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 $z>1.8$.
The bright millisecond-duration radio burst from the Galactic magnetar SGR 1935+2154 in 2020 April was a landmark event, demonstrating that at least some fast radio burst (FRB) sources could be ...magnetars. The two-component burst was temporally coincident with peaks observed within a contemporaneous short X-ray burst envelope, marking the first instance where FRB-like bursts were observed to coincide with X-ray counterparts. In this study, we detail five new radio burst detections from SGR 1935+2154, observed by the CHIME/FRB instrument between October 2020 and December 2022. We develop a fast and efficient Bayesian inference pipeline that incorporates state-of-the-art Markov chain Monte Carlo techniques and use it to model the intensity data of these bursts under a flexible burst model. We revisit the 2020 April burst and corroborate that both the radio sub-components lead the corresponding peaks in their high-energy counterparts. For a burst observed in 2022 October, we find that our estimated radio pulse arrival time is contemporaneous with a short X-ray burst detected by GECAM and HEBS, and Konus-Wind and is consistent with the arrival time of a radio burst detected by GBT. We present flux and fluence estimates for all five bursts, employing an improved estimator for bursts detected in the side-lobes. We also present upper limits on radio emission for X-ray emission sources which were within CHIME/FRB's field-of-view at trigger time. Finally, we present our exposure and sensitivity analysis and estimate the Poisson rate for FRB-like events from SGR 1935+2154 to be \(0.005^{+0.082}_{-0.004}\) events/day above a fluence of \(10~\mathrm{kJy~ms}\) during the interval from 28 August 2018 to 1 December 2022, although we note this was measured during a time of great X-ray activity from the source.
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.
We study the 10 fast radio bursts (FRBs) detected in the far side-lobe region of the CHIME telescope from 2018 August 28 to 2021 August 31. We find that the far side-lobe events have on average ...\(\sim\)500 times greater fluxes than events detected in CHIME's main lobe. We show that the side-lobe sample is therefore statistically \(\sim\)20 times closer than the main-lobe sample. The median dispersion measure (DM) excess, after removing the Galactic disk component using the NE2001 for the free electron density distribution of the Milky Way, of the 10 far side-lobe and 471 non-repeating main-lobe FRBs in the first CHIME/FRB catalog is 183.0 and 433.9 pc\;cm\(^{-3}\), respectively. By comparing the DM excesses of the two populations under reasonable assumptions, we statistically constrain that the local degenerate contributions (from the Milky Way halo and the host galaxy) and the intergalactic contribution to the excess DM of the 471 non-repeating main-lobe FRBs for the NE2001 model are 131.2\(-\)158.3 and 302.7\(-\)275.6 pc cm\(^{-3}\), respectively, which corresponds to a median redshift for the main-lobe FRB sample of \(\sim\)0.3. These constraints are useful for population studies of FRBs, and in particular for constraining the location of the missing baryons.
We present a beam pattern measurement of the Canadian Hydrogen Intensity Mapping Experiment (CHIME) made using the Sun as a calibration source. As CHIME is a pure drift scan instrument, we rely on ...the seasonal North-South motion of the Sun to probe the beam at different elevations. This semiannual range in elevation, combined with the radio brightness of the Sun, enables a beam measurement which spans ~7,200 square degrees on the sky without the need to move the telescope. We take advantage of observations made near solar minimum to minimize the impact of solar variability, which is observed to be <10% in intensity over the observation period. The resulting data set is highly complementary to other CHIME beam measurements -- both in terms of angular coverage and systematics -- and plays an important role in the ongoing program to characterize the CHIME primary beam.
The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a drift scan radio telescope operating across the 400-800 MHz band. CHIME is located at the Dominion Radio Astrophysical Observatory near ...Penticton, BC Canada. The instrument is designed to map neutral hydrogen over the redshift range 0.8 to 2.5 to constrain the expansion history of the Universe. This goal drives the design features of the instrument. CHIME consists of four parallel cylindrical reflectors, oriented north-south, each 100 m \(\times\) 20 m and outfitted with a 256 element dual-polarization linear feed array. CHIME observes a two degree wide stripe covering the entire meridian at any given moment, observing 3/4 of the sky every day due to Earth rotation. An FX correlator utilizes FPGAs and GPUs to digitize and correlate the signals, with different correlation products generated for cosmological, fast radio burst, pulsar, VLBI, and 21 cm absorber backends. For the cosmology backend, the \(N_\mathrm{feed}^2\) correlation matrix is formed for 1024 frequency channels across the band every 31 ms. A data receiver system applies calibration and flagging and, for our primary cosmological data product, stacks redundant baselines and integrates for 10 s. We present an overview of the instrument, its performance metrics based on the first three years of science data, and we describe the current progress in characterizing CHIME's primary beam response. We also present maps of the sky derived from CHIME data; we are using versions of these maps for a cosmological stacking analysis as well as for investigation of Galactic foregrounds.
