Interactions Between CRs and MCs in the Vicinity of Supernova Remnants

Supernovae are incredibly energetic events which drive the dynamic state of the interstellar medium and accelerate cosmic rays up to energies of a few PeV. I present multi-wavelength observations constraining the shocks, chemistry, dust grain processing, and magnetic fields in a large sample of supernova remnants interacting with dense clouds. These are among the most luminous Galactic sources detected by the Fermi Gamma-Ray Space Telescope. Surprisingly, spectral breaks are seen between GeV and TeV energies. Radio spectral breaks have also been detected for a few remnants, providing clear evidence that supernovae are a significant source of hadronic cosmic rays in the Galaxy. Resolving the origin of these spectral breaks will allow the physics of cosmic ray acceleration and diffusion to be probed

Extended Gamma Analysis of SNR G330.2 + 1.0

Analyzing gamma rays is an important aspect of modern astronomy and astrophysics, for they are the most powerful bands of energy on the electromagnetic spectrum. Comprehending gamma rays allows for deeper understanding of countless phenomena within our universe, such as cosmic rays. Cosmic rays are high energy particles thought to be formed via extremely violent explosions within our universe. These accelerated particles mirror conditions present in a supernova. A supernova is what occurs when a star at least 8 times as massive as our sun reaches the end of its lifespan and bursts. These explosions are the most powerful events ever to be recorded by astronomers and can be used to assist our understanding of cosmic rays in many ways. Using the Fermi Large Area Telescope (LAT), we observed the supernova remnant (SNR) G330.2+1.0. Previous X-ray observations could only characterize the spectra of a few regions within the SNR. In this project we compared previous X-ray data with the most current gamma-ray data from Fermi at GeV energy levels. While the SNR itself is not detected by Fermi, we placed the upper limits on the maximum GeV emission coming from this SNR. Our results help to discriminate between previously published models of the particle acceleration that has occurred in this SNR

Gamma Rays from Massive Star Clusters G25 & G27

Project of Merit Winner Cosmic rays have baffled astronomers for over a century, as all potential origins have yet to be determined. Most of these galactic accelerated atomic nuclei are thought to be created in two possible fashions: from a supernova, or within a massive star cluster (MSC). In this study, we analyzed gamma-ray emission coincident with two MSCs named G25 and G27. Using NASA’s Fermi Large Area Telescope (LAT), we confirmed that the sources of gamma rays are spatially extended and emit up to the maximum energies observed by the LAT. So far, only the closest MSC to Earth – called Cygnus X – has been identified as a gamma-ray source with the LAT. We find that the two recently discovered MSCs studied here – G25 and G27 – have similar properties to those of Cygnus X, making it likely these are two new MSCs detected in gamma-rays. Utilizing the studies previously conducted on G25 in 2017 and 2020, as well as new LAT data for G27, we find it plausible that these regions are producing cosmic rays. Though further studies are needed to understand the acceleration processes that occur within these regions and compare them to the Cygnus X

Searching for Dark Matter Annihilation in the Smith High-Velocity Cloud

Recent observations suggest that some high-velocity clouds may be confined by massive dark matter halos. In particular, the proximity and proposed dark matter content of the Smith Cloud make it a tempting target for the indirect detection of dark matter annihilation. We argue that the Smith Cloud may be a better target than some Milky Way dwarf spheroidal satellite galaxies and use gamma-ray observations from the Fermi Large Area Telescope to search for a dark matter annihilation signal. No significant gamma-ray excess is found coincident with the Smith Cloud, and we set strong limits on the dark matter annihilation cross section assuming a spatially-extended dark matter profile consistent with dynamical modeling of the Smith Cloud. Notably, these limits exclude the canonical thermal relic cross section ($\sim 3\times10^{-26}{\rm cm}^{3}{\rm s}^{-1}$) for dark matter masses $\lesssim 30$ GeV annihilating via the $b \bar b$ or $\tau^{+}\tau^{-}$ channels for certain assumptions of the dark matter density profile; however, uncertainties in the dark matter content of the Smith Cloud may significantly weaken these constraints.Comment: 7 pages, 5 figures. Published in Ap

Monitoring the Night Sky for IceACT

The neutral subatomic neutrinos are astronomical messengers that can provide us information to investigate the most violent astrophysical sources: supernovas, gamma-ray bursts, and cataclysmic phenomena involving black holes and neutron stars. As these astrophysical neutrinos freely travel from their point of origin without being scattered by interstellar magnetic fields, we can analyze these particles by observing cosmic-ray air showers on the Earth’s atmosphere. These are produced by the energetic neutrinos by interacting with the air particles that produce a wavefront of Cherenkov radiation. To better identify these background neutrinos, IceCube, the South Pole Neutrino Observatory, constructed an imaging air Cherenkov telescopes otherwise known as IceACT, that are located at the South Pole. These telescopes contain the resources to detect the atmospheric muons produced by the cosmic-ray air showers. Furthermore, IceACT can independently calibrate the angular reconstruction of IceCube to provide accurate results in future trials. Our objective is to further conclude that the data obtained by IceACT supports the readings by IceCube by providing an analysis that the Antarctic night sky interferes of detecting any possible indications of Cherenkov radiation. Through analyzing a sample size of 30 detected stars, we found that only about 60% of the photometric measurements are explained by a linear fit. Furthermore, calibrating the transparency of the atmosphere for IceACT measurements can be done to an uncertainty of approximately 0.5 magnitudes

