350 research outputs found
Publishing Our Own Work: Contributing to the Professional Literature Through Systematizing Sharing of Library Reports
Library employees often work on teams, committees, or task forces to do research, and investigation as part of their responsibilities in carrying out the operations of a library; however, much of this work is not published in the professional literature and is only inconsistently recorded in committee documents. As such, this work is hidden both from others in the library who might use it and from the profession at large, meaning that other libraries were not able to benefit from it. To address these challenges, the University of Illinois Library (UrbanaâChampaign) established the Library Occasional Reports Series (LibORS) in 2015. This paper presents a case study of the ongoing process of establishing LibORS. Phases of work included exploring what it would mean to commit to publishing and promoting the University Libraryâs work as an organizational practice as well as creating workflows, acquisition criteria, editorial guidelines, a report template, and communication mechanisms
X-ray states and radio emission in the black hole candidate XTE J1550-564
We report on radio and X-ray observations of the black hole candidate (BHC)
XTE J1550-564 performed during its 2000 X-ray outburst. Observations have been
conducted with the Australia Telescope Compact Array (ATCA) and have allowed us
to sample the radio behavior of XTE J1550-564 in the X-ray Low Hard and
Intermediate/Very High states. We observed optically thin radio emission from
XTE J1550-564 five days after a transition to an Intermediate/Very High state,
but we observed no radio emission six days later, while XTE J1550-564 was still
in the Intermediate/Very High state. In the Low Hard state, XTE J1550-564 is
detected with an inverted radio spectrum. The radio emission in the Low Hard
state most likely originates from a compact jet; optical observations suggest
that the synchrotron emission from this jet may extend up to the optical range.
The total power of the compact jet might therefore be a significant fraction of
the total luminosity of the system. We suggest that the optically thin
synchrotron radio emission detected five days after the transition to the
Intermediate/Very High state is due to a discrete ejection of relativistic
plasma during the state transition. Subsequent to the decay of the optically
thin radio emission associated with the state transition, it seems that in the
Intermediate/Very High state the radio emission is quenched by a factor greater
than 50, implying a suppression of the outflow. We discuss the properties of
radio emission in the X-ray states of BHCs.Comment: 15 pages, including 3 figures. Accepted for publication in ApJ,
scheduled for the vol. 553 Jun 1, 2001 issu
Deployment of spatial attention towards locations in memory representations: an EEG study
Recalling information from visual short-term memory (VSTM) involves the same neural mechanisms as attending to an actually perceived scene. In particular, retrieval from VSTM has been associated with orienting of visual attention towards a location within a spatially-organized memory representation. However, an open question concerns whether spatial attention is also recruited during VSTM retrieval even when performing the task does not require access to spatial coordinates of items in the memorized scene. The present study combined a visual search task with a modified, delayed central probe protocol, together with EEG analysis, to answer this question. We found a temporal contralateral negativity (TCN) elicited by a centrally presented go-signal which was spatially uninformative and featurally unrelated to the search target and informed participants only about a response key that they had to press to indicate a prepared target-present vs. -absent decision. This lateralization during VSTM retrieval (TCN) provides strong evidence of a shift of attention towards the target location in the memory representation, which occurred despite the fact that the present task required no spatial (or featural) information from the search to be encoded, maintained, and retrieved to produce the correct response and that the go-signal did not itself specify any information relating to the location and defining feature of the target
RXTE Observations of Cygnus X-3
In the period between May 1997 and August 1997 a series of pointed RXTE
observations were made of Cyg X-3. During this period Cyg X-3 made a transition
from a quiescent radio state to a flare state (including a major flare) and
then returned to a quiescent radio state. Analyses of the observations are made
in the context of concurrent observations in the hard X-ray (CGRO/BATSE), soft
X-ray (RXTE/ASM) and the radio (Green Bank Interferometer, Ryle Telescope, and
RATAN-600). Preliminary analyses of the observations are presented.Comment: 4 pages, 4 figures. newarcrc.sty included. To appear in 2nd Workshop
of Relativistic Jets from Galactic Sources, R.N. Ogley and S.J. Bell Burnell
eds, NewAR 42, in pres
The 590 days long term periodicity of the microquasar GRS 1915+105
We report on the discovery of a 590 days long term periodicity in the hard
X-ray component of the microquasar \grs found from a comprehensive study of
more than four years of {\it RXTE} observations. The periodicity is also
observed in the hard X-ray flux observed by BATSE, and in the radio flux as
seen with the {\it Green Bank Interferometer} and the {\it Ryle Telescope}. We
discuss various possible explanations, including the precession of a radiation
induced warped accretion disk.Comment: 6 pages, 4 figuers, accepted for publication as ApJ Lette
Discovery of extreme particle acceleration in the microquasar Cygnus X-3
The study of relativistic particle acceleration is a major topic of
high-energy astrophysics. It is well known that massive black holes in active
galaxies can release a substantial fraction of their accretion power into
energetic particles, producing gamma-rays and relativistic jets. Galactic
microquasars (hosting a compact star of 1-10 solar masses which accretes matter
from a binary companion) also produce relativistic jets. However, no direct
evidence of particle acceleration above GeV energies has ever been obtained in
microquasar ejections, leaving open the issue of the occurrence and timing of
extreme matter energization during jet formation. Here we report the detection
of transient gamma-ray emission above 100 MeV from the microquasar Cygnus X-3,
an exceptional X-ray binary which sporadically produces powerful radio jets.
