Characterization of the John A. Galt telescope for radio holography with CHIME

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) will measure the 21 cm emission of astrophysical neutral hydrogen to probe large scale structure at redshifts z=0.8-2.5. However, detecting the 21 cm signal beneath substantially brighter foregrounds remains a key challenge. Due to the high dynamic range between 21 cm and foreground emission, an exquisite calibration of instrument systematics, notably the telescope beam, is required to successfully filter out the foregrounds. One technique being used to achieve a high fidelity measurement of the CHIME beam is radio holography, wherein signals from each of CHIME's analog inputs are correlated with the signal from a co-located reference antenna, the 26 m John A. Galt telescope, as the 26 m Galt telescope tracks a bright point source transiting over CHIME. In this work we present an analysis of several of the Galt telescope's properties. We employ driftscan measurements of several bright sources, along with background estimates derived from the 408 MHz Haslam map, to estimate the Galt system temperature. To determine the Galt telescope's beam shape, we perform and analyze a raster scan of the bright radio source Cassiopeia A. Finally, we use early holographic measurements to measure the Galt telescope's geometry with respect to CHIME for the holographic analysis of the CHIME and Galt interferometric data set

Limits on the ultra-bright Fast Radio Burst population from the CHIME Pathfinder

We present results from a new incoherent-beam Fast Radio Burst (FRB) search on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) Pathfinder. Its large instantaneous field of view (FoV) and relative thermal insensitivity allow us to probe the ultra-bright tail of the FRB distribution, and to test a recent claim that this distribution's slope, $\alpha\equiv-\frac{\partial \log N}{\partial \log S}$, is quite small. A 256-input incoherent beamformer was deployed on the CHIME Pathfinder for this purpose. If the FRB distribution were described by a single power-law with $\alpha=0.7$, we would expect an FRB detection every few days, making this the fastest survey on sky at present. We collected 1268 hours of data, amounting to one of the largest exposures of any FRB survey, with over 2.4\,$\times$\,10$^5$\,deg$^2$\,hrs. Having seen no bursts, we have constrained the rate of extremely bright events to $<\!13$\,sky$^{-1}$\,day$^{-1}$ above $\sim$\,220$\sqrt{(\tau/\rm ms)}$ Jy\,ms for $\tau$ between 1.3 and 100\,ms, at 400--800\,MHz. The non-detection also allows us to rule out $\alpha\lesssim0.9$ with 95$\%$ confidence, after marginalizing over uncertainties in the GBT rate at 700--900\,MHz, though we show that for a cosmological population and a large dynamic range in flux density, $\alpha$ is brightness-dependent. Since FRBs now extend to large enough distances that non-Euclidean effects are significant, there is still expected to be a dearth of faint events and relative excess of bright events. Nevertheless we have constrained the allowed number of ultra-intense FRBs. While this does not have significant implications for deeper, large-FoV surveys like full CHIME and APERTIF, it does have important consequences for other wide-field, small dish experiments

A Detection of Cosmological 21 cm Emission from CHIME in Cross-correlation with eBOSS Measurements of the Lyman-α\alpha Forest

We report the detection of 21 cm emission at an average redshift $\bar{z} = 2.3$ in the cross-correlation of data from the Canadian Hydrogen Intensity Mapping Experiment (CHIME) with measurements of the Lyman-$\alpha$ forest from eBOSS. Data collected by CHIME over 88 days in the $400-500$~MHz frequency band ($1.8 < z < 2.5$) are formed into maps of the sky and high-pass delay filtered to suppress the foreground power, corresponding to removing cosmological scales with $k_\parallel \lesssim 0.13\ \text{Mpc}^{-1}$ at the average redshift. Line-of-sight spectra to the eBOSS background quasar locations are extracted from the CHIME maps and combined with the Lyman-$\alpha$ forest flux transmission spectra to estimate the 21 cm-Lyman-$\alpha$ cross-correlation function. Fitting a simulation-derived template function to this measurement results in a $9\sigma$ detection significance. The coherent accumulation of the signal through cross-correlation is sufficient to enable a detection despite excess variance from foreground residuals $\sim6-10$ times brighter than the expected thermal noise level in the correlation function. These results are the highest-redshift measurement of \tcm emission to date, and set the stage for future 21 cm intensity mapping analyses at $z>1.8$

