Matching Items (15)

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Probing the Radio Sky with the Low Frequency Array

Description

The LOw Frequency ARray (LOFAR) is a new and innovative radio telescope designed and constructed by the Netherlands Institute for Radio Astronomy (ASTRON). LOFAR unique capable of operating in very

The LOw Frequency ARray (LOFAR) is a new and innovative radio telescope designed and constructed by the Netherlands Institute for Radio Astronomy (ASTRON). LOFAR unique capable of operating in very low frequencies (10-240 MHz) and consists of an extensive interferometry array of dipole antenna stations distributed throughout the Netherlands and Europe which allows it to achieve superb angular resolution. I investigate a part of the northern sky to search for rare radio objects such as radio haloes and radio relics that may have not been able to have been resolved by other radio telescopes.

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Date Created
  • 2016-12

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Investigating signatures of cosmological time dilation in duration measures of prompt gamma-ray burst light curves

Description

We study the evolution with redshift of three measures of gamma-ray burst (GRB) duration (T[subscript 90], T[subscript 50] and TR[subscript 45]) in a fixed rest-frame energy band for a sample

We study the evolution with redshift of three measures of gamma-ray burst (GRB) duration (T[subscript 90], T[subscript 50] and TR[subscript 45]) in a fixed rest-frame energy band for a sample of 232 Swift/Burst Alert Telescope (BAT) detected GRBs. Binning the data in redshift we demonstrate a trend of increasing duration with increasing redshift that can be modelled with a power law for all three measures. Comparing redshift defined subsets of rest-frame duration reveals that the observed distributions of these durations are broadly consistent with cosmological time dilation. To ascertain if this is an instrumental effect, a similar analysis of Fermi/Gamma-ray Burst Monitor data for the 57 bursts detected by both instruments is conducted, but inconclusive due to small number statistics. We then investigate underpopulated regions of the duration redshift parameter space. We propose that the lack of low-redshift, long duration GRBs is a physical effect due to the sample being volume limited at such redshifts. However, we also find that the high-redshift, short duration region of parameter space suffers from censorship as any Swift GRB sample is fundamentally defined by trigger criteria determined in the observer frame energy band of Swift/BAT. As a result, we find that the significance of any evidence for cosmological time dilation in our sample of duration measures typically reduces to <2σ.

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Created

Date Created
  • 2014-11-11

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A trio of gamma-ray burst supernovae: GRB 120729A, GRB 130215A/SN 2013ez, and GRB 130831A/SN 2013fu

Description

We present optical and near-infrared (NIR) photometry for three gamma-ray burst supernovae (GRB-SNe): GRB 120729A, GRB 130215A/SN 2013ez, and GRB 130831A/SN 2013fu. For GRB 130215A/SN 2013ez, we also present optical

We present optical and near-infrared (NIR) photometry for three gamma-ray burst supernovae (GRB-SNe): GRB 120729A, GRB 130215A/SN 2013ez, and GRB 130831A/SN 2013fu. For GRB 130215A/SN 2013ez, we also present optical spectroscopy at t − t[subscript 0] = 16.1 d, which covers rest-frame 3000–6250 Å. Based on Fe ii λ5169 and Si ii λ6355, our spectrum indicates an unusually low expansion velocity of ~4000–6350 km s[superscript -1], the lowest ever measured for a GRB-SN. Additionally, we determined the brightness and shape of each accompanying SN relative to a template supernova (SN 1998bw), which were used to estimate the amount of nickel produced via nucleosynthesis during each explosion. We find that our derived nickel masses are typical of other GRB-SNe, and greater than those of SNe Ibc that are not associated with GRBs. For GRB 130831A/SN 2013fu, we used our well-sampled R-band light curve (LC) to estimate the amount of ejecta mass and the kinetic energy of the SN, finding that these too are similar to other GRB-SNe. For GRB 130215A, we took advantage of contemporaneous optical/NIR observations to construct an optical/NIR bolometric LC of the afterglow. We fit the bolometric LC with the millisecond magnetar model of Zhang & Mészáros (2001, ApJ, 552, L35), which considers dipole radiation as a source of energy injection to the forward shock powering the optical/NIR afterglow. Using this model we derive an initial spin period of P = 12 ms and a magnetic field of B = 1.1 × 10[superscript 15] G, which are commensurate with those found for proposed magnetar central engines of other long-duration GRBs.

