UMD Theses and Dissertations
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Item New Messengers & New Physics: A Survey of the High-energy Universe(2023) Crnogorcevic, Milena; Ricotti, Massimo; Caputo, Regina; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Studying the origins of the high-energy emission in the Universe can profoundly affect our fundamental understanding of the cosmic origin and its evolution at the most extreme scales. In this dissertation, I explore the high-energy observations of different astrophysical systems to inform our understanding of the theoretical frameworks used to describe them. I harness the current multimessenger infrastructure to investigate questions ranging from new physics and transient astronomy to compact objects and extended emission in the gamma-ray, gravitational-wave, and neutrino skies. The focus in the first part of this dissertation is on utilizing the Fermi Large Area Telescope (LAT) low-energy (LLE) technique to search for the light axion-like-particle (ALP) within the MeV gamma-ray emission of long gamma-ray bursts (GRBs). We perform a data-driven sensitivity analysis to determine distances for which detection of an ALP signal is possible with the LLE technique, which, in contrast to the standard LAT analysis, allows for a larger effective area for energies down to 30 MeV. Assuming an ALP mass $m_a \lesssim 10^{-10}$~eV and ALP-photon coupling $g_{a\gamma} = 5.3\times 10^{-12}$ GeV$^{-1}$, we find that the distance limit ranges from $\sim\!0.5$ to $\sim\!10$~Mpc. We demonstrate that the sensitivity of the LLE technique to detecting light ALPs is comparable to the standard LAT analysis, making it an excellent complementary---yet independent---way to search for ALPs with \textit{Fermi}. Next, we select a candidate sample of twenty-four GRBs and conduct a model comparison analysis in which we consider different GRB spectral models with and without an ALP signal component. We find that including an ALP contribution does not result in any statistically significant improvement of the fits to the data. Motivated by the delay between the ALP emission time and the time of the jet break-out associated with its ordinary long-GRB emission, we conduct a novel search for ALPs within time windows that precede the main-episode gamma-ray emission of a long GRB, focusing on the sample of sources with known precursor emission detected with LAT and LLE. We report no statistically significant detection of ALPs within the GRB precursor emission and discuss the parts of the ALP parameter space probed with this method. Multimessenger astronomy is at the heart of the remainder of this dissertation. First, I present a follow-up search for excess emission of X-rays with the Swift Burst Alert Telescope (Swift-BAT) and that of gamma rays with the Fermi Gamma-ray Burst Monitor (Fermi-GBM), in spatial and temporal correspondence to gravitational-wave events reported by the LIGO/Virgo/Kagra (LVK) Collaboration. In collaboration with the Fermi-GBM Team, we combine the observations from these two instruments to determine whether there is any statistically significant excess emission around the given gravitational-wave trigger. We report no new joint detections but present the joint flux upper limits. Finally, I present the results of the cross-correlation studies between the unresolved Fermi-LAT gamma-ray and the IceCube neutrino skies. We report no positive cross-correlation in the real-data sky maps. We then combine simulation and observation techniques to place upper limits on the fraction of neutrinos produced in proton-proton or proton-gamma interactions that occur in blazars. Assuming all gamma rays from unresolved blazars are produced from neutral pions via proton-proton interactions, we find that---for energies above 10~GeV---up to 60 % of the unresolved blazar population may contribute to the diffuse neutrino background (the fraction is 30 % for proton-gamma interactions). We also include predictions for the improved sensitivity considering 20 years of IceCube data.Item BROADBAND OBSERVATIONS OF GAMMA-RAY BURSTS AND FAST RADIO BURSTS: ENERGETICS, AFTERGLOWS, AND PHYSICAL ORIGINS(2021) Cunningham, Virginia Anne; Cenko, S. Bradley; Vogel, Stuart; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Long gamma-ray bursts (GRBs) are produced during the deaths of massive stars. They are the most powerful explosions known in the Universe and release most of their energy via a narrow cone of emission. The long-lived afterglows of the brightest GRBs detected by the \textit{Fermi} Large Area Telescope (LAT) are visible from radio to gamma-rays, and this relative abundance of broadband data makes them excellent tools for constraining theoretical models regarding their origins. Here, we use our sample of bright GRBs to test emission models beyond the canonical on-axis, top-hat jet model which has historically been applied throughout the literature. We demonstrate that many GRBs are likely to produce emission via a structured jet. We also find that derived physical parameters are highly dependent upon the fraction, $\xi$, of electrons which contribute to the synchrotron emission. Our findings for $\xi$ are contrary to what is generally assumed during GRB modeling ($\xi=1.0$), but consistent with theoretical simulations