Faraday Tomography with CHIME: The “Tadpole” Feature G137+7

A direct consequence of Faraday rotation is that the polarized radio sky does not resemble the total intensity sky at long wavelengths. We analyze G137+7, which is undetectable in total intensity but appears as a depolarization feature. We use the first polarization maps from the Canadian Hydrogen Intensity Mapping Experiment. Our 400–729 MHz bandwidth and angular resolution, – , allow us to use Faraday synthesis to analyze the polarization structure. In polarized intensity and polarization angle maps, we find a tail extending 10° from the head and designate the combined object, the tadpole. Similar polarization angles, distinct from the background, indicate that the head and tail are physically associated. The head appears as a depolarized ring in single channels, but wideband observations show that it is a Faraday rotation feature. Our investigations of H I and Hα find no connections to the tadpole. The tail suggests motion of either the gas or an ionizing star through the interstellar medium; the B2(e) star HD 20336 is a candidate. While the head features a coherent, ∼ ‑8 rad m‑2 Faraday depth, Faraday synthesis also identifies multiple components in both the head and tail. We verify the locations of the components in the spectra using QU fitting. Our results show that approximately octave-bandwidth Faraday rotation observations at ∼600 MHz are sensitive to low-density ionized or partially ionized gas, which is undetectable in other tracers

A detection of cosmological 21 cm emission from CHIME in cross-correlation with the eBOSS Lyman- forest

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a radio telescope that we built to map the large-scale structure of the Universe between redshifts 0.8 and 2.5, when dark energy is expected to begin the transition from a decelerating to an accelerating phase in the expansion of the Universe. CHIME was designed to perform an intensity mapping survey using the 21 cm line of neutral hydrogen, a novel method that has the potential to enable enormous surveys of the distant Universe, but also significant observational challenges to overcome. In this thesis, I describe contributions I made to the CHIME data acquisition system and calibration effort, culminating in a detection of cosmological 21 cm emission in cross-correlation with measurements of the Lyman- forest. The large data rate from the CHIME correlator is processed in real time by a high-performance digital pipeline, the development of which I participated in extensively. A few specific processing tasks where I led the design and implementation are highlighted in this work. In order to detect the 21 cm signal amidst the much brighter foreground emission from nearby sources, a very precise instrumental calibration is required. Calibrating the telescope's beam is a particular concern. One of many approaches being pursued for CHIME is the holographic observation of bright celestial sources in concert with a second radio telescope. I describe work I did to derive beam measurements from such observations and their analysis, including a scheme for calibrating the polarised beam response. I report the detection of 21 cm emission at an average redshift z = 2.3 in the cross-correlation of CHIME maps with measurements of the Lyman- forest from the eBOSS. Data collected by CHIME over 88 days in the 400-500 MHz frequency band (1.8 < z < 2.5) were formed into maps of the sky and high-pass delay filtered to suppress the foreground power. Line-of-sight spectra to the eBOSS background quasar locations were extracted from the CHIME maps and combined with the Lyman- forest flux transmission spectra to estimate the 21 cm-Lyman- cross-correlation function. Fitting a simulation-derived template to this measurement results in a detection of 9- significance.Science, Faculty ofPhysics and Astronomy, Department ofGraduat

Towards precision measurements of the Hubble constant with the Canadian Hydrogen Intensity Mapping Experiment

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a transit interferometer located at the Dominion Radio Astrophysical Observatory in Penticton, BC. It is designed to map large- scale structure in the universe by observing 21 cm emission from the hyperfine transition of neutral hydrogen between redshifts 0.8 and 2.5. CHIME will perform the largest volume survey of the universe yet attempted and will characterize the BAO scale and expansion history of the universe with unprecedented precision in this redshift range. CHIME achieved first light in the fall of 2017 and instrument commissioning is underway. In this work I present sensitivity forecasts and derive constraints on cosmological parameters given CHIME’s nominal survey. The broad redshift range of the observations will enable tight constraints to be placed on the Hubble constant H0 , independent of CMB or local recession velocity measurements. Precision measurements of this epoch will shed new light on the tension between direct measurements of the Hubble constant vs. those inferred from high-redshift observations, notably the CMB anisotropy. CHIME measurements together with a prior on the baryon density from measurements of deuterium abundance are enough to place constraints on H0 at the 0.5% level assuming a flat ΛCDM model, with uncertainty increasing to ∼ 1% if curvature is allowed to vary, or up to ∼ 3% for a dark energy equation of state with w/= −1. Including priors from CMB measurements, in the scenario where the datasets are consistent, narrows these uncertainties further, most significantly in the model where w is a free parameter.Science, Faculty ofPhysics and Astronomy, Department ofGraduat

A Detection of Cosmological 21 cm Emission from CHIME in Cross-correlation with eBOSS Measurements of the Lyα Forest

