70 research outputs found
X-ray absorption towards high-redshift sources: probing the intergalactic medium with blazars
The role played by the intergalactic medium (IGM) in the X-ray absorption
towards high-redshift sources has recently drawn more attention in spectral
analysis studies. Here, we study the X-ray absorption towards 15 flat-spectrum
radio quasars at , relying on high counting statistic (
photons) provided by XMM-Newton, with additional NuSTAR (and simultaneous
Swift-XRT) observations when available. Blazars can be confidently considered
to have negligible X-ray absorption along the line of sight within the host
galaxy, likely swept by the kpc-scale relativistic jet. This makes our sources
ideal for testing the absorption component along the IGM. Our new approach is
to revisit the origin of the soft X-ray spectral hardening observed in high-z
blazars in terms of X-ray absorption occurring along the IGM, with the help of
a low-z sample used as comparison. We verify that the presence of absorption in
excess of the Galactic value is the preferred explanation to explain the
observed hardening, while intrinsic energy breaks, predicted by blazars'
emission models, can easily occur out of the observing energy band in most
sources. First, we perform an indirect analysis comparing the inferred amount
of absorption in excess of the Galactic value with a simulated IGM absorption
contribution, that increases with redshift and includes both a minimum
component from diffuse IGM metals, and the additional contribution of discrete
denser intervening regions. Then, we directly investigate the warm-hot IGM with
a spectral model on the best candidates of our sample, obtaining an average IGM
density of cm and temperature of
. A more dedicated study is currently
beyond reach, but our results can be used as a stepping stone for future more
accurate analysis, involving Athena.Comment: 32 pages, 7 figures. Accepted, to be published in A&
Towards a typology of coordinating compounds in Turkish
https://www.degruyter.com/view/j/flin.2018.52.issue-2/flin-2018-0008/flin-2018-0008.xml?format=IN
Listing between lexicon and syntax: focus on frame-naming lists
http://www.italian-journal-linguistics.com/wp-content/uploads/6_Arcodia.pd
Do stellar-mass and super-massive black holes have similar dining habits?
Through the years numerous attempts have been made to connect the
phenomenology and physics of mass accretion onto stellar-mass and super-massive
black holes in a scale-invariant fashion. In this paper, we explore this
connection at the radiatively-efficient (and non-jetted) end of accretion modes
by comparing the relationship between the luminosity of the accretion disk and
corona in the two source classes. We analyse 458 RXTE-PCA archival observations
of the X-ray binary (XRB) GX339-4 focusing on the soft and soft-intermediate
states, which have been suggested to be analogous to radiatively efficient AGN.
The observed scatter in the relationship of
GX339-4 is high (dex) and significantly larger than in a
representative sample of radiatively-efficient, non- or weakly-jetted AGN
(dex). On the face of it, this would appear contrary to the
hypothesis that the systems simply scale with mass. On the other hand we also
find that GX339-4 and our AGN sample show different and
distributions, with the latter being broader in GX339-4 (dispersion of
cf. for AGN). GX339-4 also shows an overall softer slope,
with mean as opposed to for the AGN sample. Remarkably,
once similarly broad and distributions are selected, the AGN
sample overlaps nicely with GX339-4 observations in the mass-normalised plane, with a scatter of dex. This
indicates that a mass-scaling of properties might hold after all, with our
results being consistent with the disk-corona systems in AGN and XRBs
exhibiting the same physical processes, albeit under different conditions for
instance in terms of temperature, optical depth and/or electron energy
distribution in the corona, heating-cooling balance, coronal geometry and/or
black hole spin.Comment: Accepted for publication in Astronomy & Astrophysic
Disappearance of quasi-periodic-eruptions (QPEs) in GSN 069, simultaneous X-ray re-brightening, and predicted QPE re-appearance
We study the short- and long-timescale properties of quasi-periodic eruptions
(QPEs) in GSN 069 and its overall X-ray evolution over the past 11 yr using 11
XMM-Newton and 1 Chandra observations from December 2010 to December 2021. QPEs
are a transient phenomenon in GSN 069 last detected in January 2020 with a
life-time between 1 and 5.5 yr. On short timescales, the QPE intensity and
recurrence time oscillate defining alternating strong/weak QPEs and long/short
recurrence times. The quiescent level variability in observations with QPEs
exhibits a quasi-periodic oscillation (QPO) at the average
observation-dependent recurrence time peaking with a delay of a few hr w.r.t.
