The discovery of a repeating fast radio burst (FRB) source
, FRB 121102, eliminated models involving cataclysmic events for this source. No other repeating FRB has hitherto been detected despite many ...recent discoveries and follow-ups
, suggesting that repeaters may be rare in the FRB population. Here we report the detection of six repeat bursts from FRB 180814.J0422+73, one of the 13 FRBs detected
by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) FRB project
during its pre-commissioning phase in July and August 2018. These repeat bursts are consistent with originating from a single position on the sky, with the same dispersion measure, about 189 pc cm
. This traces approximately twice the expected Milky Way column density, and implies an upper limit on the source redshift of 0.1, at least a factor of about 2 closer than FRB 121102
. In some of the repeat bursts, we observe sub-pulse frequency structure, drifting, and spectral variation reminiscent of that seen in FRB 121102
, suggesting similar emission mechanisms and/or propagation effects. This second repeater, found among the first few CHIME/FRB discoveries, suggests that there exists-and that CHIME/FRB and other wide-field, sensitive radio telescopes will find-a substantial population of repeating FRBs.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Fast radio bursts (FRBs) are highly dispersed millisecond-duration radio flashes probably arriving from far outside the Milky Way
. This phenomenon was discovered at radio frequencies near 1.4 GHz ...and so far has been observed in one case
at as high as 8 GHz, but not below 700 MHz in spite of significant searches at low frequencies
. Here we report detections of 13 FRBs at radio frequencies as low as 400 MHz, on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) using the CHIME/FRB instrument
. They were detected during a telescope pre-commissioning phase, when our sensitivity and field-of-view were not yet at design specifications. Emission in multiple events is seen down to 400 MHz, the lowest radio frequency to which we are sensitive. The FRBs show various temporal scattering behaviours, with the majority significantly scattered, and some apparently unscattered to within measurement uncertainty even at our lowest frequencies. Of the 13 reported here, one event has the lowest dispersion measure yet reported, implying that it is among the closest yet known, and another has shown multiple repeat bursts, as described in a companion paper
. The overall scattering properties of our sample suggest that FRBs as a class are preferentially located in environments that scatter radio waves more strongly than the diffuse interstellar medium in the Milky Way.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The
β
-decay half lives of nuclei near the
r
-process path are critical information required for abundance calculations, especially those near neutron number
N
= 82. Specifically, the nuclei below ...doubly-magic
132
Sn are key, and play an important role in the formation and shape of the second
r
-process abundance peak. The half lives in this region are challenging to measure due to the significant
β
-delayed neutron decay branches and the population of isomeric states with half lives comparable to the ground states. However, by measuring the time distribution of γ rays, these complications can be eliminated. This requires, however, a very effcient γ-ray spectrometer since the production of isotopes in this region is very limited. The new GRIFFIN array at TRIUMF-ISAC provides the high effciency required for these measurements. Recent improvements in the quality of the beams produced at TRIUMF, employing the IG-LIS device, are outlined, as well as the current status of the ARIEL facility. The GRIFFIN spectrometer and its use are briefly described. The experiment to measure the half lives of
128-130
Cd is outlined and the results given, and some examples of the power of GRIFFIN to expand decay schemes, specifically for the decay of
128
Cd to
128
In, are given.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Excited states of \(^{129}\)In populated following the \(\beta\)-decay of \(^{129}\)Cd were experimentally studied with the GRIFFIN spectrometer at the ISAC facility of TRIUMF, Canada. A 480-MeV ...proton beam was impinged on a uranium carbide target and \(^{129}\)Cd was extracted using the Ion Guide Laser Ion Source (IG-LIS). \(\beta\)- and \(\gamma\)-rays following the decay of \(^{129}\)Cd were detected with the GRIFFIN spectrometer comprising the plastic scintillator SCEPTAR and 16 high-purity germanium (HPGe) clover-type detectors. %, along with the \(\beta\)-particles were detected with SCEPTAR. From the \(\beta\)-\(\gamma\)-\(\gamma\) coincidence analysis, 32 new transitions and 7 new excited states were established, expanding the previously known level scheme of \(^{129}\)In. The \(\log ft\) values deduced from the \(\beta\)-feeding intensities suggest that some of the high-lying states were populated by the \(\nu 0 g_{7/2} \rightarrow \pi 0 g_{9/2}\) allowed Gamow-Teller (GT) transition, which indicates that the allowed GT transition is more dominant in the \(^{129}\)Cd decay than previously reported. Observation of fragmented Gamow-Teller strengths is consistent with theoretical calculations.
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\(^{-3}\). 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 \(\sim\)10\(^\prime\). FRB 180916.J0158+65 has a burst-averaged DM = \(349.2 \pm 0.3\) pc cm\(^{-3}\) and a low DM excess over the modelled Galactic maximum (as low as \(\sim\)20 pc cm\(^{-3}\)); this source also has a Faraday rotation measure (RM) of \(-114.6 \pm 0.6\) rad m\(^{-2}\), much lower than the RM measured for FRB 121102. FRB 181030.J1054+73 has the lowest DM for a repeater, \(103.5 \pm 0.3\) pc cm\(^{-3}\), with a DM excess of \(\sim\) 70 pc cm\(^{-3}\). 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\(\sigma\) 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.
The discovery of a repeating Fast Radio Burst (FRB) source, FRB 121102, eliminated models involving cataclysmic events for this source. No other repeating FRB has yet been detected in spite of many ...recent FRB discoveries and follow-ups, suggesting repeaters may be rare in the FRB population. Here we report the detection of six repeat bursts from FRB 180814.J0422+73, one of the 13 FRBs detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) FRB project during its pre-commissioning phase in July and August 2018. These repeat bursts are consistent with originating from a single position on the sky, with the same dispersion measure (DM), ~189 pc cm-3. This DM is approximately twice the expected Milky Way column density, and implies an upper limit on the source redshift of 0.1, at least a factor of ~2 closer than FRB 121102. In some of the repeat bursts, we observe sub-pulse frequency structure, drifting, and spectral variation reminiscent of that seen in FRB 121102, suggesting similar emission mechanisms and/or propagation effects. This second repeater, found among the first few CHIME/FRB discoveries, suggests that there exists -- and that CHIME/FRB and other wide-field, sensitive radio telescopes will find -- a substantial population of repeating FRBs.
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