We report the detection of 21 cm emission at an average redshift $\bar{z}=2.3$ in the cross-correlation of data from the Canadian Hydrogen Intensity Mapping Experiment (CHIME) with measurements of the Ly α forest from eBOSS. Data collected by CHIME over 88 days in the 400–500 MHz frequency band (1.8 1.8

Detection of Cosmological 21 cm Emission with the Canadian Hydrogen Intensity Mapping Experiment

We present a detection of 21 cm emission from large-scale structure (LSS) between redshift 0.78 and 1.43 made with the Canadian Hydrogen Intensity Mapping Experiment. Radio observations acquired over 102 nights are used to construct maps that are foreground filtered and stacked on the angular and spectral locations of luminous red galaxies (LRGs), emission-line galaxies (ELGs), and quasars (QSOs) from the eBOSS clustering catalogs. We find decisive evidence for a detection when stacking on all three tracers of LSS, with the logarithm of the Bayes factor equal to 18.9 (LRG), 10.8 (ELG), and 56.3 (QSO). An alternative frequentist interpretation, based on the likelihood ratio test, yields a detection significance of 7.1 σ (LRG), 5.7 σ (ELG), and 11.1 σ (QSO). These are the first 21 cm intensity mapping measurements made with an interferometer. We constrain the effective clustering amplitude of neutral hydrogen (H i ), defined as ${{ \mathcal A }}_{{\rm{H}}\,{\rm\small{I}}}\equiv {10}^{3}\,{{\rm{\Omega }}}_{{\rm{H}}\,{\rm\small{I}}}\left({b}_{{\rm{H}}\,{\rm\small{I}}}+\langle \,f{\mu }^{2}\rangle \right)$ , where Ω _H _i is the cosmic abundance of H i , b _H _i is the linear bias of H i , and 〈 f μ ^2 〉 = 0.552 encodes the effect of redshift-space distortions at linear order. We find ${{ \mathcal A }}_{{\rm{H}}\,{\rm\small{I}}}={1.51}_{-0.97}^{+3.60}$ for LRGs ( z = 0.84), ${{ \mathcal A }}_{{\rm{H}}\,{\rm\small{I}}}={6.76}_{-3.79}^{+9.04}$ for ELGs ( z = 0.96), and ${{ \mathcal A }}_{{\rm{H}}\,{\rm\small{I}}}={1.68}_{-0.67}^{+1.10}$ for QSOs ( z = 1.20), with constraints limited by modeling uncertainties at nonlinear scales. We are also sensitive to bias in the spectroscopic redshifts of each tracer, and we find a nonzero bias Δ v = − 66 ± 20 km s ^−1 for the QSOs. We split the QSO catalog into three redshift bins and have a decisive detection in each, with the upper bin at z = 1.30 producing the highest-redshift 21 cm intensity mapping measurement thus far

The First CHIME/FRB Fast Radio Burst Catalog

We present a catalog of 535 fast radio bursts (FRBs) detected by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst (CHIME/FRB) Project between 400 and 800 MHz from 2018 July 25 to 2019 July 1, including 61 bursts from 18 previously reported repeating sources. The catalog represents the first large sample, including bursts from repeaters and non-repeaters, observed in a single survey with uniform selection effects. This facilitates comparative and absolute studies of the FRB population. We show that repeaters and apparent non-repeaters have sky locations and dispersion measures (DMs) that are consistent with being drawn from the same distribution. However, bursts from repeating sources differ from apparent non-repeaters in intrinsic temporal width and spectral bandwidth. Through injection of simulated events into our detection pipeline, we perform an absolute calibration of selection effects to account for systematic biases. We find evidence for a population of FRBs - comprising a large fraction of the overall population - with a scattering time at 600 MHz in excess of 10 ms, of which only a small fraction are observed by CHIME/FRB. We infer a power-law index for the cumulative fluence distribution of $\alpha=-1.40\pm0.11(\textrm{stat.})^{+0.060}_{-0.085}(\textrm{sys.})$, consistent with the $-3/2$ expectation for a non-evolving population in Euclidean space. We find $\alpha$ is steeper for high-DM events and shallower for low-DM events, which is what would be expected when DM is correlated with distance. We infer a sky rate of $[818\pm64(\textrm{stat.})^{+220}_{-200}({\textrm{sys.}})]/\textrm{sky}/\textrm{day}$ above a fluence of 5 Jy ms at 600 MHz, with scattering time at $600$ MHz under 10 ms, and DM above 100 pc cm$^{-3}$.Comment: 66 pages, 27 figures, 5 tables. Submitted to ApJ