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We report on the results of optical, near-infrared (NIR) and mid-infrared observations of the black hole X-ray binary candidate (BHB) MAXI J1535-571 during its 2017/2018 outburst. During the first part of the outburst (MJD 58004-58012), the source shows an optical-NIR spectrum that is consistent with an optically thin synchrotron power-law from a jet. After MJD 58015, however, the source faded considerably, the drop in flux being much more evident at lower frequencies. Before the fading, we measure a de-reddened flux density of $\gtrsim$100 mJy in the mid-infrared, making MAXI J1535-571 one of the brightest mid-infrared BHBs known so far. A significant softening of the X-ray spectrum is evident contemporaneous with the infrared fade. We interpret it as due to the suppression of the jet emission, similar to the accretion-ejection coupling seen in other BHBs. However, MAXI J1535-571 did not transition smoothly to the soft state, instead showing X-ray hardness deviations, associated with infrared flaring. We also present the first mid-IR variability study of a BHB on minute timescales, with a fractional rms variability of the light curves of $\sim 15-22 \%$, which is similar to that expected from the internal shock jet model, and much higher than the optical fractional rms ($\lesssim 7 \%$). These results represent an excellent case of multi-wavelength jet spectral-timing and demonstrate how rich, multi-wavelength time-resolved data of X-ray binaries over accretion state transitions can help refining models of the disk-jet connection and jet launching in these systems., 20 pages, 8 figures. Accepted for publication in the ApJ

Over the last 40 years enormous advances have been made in infrared astronomy. Virtually all of these can be traced to the use of space-based telescopes, which avoid the deleterious effects of the earth’s atmosphere, and continued improvements in detector sensitivity and instrument design. Since its initial and modest contributions to previous infrared space astronomy missions, starting with ISO through to Herschel, Canada has grown in stature and is now recognized as a partner of choice by leading space agencies and scientific consortia embarking on the next generation of IR space astronomy missions. This white paper reviews the history of Canada’s contributions to IR space astronomy missions and presents the case for Canadian participation in the ESA-JAXA SPICA mission, which has been selected as one of three finalists for ESA’s fifth medium class mission, M5. Observations at far-infrared (FIR) wavelengths are optimal, not only for exploring galaxy formation in the farthest reaches of the Universe, but also star formation in our own Galaxy. Indeed, the study of cold and/or enshrouded systems can only be observed in the FIR. In essence, this provides the rationale for all space astronomy missions from IRAS through to Herschel. By any measure, Herschel was an outstanding success. It has caused astronomers to re-examine their theories of star formation and provided our first large scale view of distant star forming galaxies. With the SPICA telescope actively cooled to ~8 K, the lower thermal background will enable sensitivities two to three orders of magnitude better than Herschel’s! This sensitivity increase will allow SPICA not only to label photons by their wavelength over a volume of the Universe somewhere between one and ten thousand times greater than observed with Herschel, but also, and for the first time, allow it to label photons by their polarization in our Galaxy. Together these improvements augur major advances in the field. The SPICA instrument suite consists of three independent instruments: SAFARI – a FIR spectrometer; SMI – a mid-Infrared camera and spectrometer; and B-BOP - a FIR imaging polarimeter. The key features of each instrument are presented. Canadian scientific, technical and strategic leadership in the SPICA mission is well established. As a founding member of the SPICA/SAFARI consortium, Canada not only has much greater visibility and influence on the project, but also has the opportunity to contribute high-profile flight hardware to the mission. One of the primary tasks of the initial CSA-funded SPICA SAFARI Study was to identify and leverage Canadian signature technologies to establish a potential role for Canada in SPICA. As a result of the work undertaken over the last decade, Canada has the opportunity to deliver the high-resolution spectrometer component of the SAFARI instrument; one of three critical components of SAFARI which lies at its very heart. It is key to two of the main science drivers of the mission: i) galaxy evolution through spectral measurements of galaxies at high-redshift, and; ii) disk evolution by disentangling the line and continuum components of emission from spectral measurements of disks. Both of these fields of study are areas of excellence in Canadian astronomy. Several members of the team have a wealth of experience from science exploitation of Herschel data, some playing leading roles in Herschel key projects and many have been involved in developing the science cases for SPICA. All stand ready to assume leadership roles once the mission is selected by ESA and receives mission funding from the CSA. The impact on Canadian science, in terms of return on investment by the involvement of Canadian astronomers in science exploitation with SPICA through access to the guaranteed time will be over twice that of Herschel, which was one of, if not the, highest ROI of any CSA-funded space astronomy missions. Over the last decade Canada will have invested over $5M to establish a leading role in SPICA and as a result is now positioned to build the mission critical, high-resolution spectrometer for what will be the leading infrared observatory of the next decade if it is selected by ESA in 2021. At that time, Canada will have to make a decision on whether it will sign up for the mission. This point will be the last off-ramp for any nation in the SPICA consortium. Perhaps the greatest risk at an agency level is to diminish the trust that ESA has in the CSA as a dependable partner after staying the course for over a decade. ESA will hold the Mission Selection Review, to pick the winner of the three M5 finalists in April 2021. Programmatically, a letter will be required before this date (early 2021) from the CSA to ESA effectively stating that if ESA chooses SPICA, Canada is committed to the project. Securing mission funding requires approval from the Treasury Board of Canada. A strong statement of endorsement for SPICA in the LRP is a necessary prerequisite., White paper identifier W049