IceACT Monitoring and Data Analysis

The goal of the IceACT project is to establish an array of small ACTs deployed at the South Pole for neutrino detection, CR composition studies and high energy gamma ray detection. The IceCube Neutrino Observatory at the South Pole has detected these massless subatomic particles called neutrinos. These high-energy astronomical messengers provide us information to investigate the most violent astrophysical sources: events like exploding stars, gamma-ray bursts, and cataclysmic phenomena involving black holes and neutron stars. In particular, these neutrinos have no charge, and can travel across the universe without being scattered by interstellar magnetic fields. The main background for astrophysical neutrinos are muons and neutrinos produced in the Earth’s atmosphere by cosmic-ray air showers. The showers are produced by energetic neutrinos interacting with the air particles produces a wave front of Cherenkov radiation. To better identify these background neutrinos, IceCube constructed an imaging air Cherenkov telescope dubbed IceACT. This telescope detects atmospheric muons from the cosmic-ray air showers and can independently calibrate the angular reconstruction of IceCube to provide accurate results in future trials. In furthering our research on cosmic-ray muons, having an array of IceACTs will allow dramatic improvements in IceCube’s capability to measure both astrophysical neutrinos and very high energy cosmic rays from our galaxy

An X-ray and Radio Study of the Varying Expansion Velocities in Tycho's Supernova Remnant

We present newly obtained X-ray and radio observations of Tycho's supernova remnant using {\it Chandra} and the Karl G. Jansky Very Large Array in 2015 and 2013/14, respectively. When combined with earlier epoch observations by these instruments, we now have time baselines for expansion measurements of the remnant of 12-15 year in the X-rays and 30 year in the radio. The remnant's large angular size allows for proper motion measurements at many locations around the periphery of the blast wave. We find, consistent with earlier measurements, a clear gradient in the expansion velocity of the remnant, despite its round shape. The proper motions on the western and southwestern sides of the remnant are about a factor of two higher than those in the east and northeast. We showed in an earlier work that this is related to an offset of the explosion site from the geometric center of the remnant due to a density gradient in the ISM, and using our refined measurements reported here, we find that this offset is $\sim 23"$ towards the northeast. An explosion center offset in such a circular remnant has implications for searches for progenitor companions in other remnants.Comment: Accepted for publication in ApJ Letter

Note and Comment

State Legislation Extending to Navigable Waters - In Southern Pacific Company v. Jensen, 37 Sup. Ct. -, decided May 21, 1917, the Supreme Court announces a decision in some respects of far reaching importance. It was held therein, Mr. Justice HOL.Es dissenting, that the WORKMEN\u27S COMPENSATION AcT of the State of New York did not support an award to the widow and children of a workman killed on board a ship of the\u27 Company while at the pier in New York City. Clearly the terms of the New York act covered the case, unless the fact that the accident occurred on navigable waters of the United States had a controlling effect to the contrary

A Deep X-ray View of the Synchrotron-Dominated Supernova Remnant G330.2+1.0

We present moderately deep (125 ks) {\it XMM-Newton} observations of supernova remnant G330.2$+$1.0. This remnant is one of only a few known that fall into "synchrotron-dominated" category, with the emission almost entirely dominated by a nonthermal continuum. Previous X-ray observations could only characterize the spectra of a few regions. Here, we examine the spectra from fourteen regions surrounding the entire rim, finding that the spectral properties of the nonthermal emission do not vary significantly in any systematic way from one part of the forward shock to another, unlike several other remnants of this class. We confirm earlier findings that the power-law index, $\Gamma$, ranges from about 2.1-2.5, while the absorbing column density is generally between 2.0-2.6 $\times 10^{22}$ cm$^{-2}$. Fits with the {\it srcut} model find values of the roll-off frequency in the range of 10$^{17.1} - 10^{17.5}$ Hz, implying energies of accelerated electrons of $\sim 100$ TeV. These values imply a high shock velocity of $\sim 4600$ km s$^{-1}$, favoring a young age of the remnant. Diffuse emission from the interior is nonthermal in origin as well, and fits to these regions yield similar values to those along the rim, also implying a young age. Thermal emission is present in the east, and the spectrum is consistent with a $\sim 650$ km s$^{-1}$ shock wave encountering interstellar or circumstellar material with a density of $\sim 1$ cm$^{-3}$.Comment: Accepted for publication by ApJ. Manuscript produced with emulateapj. 10 pages, 8 figure