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Created

Date Created
  • 2014-08-01

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IDENTIFYING HIGH-REDSHEFT GAMMA-RAY BURSTS WITH RATIR

Description

We present a template-fitting algorithm for determining photometric redshifts, z phot, of candidate high-redshift gamma-ray bursts (GRBs). Using afterglow photometry, obtained by the Reionization and Transients InfraRed (RATIR) camera, this

We present a template-fitting algorithm for determining photometric redshifts, z phot, of candidate high-redshift gamma-ray bursts (GRBs). Using afterglow photometry, obtained by the Reionization and Transients InfraRed (RATIR) camera, this algorithm accounts for the intrinsic GRB afterglow spectral energy distribution, host dust extinction, and the effect of neutral hydrogen (local and cosmological) along the line of sight. We present the results obtained by this algorithm and the RATIR photometry of GRB 130606A, finding a range of best-fit solutions, 5.6 < z [subscript phot] < 6.0, for models of several host dust extinction laws (none, the Milky Way, Large Magellanic Clouds, and Small Magellanic Clouds), consistent with spectroscopic measurements of the redshift of this GRB. Using simulated RATIR photometry, we find that our algorithm provides precise measures of z [subscript phot] in the ranges of 4 < z [subscript phot] lesssim 8 and 9 < z [subscript phot] < 10 and can robustly determine when z [subscript phot] > 4. Further testing highlights the required caution in cases of highly dust-extincted host galaxies. These tests also show that our algorithm does not erroneously find z [subscript phot] < 4 when z [subscript sim] > 4, thereby minimizing false negatives and allowing us to rapidly identify all potential high-redshift events.

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Created

Date Created
  • 2014-07-01

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Detections of GRBs with the Telescope DDOTI and Code Manuals

Description

At the start of this honors thesis project, a new telescope called the deca-degree optical transient imager (DDOTI) needed assistance to help it gather photometric data about Gamma Ray Bursts

At the start of this honors thesis project, a new telescope called the deca-degree optical transient imager (DDOTI) needed assistance to help it gather photometric data about Gamma Ray Bursts (GRBs). Contributions to help DDOTI produce scientifically ready reductions will be discussed.
First, performance assessment tests were run in order to prevent data backlog and optimize the way in which DDOTI reduces the data it collects. The results of these tests yielded a general framework regarding how DDOTI should reduce collected images depending on how many computer cores can be used. These tests also indicated that DDOTI’s alignment portion of the reduction code (ddoti_align) should be completed after every image is collected, while the other parts of the reduction software (ddoti_stack, ddoti_phot, ddoti_summary) should be run after every four images are collected.
Second, reductions created by DDOTI were inspected to determine if the telescope’s reduction software was working properly. Reductions were observed and indicated that two reduction related problems needed to be corrected by the research team before DDOTI would be ready for future scientific work. The first identified problem was that DDOTI’s reduction code was not properly correcting optical distortions for one of DDOTI’s two functional cameras. The second problem was that the reduction code was not correcting for atmospheric refraction. As a result, below zenith distances of approximately sixty degrees, ddoti_align was unable to align detected sources to their catalogue equivalents due to their distorted positions.
Third, code manuals were produced in both English and Spanish so that English and Spanish-speaking researchers working on DDOTI could understand how its reductions software reduces images. Functional flow chart diagrams were also produced only in English to graphically describe the flow of information through DDOTI’s reduction software.
These three contributions helped DDOTI to more accurately be able to observe GRBs. DDOTI’s improved reduction abilities were confirmed by a produced report about GRB 190129B after a 10-hour observation, and by the fact that DDOTI could accurately observed asteroid fields. In addition, code manuals and functional flow chart diagrams were all produced by the end of this project.

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Created

Date Created
  • 2019-05

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Single photon interferometry and quantum astrophysics

Description

This thesis contains an overview, as well as the history of optical interferometers. A new approach to interferometric measurements of stars is proposed and explored. Modern updates to the classic

This thesis contains an overview, as well as the history of optical interferometers. A new approach to interferometric measurements of stars is proposed and explored. Modern updates to the classic techniques are described along with some theoretical derivations showing why the method of single photon counting shows significant promise relative to the currently used amplitude interferometry.

Description of a modular intensity interferometer system using commercially available single-photon detectors is given. Calculations on the sensitivity and \emph{uv}-plane coverage using these modules mounted on existing telescopes on Kitt Peak, Arizona is presented.

