22,367 research outputs found
The Discovery and Nature of Optical Transient CSS100217:102913+404220
We report on the discovery and observations of the extremely luminous optical
transient CSS100217:102913+404220 (CSS100217 hereafter). Spectroscopic
observations show this transient was coincident with a galaxy at redshift
z=0.147, and reached an apparent magnitude of V ~ 16.3. After correcting for
foreground Galactic extinction we determine the absolute magnitude to be M_V
=-22.7 approximately 45 days after maximum light. Based on our unfiltered
optical photometry the peak optical emission was L = 1.3 x 10^45 erg s^-1, and
over a period of 287 rest-frame days had an integrated bolometric luminosity of
1.2 x 10^52 erg. Analysis of the pre-outburst SDSS spectrum of the source shows
features consistent with a Narrow-line Seyfert1 (NLS1) galaxy. High-resolution
HST and Keck followup observations show the event occurred within 150pc of
nucleus of the galaxy, suggesting a possible link to the active nuclear region.
However, the rapid outburst along with photometric and spectroscopic evolution
are much more consistent with a luminous supernova. Line diagnostics suggest
that the host galaxy is undergoing significant star formation. We use extensive
follow-up of the event along with archival CSS and SDSS data to investigate the
three most likely sources of such an event; 1) an extremely luminous supernova;
2) the tidal disruption of a star by the massive nuclear black hole; 3)
variability of the central AGN. We find that CSS100217 was likely an extremely
luminous type IIn supernova that occurred within range of the narrow-line
region of an AGN. We discuss how similar events may have been missed in past
supernova surveys because of confusion with AGN activity.Comment: submitted to Ap
Pengaruh penginapan ke atas disiplin pelajar di Universiti Tun Hussein Onn Malaysia
Kajian pengaruh penginapan ke atas disiplin pelajar di Universiti Tun Hussein Onn Malaysia (UTHM) ini memfokuskan kepada tiga objektif iaitu mengenal pasti tahap kriteria penginapan dari aspek fizikal dan bukan fizikal yang memberi kesan terhadap penginapan pelajar di UTHM, mengenal pasti kesalahan disiplin pelajar terhadap peraturan tempat penginapan mereka dan mengkaji hubungan signifikan antara disiplin pelajar dengan tahap kriteria tempat penginapan mereka. Sampel kajian dipilih secara rawak yang terdiri daripada 350 pelajar dari lima kolej kediaman iaitu Kolej Kediaman Tun Syed Nasir, Kolej Kediaman Tun Dr. Ismail, Kolej Kediaman Tun Fatimah, Kolej Kediaman Melewar dan Kolej Kediaman Perwira. Data-data kajian diperolehi daripada soal selidik dan statistik kesalahan disiplin pelajar terhadap peraturan kolej yang direkod oleh setiap Kolej Kediaman. Dapatan kajian menunjukkan kriteria penginapan pelajar dari aspek fizikal dan bukan fizikal berada pada tahap sederhana masing-masing mendapat skor min 3.01 dan 3.47. Kesalahan disiplin pelajar menunjukkan setiap 25 orang pelajar yang tinggal di Kolej Kediaman melakukan satu kes kesalahan. Dari segi hubungan signifikan antara disiplin pelajar dengan tahap kriteria penginapan pelajar di UTHM menunjukkan terdapat hubungan yang signifikan berdasarkan perbandingan yang dilakukan. Hubungan ini wujud berdasarkan kajian yang dijalankan di UTHM sahaja namun hubungan ini tidak semestinya wujud di penginapan pelajar di tempat lain
The Identification of Extreme Asymptotic Giant Branch Stars and Red Supergiants in M33 by 24 {\mu}m Variability
We present the first detection of 24 {\mu}m variability in 24 sources in the
Local Group galaxy M33. These results are based on 4 epochs of MIPS
observations, which are irregularly spaced over ~750 days. We find that these
sources are constrained exclusively to the Holmberg radius of the galaxy, which
increases their chances of being members of M33. We have constructed spectral
energy distributions (SEDs) ranging from the optical to the sub-mm to
investigate the nature of these objects. We find that 23 of our objects are
most likely heavily self-obscured, evolved stars; while the remaining source is
the Giant HII region, NGC 604. We believe that the observed variability is the
intrinsic variability of the central star reprocessed through their
circumstellar dust shells. Radiative transfer modeling was carried out to
determine their likely chemical composition, luminosity, and dust production
rate (DPR). As a sample, our modeling has determined an average luminosity of
(3.8 0.9) x 10 L and a total DPR of (2.3 0.1) x
10 M yr. Most of the sources, given the high DPRs and
short wavelength obscuration, are likely "extreme" AGB (XAGB) stars. Five of
the sources are found to have luminosities above the classical AGB limit
(M 54,000 L), which classifies them as probably
red supergiants (RSGs). Almost all of the sources are classified as oxygen
rich. As also seen in the LMC, a significant fraction of the dust in M33 is
produced by a handful of XAGB and RSG stars.Comment: 36 pages, 14 figures, 4 tables, Accepted for publication in A
