HAWC’s wide field-of-view enables unbiased observations of much of the galaxy, allowing for analysis of many candidate sources in the HAWC dataset. Recent work has allowed HAWC to start investigating ...electron diffusion around pulsars at TeV energies. Surveying electron diffusion at TeV energies along the galactic plane is a unique capability of HAWC that allows us to examine the sources of electrons in our galaxy and constrain the energy dependence of the diffusion mechanism. HAWC has already applied this model to the Geminga and Monogem pulsars. This work will expand the study to include multiple sources associated with pulsars in the latest HAWC dataset. Unlike older pulsars, lepton transport around young pulsars is likely to be dominated by advective processes. Using simple assumptions, both advective and diffusive processes predict that the size of the emission region follows a power law dependence on energy. This study has important consequences for the positron excess reported by space-based instruments; if electron diffusion is suppressed for tens of parsecs around pulsars relative to diffusion in the interstellar medium (a "two-zone" model), they may be able to explain at least part of the observed increase in the positron fraction above 10 GeV.
Pulsars, and their associated pulsar wind nebulae, are factories producing high energy electrons and positrons in our galaxy. The Dragonfly nebula is a Vela-like pulsar wind nebula in the Cygnus ...region powered by the spin down of PSR J2021+3651. The TeV γ-ray source 2HWC J2019+367 was originally discovered in 2007 by the Milagro Observatory and has been associated with this pulsar. This dissertation presents the first detailed morphological and spectral study of the TeV emission up to the highest photon energies of 2HWC J2019+367. This analysis has identified two sources, the extended source HAWC J2019+368 and the point source HAWC J2016+371. The spectral energy distribution for HAWC J2016+371 is fit by a power law with a flux normalization at 10 TeV of 2.6 ± 0.7 × 10−15 TeV−1 cm−2 s−1 and a spectral index of α = −2.32 ± 0.18. This represents the first independent confirmation of emission from supernova remnant CTB 87 at TeV energies. The γ-ray spectral energy distribution of HAWC J2019+368 significantly prefers a log parabola function, rather than a pure power law. The flux normalization at 10 TeV is 4.05 ± 0.26 × 10−14 TeV−1 cm−2 cm−2, with a spectral index α = −2.02 ± 0.06 and curvature parameter β = 0.29 ± 0.05. The morphology of HAWC J2019+368 is an asymmetric gaussian with semi-major axis a = 0.368° ± 0.021° and eccentricity e = 0.941 ± 0.017. The γ-ray flux measured in this analysis directly corresponds to the measurement of electrons with energies up to ∼ 200 TeV. An electron spectrum is fit to the data for HAWC J2019+368, assuming that the production of γ-rays is due to inverse Compton emission, and shown to be well within the energy budget of PSR J2021+3651. This supports the interpretation of the emission of HAWC J2019+368 being almost entirely due to the electrons and positrons produced by PSR J2021+3651.
The High Altitude Water Cherenkov (HAWC) Observatory is a wide-field-of-view gamma-ray observatory that is optimized to detect gamma rays between 300 GeV and several hundred TeV. The HAWC ...Collaboration recently released their third source catalog (3HWC), which contains 65 sources. One of these sources, the ultra-high-energy gamma-ray source 3HWC J1908+063, may exhibit a hardening of the spectral index at the highest energies (above 56 TeV). At least two populations of particles are needed to satisfactorily explain the highest energy emission. This second component could be leptonic or hadronic in origin. If it is hadronic in origin, it would imply the presence of protons with energies up to ~1 PeV near the source. We have searched other 3HWC sources for the presence of this spectral hardening feature. If observed, this would imply that the sources could make good PeVatron candidates.
The Ultra-High-Energy Source MGRO J1908+06 Malone, Kelly; Abeysekara, Anushka Udara; Albert, Andrea ...
Pos : proceedings of science,
07/2021, Letnik:
395
Journal Article
Recenzirano
Odprti dostop
The TeV gamma-ray source MGRO J1908+06 is one of the highest-energy sources known, with observed emission by the High Altitude Water Cherenkov (HAWC) Observatory extending well past 100 TeV. The ...source exhibits both energy-dependent morphology and a spatially-dependent spectral index. The emission is likely to be dominantly leptonic, and associated with the radio-quiet PSR J1907+0602. However, one-population models do not describe the data well; a second particle population is needed to explain the shape of the spectral energy distribution at the highest energies. This component can be well-described by either leptonic or hadronic hypotheses. We discuss this feature and implications for detection by multi-wavelength and multi-messenger experiments.
Only five binary systems have been found to emit at TeV energies. Each of these systems is composed of a massive O or B type star and a compact object (black hole or a pulsar). The type of compact ...object and the origin of the gamma-ray emission is unknown for most of these systems. Extending spectral observations to higher energies can help disentangle the nature of the compact object as well as the particle acceleration mechanisms present. Interestingly, the TeV emission from these systems does not always coincide with their emission in GeV or X-ray, which is how many such systems have been originally discovered. Increased coverage of these systems may allow HAWC to see precisely when in the orbit the TeV emission begins and ends. The HAWC Observatory detects TeV gamma-rays with high sensitivity, covering over two-thirds of the overhead sky every day. Applying a stacking method to known TeV binary systems can help HAWC enhance the signal from TeV binaries above the steady background from other sources in the galaxy. We will present results from this stacking analysis using 760 days of HAWC data.
