58 research outputs found
A GPU Spatial Processing System for CHIME
We present an overview of the Graphics Processing Unit (GPU) based spatial
processing system created for the Canadian Hydrogen Intensity Mapping
Experiment (CHIME). The design employs AMD S9300x2 GPUs and readily-available
commercial hardware in its processing nodes to provide a cost- and
power-efficient processing substrate. These nodes are supported by a
liquid-cooling system which allows continuous operation with modest power
consumption and in all but the most adverse conditions. Capable of continuously
correlating 2048 receiver-polarizations across 400\,MHz of bandwidth, the CHIME
X-engine constitutes the most powerful radio correlator currently in existence.
It receives \,Tb/s of channelized data from CHIME's FPGA-based F-engine,
and the primary correlation task requires complex
multiply-and-accumulate operations per second. The same system also provides
formed-beam data products to commensal FRB and Pulsar experiments; it
constitutes a general spatial-processing system of unprecedented scale and
capability, with correspondingly great challenges in computation, data
transport, heat dissipation, and interference shielding
Possible periodic activity in the repeating FRB 121102
The discovery that at least some Fast Radio Bursts (FRBs) repeat has ruled out cataclysmic events as the progenitors of these particular bursts. FRB 121102 is the most well-studied repeating FRB but despite extensive monitoring of the source, no underlying pattern in the repetition has previously been identified. Here, we present the results from a radio monitoring campaign of FRB 121102 using the 76 m Lovell telescope. Using the pulses detected in the Lovell data along with pulses from the literature, we report a detection of periodic behaviour of the source over the span of 5 yr of data. We predict that the source is currently ‘off’ and that it should turn ‘on’ for the approximate MJD range 59002−59089 (2020 June 2 to 2020 August 28). This result, along with the recent detection of periodicity from another repeating FRB, highlights the need for long-term monitoring of repeating FRBs at a high cadence
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, , 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 , 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\,\,10\,deg\,hrs. Having seen no
bursts, we have constrained the rate of extremely bright events to
\,sky\,day above \,220 Jy\,ms
for between 1.3 and 100\,ms, at 400--800\,MHz. The non-detection also
allows us to rule out 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, 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- Forest
We report the detection of 21 cm emission at an average redshift in the cross-correlation of data from the Canadian Hydrogen Intensity
Mapping Experiment (CHIME) with measurements of the Lyman- forest from
eBOSS. Data collected by CHIME over 88 days in the ~MHz frequency band
() are formed into maps of the sky and high-pass delay filtered
to suppress the foreground power, corresponding to removing cosmological scales
with 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- forest flux
transmission spectra to estimate the 21 cm-Lyman- cross-correlation
function. Fitting a simulation-derived template function to this measurement
results in a detection significance. The coherent accumulation of the
signal through cross-correlation is sufficient to enable a detection despite
excess variance from foreground residuals 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
CHIME/FRB Detection of Eight New Repeating Fast Radio Burst Sources
We report on the discovery of eight repeating fast radio burst (FRB) sources
found using the Canadian Hydrogen Intensity Mapping Experiment (CHIME)
telescope. These sources span a dispersion measure (DM) range of 103.5 to 1281
pc cm. They display varying degrees of activity: six sources were
detected twice, another three times, and one ten times. These eight repeating
FRBs likely represent the bright and/or high-rate end of a distribution of
infrequently repeating sources. For all sources, we determine sky coordinates
with uncertainties of 10. FRB 180916.J0158+65 has a
burst-averaged DM = pc cm and a low DM excess over the
modelled Galactic maximum (as low as 20 pc cm); this source also
has a Faraday rotation measure (RM) of rad m, much
lower than the RM measured for FRB 121102. FRB 181030.J1054+73 has the lowest
DM for a repeater, pc cm, with a DM excess of 70
pc cm. Both sources are interesting targets for multi-wavelength
follow-up due to their apparent proximity. The DM distribution of our repeater
sample is statistically indistinguishable from that of the first 12 CHIME/FRB
sources that have not repeated. We find, with 4 significance, that
repeater bursts are generally wider than those of CHIME/FRB bursts that have
not repeated, suggesting different emission mechanisms. Our repeater events
show complex morphologies that are reminiscent of the first two discovered
repeating FRBs. The repetitive behavior of these sources will enable
interferometric localizations and subsequent host galaxy identifications.Comment: 40 pages, 11 figures; accepted by ApJL on 28 September 2019; added
analysis of correlation between width and max. flux densit
CHIME/FRB Discovery of 25 Repeating Fast Radio Burst Sources
We present the discovery of 25 new repeating fast radio burst (FRB) sources
found among CHIME/FRB events detected between 2019 September 30 and 2021 May 1.
The sources were found using a new clustering algorithm that looks for multiple
events co-located on the sky having similar dispersion measures (DMs). The new
repeaters have DMs ranging from 220 pc cm to 1700 pc
cm, and include sources having exhibited as few as two bursts to as many
as twelve. We report a statistically significant difference in both the DM and
extragalactic DM (eDM) distributions between repeating and apparently
nonrepeating sources, with repeaters having lower mean DM and eDM, and we
discuss the implications. We find no clear bimodality between the repetition
rates of repeaters and upper limits on repetition from apparently nonrepeating
sources after correcting for sensitivity and exposure effects, although some
active repeating sources stand out as anomalous. We measure the repeater
fraction and find that it tends to an equilibrium of % over
our exposure thus far. We also report on 14 more sources which are promising
repeating FRB candidates and which merit follow-up observations for
confirmation.Comment: Submitted to ApJ. Comments are welcome and follow-up observations are
encouraged
Sub-second periodicity in a fast radio burst
Fast radio bursts (FRBs) are millisecond-duration flashes of radio waves that
are visible at distances of billions of light-years. The nature of their
progenitors and their emission mechanism remain open astrophysical questions.
Here we report the detection of the multi-component FRB 20191221A and the
identification of a periodic separation of 216.8(1) ms between its components
with a significance of 6.5 sigmas. The long (~3 s) duration and nine or more
components forming the pulse profile make this source an outlier in the FRB
population. Such short periodicity provides strong evidence for a neutron-star
origin of the event. Moreover, our detection favours emission arising from the
neutron-star magnetosphere, as opposed to emission regions located further away
from the star, as predicted by some models.Comment: Updated to conform to the accepted versio
Periodic activity from a fast radio burst source
Fast radio bursts (FRBs) are bright, millisecond-duration radio transients
originating from extragalactic distances. Their origin is unknown. Some FRB
sources emit repeat bursts, ruling out cataclysmic origins for those events.
Despite searches for periodicity in repeat burst arrival times on time scales
from milliseconds to many days, these bursts have hitherto been observed to
appear sporadically, and though clustered, without a regular pattern. Here we
report the detection of a day periodicity (or possibly a
higher-frequency alias of that periodicity) from a repeating FRB
180916.J0158+65 detected by the Canadian Hydrogen Intensity Mapping Experiment
Fast Radio Burst Project (CHIME/FRB). In 38 bursts recorded from September
16th, 2018 through February 4th, 2020, we find that all bursts arrive in a
5-day phase window, and 50% of the bursts arrive in a 0.6-day phase window. Our
results suggest a mechanism for periodic modulation either of the burst
emission itself, or through external amplification or absorption, and disfavour
models invoking purely sporadic processes
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