Session B17: Galactic Sources and Cosmic-ray Accelerators

Abstract Unavailable

Abstract moved to session X14   

$\beta$-delayed $\gamma$ decay of $^{20}$Mg and the $^{19}$Ne(p,$\gamma$)$^{20}$Na breakout reaction in Type I X-ray bursts

Certain astrophysical environments such as thermonuclear outbursts on accreting neutron stars (Type-I X-ray bursts) are hot enough to allow for breakout from the Hot CNO hydrogen burning cycles to the rapid proton capture (rp) process. An important breakout reaction sequence is $^{15}$O($\alpha$,$\gamma$)$^{19}$Ne(p,$\gamma$)$^{20}$Na and the $^{19}$Ne(p,$\gamma$)$^{20}$Na reaction rate is expected to be dominated by a single resonance at 457 keV above the proton threshold in $^{20}$Na. The reaction rate depends strongly on whether this $^{20}$Na state at excitation energy 2647 keV has spin and parity of 1$^+$ or 3$^+$. Previous $^{20}$Mg ($J^\pi$=0$^+$) $\beta^+$ decay experiments have relied almost entirely on searches for $\beta$-delayed proton emission from this resonance in $^{20}$Na to limit the log $ft$ value. However there is a non-negligible $\gamma$-ray branch expected that must also be limited experimentally to determine the log $ft$ value and constrain $J^\pi$. We have measured the $\beta$-delayed $\gamma$ decay of $^{20}$Mg to complement previous $\beta$-delayed proton decay work and provide the first complete limit based on all energetically allowed decay channels through the 2647 keV state. Our limit confirms a 1$^+$ assignment for this state is highly unlikely.   

Understanding the Very High Energy Emission from the possible PWN 2HWC J2019+367 with HAWC

In the TeV sky, the Cygnus region is one of the brightest areas outside of the inner galaxy. Because it is an active extended star-forming region, it has been heavily studied for decades, making it perfect target for multi-wavelength studies. Originally discovered in 2007 by the Milagro Observatory, the TeV gamma-ray source MGRO J2019+37 is also detected by The High Altitude Water Cherenkov Observatory (HAWC) as 2HWC J2019+367. HAWC is a wide field-of-view high duty cycle gamma-ray telescope located in Sierra Negra, Mexico with currently unrivaled sensitivity at the highest photon energies. Most recently, HAWC has observed gamma-ray emission beyond 50 TeV for 2HWC J2019+367. This source has long been thought to be associated with PSR J2021+3651 but previous studies have never been able to conclusively prove the association. In this work, we present detailed spectral and morphological studies of 2HWC J2019+367 at the highest energies using the latest data from the HAWC Observatory.   

Exoplanet Phase Curve Information Content: Towards Optimized Observing Strategies

Exoplanet phase curves are comprised of two photometric effects: the reflection of incident starlight, and the thermal emission of radiation from the planet's atmosphere or surface. The reflection and thermal emission from the day-side of the planet manifest in photometry as nearly sinusoidal brightness variations as different portions of the day-side wax and wane over the course of an orbit. These effects, although small, are detectable for many short period hot Jupiters and even some super-Earths. Physical mechanisms have been identified which act to shift the phase curve maximum of tidally locked close in planets to the left, or to the right of the secondary eclipse. Using information-theoretic techniques, and Bayesian inference we investigate the most important parts of exoplanet phase curves with two primary goals. First, to determine which parts of the phase curve are important for constraining certain planetary properties such as the albedo, brightness temperature, and bright spot shift, and second to determine if the entire phase curve must be observed to constrain these properties. The latter would have significant implications for optimizing future observing strategies when applying for observation time on next generation telescopes like JWST and CHEOPS.   

Studying Galactic Compact Binary Systems with HAWC at Multi-TeV Energies

Compact binary systems can emit very high energy gamma rays via particle acceleration and interactions within jets and accretion disks. Measurements of these objects can help explain mechanisms of cosmic-ray acceleration and propagation, which are not fully understood. The High Altitude Water Cherenkov (HAWC) Observatory is a wide field-of-view and high-uptime detector of TeV gamma rays that is capable of long-term measurements of transient and periodic sources such as compact binaries. We report on observations of several Galactic binaries with HAWC, and discuss ongoing multi-wavelength campaigns as well as modeling of gamma-ray backgrounds in the Northern Hemisphere.   

