Browsing by Author "Moiseev, A."
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Item High-Energy Polarimetry - a new window to probe extreme physics in AGN jets(2019-03-11) Rani, B.; Zhang, H.; Hunter, S. D.; Kislat, F.; Böttcher, M.; McEnery, J. E.; Thompson, D. J.; Giannios, D.; Guo, F.; Li, H.; Baring, M.; Agudo, I.; Buson, S.; Petropoulou, M.; Pavlidou, V.; Angelakis, E.; Myserlis, I.; Wadiasingh, Z.; Silva, R. M. Curado da; Kilian, P.; Guiriec, S.; Bozhilov, V. V.; Hodgson, J.; Antón, S.; Kazanas, D.; Coppi, P.; Venters, T.; Longo, F.; Bottacini, E.; Ojha, R.; Zhang, B.; Ciprini, S.; Moiseev, A.; Shrader, C.The constantly improving sensitivity of ground-based and space-borne observatories has made possible the detection of high-energy emission (X-rays and gamma-rays) from several thousands of extragalactic sources. Enormous progress has been made in measuring the continuum flux enabling us to perform imaging, spectral and timing studies. An important remaining challenge for high-energy astronomy is measuring polarization. The capability to measure polarization is being realized currently at X-ray energies (e.g. with IXPE), and sensitive gamma-ray telescopes capable of measuring polarization, such as AMEGO, AdEPT, e-ASTROGAM, etc., are being developed. These future gamma-ray telescopes will probe the radiation mechanisms and magnetic fields of relativistic jets from active galactic nuclei at spatial scales much smaller than the angular resolution achieved with continuum observations of the instrument. In this white paper, we discuss the scientific potentials of high-energy polarimetry, especially gamma-ray polarimetry, including the theoretical implications, and observational technology advances being made. In particular, we will explore the primary scientific opportunities and wealth of information expected from synergy of multi-wavelength polarimetry that will be brought to multi-messenger astronomy.Item Neutrinos, Cosmic Rays and the MeV Band(2019-03-13) Ojha, R.; Zhang, H.; Kadler, M.; Neilson, N. K.; Kreter, M.; McEnery, J.; Buson, S.; Caputo, R.; Coppi, P.; D'Ammando, F.; Angelis, A. De; Fang, K.; Giannios, D.; Guiriec, S.; Guo, F.; Kopp, J.; Krauss, F.; Li, H.; Meyer, M.; Moiseev, A.; Petropoulou, M.; Prescod-Weinstein, C.; Rani, B.; Shrader, C.; Venters, T.; Wadiasingh, Z.The possible association of the blazar TXS 0506+056 with a high-energy neutrino detected by IceCube holds the tantalizing potential to answer three astrophysical questions: 1. Where do high-energy neutrinos originate? 2. Where are cosmic rays produced and accelerated? 3. What radiation mechanisms produce the high-energy gamma-rays in blazars? The MeV gamma-ray band holds the key to these questions, because it is an excellent proxy for photo-hadronic processes in blazar jets, which also produce neutrino counterparts. Variability in MeV gamma-rays sheds light on the physical conditions and mechanisms that take place in the particle acceleration sites in blazar jets. In addition, hadronic blazar models also predict a high level of polarization fraction in the MeV band, which can unambiguously distinguish the radiation mechanism. Future MeV missions with a large field of view, high sensitivity, and polarization capabilities will play a central role in multi-messenger astronomy, since pointed, high-resolution telescopes will follow neutrino alerts only when triggered by an all-sky instrument.Item New mission concept: Galactic Explorer with a Coded Aperture Mask Compton Telescope (GECCO)(Proceedings of Science, 2022-03-18) Moiseev, A.; Cannady, Nicholas; Negro, Michela; Sturner, Steven; GECCO collaboration; et alWe present a novel concept for a next-generation γ-ray telescope that will cover the hard X-ray - soft γ-ray region. Despite the progress made by the European Space Observatory INTEGRAL, this energy range is still under-explored. GECCO will conduct high-sensitivity measurements of the cosmic γ-radiation in the energy range from 50-100 keV to ∼10 MeV and create intensity maps with high spectral and spatial resolution, focusing on sensitive separation of diffuse and point-source components. These observations will enable the following major objectives for GECCO: a) understand the nature, composition and fine structure of the inner Galaxy b) localize and discern the origin(s) of the positron annihilation 511 keV line, c) resolve Galactic chemical evolution and sites of explosive element synthesis d) provide identification and precise localization of gravitational wave and neutrino events e) test as-yet unexplored candidates for the dark matter The instrument is based on a novel CdZnTe Imaging calorimeter and a deployable coded aperture mask. The unique feature of GECCO is that it combines the advantages of two techniques – the high-angular resolution possible with coded mask imaging, and a Compton telescope mode providing high sensitivity measurements of diffuse radiation. Expected GECCO performance is as follows: energy resolution <1% at 0.5-5 MeV, angular resolution ∼1 arcmin in the Mask mode (3-4 degree field-of-view, ∼2,000 cm2 effective area), and 3-5 degrees in the Compton mode (~60 degree field-of-view, ∼500 cm2 effective area). The continuum sensitivity is expected to be ~ 10-6 MeV/cm2/s at 1 MeV. GECCO can be considered for a future NASA Explorer mission.