Molecular transitions recently discovered at redshift zabs= 2.059 towards the bright background quasar J2123−0050 are analysed to limit cosmological variation in the proton‐to‐electron mass ratio, μ≡mp/me. Observed with the Keck telescope, the optical echelle spectrum has the highest resolving power and largest number (86) of H2 transitions in such analyses so far. Also, (seven) HD transitions are used for the first time to constrain μ‐variation. These factors, and an analysis employing the fewest possible free parameters, strongly constrain μ's relative deviation from the current laboratory value: Δμ/μ= (+5.6 ± 5.5stat± 2.9sys) × 10−6, indicating an insignificantly larger μ in the absorber. This is the first Keck result to complement recent null constraints from three systems at zabs > 2.5 observed with the Very Large Telescope. The main possible systematic errors stem from wavelength calibration uncertainties. In particular, distortions in the wavelength solution on echelle order scales are estimated to contribute approximately half the total systematic error component, but our estimate is model dependent and may therefore under or overestimate the real effect, if present. To assist future μ‐variation analyses of this kind, and other astrophysical studies of H2 in general, we provide a compilation of the most precise laboratory wavelengths and calculated parameters important for absorption‐line work with H2 transitions redwards of the hydrogen Lyman limit.
Fast radio bursts (FRBs) are bright, millisecond-duration radio transients originating from extragalactic distances 1 . Their origin is unknown. Some FRB sources emit repeat bursts, ruling out cataclysmic origins for those events [2][3][4] . Despite searches for periodicity in repeat burst arrival times on time scales from milliseconds to many days 2, 5-7 , these bursts have hitherto been observed to appear sporadically, and though clustered 8 , without a regular pattern. Here we report the detection of a 16.35 ± 0.18 day periodicity from a repeating FRB 180916.J0158+65 detected by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst Project (CHIME/FRB) 4, 9 . In 28 bursts recorded from 16th September 2018 through 30th October 2019, we find that bursts arrive in a 4.0-day phase window, with some cycles showing no bursts, and some showing multiple bursts, within CHIME's limited daily exposure. 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.Last year the CHIME/FRB collaboration reported the discovery of eight new repeating FRB sources 4 , including FRB 180916.J0158+65, which was recently localized to a star-forming region in a nearby massive spiral galaxy at redshift 0.0337±0.0002 10 . From September 2018 to November 2019, CHIME/FRB has detected a total of 28 bursts from FRB 180916.J0158+65, which remains the most active source from this recent CHIME/FRB repeater sample. The barycentric arrival times for the 28 bursts (including those has been published before) from FRB 180916.J0158+65, corrected for delays from pulse dispersion, are listed in Extended Data Table 1.To search for periodicity, the burst arrival times (spanning a 400-day time range) were folded with different periods from 1.57 to 62.8 days (see Methods), with a Pearson's χ 2 test applied to each resulting profile with 8 phase bins 11 . A reduced χ 2 1 with respect to a uniform distribution indicates a periodicity unlikely to arise by chance. Furthermore, to account for the possible non-Poissonian statistics of the bursts 12 , we have applied the search with different weighting schemes that consider clustered bursts of different time range to be correlated events (see Methods).Searches with different weightings return periodograms of similar shape and have the same primary peak with significance varying between 3.5 − 8σ. As an example, the reduced χ 2 versus period using a weighting that counts only active days instead of individual events is shown in Figure 1a. A distinct peak is detected at 16.35 ± 0.18 days, with
We present a catalog of 536 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 62 bursts from 18 previously reported repeating sources. The catalog represents the first large sample, including bursts from repeaters and nonrepeaters, 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 nonrepeaters 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 nonrepeaters 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—composing 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 α = − 1.40 ± 0.11 ( stat. ) − 0.09 + 0.06 ( sys. ) , consistent with the −3/2 expectation for a nonevolving population in Euclidean space. We find that α 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 [ 820 ± 60 ( stat. ) − 200 + 220 ( sys. ) ] / sky / day above a fluence of 5 Jy ms at 600 MHz, with a scattering time at 600 MHz under 10 ms and DM above 100 pc cm−3.
We report on the discovery of a high-velocity narrow absorption line outflow in the redshift 2.3 quasar J212329.46 − 005052.9. Five distinct outflow systems are detected with velocity shifts from −9710 to −14 050 km s −1 and C IV λλ1548, 1551 linewidths of FWHM ≈ 62-164 km s −1 . This outflow is remarkable for having high speeds and a degree of ionization similar to broad absorption line (BAL) flows, but linewidths roughly 100 times narrower than BALs and no apparent X-ray absorption. This is also, to our knowledge, the highest-velocity narrow absorption line system confirmed to be in a quasar outflow by all three indicators of line variability, smooth superthermal line profiles and doublet ratios that require partial covering of the quasar continuum source. All five systems have stronger absorption in O VI λλ1032, 1038 than C IV with no lower ionization metal lines detected. Their line variabilities also appear coordinated, with each system showing larger changes in C IV than O VI and line strength variations accompanied by nearly commensurate changes in the absorber covering fractions. The metallicity is approximately twice solar.These data require five distinct outflow structures with similar kinematics, physical conditions and characteristic sizes of order 0.01-0.02 pc (based on partial covering). The coordinated line variations, occurring on time-scales ≤0.63 yr (quasar frame), are best explained by global changes in the outflow ionization caused by changes in the quasar's ionizing flux. An upper limit on the acceleration, 3 km s −1 yr −1 , is consistent with blobs of gas that are gravitationally unbound and coasting freely 5 pc from the central black hole. Additional constraints from the variability time indicate that the full range of plausible distances is 5 R 1100 pc. However, if these small absorbing structures were created in the inner flow, they should be near the ∼5 pc minimum radius because they can travel just a few pc before dissipating (without external confinement). An apparent double line-lock in C IV suggests that the flow was radiatively accelerated and its present trajectory is within ∼16 • of the radial (line-of-sight) direction. The absence of strong X-ray absorption shows that radiative shielding in the far-UV and X-rays is not needed to maintain moderate BAL-like ionizations and therefore, apparently, it is not needed to facilitate the radiative acceleration to high speeds. We argue that the ionization is moderated, instead, by high gas densities in small outflow substructures. Finally, we estimate that the kinetic energy yield from this outflow is at least 2 orders of magnitude too low to be important for feedback to the host galaxy's evolution.
We report the detection of a single burst from the first-discovered repeating Fast Radio Burst source, FRB 121102, with CHIME/FRB, which operates in the frequency band 400-800 MHz. The detected burst occurred on 2018 November 19 and its emission extends down to at least 600 MHz, the lowest frequency detection of this source yet. The burst, detected with a significance of 23.7σ, has fluence 12±3 Jy ms and shows complex time and frequency morphology. The 34 ms width of the burst is the largest seen for this arXiv:1906.11305v1 [astro-ph.HE]
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