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Register a new userCHIME/FRB Catalog 1 results: statistical cross-correlations with large-scale structure
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Added by
Masoud Rafiei-Ravandi
Publication date
2021
fields
Physics
and research's language is
English
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The CHIME/FRB Project has recently released its first catalog of fast radio bursts (FRBs), containing 492 unique sources. We present results from angular cross-correlations of CHIME/FRB sources with galaxy catalogs. We find a statistically significant ($p$-value $sim 10^{-4}$, accounting for look-elsewhere factors) cross-correlation between CHIME FRBs and galaxies in the redshift range $0.3 lesssim z lesssim 0.5$, in three photometric galaxy surveys: WISE$times$SCOS, DESI-BGS, and DESI-LRG. The level of cross-correlation is consistent with an order-one fraction of the CHIME FRBs being in the same dark matter halos as survey galaxies in this redshift range. We find statistical evidence for a population of FRBs with large host dispersion measure ($sim 400$ pc cm$^{-3}$), and show that this can plausibly arise from gas in large halos ($M sim 10^{14} M_odot$), for FRBs near the halo center ($r lesssim 100$ kpc). These results will improve in future CHIME/FRB catalogs, with more FRBs and better angular resolution.
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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 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 $alpha=-1.40pm0.11(textrm{stat.})^{+0.06}_{-0.09}(textrm{sys.})$, 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 $[820pm60(textrm{stat.})^{+220}_{-200}({textrm{sys.}})]/textrm{sky}/textrm{day}$ 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$^{-3}$.
Understanding the origin of fast radio bursts (FRBs) is a central unsolved problem in astrophysics that is severely hampered by their poorly determined distance scale. Determining the redshift distribution of FRBs appears to require arcsecond angular resolution, in order to associate FRBs with host galaxies. In this paper, we forecast prospects for determining the redshift distribution without host galaxy associations, by cross-correlating FRBs with a galaxy catalog such as the SDSS photometric sample. The forecasts are extremely promising: a survey such as CHIME/FRB that measures catalogs of $sim 10^3$ FRBs with few-arcminute angular resolution can place strong constraints on the FRB redshift distribution, by measuring the cross-correlation as a function of galaxy redshift $z$ and FRB dispersion measure $D$. In addition, propagation effects from free electron inhomogeneities modulate the observed FRB number density, either by shifting FRBs between dispersion measure (DM) bins or through DM-dependent selection effects. We show that these propagation effects, coupled with the spatial clustering between galaxies and free electrons, can produce FRB-galaxy correlations which are comparable to the intrinsic clustering signal. Such effects can be disentangled based on their angular and $(z, D)$ dependence, providing an opportunity to study not only FRBs but the clustering of free electrons.
We present a synthesis of fast radio burst (FRB) morphology (the change in flux as a function of time and frequency) as detected in the 400-800 MHz octave by the FRB project on the Canadian Hydrogen Intensity Mapping Experiment (CHIME/FRB), using events from the first CHIME/FRB catalog. The catalog consists of 61 bursts from 18 repeating sources, plus 474 one-off FRBs, detected between 2018 July 25 and 2019 July 2. We identify four observed archetypes of burst morphology (simple broadband, simple narrowband, temporally complex and downward drifting) and describe relevant instrumental biases that are essential for interpreting the observed morphologies. Using the catalog properties of the FRBs, we confirm that bursts from repeating sources, on average, have larger widths and we show, for the first time, that bursts from repeating sources, on average, are narrower in bandwidth. This difference could be due to a beaming or propagation effects, or it could be intrinsic to the populations. We discuss potential implications of these morphological differences for using FRBs as astrophysical tools.
We present a Monte Carlo-based population synthesis study of fast radio burst (FRB) dispersion and scattering focusing on the first catalog of sources detected with the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst (CHIME/FRB) project. We simulate intrinsic properties and propagation effects for a variety of FRB population models and compare the simulated distributions of dispersion measures (DMs) and scattering timescales with the corresponding distributions from the CHIME/FRB catalog. Our simulations confirm the results of previous population studies, which suggested that the interstellar medium of the host galaxy alone cannot explain the observed scattering timescales of FRBs. We therefore consider additional sources of scattering, namely, the circumgalactic medium (CGM) of intervening galaxies and the circumburst medium whose properties are modeled based on typical Galactic plane environments. We find that a population of FRBs with scattering contributed by these media is marginally consistent with the CHIME/FRB catalog. In this scenario, our simulations favor a population of FRBs offset from their galaxy centers over a population which is distributed along the spiral arms. However, if the models proposing the CGM as a source of intense scattering are incorrect, then we conclude that FRBs must inhabit environments with more extreme properties than those inferred for pulsars in the Milky Way.
We demonstrate the blind interferometric detection and localization of two fast radio bursts (FRBs) with 2- and 25-arcsecond precision on the 400-m baseline between the Canadian Hydrogen Intensity Mapping Experiment (CHIME) and the CHIME Pathfinder. In the same spirit as very long baseline interferometry (VLBI), the telescopes were synchronized to separate clocks, and the channelized voltage (herein referred to as baseband) data were saved to disk with correlation performed offline. The simultaneous wide field of view and high sensitivity required for blind FRB searches implies a high data rate -- 6.5 terabits per second (Tb/s) for CHIME and 0.8 Tb/s for the Pathfinder. Since such high data rates cannot be continuously saved, we buffer data from both telescopes locally in memory for $approx 40$ s, and write to disk upon receipt of a low-latency trigger from the CHIME Fast Radio Burst Instrument (CHIME/FRB). The $approx200$ deg$^2$ field of view of the two telescopes allows us to use in-field calibrators to synchronize the two telescopes without needing either separate calibrator observations or an atomic timing standard. In addition to our FRB observations, we analyze bright single pulses from the pulsars B0329+54 and B0355+54 to characterize systematic localization errors. Our results demonstrate the successful implementation of key software, triggering, and calibration challenges for CHIME/FRB Outriggers: cylindrical VLBI outrigger telescopes which, along with the CHIME telescope, will localize thousands of single FRB events to 50 milliarcsecond precision.
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