The last decade has brought about a profound transformation in multimessenger science. Ten years ago, facilities had been built or were under construction that would eventually discover the nature of ...objects in our universe could be detected through multiple messengers. Nonetheless, multimessenger science was hardly more than a dream. The rewards for our foresight were finally realized through IceCube's discovery of the diffuse astrophysical neutrino flux, the first observation of gravitational waves by LIGO, and the first joint detections in gravitational waves and photons and in neutrinos and photons. Today we live in the dawn of the multimessenger era. The successes of the multimessenger campaigns of the last decade have pushed multimessenger science to the forefront of priority science areas in both the particle physics and the astrophysics communities. Multimessenger science provides new methods of testing fundamental theories about the nature of matter and energy, particularly in conditions that are not reproducible on Earth. This white paper will present the science and facilities that will provide opportunities for the particle physics community renew its commitment and maintain its leadership in multimessenger science.
Gamma-rays, the most energetic photons, carry information from the far reaches of extragalactic space with minimal interaction or loss of information. They bring messages about particle acceleration ...in environments so extreme they cannot be reproduced on earth for a closer look. Gamma-ray astrophysics is so complementary with collider work that particle physicists and astroparticle physicists are often one in the same. Gamma-ray instruments, especially the Fermi Gamma-ray Space Telescope, have been pivotal in major multi-messenger discoveries over the past decade. There is presently a great deal of interest and scientific expertise available to push forward new technologies, to plan and build space- and ground-based gamma-ray facilities, and to build multi-messenger networks with gamma rays at their core. It is therefore concerning that before the community comes together for planning exercises again, much of that infrastructure could be lost to a lack of long-term planning for support of gamma-ray astrophysics. Gamma-rays with energies from the MeV to the EeV band are therefore central to multiwavelength and multi-messenger studies to everything from astroparticle physics with compact objects, to dark matter studies with diffuse large scale structure. These goals and new discoveries have generated a wave of new gamma-ray facility proposals and programs. This paper highlights new and proposed gamma-ray technologies and facilities that have each been designed to address specific needs in the measurement of extreme astrophysical sources that probe some of the most pressing questions in fundamental physics for the next decade. The proposed instrumentation would also address the priorities laid out in the recent Astro2020 Decadal Survey, a complementary study by the astrophysics community that provides opportunities also relevant to Snowmass.
The management of thrombosis and bacterial infection is critical to ensure the functionality of medical devices. While administration of anticoagulants is the current antithrombotic clinical ...practice, a variety of complications, such as uncontrolled hemorrhages or heparin-induced thrombocytopenia, can occur. Additionally, infection rates remain a costly and deadly complication associated with use of these medical devices. It has been hypothesized that if a synthetic surface could mimic the biochemical mechanisms of the endothelium of blood vessels, thrombosis could be reduced, anticoagulant use could be avoided, and infection could be prevented. Herein, the interfacial biochemical effects of the endothelium were mimicked by altering the surface of medical grade silicone rubber (SR). Surface modification was accomplished via heparin surface immobilization (Hep) and the inclusion of a nitric oxide (NO) donor into the SR polymeric matrix to achieve synergistic effects (Hep-NO-SR). An in vitro bacteria adhesion study revealed that Hep-NO-SR exhibited a 99.46 ± 0.17% reduction in viable bacteria adhesion compared to SR. An in vitro platelet study revealed Hep-NO-SR reduced platelet adhesion by 84.12 ± 6.19% compared to SR, while not generating a cytotoxic response against fibroblast cells. In a 4 h extracorporeal circuit model without systemic anticoagulation, all Hep-NO-SR samples were able to maintain baseline platelet count and device patency; whereas 66% of SR samples clotted within the first 2 h of study. Results indicate that Hep-NO-SR creates a more hemocompatible and antibacterial surface by mimicking two key biochemical functions of the native endothelium.
Under an applied magnetic field, superparamagnetic Fe3O4 nanoparticles with complementary DNA strands assemble into crystalline, pseudo‐1D elongated superlattice structures. The assembly process is ...driven through a combination of DNA hybridization and particle dipolar coupling, a property dependent on particle composition, size, and interparticle distance. The DNA controls interparticle distance and crystal symmetry, while the magnetic field leads to anisotropic crystal growth. Increasing the dipole interaction between particles by increasing particle size or external field strength leads to a preference for a particular crystal morphology (e.g., rhombic dodecahedra, stacked clusters, and smooth rods). Molecular dynamics simulations show that an understanding of both DNA hybridization energetic and magnetic interactions is required to predict the resulting crystal morphology. Taken together, the data show that applied magnetic fields with magnetic nanoparticles can be deliberately used to access nanostructures beyond what is possible with DNA hybridization alone.
DNA programmable assembly in combination with applied magnetic fields is used to direct magnetite nanoparticles into high‐aspect‐ratio superlattice crystals with various morphologies. A range of field strengths, nanoparticle core diameters, particle symmetries, and DNA lengths are explored to understand the competition between hybridization and magnetic dipole–dipole coupling interactions.
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