49 research outputs found
Dense matter with eXTP
In this White Paper we present the potential of the Enhanced X-ray Timing and
Polarimetry (eXTP) mission for determining the nature of dense matter; neutron
star cores host an extreme density regime which cannot be replicated in a
terrestrial laboratory. The tightest statistical constraints on the dense
matter equation of state will come from pulse profile modelling of
accretion-powered pulsars, burst oscillation sources, and rotation-powered
pulsars. Additional constraints will derive from spin measurements, burst
spectra, and properties of the accretion flows in the vicinity of the neutron
star. Under development by an international Consortium led by the Institute of
High Energy Physics of the Chinese Academy of Science, the eXTP mission is
expected to be launched in the mid 2020s.Comment: Accepted for publication on Sci. China Phys. Mech. Astron. (2019
Neutrinos, Cosmic Rays and the MeV Band
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.Comment: White paper submitted to the Astro2020 Decadal Surve
Energetic Particles of Cosmic Accelerators I: Galactic Accelerators
The high-energy universe has revealed that energetic particles are ubiquitous in the cosmos and play a vital role in the cultivation of cosmic environments on all scales. Our pursuit of more than a century to uncover the origins and fate of these cosmic energetic particles has given rise to some of the most interesting and challenging questions in astrophysics. Energetic particles in our own galaxy, galactic cosmic rays (GCRs), engage in a complex interplay with the interstellar medium and magnetic fields in the galaxy, giving rise to many of its key characteristics. For instance, GCRs act in concert with galactic magnetic fields to support its disk against its own weight. GCR ionization and heating are essential ingredients in promoting and regulating the formation of stars and protostellar disks. GCR ionization also drives astrochemistry, leading to the build up of complex molecules in the interstellar medium. GCR transport throughout the galaxy generates and maintains turbulence in the interstellar medium, alters its multi-phase structure, and amplifies magnetic fields. GCRs could even launch galactic winds that enrich the circumgalactic medium and alter the structure and evolution of galactic disks. As crucial as they are for many of the varied phenomena in our galaxy, there is still much we do not understand about GCRs. While they have been linked to supernova remnants (SNRs), it remains unclear whether these objects can fully account for their entire population, particularly at the lower (approximately less than 1 GeV per nucleon) and higher (~PeV) ends of the spectrum. In fact, it is entirely possible that the SNRs that have been found to accelerate CRs merely re-accelerate them, leaving the origins of the original GCRs a mystery. The conditions for particle acceleration that make SNRs compelling source candidates are also likely to be present in sources such as protostellar jets, superbubbles, and colliding wind binaries (CWBs), but we have yet to ascertain their roles in producing GCRs. For that matter, key details of diffusive shock acceleration (DSA) have yet to be revealed, and it remains to be seen whether DSA can adequately explain particle acceleration in the cosmos. This White Paper is the first of a two-part series highlighting the most well-known high-energy cosmic accelerators and contributions that MeV gamma-ray astronomy will bring to understanding their energetic particle phenomena. For the case of GCRs, MeV astronomy will: 1) Search for fresh acceleration of GCRs in SNRs; 2) Test the DSA process, particularly in SNRs and CWBs; 3) Search for signs of CR acceleration in protostellar jets and superbubbles
Energetic Particles of Cosmic Accelerators II: Active Galactic Nuclei and Gamma-ray Bursts
The high-energy universe has revealed that energetic particles are ubiquitous
in the cosmos and play a vital role in the cultivation of cosmic environments
on all scales. Though they play a key role in cultivating the cosmological
environment and/or enabling our studies of it, there is still much we do not
know about AGNs and GRBs, particularly the avenue in which and through which
they supply radiation and energetic particles, namely their jets. This White
Paper is the second of a two-part series highlighting the most well-known
high-energy cosmic accelerators and contributions that MeV gamma-ray astronomy
will bring to understanding their energetic particle phenomena. The focus of
this white paper is active galactic nuclei and gamma-ray bursts.Comment: 11 pages (including references), 2 figures; Submitted to the
Astro2020 call for science white paper
Prospects for Pulsar Studies at MeV Energies
Enabled by the Fermi Large Area Telescope, we now know that pulsars fill the gamma-ray sky, and we are beginning to understand their emission mechanism and their distribution throughout the Galaxy. To address key questions calls for a sensitive, wide-field MeV telescope, which can detect the population of MeV-peaked pulsars hinted at by Fermi
Relative-locality distant observers and the phenomenology of momentum-space geometry
We study the translational invariance of the relative-locality framework
proposed in arXiv:1101.0931, which had been previously established only for the
case of a single interaction. We provide an explicit example of boundary
conditions at endpoints of worldlines, which indeed ensures the desired
translational invariance for processes involving several interactions, even
when some of the interactions are causally connected (particle exchange). We
illustrate the properties of the associated relativistic description of distant
observers within the example of a -Poincar\'e-inspired momentum-space
geometry, with de Sitter metric and parallel transport governed by a non-metric
and torsionful connection. We find that in such a theory simultaneously-emitted
massless particles do not reach simultaneously a distant detector, as expected
in light of the findings of arXiv:1103.5626 on the implications of non-metric
connections. We also show that the theory admits a free-particle limit, where
the relative-locality results of arXiv:1102.4637 are reproduced. We establish
that the torsion of the -Poincar\'e connection introduces a small (but
observably-large) dependence of the time of detection, for
simultaneously-emitted particles, on some properties of the interactions
producing the particles at the source.Comment: 45 pages, 10 figure
Report of the Topical Group on Cosmic Probes of Dark Matter for Snowmass 2021
Cosmological and astrophysical observations currently provide the only
robust, positive evidence for dark matter. Cosmic probes of dark matter, which
seek to determine the fundamental properties of dark matter through
observations of the cosmos, have emerged as a promising means to reveal the
nature of dark matter. This report summarizes the current status and future
potential of cosmic probes to inform our understanding of the fundamental
nature of dark matter in the coming decade.Comment: Report of the CF3 Topical Group for Snowmass 2021; 35 pages, 10
figures, many references. V3 updates Fig 3-2 and the author lis
Prompt Emission Polarimetry of Gamma-Ray Bursts
Many aspects of astrophysical jets can be studied by measuring the polarization of the prompt emission from GRBs. Theoretical models show that a more complete understanding of the inner structure of GRBs, including the geometry and physical processes close to the central engine, can only be achieved by gamma-ray polarimetry