Determining fundamental stellar properties is essential for testing models of stellar evolution as well as for deriving physical properties of transiting exoplanets. The proposed method shows great promise in measuring the angular size of stars. Simulations indicate that it is possible to measure stellar diameters of bright stars with AB magnitude <6 with a precision of >5% in a single night of observation.

Additionally, a description is given of a custom time-to-digital converter designed to time tag individual photons from multiple single-photon detectors with high count rate, continuous data logging, and low systematics. The instrument utilizes a tapped-delay line approach on an FPGA chip which allows for sub-clock resolution of <100 ps. The TDC is implemented on a Re-configurable Open Architecture Computing Hardware Revision 2 (ROACH2) board which allows for continuous data streaming and time tagging of up to 20 million events per second. The functioning prototype is currently set-up to work with up to ten independent channels. Laboratory characterization of the system, including RF, pick up and mitigation, as well as measurement of in-lab photon correlations from an incoherent light source (artificial star), are presented. Additional improvements to the TDC will also be discussed, such as improving the data transfer rate by a factor of 10 via an SDP+ Mezzanine card and PCIe 2SFP+ 10 Gb card, as well as scaling to 64 independent channels.

Furthermore, a modified nulling interferometer with image inversion is proposed, for direct imaging of exoplanets below the canonical Rayleigh resolution limit. Image inversion interferometry relies on splitting incoming radiation from a source, either spatially rotating or reflecting the electric field from one arm of the interferometer before recombining the signals and detecting the resulting images in the two output ports with an array of high-speed single-photon detectors. Sources of incoming radiation that have cylindrical symmetry and are centered on the rotation axis will cancel in one of the output ports and add in the other output port. The ability to suppress light from a host star, as well as the ability to resolve past the Rayleigh limit, enables sensitive detection of exoplanets from a stable environment without the need for a coronagraph. The expected number of photons and the corresponding variance in the measurement for different initial contrast ratios are shown, with some first-order theoretical instrumental errors.

Lastly, preliminary results from a sizeable photometric survey are presented. This survey is used to derive bolometric flux alongside from angular size measurements and the effective stellar temperatures.

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Agent

Created

Date Created
  • 2018

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The study of astronomical transients in the infrared

Description

Several key, open questions in astrophysics can be tackled by searching for and

mining large datasets for transient phenomena. The evolution of massive stars and

compact objects can be studied over cosmic

Several key, open questions in astrophysics can be tackled by searching for and

mining large datasets for transient phenomena. The evolution of massive stars and

compact objects can be studied over cosmic time by identifying supernovae (SNe) and

gamma-ray bursts (GRBs) in other galaxies and determining their redshifts. Modeling

GRBs and their afterglows to probe the jets of GRBs can shed light on the emission

mechanism, rate, and energetics of these events.

In Chapter 1, I discuss the current state of astronomical transient study, including

sources of interest, instrumentation, and data reduction techniques, with a focus

on work in the infrared. In Chapter 2, I present original work published in the

Proceedings of the Astronomical Society of the Pacific, testing InGaAs infrared

detectors for astronomical use (Strausbaugh, Jackson, and Butler 2018); highlights of

this work include observing the exoplanet transit of HD189773B, and detecting the

nearby supernova SN2016adj with an InGaAs detector mounted on a small telescope

at ASU. In Chapter 3, I discuss my work on GRB jets published in the Astrophysical

Journal Letters, highlighting the interesting case of GRB 160625B (Strausbaugh et al.

2019), where I interpret a late-time bump in the GRB afterglow lightcurve as evidence

for a bright-edged jet. In Chapter 4, I present a look back at previous years of

RATIR (Re-ionization And Transient Infra-Red Camera) data, with an emphasis on

the efficiency of following up GRBs detected by the Fermi Space Telescope, before

some final remarks and brief discussion of future work in Chapter 5.

Contributors

Agent

Created

Date Created
  • 2019

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H-alpha emitting galaxies at z ~0.6 in the deep and wide narrowband survey

Description

New measurements of the Hα luminosity function (LF) and star formation rate

(SFR) volume density are presented for galaxies at z∼0.62 in the COSMOS field.

These results are part of the Dee

New measurements of the Hα luminosity function (LF) and star formation rate

(SFR) volume density are presented for galaxies at z∼0.62 in the COSMOS field.

These results are part of the Deep And Wide Narrowband Survey (DAWN), a unique

infrared imaging program with large areal coverage (∼1.1 deg 2 over 5 fields) and

sensitivity (9.9 × 10 −18 erg/cm 2 /s at 5σ).

