Bulletin of the American Physical Society
APS April Meeting 2021
Volume 66, Number 5
Saturday–Tuesday, April 17–20, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session D09: Gamma Ray Astronomy: GalacticLive
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Sponsoring Units: DAP Chair: Andrea Albert, LANL |
Saturday, April 17, 2021 1:30PM - 1:42PM Live |
D09.00001: Very-high-energy Observation of the Stellar Superbubble in the Cygnus Region Binita Hona Stellar superbubbles powered by massive stellar associations have been postulated to be cosmic-ray factories and possible PeV accelerators. The Cygnus Cocoon near the OB2 stellar association is the first stellar superbubble detected in gamma rays. The Fermi-LAT observation up to 100 GeV finds a young cosmic-ray population, either protons or electrons, that are freshly accelerated in the Cocoon. The conclusive proof of PeV acceleration in the Cocoon will identify the OB2 stellar association as a PeV cosmic-ray accelerator. However, the Cocoon has been studied only up to 10 TeV. To understand the PeV physics, we need studies beyond 10 TeV. In this study using 1343 days of HAWC data, the Cygnus Cocoon is observed at the highest photon energy. The particles accelerated in the Cygnus Cocoon are identified as protons with energies up to hundreds of TeV and we present a spectral energy distribution of the Cocoon up to 200 TeV. In our study, we find a spectral softening above 1 TeV, which can either be due to the leakage of cosmic rays from the superbubble or an upper limit to particle acceleration energy by the stellar winds. [Preview Abstract] |
Saturday, April 17, 2021 1:42PM - 1:54PM Live |
D09.00002: A Comparison of the Galactic plane observed by HAWC and H.E.S.S. Jordan Goodman The High Altitude Water Cherenkov (HAWC) observatory and the High Energy Stereoscopic System (H.E.S.S.) are two leading instruments in the ground-based very high energy \textunderscore \textunderscore -ray domain. HAWC is based on the water Cherenkov detection techniques while H.E.S.S. is an array of Imaging Atmospheric Cherenkov Telescopes (IACT). In this talk we present results of a new analysis of the H.E.S.S. Galactic plane data, aiming at making a comparable analysis between H.E.S.S. and HAWC. We present a comparison of the Galactic plane observed by both instruments concentrating on sources seen in HAWC, but not previously observed by H.E.S.S.. The overall \textunderscore \textunderscore -ray flux of the Galactic plane is compared between HAWC and H.E.S.S. using the new analysis and the differences between them are presented. [Preview Abstract] |
Saturday, April 17, 2021 1:54PM - 2:06PM Live |
D09.00003: HAWC study of the ultra-high-energy gamma-ray source MGRO J1908+06 Kelly Malone MGRO J1908+06 is one of the highest-energy known gamma-ray sources, with emission detected by the High Altitude Water Cherenkov Observatory (HAWC) extending past 200 TeV. HAWC is a gamma-ray detector located in Puebla, Mexico. Theoretical models using the HAWC data indicate that this source is largely leptonic, possibly driven by PSR J1907+0602, a radio-quiet pulsar. However, a second population is needed to fit the highest-energy gamma-ray emission. This component can be fit to either leptonic or hadronic hypotheses. This has implications for detections by multi-messenger experiments. [Preview Abstract] |
Saturday, April 17, 2021 2:06PM - 2:18PM Live |
D09.00004: TeV Analysis of Probable PWN Component 3HWC J2031+415 Ian Herzog The Cygnus Cocoon region is a complex region containing an OB star cluster that is visible in the TeV energy range. Located in this region is 3HWC J2031+415, a significant TeV gamma ray source whose emission is probably associated with 2 components, the Cygnus OB2 star cluster and a pulsar wind nebula (PWN). In this work, several modelling methods are presented to best describe the emission. These models disentangle emission believed to be from the Cocoon and isolate the component emitted by the probable PWN. I will present several spectral models to describe the emission of the probable PWN using 1523 days of data from the High-Altitude Water Cherenkov (HAWC) observatory. I will also present an energy morphology study of the PWN component of 3HWC J2031+415 in the 1 to 100 TeV energy range. [Preview Abstract] |
Saturday, April 17, 2021 2:18PM - 2:30PM Live |
D09.00005: Broadband modeling of the energy spectrum of the Supernova Remnant IC 443 Leah Hunt, Miguel Mostafa Supernova explosions often lead to the interaction between the supernova remnants (SNRs) and molecular clouds. Shocks in SNRs are one of the candidate sources of galactic cosmic rays, and these interaction sites provide a laboratory to study the energetics of these particle accelerators. The SNR IC 443 is one of the most thoroughly studied, and one of the clearest examples of interaction with molecular clouds. IC 443 radiates broadband emission from radio to gamma-rays, where it has been established as a strong emitter in the 1 to 50 GeV domain and in the 90 GeV to 2 TeV band. Our analysis of HAWC data extends the study of IC 443 up to tens of TeV. We will show that the multi-TeV emission as seen with HAWC is strongly correlated with the GeV morphology observed with Fermi-LAT and extends over the entire surface of the remnant. We will present the multi-wavelength non-thermal emission from radio to gamma-ray bands modeled through synchrotron, bremsstrahlung, inverse Compton, and pion-decay emission mechanisms. [Preview Abstract] |
