436 research outputs found
Synchrotron Afterglow Model for AT 2022cmc: Jetted Tidal Disruption Event or Engine-Powered Supernova?
AT 2022cmc is a luminous optical transient ( erg
s) accompanied by decaying non-thermal X-rays (peak duration days and isotropic energy erg) and a
long-lived radio/mm synchrotron afterglow, which has been interpreted as a
jetted tidal disruption event (TDE). Both an equipartition analysis and a
detailed afterglow model reveals the radio/mm emitting plasma to be expanding
mildly relativistically (Lorentz factor ) with an opening
angle and roughly fixed energy erg into an external medium of density profile with , broadly similar to that of the first jetted TDE
candidate Swift J1644+57 and consistent with Bondi accretion at a rate onto a black hole before the
outburst. The rapidly decaying optical emission over the first days is
consistent with fast-cooling synchrotron radiation from the same forward shock
as the radio/mm emission, while the bluer slowly decaying phase to follow
likely represents a separate thermal emission component. Emission from the
reverse shock may have peaked during the first days, but whose non-detection in
the optical band places an upper bound on the
Lorentz factor of the unshocked jet. Although a TDE origin for AT 2022cmc is
indeed supported by some observations, the vast difference between the
short-lived jet activity phase days relative to the
months-long thermal optical emission, also challenges this scenario. A stellar
core-collapse event giving birth to a magnetar or black hole engine of peak
duration day offers an alternative model also consistent with the
circumburst environment, if interpreted as a massive-star wind.Comment: 11 pages, 9 figures, 2 tables, accepted for publication in MNRA
Light Curve Model for Luminous Red Novae and Inferences about the Ejecta of Stellar Mergers
The process of unstable mass transfer in a stellar binary can result in
either a complete merger of the stars or successful removal of the donor
envelope leaving a surviving more compact binary. "Luminous red nova" (LRN) are
the class of optical transients believed to accompany such merger/common
envelope events. Past works typically model LRNe using analytic formulae for
supernova light curves which make assumptions (e.g., radiation dominated
ejecta, neglect of hydrogen recombination energy) not justified in stellar
mergers due to the lower velocities and specific thermal energy of the ejecta.
We present a one-dimensional model of LRN light curves, which accounts for
these effects. Consistent with observations, we find that LRNe typically
possess two light curve peaks, an early phase powered by initial thermal energy
of the hot, fastest ejecta layers and a later peak powered by hydrogen
recombination from the bulk of the ejecta. We apply our model to a sample of
LRNe to infer their ejecta properties (mass, velocity, and launching radius)
and compare them to the progenitor donor star properties from pre-transient
imaging. We define a maximum luminosity achievable for a given donor star in
the limit that the entire envelope is ejected, finding that several LRNe
violate this limit. Shock interaction between the ejecta and pre-dynamical
mass-loss, may provide an additional luminosity source to alleviate this
tension. Our model can also be applied to the merger of planets with stars or
stars with compact objects.Comment: 24 pages, 13 figures, 1 table, accepted for publication in Ap
Pure Gravity Mediation of Supersymmetry Breaking at the LHC
Supersymmetric theories which can allow for a 125 GeV Higgs mass and also
solve the naturalness and susy flavor problems now require a fair degree of
complexity. Here we consider the simplest possibility for supersymmetry near
the weak scale, but with the requirement of naturalness dropped. In "pure
gravity mediation", all supersymmetric particles except for the gauginos lie at
tens to thousands of TeV, with the gauginos obtaining loop suppressed masses
automatically by anomaly mediation and higgsino threshold corrections. The
gauginos are the lightest superpartners, and we investigate the current
collider constraints on their masses, as well as the future reach of the LHC.