The present sample, based on a single DAWN field, contains 116 Hα emission-

line candidates at z∼0.62, 25% of which have spectroscopic confirmations. These

candidates have been selected through comparison of narrow and broad-band images

in the infrared and through matching with existing catalogs in the COSMOS field.

The dust-corrected LF is well described by a Schechter function with L* = 10 42.64±0.92

erg s −1 , Φ* = 10 −3.32±0.93 Mpc −3 (L* Φ* = 10 39.40±0.15 ), and α = −1.75 ± 0.09. From

this LF, a SFR density of ρ SF R =10 −1.37±0.08 M○ yr −1 Mpc −3 was calculated. An

additional cosmic variance uncertainty of ∼ 20% is also expected. Both the faint

end slope and luminosity density that are derived are consistent with prior results at

similar redshifts, with reduced uncertainties.

An analysis of these Hα emitters’ sizes is also presented, showing a direct corre-

lation between the galaxies’ sizes and their Hα emission.

Contributors

Agent

Created

Date Created
  • 2017

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The evolution of escaping ionizing radiation from galaxies and active galactic nuclei through cosmic time

Description

Reionization is the phase transition of intergalactic atoms from being neutral to

becoming fully ionized. This process began ∼400 Myr after the Big Bang, when the first

stars and black holes began

Reionization is the phase transition of intergalactic atoms from being neutral to

becoming fully ionized. This process began ∼400 Myr after the Big Bang, when the first

stars and black holes began emitting ionizing radiation from stellar photospheres and

accretion disks. Reionization completed when all of the neutral matter between galaxies

became ionized ∼1 Gyr after the Big Bang, and the Universe became transparent as

it is today.

Characteristics of the galaxies that drove reionization are mostly unknown. The

physical mechanisms that create ionizing radiation inside these galaxies, and the

paths for this light to escape are even more unclear. To date, only a small fraction of

the numerous searches for this escaping light have been able to detect a faint signal

from distant galaxies, and no consensus on how Reionization was completed has been

established.

In this dissertation, I discuss the evolution of the atomic matter between galaxies

from its initially ionized state, to its current re-ionized state, potential sources of

re-ionizing energy, and the theoretical and observational status of the characteristics of

these sources. I also present new constraints on what fraction of the ionizing radiation

escapes from galaxies using Hubble Space Telescope UV imaging, theoretical models

of the stellar and accretion disk radiation, and models of the absorption of ionizing

radiation by the intergalactic medium.

Contributors

Agent

Created

Date Created
  • 2019

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The development of unique focal planes for high-resolution suborbital and ground-based exploration

Description

The development of new Ultra-Violet/Visible/IR range (UV/Vis/IR) astronomical instrumentation that use novel approaches for imaging and increase the accessibility of observing time for more research groups is essential for rapid

The development of new Ultra-Violet/Visible/IR range (UV/Vis/IR) astronomical instrumentation that use novel approaches for imaging and increase the accessibility of observing time for more research groups is essential for rapid innovation within the community. Unique focal planes that are rapid-prototyped, low cost, and provide high resolution are key.

In this dissertation the emergent designs of three unique focal planes are discussed. These focal planes were each designed for a different astronomical platform: suborbital balloon, suborbital rocket, and ground-based observatory. The balloon-based payload is a hexapod-actuated focal plane that uses tip-tilt motion to increase angular resolution through the removal of jitter – known as the HExapod Resolution-Enhancement SYstem (HERESY), the suborbital rocket imaging payload is a Jet Propulsion Laboratory (JPL) delta-doped charge-coupled device (CCD) packaged to survive the rigors of launch and image far-ultra-violet (FUV) spectra, and the ground-based observatory payload is a star centroid tracking modification to the balloon version of HERESY for the tip-tilt correction of atmospheric turbulence.

The design, construction, verification, and validation of each focal plane payload is discussed in detail. For HERESY’s balloon implementation, pointing error data from the Stratospheric Terahertz Observatory (STO) Antarctic balloon mission was used to form an experimental lab test setup to demonstrate the hexapod can eliminate jitter in flight-like conditions. For the suborbital rocket focal plane, a harsh set of unit-level tests to ensure the payload could survive launch and space conditions, as well as the characterization and optimization of the JPL detector, are detailed. Finally, a modification of co-mounting a fast-read detector to the HERESY focal plane, for use on ground-based observatories, intended to reduce atmospherically induced tip-tilt error through the centroid tracking of bright natural guidestars, is described.

Contributors

Agent

Created

Date Created
  • 2019