Saturday, April 17, 2021 2:30PM - 2:42PM Live |
D09.00006: Gamma Rays from Fast Black-Hole Winds Chris Karwin, Marco Ajello, Rebecca Diesing, Damiano Caprioli Massive black holes at the centers of galaxies can launch powerful wide-angle winds that, if sustained over time, can unbind the gas from the stellar bulges of galaxies. These winds may be responsible for the observed scaling relation between the masses of the central black holes and the velocity dispersions of stars in galactic bulges. Propagating through the galaxy, the wind should interact with the interstellar medium creating a strong shock, similar to those observed in supernovae explosions, which is able to accelerate charged particles to high energies. Here we report the Fermi Large Area Telescope detection of gamma-ray emission from these shocks in a small sample of galaxies exhibiting energetic winds. The detection implies that energetic black-hole winds transfer ~0.04% of their mechanical power to gamma rays and that the gamma-ray emission attests to the onset of the wind-host interaction. [Preview Abstract] |
Saturday, April 17, 2021 2:42PM - 2:54PM Live |
D09.00007: MeV Gamma Rays from Fission: A Distinct Signature of Actinide Production in Neutron Star Mergers Xilu Wang, Nicole Vassh, Trevor Sprouse, Matthew Mumpower, Ramona Vogt, Jorgen Randrup, Rebecca Surman Neutron star mergers (NSMs) are the first verified site of rapid neutron capture ($r$-process) nucleosynthesis, and could emit gamma rays from the radioactive isotopes synthesized in the neutron-rich ejecta. These MeV gamma rays may provide a unique and direct probe of the NSM environment as well insight into the nature of the $r$ process, just as observed gammas from the $^{56}$Ni radioactive decay chain provide a window into supernova nucleosynthesis. In this work, we include the photons from fission processes for the first time in estimates of the MeV gamma-ray signal expected from a NSM event. We consider NSM ejecta compositions with a range of neutron richness and find a dramatic difference in the predicted signal depending on whether or not fissioning nuclei are produced. The difference is most striking at photon energies above $\sim3.5$ MeV and at a relatively late time, several days after the merger event, when the ejecta is optically thin. We estimate that a Galactic NSM could be detectable by a next generation gamma-ray detector such as AMEGO in the MeV range, up to $\sim10^4$ days after the merger, if fissioning nuclei are robustly produced in the event. [Preview Abstract] |
Saturday, April 17, 2021 2:54PM - 3:06PM Live |
D09.00008: Detection of very-high-energy gamma rays from the Crab Nebula with the prototype Schwarzschild-Couder Telescope Leslie Taylor The Schwarzschild-Couder Telescope (SCT) is a candidate for the medium-sized telescope in the Cherenkov Telescope Array (CTA), the next-generation ground-based observatory for very-high-energy gamma-ray astronomy. CTA will have unparalleled sensitivity and angular resolution and will detect gamma-ray sources nearly 100 times faster than current arrays, enabling valuable multiwavelength and multimessenger observations. A prototype SCT (pSCT) has been constructed at the Fred Lawrence Whipple Observatory. The pSCT uses a dual-mirror design with a 9.7 m primary mirror. It has a large field of view (2.68$^{\mathrm{o}})$, a higher resolution, and double the sensitivity compared to current single-mirror telescope designs. The high-resolution camera uses densely packed silicon photomultipliers and state-of-the-art electronics, capable of imaging air showers with waveform readout at a rate of one billion samples per second. It is currently partially instrumented with 1600 pixels. The pSCT was inaugurated in January 2019, with commissioning continuing throughout that year. The first campaign of observations with the pSCT was conducted in January and February of 2020. Gamma-ray emission from the Crab Nebula was detected with a significance of 8.6 sigma. An upgrade to the pSCT camera is currently underway. The upgrade will fully populate the focal plane - increasing the field of view to 8.04$^{\mathrm{o}}$. The upgrade will also include lower noise electronics allowing for better energy reconstruction and lower energy thresholds. [Preview Abstract] |
Saturday, April 17, 2021 3:06PM - 3:18PM Live |
D09.00009: Study of the eHWC J1825-134 Region with the Newest HAWC Data Dezhi Huang eHWC J1825-134 is one of the brightest galactic gamma-ray sources above tens of TeV in the High Altitude Water Cherenkov Gamma-Ray Observatory (HAWC) field of view. In recent HAWC studies, it was revealed that a new point source inside this region has a spectral energy distribution (SED) extending beyond 200 TeV without any cutoff. These ultra high energy gamma-rays could be either produced by PeV electrons up-scattering the cosmic microwave background (CMB) photons through Inverse Compton scattering (IC) or by PeV cosmic rays colliding with the ambient gas. The location of this new point source is near a high density giant molecular cloud. Investigating HAWC data shows that eHWC J1825-134 is a candidate for a galactic PeVatron that accelerate particles up to PeV energies. [Preview Abstract] |
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