which predict lower values. Lower predictions for $\xi$ would impact our current understanding of GRBs, implying denser environments and higher energetics than commonly assumed. Fast radio bursts (FRBs) are extremely bright, short-duration pulses at radio frequencies that were only confirmed as true astrophysical sources a decade ago. Although the field has experienced major leaps in recent years, many questions regarding their progenitors and emission processes remain. The identification of counterparts at higher energies is critical to understanding the physical origins of FRBs. Here, we report on an archival search of previously identified FRBs with the \textit{Fermi} Gamma-ray Burst Monitor (GBM), the \textit{Fermi}-LAT, and the \textit{Swift} Burst Alert Telescope (BAT). We find no significant X-ray or gamma-ray counterparts but report upper limits on the high-energy fluence, $f_{\gamma}$, for each FRB in our sample. We also report lower limits on the ratio of radio to high-energy fluence ($\nicefrac{f_{r}}{f_{\gamma}}$). We discuss the implications of our results on several FRB progenitor theories, including pulsar-like analogs and magnetar flares.Item Gamma-ray Bursts: Lighting up the High-Redshift Universe(2017) Toy, Vicki; Veilleux, Sylvain; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Gamma-ray bursts (GRBs) are the most luminous events in the Universe with Eγ,iso ∼ 10^48−54 erg. Leading models hypothesize that GRBs are created from inter- nal collisions within collimated and ultrarelativistic jets. The jets then shock-heat the surrounding material (e.g. interstellar medium) to create GRB afterglows. These afterglows are extremely useful probes of the Universe because long GRBs are (1) bright events that can be used as backlights for absorption studies, (2) able to probe at all redshifts massive stars exist, and (3) transient events that allow us to follow- up on the host galaxies at late times. In this thesis we study the environments of GRBs. We first explore the relationship between GRB and supernova (SN) using a nearby GRB-SN (GRB 130702A/SN 2013dx) at z = 0.145. There are only nine other GRB-SNe that were close enough to have extensive spectroscopic and photometric follow-up of the SN at late times. We create a quasi-bolometic light curve of SN 2013dx and fit an analytical equation to the quasi-bolometric light curve combined with measurements of the photospheric velocity to determine SN parameters: mass of 56Ni, kinetic energy, and ejecta mass. We examine the relationship between SN parameters and Eγ,iso for the 10 well-studied GRB-SNe, but find no correlations despite numerical simulation predictions that the mass of 56Ni should correlate with the degree of asymmetry. We then move to larger distance scales and use GRB afterglows as bright back- lights to study distant galaxies. We examine the galactic environments of Damped Lyman-α systems (DLAs; NHI ≥ 10^20.3 cm^−2 ) identified with GRB afterglows at z ∼ 2 − 6. We use late-time photometry after the GRB afterglow has faded to determine star formation rates (SFRs) from rest-frame ultraviolet measurements or spectral energy distribution (SED) models from multiband photometry. We com- pare our sample’s SFRs to a sample of quasars (QSOs) DLA host galaxies. Despite the overlapping NHI and redshift ranges, our GRB-DLA galaxies have much larger SFRs than the QSO-DLA host galaxy sample; this may suggest that the QSO-DLA and GRB-DLA galaxy populations are different. We also compare star formation efficiencies to the local Universe and simulations at z = 3. A large portion of this thesis has focused on the development of a new ground- based GRB afterglow follow-up instrument, the Rapid infrared IMAger-Spectrometer (RIMAS), that will target high-redshift GRB afterglows to study early galaxy envi- ronments. RIMAS covers 0.97-2.37 μm and can simultaneously observe two band- passes in any observing mode: photometry, low-resolution spectroscopy (R ∼ 30), or high-resolution spectroscopy (R ∼ 4000). In particular, this thesis focuses on RIMAS’s three detectors: two science grade Teledyne HgCdTe Astronomy Wide Area Infrared Imager with 2K x 2K, Reference Pixels and Guide Mode (H2RG) and a slit-viewer Spitzer Legacy Indium-Antimonide (InSb) array. We describe the detector hardware and characterization in detail and discuss general infrared detector troubleshooting methods at both cryogenic and room temperatures. Several software packages have been developed for RIMAS throughout this thesis work. We introduce RIMAS’s quick reduction pipeline that takes raw images from a single acquisition and returns a single result frame. We then present a generalized data reduction pipeline that we have tested on two currently operational photometers. We also describe our detailed and realistic RIMAS throughput models for all three observing modes as well as our online observer calculators with these throughput models. All of our data products are open source and are publicly available on Github repositories with detailed documentation.Item Near-infrared Instrumentation For Rapid-response Astronomy(2016) Capone, John Isaac; Veilleux, Sylvain; Kutyrev, Alexander S; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ɣ-ray bursts (GRBs) are the Universe's most luminous transient events. Since the discovery