Four gamma-ray flares (each lasting 1-2 days) were detected by the AGILE
satellite simultaneously with special spectral states of Cygnus X-3 during the
period mid-2007/mid-2009. Our observations show that very efficient particle
acceleration and gamma-ray propagation out of the inner disk of a microquasar
usually occur a few days before major relativistic jet ejections. Flaring
particle energies can be thousands of times larger than previously detected
maximum values (with Lorentz factors of 105 and 102 for electrons and protons,
respectively). We show that the transitional nature of gamma-ray flares and
particle acceleration above GeV energies in Cygnus X-3 is clearly linked to
special radio/X-ray states preceding strong radio flares. Thus gamma-rays
provide unique insight into the nature of physical processes in microquasars.Comment: 29 pages (including Supplementary Information), 8 figures, 2 tables
version submitted to Nature on August 7, 2009 (accepted version available at
http://www.nature.com/nature/journal/vaop/ncurrent/pdf/nature08578.pdf
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Photometric observations of the radio bright B[e]/X-ray binary CI Cam
We present multiwavelength (optical, IR, radio) observations of CI Cam, the optical counterpart to the transient X-ray source XTE J0421+560. Pre-outburst quiescent observations reveal the presence of a dusty envelope around the system. Pronounced short term variability is observed at all wavebands from U-K, but no indication of prior flaring of a similar magnitude to the 1998 April outburst is found in these data.
Data obtained during the 1998 April X-ray flare reveal pronounced optical-radio flaring. The optical flux was observed to quickly return to quiescent levels, while the radio flare was of much longer duration. The optical component is likely to result from a combination of free-free/free-bound emission, emission line and thermal dust emission, caused by re-radiation of the X-ray flux, while the behaviour of the multiwavelength radio data is consistent with emission from expanding ejecta emitting via the synchrotron mechanism.
Post-outburst (1998 August-1999 March) U-M broadband photometric observations reveal that while the optical (UBV) flux remains at pre-outburst quiescent levels, near IR (JHKLM) fluxes exceed the pre-outburst fluxes by ~0.5 magnitudes. Modelling the pre- and post-outburst spectral energy distribution of CI Cam reveals that the structure and/or composition of the dusty component of the circumstellar envelope appears to have changed. Due to a lack of information on the precise chemical composition of the dust within the system several explanations for this behaviour are possible, such as the production of new dust at the inner edge of the envelope, or modification of the composition of the dust due to X-ray irradiation
The Burst and Transient Source Experiment (BATSE) Earth Occultation Catalog of Low-Energy Gamma-Ray Sources
The Burst and Transient Source Experiment (BATSE), aboard the Compton Gamma
Ray Observatory (CGRO), provided a record of the low-energy gamma-ray sky
(20-1000 keV) between 1991 April and 2000 May (9.1y). Using the Earth
Occultation Technique to extract flux information, a catalog of sources using
data from the BATSE large area detectors has been prepared. The first part of
the catalog consists of results from the monitoring of 58 sources, mostly
Galactic. For these sources, we have included tables of flux and spectral data,
and outburst times for transients. Light curves (or flux histories) have been
placed on the world wide web. We then performed a deep-sampling of 179 objects
(including the aforementioned 58 objects) combining data from the entire 9.1y
BATSE dataset. Source types considered were primarily accreting binaries, but a
small number of representative active galaxies, X-ray-emitting stars, and
supernova remnants were also included. The deep sample results include definite
detections of 83 objects and possible detections of 36 additional objects. The
definite detections spanned three classes of sources: accreting black hole and
neutron star binaries, active galaxies and supernova remnants. Flux data for
the deep sample are presented in four energy bands: 20-40, 40-70, 70-160, and
160-430 keV. The limiting average flux level (9.1 y) for the sample varies from
3.5 to 20 mCrab (5 sigma) between 20 and 430 keV, depending on systematic
error, which in turn is primarily dependent on the sky location. To strengthen
the credibility of detection of weaker sources (5-25 mCrab), we generated Earth
occultation images, searched for periodic behavior using FFT and epoch folding
methods, and critically evaluated the energy-dependent emission in the four
flux bands.Comment: 64 pages, 17 figures, abstract abridged, Accepted by ApJ
SPI/INTEGRAL observation of the Cygnus region
We present the analysis of the first observations of the Cygnus region by the
SPI spectrometer onboard the Integral Gamma Ray Observatory, encompassing
600 ks of data. Three sources namely Cyg X-1, Cyg X-3 and EXO 2030+375
were clearly detected. Our data illustrate the temporal variability of Cyg X-1
in the energy range from 20 keV to 300 keV. The spectral analysis shows a
remarkable stability of the Cyg X-1 spectra when averaged over one day
timescale. The other goal of these observations is SPI inflight calibration and
performance verification. The latest objective has been achieved as
demonstrated by the results presented in this paper.Comment: 6 pages, 10 figures, accepted for publication in A&A (special
INTEGRAL volume
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