arXiv subjects

Masoud Rafiei-Ravandi

Publications and source records attributed to Masoud Rafiei-Ravandi.

40 records · Page 3Linked to original sources

arXiv2021

CHIME/FRB Catalog 1 results: statistical cross-correlations with large-scale structure

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.

astro-ph.CO↗

arXiv2021

Fast Radio Burst Morphology in the First CHIME/FRB Catalog

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.

astro-ph.HE↗

arXiv2019

Characterizing fast radio bursts through statistical cross-correlations

Understanding the origin of fast radio bursts (FRB's) is a central unsolved problem in astrophysics that is severely hampered by their poorly determined distance scale. Determining the redshift distribution of FRB's appears to require arcsecond angular resolution, in order to associate FRB's with host galaxies. In this paper, we forecast prospects for determining the redshift distribution without host galaxy associations, by cross-correlating FRB's 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 $\sim 10^3$ FRB's 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 FRB's 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 FRB's but the clustering of free electrons.

astro-ph.CO↗

arXiv2019

Observations of Fast Radio Bursts at Frequencies down to 400 Megahertz

Fast radio bursts (FRBs) are highly dispersed millisecond-duration radio flashes likely arriving from far outside the Milky Way galaxy. This phenomenon was discovered at radio frequencies near 1.4 GHz and to date 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 FRBs at radio frequencies as low as 400 MHz, on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) using the CHIME/FRB instrument. We present 13 FRBs 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 a variety of 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 it is among the closest yet known, and another has shown multiple repeat bursts, as described in a companion paper. Our low-scattering events suggest that efforts to detect FRBs at radio frequencies below 400 MHz will eventually be successful. 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 (ISM) in the Milky Way.

astro-ph.HE↗