppression of the mad is symptomatic of Western parochialism, while her proposed transmutation of putative psychopathology from limit upon identity to parameter of successful identity is open to contestation. Moreover, unless one accepts Hornstein’s porous vision of mad identity, her self-ascribed insider status in relation to the mad community may present a problematic “re-colonization” of mad experience
Evidence for X-ray synchrotron emission from simultaneous mid-IR to X-ray observations of a strong Sgr A* flare
This paper reports measurements of Sgr A* made with NACO in L' -band (3.80
um), Ks-band (2.12 um) and H-band (1.66 um) and with VISIR in N-band (11.88 um)
at the ESO VLT, as well as with XMM-Newton at X-ray (2-10 keV) wavelengths. On
4 April, 2007, a very bright flare was observed from Sgr A* simultaneously at
L'-band and X-ray wavelengths. No emission was detected using VISIR. The
resulting SED has a blue slope (beta > 0 for nuL_nu ~ nu^beta, consistent with
nuL_nu ~ nu^0.4) between 12 micron and 3.8 micron.
For the first time our high quality data allow a detailed comparison of
infrared and X-ray light curves with a resolution of a few minutes. The IR and
X-ray flares are simultaneous to within 3 minutes. However the IR flare lasts
significantly longer than the X-ray flare (both before and after the X-ray
peak) and prominent substructures in the 3.8 micron light curve are clearly not
seen in the X-ray data. From the shortest timescale variations in the L'-band
lightcurve we find that the flaring region must be no more than 1.2 R_S in
size.
The high X-ray to infrared flux ratio, blue nuL_nu slope MIR to L' -band, and
the soft nuL_nu spectral index of the X-ray flare together place strong
constraints on possible flare emission mechanisms. We find that it is
quantitatively difficult to explain this bright X-ray flare with inverse
Compton processes. A synchrotron emission scenario from an electron
distribution with a cooling break is a more viable scenario.Comment: ApJ, 49 pages, 9 figure
Simultaneous NIR/sub-mm observation of flare emission from SgrA*
We report on a successful, simultaneous observation and modeling of the
sub-millimeter to near-infrared flare emission of the Sgr A* counterpart
associated with the super-massive black hole at the Galactic center. Our
modeling is based on simultaneous observations that have been carried out on 03
June, 2008 using the NACO adaptive optics (AO) instrument at the ESO VLT and
the LABOCA bolometer at the APEX telescope. Inspection and modeling of the
light curves show that the sub-mm follows the NIR emission with a delay of
1.5+/-0.5 hours. We explain the flare emission delay by an adiabatic expansion
of the source components.Comment: 12 pages, 9 figures, 3 tables, in press with A&
Methods for detecting flaring structures in Sagittarius A* with high frequency VLBI
The super massive black hole candidate, Sagittarius A*, exhibits variability
from radio to X-ray wavelengths on time scales that correspond to < 10
Schwarzschild radii. We survey the potential of millimeter-wavelength VLBI to
detect and constrain time variable structures that could give rise to such
variations, focusing on a model in which an orbiting hot spot is embedded in an
accretion disk. Non-imaging algorithms are developed that use interferometric
closure quantities to test for periodicity, and applied to an ensemble of
hot-spot models that sample a range of parameter space. We find that structural
periodicity in a wide range of cases can be detected on most potential VLBI
arrays using modern VLBI instrumentation. Future enhancements of mm/sub-mm VLBI
arrays including phased array processors to aggregate VLBI station collecting
area, increased bandwidth recording, and addition of new VLBI sites all
significantly aid periodicity detection. The methods described herein can be
applied to other models of Sagittarius A*, including jet outflows and
Magneto-Hydrodynamic accretion simulations.Comment: Submitted to Ap
Coordinated mm/sub-mm observations of Sagittarius A* in May 2007
At the center of the Milky Way, with a distance of ~8 kpc, the compact source
Sagittarius A* (SgrA*) can be associated with a super massive black hole of
~4x10^6 solar masses. SgrA* shows strong variability from the radio to the
X-ray wavelength domains. Here we report on simultaneous
NIR/sub-millimeter/X-ray observations from May 2007 that involved the NACO
adaptive optics (AO) instrument at the European Southern Observatory's Very
Large Telescope, the Australian Telescope Compact Array (ATCA), the US mm-array
CARMA, the IRAM 30m mm-telescope, and other telescopes. We concentrate on the
time series of mm/sub-mm data from CARMA, ATCA, and the MAMBO bolometer at the
IRAM 30m telescope.Comment: 7 pages, 3 figures, contribution for the conference "The Universe
under the Microscope" (AHAR 2008), to be published in Journal of Physics:
Conference Series by Institute of Physics Publishin
A contemporaneous infrared flash from a long gamma-ray burst: an echo from the central engine
The explosion that results in a cosmic gamma-ray burst (GRB) is thought to
produce emission from two physical processes -- the activity of the central
engine gives rise to the high-energy emission of the burst through internal
shocking and the subsequent interaction of the flow with the external
environment produces long-wavelength afterglow. While afterglow observations
continue to refine our understanding of GRB progenitors and relativistic
shocks, gamma-ray observations alone have not yielded a clear picture of the
origin of the prompt emission nor details of the central engine. Only one
concurrent visible-light transient has been found and was associated with
emission from an external shock. Here we report the discovery of infrared (IR)
emission contemporaneous with a GRB, beginning 7.2 minutes after the onset of
GRB 041219a. Our robotic telescope acquired 21 images during the active phase
of the burst, yielding the earliest multi-colour observations of any
long-wavelength emission associated with a GRB. Analysis of an initial IR pulse
suggests an origin consistent with internal shocks. This opens a new
possibility to study the central engine of GRBs with ground-based observations
at long wavelengths.Comment: Accepted to Nature on March 1, 2005. 9 pages, 4 figures, nature12.cls
and nature1.cls files included. This paper is under press embargo until print
publicatio
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