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We present an extensive contemporaneous X-ray and radio campaign performed on the repeating fast radio burst (FRB) source FRB 20220912A for 8 weeks immediately following the source's detection by CHIME/FRB. This includes X-ray data from XMM-Newton, NICER, and Swift, and radio detections of FRB 20220912A from CHIME/Pulsar and Effelsberg. We detect no significant X-ray emission at the time of 30 radio bursts with upper limits on a 0.5–10.0 keV X-ray fluence of (1.5–14.5) × 10−10 erg cm−2 (99.7% credible interval, unabsorbed) on a timescale of 100 ms. Translated into a fluence ratio η x/r = F X-ray/ F radio, this corresponds to η x/r < 7 × 106. For persistent emission from the location of FRB 20220912A, we derive a 99.7% 0.5–10.0 keV isotropic flux limit of 8.8 × 10−15 erg cm−2 s−1 (unabsorbed) or an isotropic luminosity limit of 1.4 × 1041 erg s−1 at a distance of 362.4 Mpc. We derive a hierarchical extension to the standard Bayesian treatment of low-count and background-contaminated X-ray data, which allows the robust combination of multiple observations. This methodology allows us to place the best (lowest) 99.7% credible interval upper limit on an FRB η x/r to date, η x/r < 2 × 106, assuming that all 30 detected radio bursts are associated with X-ray bursts with the same fluence ratio. If we instead adopt an X-ray spectrum similar to the X-ray burst observed contemporaneously with FRB-like emission from the Galactic magnetar SGR 1935+2154 detected on 2020 April 28, we derive a 99.7% credible interval upper limit on η x/r of 8 × 105, which is only 3 times the observed value of η x/r for SGR 1935+2154. [ABSTRACT FROM AUTHOR]

The CHIME/FRB project has detected hundreds of fast radio bursts (FRBs), providing an unparalleled population to statistically probe the foreground media that they illuminate. One such foreground medium is the ionized halo of the Milky Way (MW). We estimate the total Galactic electron column density from FRB dispersion measures (DMs) as a function of Galactic latitude using four different estimators, including ones that assume spherical symmetry of the ionized MW halo and ones that imply more latitudinal variation in density. Our observation-based constraints of the total Galactic DM contribution for ∣ b ∣ ≥ 30°, depending on the Galactic latitude and selected model, span 87.8–141 pc cm−3. This constraint implies upper limits on the MW halo DM contribution that range over 52–111 pc cm−3. We discuss the viability of various gas density profiles for the MW halo that have been used to estimate the halo's contribution to DMs of extragalactic sources. Several models overestimate the DM contribution, especially when assuming higher halo gas masses (∼3.5 × 1012 M ⊙). Some halo models predict a higher MW halo DM contribution than can be supported by our observations unless the effect of feedback is increased within them, highlighting the impact of feedback processes in galaxy formation. [ABSTRACT FROM AUTHOR]

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 400â€"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 62 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 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. [ABSTRACT FROM AUTHOR]

We present the results of Rossi X-ray Timing Explorer and Swift monitoring observations of the magnetar 1E 1547.0–5408 following the pulsar's radiative outbursts in 2008 October and 2009 January. We report on a study of the evolution of the timing properties and the pulsed flux from 2008 October 4 through 2009 December 26. In our timing study, a phase-coherent analysis shows that for the first 29 days following the 2008 outburst, there was a very fast increase in the magnitude of the rotational frequency derivative , such that was a factor of ∼60 larger than that reported in data from 2007. This magnitude increase occurred in concert with the decay of the pulsed flux following the start of the 2008 event. Following the 2009 outburst, for the first 23 days, was consistent with zero, and had returned to close to its 2007 value. In contrast to the 2008 event, the 2009 outburst showed a major increase in persistent flux, relatively little change in the pulsed flux, and sudden significant spectral hardening ∼15 days after the outburst. We show that, excluding the month following each of the outbursts, and because of the noise and the sparsity in the data, multiple plausible timing solutions fit the pulsar's frequency behavior. We note similarities in the behavior of 1E 1547.0–5408 following the 2008 outburst to that seen in the AXP 1E 1048.1–5937 following its 2001-2002 outburst and discuss this in terms of the magnetar model. [ABSTRACT FROM AUTHOR]