2,057 research outputs found
Exploring ‘events’ as an information systems research methodology
This paper builds upon existing research and commentary from a variety of disciplinary sources including Information Systems, Organisational and Management Studies, and the Social Sciences that focus upon the meaning, significance and impact of ‘events’ in both an
organisational and a social sense. The aim of this paper is to define how the examination of the event is an appropriate, viable and useful Information Systems methodology. Our argument is that focusing on the ‘event’ enables the researcher to more clearly observe and capture the complexity, multiplicity and mundaneity of everyday lived experience. The use and notion of ‘event’ has the potential to reduce the methodological dilemmas associated
with the micromanagement of the research process – an inherent danger of traditional and ‘virtual' ethnographic approaches. Similarly, this paper addresses the over-emphasis upon managerialist, structured and time-fixated praxis that is currently symptomatic of Information Systems research. All of these concerns are pivotal points of critique found within eventoriented literature. An examination of event-related theory within interpretative disciplines directs the focus of this paper towards the more specific realm of the ‘event scene’. The notion of the ‘event scene’ originated in the action based (and anti-academy) imperatives of the Situationists and emerged in an academic sense as critical situational analysis. Event scenes are a focus for contemporary critical theory where they are utilised as a means of representing theoried
inquiry in order to loosen the restrictions that historical and temporally bound analysis imposes upon most interpretative approaches. The use of event scenes as the framework for critiquing established conceptual assumptions is exemplified by their use in CTheory. In this
journal's version and articulation of the event scene poetry, commentary, multi-vocal narrative and other techniques are legitimated as academic forms. These various forms of multi-dimensional expression are drawn upon to enrich the understandings of the ‘event’, to
extricate its meaning and to provide a sense of the moment from which the point of analysis stems. The objective of this paper is to advocate how Information Systems research can (or should) utilize an event scene oriented methodology
The Megamaser Cosmology Project: I. VLBI observations of UGC 3789
The Megamaser Cosmology Project (MCP) seeks to measure the Hubble Constant
(Ho) in order to improve the extragalactic distance scale and constrain the
nature of dark energy. We are searching for sources of water maser emission
from AGN with sub-pc accretion disks, as in NGC 4258, and following up these
discoveries with Very Long Baseline Interferometric (VLBI) imaging and spectral
monitoring. Here we present a VLBI map of the water masers toward UGC 3789, a
galaxy well into the Hubble Flow. We have observed masers moving at rotational
speeds up to 800 km/s at radii as small as 0.08 pc. Our map reveals masers in a
nearly edge-on disk in Keplerian rotation about a 10^7 Msun supermassive black
hole. When combined with centripetal accelerations, obtained by observing
spectral drifts of maser features (to be presented in Paper II), the UGC 3789
masers may provide an accurate determination of Ho, independent of luminosities
and metallicity and extinction corrections.Comment: 18 pages, 3 figures, 4 table
Pulse Profiles, Accretion Column Dips and a Flare in GX 1+4 During a Faint State
The Rossi X-ray Timing Explorer (RXTE) spacecraft observed the X-ray pulsar
GX 1+4 for a period of 34 hours on July 19/20 1996. The source faded from an
intensity of ~20 mCrab to a minimum of <~0.7 mCrab and then partially recovered
towards the end of the observation. This extended minimum lasted ~40,000
seconds. Phase folded light curves at a barycentric rotation period of
124.36568 +/- 0.00020 seconds show that near the center of the extended minimum
the source stopped pulsing in the traditional sense but retained a weak dip
feature at the rotation period. Away from the extended minimum the dips are
progressively narrower at higher energies and may be interpreted as
obscurations or eclipses of the hot spot by the accretion column. The pulse
profile changed from leading-edge bright before the extended minimum to
trailing-edge bright after it. Data from the Burst and Transient Source
Experiment (BATSE) show that a torque reversal occurred <10 days after our
observation. Our data indicate that the observed rotation departs from a
constant period with a Pdot/P value of ~-1.5% per year at a 4.5 sigma
significance. We infer that we may have serendipitously obtained data, with
high sensitivity and temporal resolution about the time of an accretion disk
spin reversal. We also observed a rapid flare which had some precursor
activity, close to the center of the extended minimum.Comment: 19 pages, 6 figures, accepted for publication in Astrophysical
Journal (tentatively scheduled for vol. 529 #1, 20 Jan 2000
The optical counterpart of SAX J1808.4-3658, the transient bursting millisecond X-ray pulsar
A set of CCD images have been obtained during the decline of the X-ray
transient SAX J1808.4-3658 during April-June 1998. The optical counterpart has
been confirmed by several pieces of evidence. The optical flux shows a
modulation on several nights which is consistent with the established X-ray
binary orbit period of 2 hours. This optical variability is roughly in
antiphase with the weak X-ray modulation. The source mean magnitude of V=16.7
on April 18 declined rapidly after April 22. From May 2 onwards the magnitude
was more constant at around V=18.45 but by June 27 was below our sensitivity
limit. The optical decline precedes the rapid second phase of the X-ray
decrease by 3 +/- 1 days. The source has been identified on a 1974 UK Schmidt
plate at an estimated magnitude of ~20. The nature of the optical companion is
discussed.Comment: 5 pages, 3 figures; published in MNRAS, March 15th 199
Toward a New Distance to the Active Galaxy NGC 4258: II. Centripetal Accelerations and Investigation of Spiral Structure
We report measurements of centripetal accelerations of maser spectral
components of NGC 4258 for 51 epochs spanning 1994 to 2004. This is the second
paper of a series, in which the goal is determination of a new geometric maser
distance to NGC 4258 accurate to possibly ~3%. We measure accelerations using a
formal analysis method that involves simultaneous decomposition of maser
spectra for all epochs into multiple, Gaussian components. Components are
coupled between epochs by linear drifts (accelerations) from their centroid
velocities at a reference epoch. For high-velocity emission, accelerations lie
in the range -0.7 to +0.7 km/s/yr indicating an origin within 13 degrees of the
disk midline (the perpendicular to the line-of-sight to the black hole).