CASTOR (The Cosmological Advanced Survey Telescope for Optical and UV Research) is a proposed Canadian-led flagship mission designed to provide high-resolution imaging and spectroscopy in the UV/blue-optical spectral region (0.15-0.55 microns). In the current design, the imager will cover a 0.25 sq. deg. field of view simultaneously in three bands, providing a hundred-fold improvement in survey speed over the legendary, but aging, Hubble Space Telescope (HST). In addition, a multi-object Digital Micro-Mirror (DMD) spectrograph, covering an adjacent field of view, will provide moderate- to high-resolution UV spectroscopy, while a wide-field, low-resolution spectroscopic capability will be provided by a grism. CASTOR's UV imaging and spectroscopic capabilities will enable a vast range of science in the post-HST era, including the physics of star formation from our galaxy to the distant universe, exploring the atmospheres of exoplanets, improving constraints on dark energy, and studying the properties of the outer solar system. CASTOR's data will far surpass any previous UV/blue-optical surveys in terms of sensitivity and angular resolution and will provide complementary capabilities to longer-wavelength data from the Euclid and WFIRST missions, as well as the ground-based LSST. CASTOR will be a strategic asset for Canadian astronomy in the coming decade, showcase the capabilities of Canadian aerospace companies on a global stage, and provide unprecedented opportunities for education and public outreach. A series of CSA-sponsored scientific and technical studies carried out during the past decade have advanced the mission concept to a mature state, and international partners are now waiting for a commitment by Canada., White paper identifier W018

The next generation of electromagnetic and gravitational wave observatories will open unprecedented windows to the birth of the first supermassive black holes. This has the potential to reveal their origin and growth in the first billion years, as well as the signatures of their formation history in the local Universe. With this in mind, we outline three key focus areas which will shape research in the next decade and beyond: What were the "seeds" of the first quasars; were there multiple channels, and can we differentiate between them, either for high-z objects and/or SMBHs today; how did some reach a billion solar masses before z~7? How does black hole growth change over cosmic time, and how did the early growth of black holes shape their host galaxies? Conversely, how did the first stars in primordial galaxies influence the conditions for early SMBH growth; what can we learn from intermediate mass black holes (IMBHs) and dwarf galaxies today? Can we unravel the physics of black hole accretion, understanding both inflows and outflows (jets and winds) in the context of the theory of general relativity? Is it valid to use these insights to scale between stellar and supermassive BHs, i.e., is black hole accretion really scale invariant? In the following, we identify opportunities for the Canadian astronomical community to play a leading role in addressing these issues, in particular by leveraging our strong involvement in the Event Horizon Telescope, the James Webb Space Telescope (JWST), Euclid, the Maunakea Spectroscopic Explorer (MSE), the Thirty Meter Telescope (TMT), the Square Kilometer Array (SKA), the Cosmological Advanced Survey Telescope for Optical and ultraviolet Research (CASTOR), and more. We also discuss synergies with future space-based gravitational wave (LISA) and X-ray (e.g., Athena, Lynx) observatories, as well as the necessity for collaboration with the stellar and galactic evolution communities to build a complete picture of the birth of SMBHs, and their growth and their influence over the history of the Universe., White paper identifier W034