We consider gluino pair production with a jets + missing energy signature, as
well as events with disappearing charged tracks caused by charged winos
decaying into their neutral partners. We show that presently, gluino masses
less than about 1 TeV and wino masses less than about 300 GeV are excluded, and
that the 14 TeV LHC can probe gluino masses up to about 2 TeV and wino masses
up to 1 TeV.Comment: 22 pages, 5 figure
Open Versus Closed Conference Calls: The Determinants and Effects of Broadening Access to Disclosure
Recent advances in information technology allow firms to provide broader access to their disclosures. We examine the determinants and effects of the decision to provide unlimited real-time access to conference calls (i.e., “open” conference calls). Our evidence suggests that the decision to provide open calls is associated with the composition of a firm\u27s investor base and, to some degree, the complexity of its financial information. We also find that open calls are associated with a greater increase in small trades (consistent with individuals trading on information released during the call) and higher price volatility during the call period
Andreev Bound States at the Interface of Antiferromagnets and d-wave Superconductors
We set up a simple transfer matrix formalism to study the existence of bound
states at interfaces and in junctions between antiferromagnets and d-wave
superconductors. The well-studied zero energy mode at the {110} interface
between an insulator and a d-wave superconductor is spin split when the
insulator is an antiferromagnet. This has as a consequence that any competing
interface induced superconducting order parameter that breaks the time reversal
symmetry needs to exceed a critical value before a charge current is induced
along the interface.Comment: 4 pages, 3 figure
Instructive Role of the Microenvironment in Preventing Renal Fibrosis
Accumulation of myofibroblasts is a hallmark of renal fibrosis. A significant proportion of myofibroblasts has been reported to originate via endothelial-mesenchymal transition. We initially hypothesized that exposing myofibroblasts to the extract of endothelial progenitor cells (EPCs) could reverse this transition. Indeed, in vitro treatment of transforming growth factor-beta1 (TGF-beta1)-activated fibroblasts with EPC extract prevented expression of alpha-smooth muscle actin (alpha-SMA); however, it did not enhance expression of endothelial markers. In two distinct models of renal fibrosis-unilateral ureteral obstruction and chronic phase of folic acid-induced nephropathy-subcapsular injection of EPC extract to the kidney prevented and reversed accumulation of alpha-SMA-positive myofibroblasts and reduced fibrosis. Screening the composition of EPC extract for cytokines revealed that it is enriched in leukemia inhibitory factor (LIF) and vascular endothelial growth factor. Only LIF was capable of reducing fibroblast-to-myofibroblast transition of TGF-beta1-activated fibroblasts. In vivo subcapsular administration of LIF reduced the number of myofibroblasts and improved the density of peritubular capillaries; however, it did not reduce the degree of fibrosis. A receptor-independent ligand for the gp130/STAT3 pathway, hyper-interleukin-6 (hyper-IL-6), not only induced a robust downstream increase in pluripotency factors Nanog and c-Myc but also exhibited a powerful antifibrotic effect. In conclusion, EPC extract prevented and reversed fibroblast-to-myofibroblast transition and renal fibrosis. The component of EPC extract, LIF, was capable of preventing development of the contractile phenotype of activated fibroblasts but did not eliminate TGF-beta1-induced collagen synthesis in cultured fibroblasts and models of renal fibrosis, whereas a receptor-independent gp130/STAT3 agonist, hyper-IL-6, prevented fibrosis. In summary, these studies, through the evolution from EPC extract to LIF and then to hyper-IL-6, demonstrate the instructive role of microenvironmental cues and may provide in the future a facile strategy to prevent and reverse renal fibrosis. Stem Cells Translational Medicine 2017;6:992-1005
The Grizzly, March 2, 2017
Student Premieres Self-Produced Film on Campus • SPINT Houses to Host Events to Interest Applicants for Next Year • International Perspective: A Japanese Student\u27s Reflection on Exchange Programs • Q&A with Last Year\u27s Faculty Award Winners • Setting the Bar High: Mock Trial Races Toward Success • UC Senior Sprints to the Finish Line • Opinions: The U-Imagine Center Undermines Liberal Education; Entrepreneurship Enhances Liberal Education at UC • Men\u27s Basketball Breaks Nine-Year Drought, Advances to Conference Playoffs • Four for Four: Ursinus Women\u27s Swimming Caps Off Perfect Four Yearshttps://digitalcommons.ursinus.edu/grizzlynews/1662/thumbnail.jp
The Cosmic Infrared Background Experiment
We are developing a rocket-borne instrument (the Cosmic Infrared Background
ExpeRiment, or CIBER) to search for signatures of primordial galaxy formation
in the cosmic near-infrared extra-galactic background. CIBER consists of a
wide-field two-color camera, a low-resolution absolute spectrometer, and a
high-resolution narrow-band imaging spectrometer. The cameras will search for
spatial fluctuations in the background on angular scales from 7 arcseconds to 2
degrees over a range of angular scales poorly covered by previous experiments.
CIBER will determine if the fluctuations reported by the IRTS arise from
first-light galaxies or have a local origin. In a short rocket flight CIBER has
sensitivity to probe fluctuations 100 times fainter than IRTS/DIRBE. By jointly
observing regions of the sky studied by Spitzer and ASTRO-F, CIBER will build a
multi-color view of the near-infrared background, accurately assessing the
contribution of local (z = 1-3) galaxies to the observed background
fluctuations, allowing a deep and comprehensive survey for first-light galaxy
background fluctuations. The low-resolution spectrometer will search for a
redshifted Lyman cutoff feature between 0.8 - 2.0 microns. The high-resolution
spectrometer will trace zodiacal light using the intensity of scattered
Fraunhofer lines, providing an independent measurement of the zodiacal emission
and a new check of DIRBE zodiacal dust models. The combination will
systematically search for the infrared excess background light reported in
near-infrared DIRBE/IRTS data, compared with the small excess reported at
optical wavelengths.Comment: 11 pages, 3 figures; To appear in proceedings of UC Irvine May 2005
workshop on "First Light & Reionization", eds. E. Barton & A. Cooray, New
Astronomy Reviews, in pres
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