Comparison of high-velocity emission projected positions in VLBI images, with
those derived from acceleration data, provides evidence that masers trace real
gas dynamics. High-velocity emission accelerations do not support a model of
trailing shocks associated with spiral arms in the disk. However, we find
strengthened evidence for spatial periodicity in high-velocity emission, of
wavelength 0.75 mas. This supports suggestions of spiral structure due to
density waves in the nuclear accretion disk of an active galaxy. Accelerations
of low-velocity (systemic) emission lie in the range 7.7 to 8.9 km/s/yr,
consistent with emission originating from a concavity where the thin, warped
disk is tangent to the line-of-sight. A trend in accelerations of low-velocity
emission as a function of Doppler velocity may be associated with disk geometry
and orientation, or with the presence of spiral structure.Comment: Accepted to ApJ, 48 pages and 20 figure
New H2O masers in Seyfert and FIR bright galaxies
Extragalactic water vapor masers with 50, 1000, 1, and 230 solar (isotropic)
luminosities were detected toward Mrk1066 (UGC2456), Mrk34, NGC3556 and Arp299,
respectively. The interacting system Arp299 appears to show two maser hotspots
separated by 20 arcsec. A statistical analysis of 53 extragalactic H2O sources
indicates (1) that the correlation between IRAS Point Source and H2O
luminosities, established for individual star forming regions in the galactic
disk, also holds for AGN dominated megamaser galaxies, (2) that maser
luminosities are not correlated with 60/100 micron color temperatures and (3)
that only a small fraction of the luminous megamasers detectable with 100-m
sized telescopes have so far been identified. The slope of the H2O luminosity
function, -1.5, indicates that the number of detectable masers is almost
independent of their luminosity. If the LF is not steepening at very high maser
luminosities, H2O megamasers at significant redshifts should be detectable with
present day state-of-the-art facilities.Comment: 16 pages, 10 postscript figures; style file: aa.cls. Accepted for
publication in the Main Journal of Astronomy & Astrophysic
Towards Proper Motions in the Local Group
Key and still largely missing parameters for measuring the mass content and
distribution of the Local Group are the proper motion vectors of its member
galaxies. The problem when trying to derive the gravitational potential of the
Local Group is that usually only radial velocities are known, and hence
statistical approaches have to be used. The expected proper motions for
galaxies within the Local Group, ranging from 20 to 100 as/yr, are
detectable with VLBI using the phase-referencing technique. We present
phase-referencing observations of bright masers in IC~10 and M33 with respect
to background quasars. We observed the HO masers in IC10 three times over a
period of two months to check the accuracy of the relative positions. The
relative positions were obtained by modeling the interferometer phase data for
the maser sources referenced to the background quasars. The model allowed for a
relative position shift for the source and a single vertical atmospheric delay
error in the correlator model for each antenna. The rms of the relative
positions for the three observations is only 0.01 mas, which is approximately
the expected position error due to thermal noise. Also, we present a method to
measure the geometric distance to M33. This will allow re-calibration of the
extragalactic distance scale based on Cepheids. The method is to measure the
relative proper motions of two HO maser sources on opposite sides of M33.
The measured angular rotation rate, coupled with other measurements of the
inclination and rotation speed of the galaxy, yields a direct distance
measurement.Comment: 4 pages, Proceedings of the 6th European VLBI Network Symposium, Ros,
E., Porcas, R.W., Zensus, J.A. (eds.), MPIfR, Bonn, Germany (2002); Also
availabe http://www.mpifr-bonn.mpg.de/staff/abrunthaler/brunthal01.p
The supermassive black hole in the Seyfert 2 galaxy NGC 5252
We present results from HST/STIS long-slit spectroscopy of the gas motions in
the nuclear region of the Seyfert 2 galaxy NGC 5252. The observed velocity
field is consistent with gas in regular rotation with superposed localized
patches of disturbed gas. The dynamics of the circumnuclear gas can be
accurately reproduced by adding to the stellar mass component a compact dark
mass of MBH = 0.95 (-0.45;+1.45) 10E9 M(sun), very likely a supermassive black
hole. Contrarily to results obtained in similar studies rotational broadening
is sufficient to reproduce also the behaviour of line widths. The MBH estimated
for NGC 5252 is in good agreement with the correlation between MBH and bulge
mass. The comparison with the MBH vs sigma relationship is less stringent
(mostly due to the relatively large error in sigma); NGC 5252 is located above
the best fit line by between 0.3 and 1.2 dex, i.e. 1 - 4 times the dispersion
of the correlation. Both the galaxy's and MBH of NGC 5252 are substantially
larger than those usually estimated for Seyfert galaxies but, on the other
hand, they are typical of radio-quiet quasars. Combining the determined MBH
with the hard X-ray luminosity, we estimate that NGC 5252 is emitting at a
fraction ~ 0.005 of L(Edd). In this sense, this active nucleus appears to be a
quasar relic, now probably accreting at a low rate, rather than a low black
hole mass counterpart of a QSO.Comment: Accepted for publication in A&
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