Abstract
In 2016, the Compton Spectrometer and Imager (COSI) had a successful 46 day flight on board NASA’s Super Pressure Balloon platform. In this work, we report measurements of the Galactic ...diffuse continuum emission (GDCE) observed toward the inner Galaxy during the flight, which in the COSI energy band (0.2–5 MeV) is primarily generated from inverse Compton radiation. Within uncertainties, we find overall good agreement with previous measurements from INTEGRAL/SPI and COMPTEL. Based on these initial findings, we discuss the potential for further probing the GDCE with the 2016 COSI balloon data, as well as prospects for the upcoming satellite mission.
In 2016 the Compton Spectrometer and Imager (COSI) had a successful 46-day flight onboard NASA's Super Pressure Balloon platform. In this work we report measurements of the Galactic diffuse continuum ...emission (GDCE) observed towards the inner Galaxy during the flight, which in the COSI energy band (0.2 - 5 MeV) is primarily generated from inverse Compton radiation. Within uncertainties we find overall good agreement with previous measurements from INTEGRAL/SPI and COMPTEL. Based on these initial findings, we discuss the potential for further probing the GDCE with the 2016 COSI balloon data, as well as prospects for the upcoming satellite mission.
In recent years we have seen major advances in multi-messenger astronomy. A milestone was achieved by identifying the electromagnetic counterpart of the gravitational wave event GW170817 detected by ...LIGO and Virgo. Similar efforts led to a set of neutrinos detected by IceCube to be associated with the blazar TXS 0506+056. Both demonstrate the potential of using multiple types of probes to study an astrophysical source. The High-Altitude Water Cherenkov Observatory (HAWC), located in the state of Puebla, Mexico, is a wide field instrument (~2 sr) sensitive to very-high-energy gamma rays (~0.1-100 TeV) which can operate with a large duty cycle (>95%). These characteristics make it well suited to look for transient events correlated with other astronomical messengers. In this work we present a maximum likelihood analysis framework developed to search and analyze signals in HAWC data of arbitrary timescales. We apply this method to search for very-high-energy gamma-ray counterparts of gravitational waves in short timescales (0.3-1000 s). We show that we would be able to either detect or meaningfully constrain the very-high-energy component of a gamma-ray burst within the binary neutron star merger horizon of current gravitational wave detectors if it occurs in our field of view. We did not find evidence for emission for any of the events analyzed. The source location of GW170817 was not observable by HAWC at the time of the merger. We also set flux upper bounds for TXS 0506+056 during the periods when the neutrino flares were identified. For the flare between September 2014 and March 2015 these are the only available limits at very high energy, and are consistent with the low state in high-energy gamma rays reported by the Fermi-LAT Collaboration.
Primordial Black Holes (PBHs) are black holes that may have been created by density fluctuations in the early Universe and could be as massive as supermassive black holes or as small as the Planck ...scale. It is believed that a black hole has a temperature inversely proportional to its mass and will thermally emit all species of fundamental particles via Hawking Radiation. PBHs with initial masses of ~5e14 g (approximately one gigaton) should be expiring today with bursts of high-energy gamma radiation in the GeV – TeV energy range. The High Altitude Water Cherenkov (HAWC) Observatory is sensitive to particles with energies of 300 GeV – 100 TeV, which corresponds to the high end of the PBH burst spectrum. With its large instantaneous field of view of ~2 sr and a duty cycle above 95%, the HAWC Observatory is well suited to perform an all-sky search for PBH bursts. We conducted a search on 959 days of gamma-ray data from HAWC by optimizing a previous gamma-ray burst transient search to the PBH burst energy spectrum, and placed the strongest upper limits on the local PBH burst rate density at the 99% confidence level.
The High-Altitude Water Cherenkov Observatory (HAWC) is a large field of view (~2 sr) continuously operating experiment sensitive to very-high energy (VHE) gamma rays (~0.3-100 TeV). These ...characteristics make it well suited for observing or constraining the VHE emission of rapid transients such as some gravitational waves progenitors. Of special interest are the events at low redshift where the attenuation due to the extragalactic background light is minimal. This is the case for binary neutron star mergers in the horizon of the LIGO and Virgo experiments, for which HAWC can either detect or place constraining limits on events occurring in our field of view. We report on our search for counterparts of the gravitational waves detected by LIGO and Virgo.
The atmospheric response for MeV $\gamma$ rays ($\sim$ 0.1 $-$ 10 MeV) can be
characterized in terms of two observed components. The first component is due
to photons that reach the detector without ...scattering. The second component is
due to photons that reach the detector after scattering one or more times.
While the former can be determined in a straightforward manner, the latter is
much more complex to quantify, as it requires tracking the transport of all
source photons that are incident on Earth's atmosphere. The scattered component
can cause a significant energy-dependent distortion in the measured spectrum,
which is important to account for when making balloon-borne observations. In
this work we simulate the full response for $\gamma$-ray transport in the
atmosphere. We find that the scattered component becomes increasingly more
significant towards lower energies, and at 0.1 MeV it may increase the measured
flux by as much as a factor of $\sim2-4$, depending on the photon index and
off-axis angle of the source. This is particularly important for diffuse
sources, whereas the effect from scattering can be significantly reduced for
point sources observed with an imaging telescope.
The High-Altitude Water Cherenkov Observatory (HAWC) is a large field of view (\(\sim\)2sr) instrument sensitive to very-high energy gamma rays (\(\sim\)0.5-100TeV). It is located in central Mexico ...(19\(^\circ\)N) and has a high duty cycle (\(\sim\)95%). These characteristics allow it to continuously monitor \(\sim\)2/3 of the sky, looking for transient events, such as flares from Active Galactic Nuclei or possibly other unknown phenomena. Presented here is an unbiased real-time monitoring on hours timescales which provides daily flux measurements for all locations in our observable sky promptly after they leave our field of view. These measurements are then used to follow known TeV sources and to perform a blind search. The alerts generated from these analyses, some of which have been made public through the Astronomer's Telegraph, can trigger small field of view instruments, enabling deep observations of sources during their high state activity which can constrain acceleration mechanisms. Additionally, these measurements allow us to respond quickly to external alerts.
The All-sky Medium Energy Gamma-ray Observatory eXplorer (AMEGO-X) is designed to identify and characterize gamma rays from extreme explosions and accelerators. The main science themes include: ...supermassive black holes and their connections to neutrinos and cosmic rays; binary neutron star mergers and the relativistic jets they produce; cosmic ray particle acceleration sources including Galactic supernovae; and continuous monitoring of other astrophysical events and sources over the full sky in this important energy range. AMEGO-X will probe the medium energy gamma-ray band using a single instrument with sensitivity up to an order of magnitude greater than previous telescopes in the energy range 100 keV to 1 GeV that can be only realized in space. During its three-year baseline mission, AMEGO-X will observe nearly the entire sky every two orbits, building up a sensitive all-sky map of gamma-ray sources and emission. AMEGO-X was submitted in the recent 2021 NASA MIDEX Announcement of Opportunity.
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