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 (CHIME). Radio observations ...acquired over 102 nights are used to construct maps which are foreground filtered and stacked on the angular and spectral locations of luminous red galaxies (LRG), emission line galaxies (ELG), and quasars (QSO) 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 \(7.1\sigma\) (LRG), \(5.7\sigma\) (ELG), and \(11.1\sigma\) (QSO). These are the first 21-cm intensity mapping measurements made with an interferometer. We constrain the effective clustering amplitude of neutral hydrogen (HI), defined as \(\mathcal{A}_{\rm HI}\equiv 10^{3}\,\Omega_\mathrm{HI}\left(b_\mathrm{HI}+\langle\,f\mu^{2}\rangle\right)\), where \(\Omega_\mathrm{HI}\) is the cosmic abundance of HI, \(b_\mathrm{HI}\) is the linear bias of HI, and \(\langle\,f\mu^{2}\rangle=0.552\) encodes the effect of redshift-space distortions at linear order. We find \(\mathcal{A}_\mathrm{HI}=1.51^{+3.60}_{-0.97}\) for LRGs \((z=0.84)\), \(\mathcal{A}_\mathrm{HI}=6.76^{+9.04}_{-3.79}\) for ELGs \((z=0.96)\), and \(\mathcal{A}_\mathrm{HI}=1.68^{+1.10}_{-0.67}\) 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 find a non-zero bias \(\Delta\,v= -66 \pm 20 \mathrm{km/s}\) 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.
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 \(z>1.8\).
Nanoparticles of Mn ferrite (MnxFe3−xO4, x = 0.0, 0.2, 0.6, and 0.8) have been successfully prepared by the co-precipitation method using the organic base ethanolamine as the chelating agent. The XRD ...measurements show well crystalline nano-ferrite particles with a lattice parameter gradually increasing with increasing Mn ions substitution. In contrast, XPS spectra show the existence of Mn3+ and Mn4+ with a crystalline size behavior. Small particle sizes and large specific surface areas in the range of 180–120 m2/g have been detected by HRTEM and BET measurements. The large values of specific surface areas nominate the samples to be good candidates for chemical and biological applications. The FT-IR and Raman spectra have supported the Rietveld refinement of XRD without forming any impurity phases. As Mn doping increases, the FMR and VSM mea-surements have indicated magnetic enhancement in the Mn nanoferrite.
•Nanosized MnxFe3−xO4 were prepared by the co-precipitation method.•Organic base ethanolamine was used as the chelating agent at preparation.•Lattice parameters gradually increased with increasing Mn concentration.•Large specific surface areas in the range of 180–120 m2/g was detected.•Spontaneous magnetization increased with increasing Mn concentration.
Manganese-doped Mn
x
Fe
3−
x
O
4
(
x
= 0.0, 0.2, 0.6, 0.8) spinel ferrites were produced
via
co-precipitation using the ethanolamine. XRD results confirmed the formation of the spinel phase. The ...well-crystallized particles of the ferrite spinel phase had linear sizes in the range of 5-9 nm. It was found that the lattice parameter increases gradually as the Mn concentration is increased. XPS data supported the presence of Mn
3+
and Mn
4+
in the nanosized crystallites. A large specific surface area of 124-143 m
2
g
−1
was calculated using HRTEM and BET. The spontaneous magnetization increases monotonically from ∼51 emu g
−1
for
x
= 0.0 up to ∼106 emu g
−1
for
x
= 0.8. By contrast, the remanent magnetization changed non-monotonically from ∼3 emu g
−1
for
x
= 0.0 up to ∼11 emu g
−1
for
x
= 0.8, with a local maximum of ∼7 emu g
−1
for
x
= 0.2 and a local minimum of ∼3 emu g
−1
for
x
= 0.6. The coercivity also changed non-monotonically from ∼4 Oe for
x
= 0.0 up to ∼9 Oe for
x
= 0.8, with a minimum of ∼1 Oe for
x
= 0.2. The ordered magnetic moments for each sub-lattice were computed. The large values of the specific surface area indicate that the samples are good candidates for chemical and biological applications. The FT-IR and Raman spectra obtained supported the Rietveld refinement of XRD without forming any impurity phases. With an increase in the Mn concentration, magnetic investigations indicated an enhancement in the magnetic parameters of the obtained nanostructured samples.
Samples of ferrite spinels doped with manganese cations were obtained
via
organic co-precipitation, and their structure, morphology and magnetic properties were studied.