GeV-TeV Gamma-Ray Study at the Fermi Cocoon Region with HAWC and Fermi-LAT data

The Cygnus region hosts multiple gamma-ray source types such as pulsar wind nebulae, supernova remnants, binary systems and star clusters. For instance, Fermi-LAT found gamma-ray emission at GeV energies due to a cocoo~of freshly accelerated cosmic rays, which is co-located with a known PWN seen by Hegra, VERITAS and other TeV gamma-ray observatories. The High Altitude Water Cherenkov (HAWC) Observatory has been collecting data from the direction of this region continuously since 2014. One of the sources reported in the 2HWC catalog, 2HWC J2031+415 overlaps with the TeV PWN as well as the cocoon region reported by Fermi-LAT. The study of HAWC data will provide more information regarding the morphology, emission origin, and the correlation with the GeV emission. This presentation will discuss results obtained from data collected with the HAWC Observatory and other instruments and multi-wavelength comparison to provide a deeper understanding of the 2HWC J2031+415 region across five decades of energy.   

The Gamma Cygni SNR at the Highest Energies

The gamma Cygni SNR is a middle-aged supernova remnant in the Cygnus region. It is known to emit gamma rays at least up to 1 TeV, and it may be connected to the Cygnus cocoon, a volume of freshly accelerated cosmic rays in the Cygnus region. Gamma Cygni displays an extended, shell-like morphology with multiple hotspots inside the remnant, observed in radio, X-rays, and gamma rays. The High Altitude Water Cherenkov (HAWC) Observatory has also detected a gamma-ray source (2HWC J2020+403) which is spatially coincident with the remnant. Currently, it is not known whether the non-thermal emission is caused by leptonic or hadronic processes. We will use data taken by the HAWC Observatory and other gamma-ray instruments to investigate particle acceleration in the remnant.   

Understanding Galactic Cosmic Ray Accelerators with VERITAS

The Galaxy carries a small but quite significant population of highly energetic denizens: supernova remnants with fast shocks, pulsars with powerful winds, intensely-interacting binary systems built from a compact object and a massive star. All of these environments conspire to generate nonthermal populations of particles, and radiation produced by these particles is gradually revealing the methods by which Nature accelerates cosmic rays, as well as the ways in which those cosmic rays escape and diffuse into the interstellar medium. In this talk, we discuss advances in our understanding of these environments and processes provided by recent results from VERITAS, an array of ground-based imaging air-Cherenkov telescopes located at the Whipple Observatory in southern Arizona and sensitive to gamma rays in the energy range from 85 GeV to > 30 TeV. These results include studies of cosmic-ray acceleration in the supernova remnants Cassiopeia A and IC 443, as well as the remarkable Fall 2017 periastron passage of VER J2032+4127, the binary system containing PSR J2032+4127 and the Be star MT91 213 with a 50-year period.   

PeVatron candidates in the first 30 months of HAWC data

Galactic cosmic rays are observed at PeV energies, so at least a few sources that accelerate to these energies are expected to exist. However, only one such source has been identified: the Galactic Center. Since one of the signatures of a PeVatron is a hadronic, hard spectrum that extends without any apparent spectral cutoff, high-energy ($>$ 50 TeV) gamma-ray observations are important in identifying and studying PeVatron candidates. The High Altitude Water Cherenkov (HAWC) Observatory, located at 4100 m in Puebla, Mexico, has sensitivity to gamma rays at these previously largely unexplored energies. With an instantaneous field of view of $\sim$2sr and a duty cycle $>$ 95$\%$, it is well suited to performing all-sky surveys. I will discuss high-energy sources seen in the Galactic plane in the first 30 months of data from HAWC and discuss which ones may be identified as PeVatron candidates. I will also briefly discuss the energy estimation method used by HAWC.