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  1. Free, publicly-accessible full text available April 1, 2023
  2. Abstract HESS J0632+057 belongs to a rare subclass of binary systems that emit gamma rays above 100 GeV. It stands out for its distinctive high-energy light curve, which features a sharp “primary” peak and broader “secondary” peak. We present the results of contemporaneous observations by NuSTAR and VERITAS during the secondary peak between 2019 December and 2020 February, when the orbital phase ( ϕ ) is between 0.55 and 0.75. NuSTAR detected X-ray spectral evolution, while VERITAS detected TeV emission. We fit a leptonic wind-collision model to the multiwavelength spectra data obtained over the four NuSTAR and VERITAS observations, constraining the pulsar spin-down luminosity and the magnetization parameter at the shock. Despite long-term monitoring of the source from 2019 October to 2020 March, the MDM observatory did not detect significant variation in H α and H β line equivalent widths, an expected signature of Be-disk interaction with the pulsar. Furthermore, fitting folded Swift-XRT light-curve data with an intrabinary shock model constrained the orbital parameters, suggesting two orbital phases (at ϕ D = 0.13 and 0.37), where the pulsar crosses the Be-disk, as well as phases for the periastron ( ϕ 0 = 0.30) and inferior conjunction ( ϕ IFC =more »0.75). The broadband X-ray spectra with Swift-XRT and NuSTAR allowed us to measure a higher neutral hydrogen column density at one of the predicted disk-passing phases.« less
    Free, publicly-accessible full text available December 1, 2022
  3. Hallibert, Pascal ; Hull, Tony B. ; Kim, Daewook ; Keller, Fanny (Ed.)
    The Cherenkov Telescope Array (CTA) is the next-generation ground-based observatory for very-high-energy gamma rays. One candidate design for CTA's medium-sized telescopes consists of the Schwarzschild-Couder Telescope (SCT), featuring innovative dual-mirror optics. The SCT project has built and is currently operating a 9.7-m prototype SCT (pSCT) at the Fred Lawrence Whipple Observatory (FLWO); such optical design enables the use of a compact camera with state-of-the art silicon photomultiplier detectors. A partially-equipped camera has recently successfully detected the Crab Nebula with a statistical significance of 8.6 standard deviations. A funded upgrade of the pSCT focal plane sensors and electronics is currently ongoing, which will bring the total number of channels from 1600 to 11328 and the telescope field of view from about 2.7° to 8° . In this work, we will describe the technical and scientific performance of the pSCT.
  4. null (Ed.)