of GRBs was announced in 1973, efforts have been ongoing to obtain data over a broader range of the electromagnetic spectrum at the earliest possible times following the initial detection. The discovery of the theorized ``afterglow'' emission in radio through X-ray bands in the late 1990s confirmed the cosmological nature of these events. At present, GRB afterglows are among the best probes of the early Universe (z ≳ 9). In addition to informing theories about GRBs themselves, observations of afterglows probe the circum-burst medium (CBM), properties of the host galaxies and the progress of cosmic reionization. To explore the early-time variability of afterglows, I have developed a generalized analysis framework which models near-infrared (NIR), optical, ultra-violet (UV) and X-ray light curves without assuming an underlying model. These fits are then used to construct the spectral energy distribution (SED) of afterglows at arbitrary times within the observed window. Physical models are then used to explore the evolution of the SED parameter space with time. I demonstrate that this framework produces evidence of the photodestruction of dust in the CBM of GRB 120119A, similar to the findings from a previous study of this afterglow. The framework is additionally applied to the afterglows of GRB 140419A and GRB 080607. In these cases the evolution of the SEDs appears consistent with the standard fireball model. Having introduced the scientific motivations for early-time observations, I introduce the Rapid Infrared Imager-Spectrometer (RIMAS). Once commissioned on the 4.3 meter Discovery Channel Telescope (DCT), RIMAS will be used to study the afterglows of GRBs through photometric and spectroscopic observations beginning within minutes of the initial burst. The instrument will operate in the NIR, from 0.97 μm to 2.37 μm, permitting the detection of very high redshift (z ≳ 7) afterglows which are attenuated at shorter wavelengths by Lyman-ɑ absorption in the intergalactic medium (IGM). A majority of my graduate work has been spent designing and aligning RIMAS's cryogenic (~80 K) optical systems. Design efforts have included an original camera used to image the field surrounding spectroscopic slits, tolerancing and optimizing all of the instrument's optics, thermal modeling of optomechanical systems, and modeling the diffraction efficiencies for some of the dispersive elements. To align the cryogenic optics, I developed a procedure that was successfully used for a majority of the instrument's sub-assemblies. My work on this cryogenic instrument has necessitated experimental and computational projects to design and validate designs of several subsystems. Two of these projects describe simple and effective measurements of optomechanical components in vacuum and at cryogenic temperatures using an 8-bit CCD camera. Models of heat transfer via electrical harnesses used to provide current to motors located within the cryostat are also presented.Item Detecting High-Energy Emission from Gamma-Ray Bursts with EGRET and GLAST(2005-07-25) Wren, David Nathan; Ritz, Steven M; Sullivan, Gregory W; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The research described in this dissertation explores the detection of high-energy emission from gamma-ray bursts (GRBs) with EGRET and GLAST. Data from the EGRET experiment were searched for evidence of ~1-250 MeV emission that preceded or followed gamma-ray bursts on a time scale of hours. This led to the discovery of a gamma-ray burst with high-energy, post-quiescent emission from the prompt phase that was coincident with lower-energy (keV) emission. To do detailed event filtering studies for the GLAST Large Area Telescope (LAT), the flight software event filter was embedded in the standard science analysis environment. The event trigger rate, reasons why it must be reduced, and hardware-level methods of reducing it are studied. Much work was done to improve the performance of the prototype event filter, and additional work was done to develop algorithms to allow the LAT to distinguish Earth albedo photons from celestial gamma-rays, and to eliminate albedo events from the data stream. It is shown that it is possible to reduce the background rate to meet LAT mission requirements, while simultaneously keeping the gamma-ray acceptance rate high enough to exceed the relevant LAT requirements for those events. Using the onboard event filter, real-time, onboard, gamma-ray burst detection was then studied. A detection algorithm had been developed by members of the LAT collaboration, but the algorithm required a lower onboard background rate than the basic LAT requirement for downlink, in addition to knowledge of incident gamma-ray directions. Therefore, several methods of reducing the background rate to acceptable levels were provided, and onboard track reconstruction methods were created and tested. GRB detection was tested for two background filters and two track reconstruction methods for simulated bursts that had realistic light curves and spectral characteristics. With prototype background cuts, track reconstruction, and burst detection algorithms, the LAT burst detection requirements were exceeded. Suggestions were offered about how to enhance burst detection performance in the coming months before GLAST is launched.