STEM + Art = STEAM

Science, Technology, Engineering and Math – the STEM subjects – alone will not lead to the kind of breathtaking innovation the 21st century demands...So what does it mean to add Art to turn STEM to STEAM

High-Energy Emission from Interacting Supernovae: New Constraints on Cosmic-Ray Acceleration in Dense Circumstellar Environments

Supernovae (SNe) with strong interactions with circumstellar material (CSM) are promising candidate sources of high-energy neutrinos and gamma rays, and have been suggested as an important contributor to Galactic cosmic rays beyond 1 PeV. Taking into account the shock dissipation by a fast velocity component of SN ejecta, we present comprehensive calculations of the non-thermal emission from SNe powered by shock interactions with a dense wind or CSM. Remarkably, we consider electromagnetic cascades in the radiation zone and subsequent attenuation in the pre-shock CSM. A new time-dependent phenomenological prescription provided by this work enables us to calculate gamma-ray, hard X-ray, radio, and neutrino signals, which originate from cosmic rays accelerated by the diffusive shock acceleration mechanism. We apply our results to SN IIn 2010jl and SN Ib/IIn 2014C, for which the model parameters can be determined from the multi-wavelength data. For SN 2010jl, the more promising case, by using the the latest Fermi Large Area Telescope (LAT) Pass 8 data release, we derive new constraints on the cosmic-ray energy fraction, <0.05-0.1. We also find that the late-time radio data of these interacting SNe are consistent with our model. Further multi-messenger and multi-wavelength observations of nearby interacting SNe should give us new insights into the diffusive shock acceleration in dense environments as well as pre-SN mass-loss mechanisms.Comment: 16 pages, 10 figures, 3 tables, accepted for publication in ApJ. Results and conclusions unchange

Divergent Thinking | RISD President

Innovation happens when convergent thinkers—people who march straight ahead towards a clearly defined goal—combine forces with divergent thinkers, those who may wander professionally but who are comfortable being uncomfortable and who look for what is real. RISD harbors a lot of divergent, agile thinkers. . . . – John Maeda, RISD President 2008-13https://digitalcommons.risd.edu/risdxyz_fall2013/1004/thumbnail.jp

Cultural Context | RISD President

Art and design remind us to look at things from different angles and to value what is unique about ourselves and our culture… . John Maeda, RISD President 2008-12https://digitalcommons.risd.edu/risdxyz_springsummer2013/1003/thumbnail.jp

X-ray Measurements of the Particle Acceleration Properties at Inward Shocks in Cassiopeia A

We present new evidence that the bright non-thermal X-ray emission features in the interior of the Cassiopeia A supernova remnant (SNR) are caused by inward moving shocks based on Chandra and NuSTAR observations. Several bright inward-moving filaments were identified using monitoring data taken by Chandra in 2000-2014. These inward-moving shock locations are nearly coincident with hard X-ray (15-40 keV) hot spots seen by NuSTAR. From proper motion measurements, the transverse velocities were estimated to be in the range $\sim$2,100-3,800 km s$^{-1}$ for a distance of 3.4 kpc. The shock velocities in the frame of the expanding ejecta reach values of $\sim$5,100-8,700 km s$^{-1}$, slightly higher than the typical speed of the forward shock. Additionally, we find flux variations (both increasing and decreasing) on timescales of a few years in some of the inward-moving shock filaments. The rapid variability timescales are consistent with an amplified magnetic field of $B \sim$ 0.5-1 mG. The high speed and low photon cut-off energy of the inward-moving shocks are shown to imply a particle diffusion coefficient that departs from the Bohm regime ($k_0 = D_0/D_{\rm 0,Bohm} \sim$ 3-8) for the few simple physical configurations we consider in this study. The maximum electron energy at these shocks is estimated to be $\sim$8-11 TeV, smaller than the values of $\sim$15-34 TeV inferred for the forward shock. Cassiopeia A is dynamically too young for its reverse shock to appear to be moving inward in the observer frame. We propose instead that the inward-moving shocks are a consequence of the forward shock encountering a density jump of $\gtrsim$ 5-8 in the surrounding material.Comment: 16 pages, 8 figures, accepted for publication in Ap

Introduction: Immersed in Lithics

The idea of holding a conference to discuss how we can explore what affects our approaches to, and understanding of, lithic artefacts and their analysis emerged from a hands-on workshop entitled Northern Knap-in in November 2014. In that workshop we wanted to explore how prehistoric people in the north of England, which is perceived by many as being a (lithic)resource-poor region, might have adapted to the lack of good quality flint and chert for tool manufacture and so we experimented with the working of non-flint raw materials. Many things emerged from that day including how the experimental knapping of materials other than flint allowed us to think outside the conventional box, and how communal knapping and grinding demonstrated some of the different ways that people interacted and adapted to each other’s rhythm when making artefacts. We were also struck (excuse the pun) by how much non-lithic specialists contributed to the questions we raise in lithic analysis. This brought home to us the importance of finding other, sometimes non- conventional, ways in which we can engage with the past. This eventually led to the Immersed in Lithics Conference in February 2016

Relativistic Radiative Transfer for Spherical Flows

We present a new complete set of Lagrangian relativistic hydrodynamical equations describing the transfer of energy and momentum between a standard fluid and a radiation fluid in a general non-stationary spherical flow. The new set of equations has been derived for a particular application to the study of the cosmological Quark--Hadron transition but can also be used in other contexts.Comment: 28 pages, 9 postscript figs, Plain Te