the preceding QPE. A significant late-time X-ray re-brightening starting with
the QPE disappearance is observed in the long-term light curve of the quiescent
emission, and the overall X-ray evolution follows the relation expected from
constant-area blackbody emission. QPEs in GSN 069 are consistent with being
produced by repeating tidal stripping events of a white dwarf (WD) donor in a
highly eccentric orbit around the supermassive black hole, one QPE being
produced at each pericenter passage. Our data suggest that the WD was partially
disrupted when QPEs disappeared in GSN 069, giving rise to the observed X-ray
re-brightening. We predict the re-appearance of QPEs in GSN 0699 in the near
future with different recurrence times than currently detected QPEs, as the
surviving core will again suffer a series of tidal stripping events at
pericenter passage.Comment: Submitted to A&A. Comments welcom
Tormund's return: Hints of quasi-periodic eruption features from a recent optical tidal disruption event
Quasi-periodic eruptions (QPEs) are repeating thermal X-ray bursts associated
with accreting massive black holes, the precise underlying physical mechanisms
of which are still unclear. We present a new candidate QPE source, AT 2019vcb
(nicknamed Tormund by the ZTF collaboration), which was found during an
archival search for QPEs in the XMM-Newton archive. It was first discovered in
2019 as an optical tidal disruption event (TDE) at , and its X-ray
follow-up exhibited QPE-like properties. Our goals are to verify its robustness
as QPE candidate and to investigate its properties to improve our understanding
of QPEs. We performed a detailed study of the X-ray spectral behaviour of this
source over the course of the XMM-Newton archival observation. We also report
on recent Swift and NICER follow-up observations to constrain the source's
current activity and overall lifetime, as well as an optical spectral
follow-up. The first two Swift detections and the first half of the 30 ks
XMM-Newton exposure of Tormund displayed a decaying thermal emission typical of
an X-ray TDE. However, the second half of the exposure showed a dramatic rise
in temperature (from 53 to 114 eV) and 0.2-2 keV luminosity (from
to erg s). The late-time NICER
follow-up indicates that the source is still X-ray bright more than three years
after the initial optical TDE. Although only a rise phase was observed,
Tormund's strong similarities with a known QPE source (eRO-QPE1) and the
impossibility to simultaneously account for all observational features with
alternative interpretations allow us to classify Tormund as a candidate QPE. If
confirmed as a QPE, it would further strengthen the observational link between
TDEs and QPEs. It is also the first QPE candidate for which an associated
optical TDE was directly observed, constraining the formation time of QPEs.Comment: Accepted for publication in A&A, 20 pages, 17 figure
Designing and managing music festival experiences to enhance attendees’ psychological and social benefits
Attendance and participation at popular music festivals has become an important and increasingly common experience for people in many Western societies, yet little is known about the kinds of benefits visitors perceive they gain as a result of attending. This research explores attendees’ perceptions of the psychological and social benefits associated with their attendance of the Woodford Folk Music Festival in Queensland (Australia). Based upon the research findings, music festival management strategies are suggested to improve the design of festival experiences to better cater to the artistic, musical, social and psychological needs of attendees thereby increasing the impact and depth of the experience
A Review of Web-Based Job Advertisements for Australian Event Management Positions
Strong growths in the Australian event management industry, ongoing technological changes and the internationalisation of the market place has spurred the need for appropriately educated and trained event managers and for a re-evaluation of educational and job training curriculum to meet these new challenges. In order for Australia to position itself as a world leader in event management, it is important to provide consistent high professional standards and event managers that not only meet, but exceed the demands of the industry. While there is some literature that focuses on the tourism and leisure job market (Crossley, 1992; Keung & Pine, 2000), and a small but developing literature base that focuses on event management training (Harris & Jago, 1999; Hawkins & Goldbatt, 1995) relatively little consideration has been given to a national agenda for event management skilling. To provide an indication of current employer requirements, a nationwide study of job advertisements in event management has commenced. The aims of the study are to further the understanding of the educational needs and training requirements of the industry; to ascertain the learned skills and personal attributes sought from event managers; to determine the compatibility of industry demands with current educational and vocational provisions; and to suggest post-secondary institutional avenues through which event management education and training needs can be pursued. This is an ongoing study and it is hoped that it will contribute towards a broad scale understanding of the event management job market. More importantly however, it can be used as the basis for curriculum evaluation and training needs, and create a better understanding and compatibility between event management education and industry practice. This paper reports the preliminary results from a content analysis of approximately 100 web-based job advertisements. Email alert accounts were established with several search engines to gather a sample of event management related job advertisements from around Australia. An analytical framework was devised for the analysis of the advertisements themselves. The results reveal several interesting trends including the geographical concentration of the event management job market, the range of industries that require event management specialists or event management skills, and a series of required skills and key attributes of event managers. The results of this study establish a platform from which to develop a classification of event management skills required by the industry
Live to die another day: the rebrightening of AT2018fyk as a repeating partial tidal disruption event
Stars that interact with supermassive black holes (SMBHs) can either be
completely or partially destroyed by tides. In a partial tidal disruption event
(TDE) the high-density core of the star remains intact, and the low-density,
outer envelope of the star is stripped and feeds a luminous accretion episode.
The TDE AT2018fyk, with an inferred black hole mass of
M, experienced an extreme dimming event at X-ray (factor of 6000)
and UV (factor 15) wavelengths 500--600 days after discovery. Here
we report on the re-emergence of these emission components roughly 1200 days
after discovery. We find that the source properties are similar to those of the
pre-dimming accretion state, suggesting that the accretion flow was rejuvenated
to a similar state. We propose that a repeating partial TDE, where the
partially disrupted star is on a day orbit about the SMBH and is
periodically stripped of mass during each pericenter passage, powers its unique
lightcurve. This scenario provides a plausible explanation for AT2018fyk's
overall properties, including the rapid dimming event and the rebrightening at
late times. We also provide testable predictions for the behavior of the
accretion flow in the future: if the second encounter was also a partial
disruption then we predict another strong dimming event around day 1800 (August
2023), and a subsequent rebrightening around day 2400 (March 2025). This source
provides strong evidence of the partial disruption of a star by a SMBH.Comment: ApJ Letters, accepted for publicatio
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