The Maunakea Spectroscopic Explorer (MSE) is a project to design and construct a wide-field spectroscopic telescope at a site with excellent natural seeing, and in so doing to continue the tradition of Canadian leadership in wide-field astronomy established with the Canada-France-Hawaii Telescope. MSE is an end-to-end science platform for the design, execution and scientific exploitation of transformative, high-precision spectroscopic surveys at low-, medium-, and high-resolution from 0.37 to 1.8 microns. It will unveil the composition and dynamics of the faint Universe and impact nearly every field of astrophysics across spatial scales from individual stars to the largest scale structures in the Universe. Major pillars in the MSE science program include: (i) high spectral resolution Gaia follow-up to understand the chemistry and dynamics of the distant Milky Way in unprecedented detail; (ii) a revolutionary study of galaxy formation and evolution over billions of years back to `cosmic noon' when the Universe was at its peak of star formation; (iii) a large-volume, redshift survey to constrain inflationary physics and determine the mass of the neutrino; (iv) high fidelity measurements of the density profiles of the dark matter halos of Milky Way satellites; and (v) the largest sample yet of quasars with black hole masses measured from reverberation mapping, used to calibrate relationships enabling black hole mass estimates for millions of quasars. The MSE design features an 11.25m aperture telescope dedicated to multi-object spectroscopy over a 1.5 square degree field of view. A total of 3249 fibers will feed spectrographs operating at low (R ~= 3000) and moderate (R ~= 6000) spectral resolution, and an additional 1083 fibers will simultaneously feed high resolution spectrographs (R ~= 20,000-40,000). It is expected that 80% of useful observing time will be dedicated to large, multi-year Legacy Surveys proposed by MSE partners and chosen in a competitive, peer-reviewed process. The remaining 20% of observing time will be allocated to the partners, based on their relative share in MSE, for smaller Strategic Surveys. All MSE data will be available to all partners, with a proprietary period of several years before becoming publicly available. A set of Design Reference Surveys will be created and iterated during the design and construction phases so that the MSE science community is ready to propose surveys that take full advantage of all of the capabilities of MSE. Numerous international studies have concluded that the capabilities provided by MSE would be a critical hub in the emerging international network of front-line astronomical facilities over the coming decades, naturally complementing and extending the scientific power of TMT, SKA, Euclid, LSST, and many other facilities. High rankings in ongoing national reviews and success in peer-reviewed funding competitions will pave the way for detailed design of MSE in 2021-2025, construction in 2026-2031, and operation in the 2030s and well beyond. The cost to build the MSE conceptual design is US$420M, including risk margins, and the cost to operate the facility is estimated at US$25M/year, all in 2018 dollars. A model with several roughly equal major partners instead of one dominant partner is anticipated. The current MSE partnership consists of Canada, France, U. Hawaii, Australia, China, and India, plus observers from Texas A&M University, the US National Optical Astronomy Observatories, and a consortium of UK universities and research institutes. The MSE Science Team consists of approximately 400 scientists worldwide, including about 36 from Canada and an equal number from France, exceeded only by the number of members from the US. Recommendations: It is not realistic to expect that Canada can be a part of every single scientifically exciting astronomical facility that exists, will be built, or is proposed. Projects and facilities undertaken at a national level in Canada therefore need to be strategic investments that increase scientific and industrial capacity, build upon strengths, leverage past investments, and provide collaborative and leadership opportunities within the worldwide community. The MSE project fulfills those criteria and fills a major missing link in the future international network of multi-wavelength astronomical facilities. In that context, and given the benefits of an MSE facility to the Canadian community, we recommend: 1) that the community prioritizes continued Canadian involvement in the MSE project through its preliminary design phase, its final design phase, and its construction and operation on a suitable site, subject to successful design reviews and successful funding by an international partnership. 2) that the community supports a Canadian share in an MSE facility of at least 20%, ensuring that Canada has a significant voice in the project as one of the top 3 or 4 partners., White paper identifier W030

The past decade has seen a revolution in the field of radio transients.Fast Radio Bursts "exploded" on the scene and represent one of the most interesting puzzles in astrophysics today. TheCHIME FastRadio Burst project has recently emerged as a world-leader in the field, offering potential for determining the nature of these objects and for realizing their potential as novel cosmic probes.Meanwhile, the area of "slow'' radio transients, traditionally associated with accreting sources and associated jets, is also undergoing a renaissance as part of advances in time-domain and multi-messenger astrophysics, the latter thanks to aLIGO/Virgo. This white paper will review the key science questions to be addressed by observations of FRBs and radio transients, and map the relevant observational requirements onto new and envisioned future radio telescopes and instruments, including CHIME, CHIME/FRB, CHIME/Outriggers, CHORD, JVLA, SKA, and ngVLA., White paper identifier W058

The Large Synoptic Survey Telescope (LSST) is set to begin commissioning its instruments in 2021, with science verification commencing in 2022 and science operations in 2023. With its large field of view and 3.2 Gigapixel camera, it will scan 18,000 square degrees every few nights from 320-1050 nm. This cadence will not only build a deep co-added map of the sky to ~25th magnitude in its wide field and ~28th magnitude in its deep fields, but will enable transient science on the largest scale. It will produce millions of ‘alerts’ for bright new celestial objects each night. By the end of the nominal 11th data release, it will deliver 18 billion objects in 5.5 million images. LSST will revolutionize photometric survey science.There are a wide range of scientific collaborations under the LSST umbrella: the Stars, Milky Way and the Local Volume Collaboration, the Transients and Variable Stars Collaboration, the Dark Energy Science Collaboration, The Solar System Science Collaboration, The Active Galactic Nuclei Collaboration, the Strong Lensing Collaboration and the Informatics and Statistics Science Collaboration. We highlight the LSST science cases relevant to the Canadian community, and describe how LSST data will complement and transform science in these areas. In a separate white paper, we discuss the varied Canadian data access needs and LSST data products. We will describe how coordination with current and planned facilities and programs with Canadian participation and leadership, namely CFHT, CFIS/UNIONS, MSE, Gemini, and Euclid will leverage these science efforts even further. We discuss the proposed model for participation in LSST and motivate why a coordinated national strategy for Canadian data access is essential to ensuring both the continued Canadian scientific leadership in LSST, and how investing in the infrastructure and training necessary for LSST partnership would therefore be strategic for Canadian astronomy., White paper identifier W051

Jets produced by compact stars are the ideal laboratories for understanding jets in general due to the ability to measure accretors properties accurately, and the short timescales of variability of the systems. We outline what is needed to move forward with understanding jet production in X-ray binaries.