160 research outputs found
Optical polarization reveals colliding stellar stream shocks in a tidal disruption event
Supermassive black holes have been known to disrupt passing stars producing
outbursts called Tidal Disruption Events offering a unique view on the early
stages of accretion disk and jet formation. The advent of large scale optical
time-domain surveys has significantly increased the number of known events and
challenged our understanding of their dynamics and emission processes. Here, we
present the linear polarization curve of the most polarized tidal disruption
without any indication of contribution from a jet to the emission. Our
observations demonstrate that optical TDE emission can be powered by tidal
stream shocks.Comment: 36 pages, 7 figures, author's version of the paper accepted in
Scienc
Neutral and Cationic Rare Earth Metal Alkyl and Benzyl Compounds with the 1,4,6-Trimethyl-6-pyrrolidin-1-yl-1,4-diazepane Ligand and Their Performance in the Catalytic Hydroamination/Cyclization of Aminoalkenes
A new neutral tridentate 1,4,6-trimethyl-6-pyrrolidin-1-yl-1,4-diazepane (L) was prepared. Reacting L with trialkyls M(CH2SiMe3)3(THF)2 (M = Sc, Y) and tribenzyls M(CH2Ph)3(THF)3 (M = Sc, La) yielded trialkyl complexes (L)M(CH2SiMe3)3 (M = Sc, 1; M = Y, 2) and tribenzyl complexes (L)M(CH2Ph)3 (M = Sc, 3; M = La, 4). Complexes 1 and 2 can be converted to their corresponding ionic compounds [(L)M(CH2SiMe3)2(THF)][B(C6H5)4] (M = Sc, Y) by reaction with [PhNMe2H][B(C6H5)4] in THF. Complexes 3 and 4 can be converted to cationic species [(L)M(CH2Ph)2]+ by reaction with [PhNMe2H][B(C6F5)4] in C6D5Br in the absence of THF. The neutral complexes 1-4 and their cationic derivatives were studied as catalysts for the hydroamination/cyclization of 2,2-diphenylpent-4-en-1-amine and N-methylpent-4-en-1-amine reference substrates and compared with ligand-free Sc, Y, and La neutral and cationic catalysts. The most effective catalysts in the series were the cationic L-yttrium catalyst (for 2,2-diphenylpent-4-en-1-amine) and the cationic lanthanum systems (for N-methylpent-4-en-1-amine). For the La catalysts, evidence was obtained for release of L from the metal during catalysis.
A comparative study on the convergence rate of some iteration methods involving contractive mappings
The Young Supernova Experiment: Survey Goals, Overview, and Operations
Time domain science has undergone a revolution over the past decade, with
tens of thousands of new supernovae (SNe) discovered each year. However,
several observational domains, including SNe within days or hours of explosion
and faint, red transients, are just beginning to be explored. Here, we present
the Young Supernova Experiment (YSE), a novel optical time-domain survey on the
Pan-STARRS telescopes. Our survey is designed to obtain well-sampled
light curves for thousands of transient events up to . This
large sample of transients with 4-band light curves will lay the foundation for
the Vera C. Rubin Observatory and the Nancy Grace Roman Space Telescope,
providing a critical training set in similar filters and a well-calibrated
low-redshift anchor of cosmologically useful SNe Ia to benefit dark energy
science. As the name suggests, YSE complements and extends other ongoing
time-domain surveys by discovering fast-rising SNe within a few hours to days
of explosion. YSE is the only current four-band time-domain survey and is able
to discover transients as faint 21.5 mag in and 20.5 mag in
, depths that allow us to probe the earliest epochs of stellar explosions.
YSE is currently observing approximately 750 square degrees of sky every three
days and we plan to increase the area to 1500 square degrees in the near
future. When operating at full capacity, survey simulations show that YSE will
find 5000 new SNe per year and at least two SNe within three days of
explosion per month. To date, YSE has discovered or observed 8.3% of the
transient candidates reported to the International Astronomical Union in 2020.
We present an overview of YSE, including science goals, survey characteristics
and a summary of our transient discoveries to date.Comment: ApJ, in press; more information at https://yse.ucsc.edu
The broad-lined Type-Ic supernova SN 2022xxf with extraordinary two-humped light curves
We report on our study of supernova (SN) 2022xxf based on observations
obtained during the first four months of its evolution. The light curves (LCs)
display two humps of similar maximum brightness separated by 75 days,
unprecedented for a broad-lined (BL) Type Ic supernova (SN IcBL). SN 2022xxf is
the most nearby SN IcBL to date (in NGC 3705, , at a distance of
about 20 Mpc). Optical and near-infrared photometry and spectroscopy are used
to identify the energy source powering the LC. Nearly 50 epochs of high
signal-to-noise-ratio spectroscopy were obtained within 130 days, comprising an
unparalleled dataset for a SN IcBL, and one of the best-sampled SN datasets to
date. The global spectral appearance and evolution of SN 2022xxf points to
typical SN Ic/IcBL, with broad features (up to km s) and a
gradual transition from the photospheric to the nebular phase. However, narrow
emission lines (corresponding to km s) are present in
the spectra from the time of the second rise, suggesting slower-moving
circumstellar material (CSM). These lines are subtle, in comparison to the
typical strong narrow lines of CSM-interacting SNe, for example, Type IIn, Ibn,
and Icn, but some are readily noticeable at late times such as in Mg I
5170 and [O I] 5577. Unusually, the near-infrared spectra
show narrow line peaks in a number of features formed by ions of O and Mg. We
infer the presence of CSM that is free of H and He. We propose that the
radiative energy from the ejecta-CSM interaction is a plausible explanation for
the second LC hump. This interaction scenario is supported by the color
evolution, which progresses to the blue as the light curve evolves along the
second hump, and the slow second rise and subsequent rapid LC drop. (Abstract
abridged)Comment: Accepted versio
From Architectured Materials to Large-Scale Additive Manufacturing
The classical material-by-design approach has been extensively perfected by materials scientists, while engineers have been optimising structures geometrically for centuries. The purpose of architectured materials is to build bridges across themicroscale ofmaterials and themacroscale of engineering structures, to put some geometry in the microstructure. This is a paradigm shift. Materials cannot be considered monolithic anymore. Any set of materials functions, even antagonistic ones, can be envisaged in the future. In this paper, we intend to demonstrate the pertinence of computation for developing architectured materials, and the not-so-incidental outcome which led us to developing large-scale additive manufacturing for architectural applications
Target-of-opportunity Observations of Gravitational-wave Events with Vera C. Rubin Observatory
The discovery of the electromagnetic counterpart to the binary neutron star (NS) merger GW170817 has opened the era of gravitational-wave multimessenger astronomy. Rapid identification of the optical/infrared kilonova enabled a precise localization of the source, which paved the way to deep multiwavelength follow-up and its myriad of related science results. Fully exploiting this new territory of exploration requires the acquisition of electromagnetic data from samples of NS mergers and other gravitational-wave sources. After GW170817, the frontier is now to map the diversity of kilonova properties and provide more stringent constraints on the Hubble constant, and enable new tests of fundamental physics. The Vera C. Rubin Observatory’s Legacy Survey of Space and Time can play a key role in this field in the 2020s, when an improved network of gravitational-wave detectors is expected to reach a sensitivity that will enable the discovery of a high rate of merger events involving NSs (∼tens per year) out to distances of several hundred megaparsecs. We design comprehensive target-of-opportunity observing strategies for follow-up of gravitational-wave triggers that will make the Rubin Observatory the premier instrument for discovery and early characterization of NS and other compact-object mergers, and yet unknown classes of gravitational-wave events
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