Short term Variability of the Sun Earth System: An Overview of Progress Made during the CAWSES II Period
This paper presents an overview of results obtained during the CAWSES II
period on the short term variability of the Sun and how it affects the near
Earth space environment. CAWSES II was planned to examine the behavior of the
solar terrestrial system as the solar activity climbed to its maximum phase in
solar cycle 24. After a deep minimum following cycle 23, the Sun climbed to a
very weak maximum in terms of the sunspot number in cycle 24 (MiniMax24), so
many of the results presented here refer to this weak activity in comparison
with cycle 23. The short term variability that has immediate consequence to
Earth and geospace manifests as solar eruptions from closed field regions and
high speed streams from coronal holes. Both electromagnetic (flares) and mass
emissions (coronal mass ejections, CMEs) are involved in solar eruptions, while
coronal holes result in high speed streams that collide with slow wind forming
the so called corotating interaction regions (CIRs). Fast CMEs affect Earth via
leading shocks accelerating energetic particles and creating large geomagnetic
storms. CIRs and their trailing high speed streams (HSSs), on the other hand,
are responsible for recurrent small geomagnetic storms and extended (days) of
auroral zone activity, respectively. The latter lead to the acceleration of
relativistic magnetospheric killer electrons. One of the major consequences of
the weak solar activity is the altered physical state of the heliosphere that
has serious implications for the shock-driving and storm causing properties of
CMEs. Finally, a discussion is presented on extreme space weather events
prompted by the 2012 July 23 super storm event that occurred on the backside of
the Sun. Many of these studies were enabled by the simultaneous availability of
remote-sensing and in situ observations from multiple vantage points with
respect to the Sun Earth line.Comment: 85 pages, 30 figures, 2 tables, Accepted for publication in Progress
in Earth and Planetary Science on April 13, 201
Storyline description of Southern Hemisphere midlatitude circulation and precipitation response to greenhouse gas forcing
As evidence of climate change strengthens, knowledge of its regional implications becomes an urgent need for decision making. Current understanding of regional precipitation changes is substantially limited by our understanding of the atmospheric circulation response to climate change, which to a high degree remains uncertain. This uncertainty is reflected in the wide spread in atmospheric circulation changes projected in multimodel ensembles, which cannot be directly interpreted in a probabilistic sense. The uncertainty can instead be represented by studying a discrete set of physically plausible storylines of atmospheric circulation changes. By mining CMIP5 model output, here we take this broader perspective and develop storylines for Southern Hemisphere (SH) midlatitude circulation changes, conditioned on the degree of global-mean warming, based on the climate responses of two remote drivers: the enhanced warming of the tropical upper troposphere and the strengthening of the stratospheric polar vortex. For the three continental domains in the SH, we analyse the precipitation changes under each storyline. To allow comparison with previous studies, we also link both circulation and precipitation changes with those of the Southern Annular Mode. Our results show that the response to tropical warming leads to a strengthening of the midlatitude westerly winds, whilst the response to a delayed breakdown (for DJF) or strengthening (for JJA) of the stratospheric vortex leads to a poleward shift of the westerly winds and the storm tracks. However, the circulation response is not zonally symmetric and the regional precipitation storylines for South America, South Africa, South Australia and New Zealand exhibit quite specific dependencies on the two remote drivers, which are not well represented by changes in the Southern Annular Mode
Handbook for the estimation of microwave propagation effects: Link calculations for earth-space paths (path loss and noise estimation)
A single model for a standard of comparison for other models when dealing with rain attenuation problems in system design and experimentation is proposed. Refinements to the Global Rain Production Model are incorporated. Path loss and noise estimation procedures as the basic input to systems design for earth-to-space microwave links operating at frequencies from 1 to 300 GHz are provided. Topics covered include gaseous absorption, attenuation by rain, ionospheric and tropospheric scintillation, low elevation angle effects, radome attenuation, diversity schemes, link calculation, and receiver noise emission by atmospheric gases, rain, and antenna contributions
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