Abstract
The object FRB 20180916B is a well-studied repeating fast radio burst source. Its proximity (∼150 Mpc), along with detailed studies of the bursts, has revealed many clues about its nature, ...including a 16.3 day periodicity in its activity. Here we report on the detection of 18 bursts using LOFAR at 110–188 MHz, by far the lowest-frequency detections of any FRB to date. Some bursts are seen down to the lowest observed frequency of 110 MHz, suggesting that their spectra extend even lower. These observations provide an order-of-magnitude stronger constraint on the optical depth due to free–free absorption in the source’s local environment. The absence of circular polarization and nearly flat polarization angle curves are consistent with burst properties seen at 300–1700 MHz. Compared with higher frequencies, the larger burst widths (∼40–160 ms at 150 MHz) and lower linear polarization fractions are likely due to scattering. We find ∼2–3 rad m
−2
variations in the Faraday rotation measure that may be correlated with the activity cycle of the source. We compare the LOFAR burst arrival times to those of 38 previously published and 22 newly detected bursts from the uGMRT (200–450 MHz) and CHIME/FRB (400–800 MHz). Simultaneous observations show five CHIME/FRB bursts when no emission is detected by LOFAR. We find that the burst activity is systematically delayed toward lower frequencies by about 3 days from 600 to 150 MHz. We discuss these results in the context of a model in which FRB 20180916B is an interacting binary system featuring a neutron star and high-mass stellar companion.
We report on the detection of seven bursts from the periodically active, repeating fast radio burst (FRB) source FRB 180916.J0158+65 in the 300-400 MHz frequency range with the Green Bank Telescope ...(GBT). Emission in multiple bursts is visible down to the bottom of the GBT band, suggesting that the cutoff frequency (if it exists) for FRB emission is lower than 300 MHz. Observations were conducted during predicted periods of activity of the source, and had simultaneous coverage with the Low Frequency Array (LOFAR) and the FRB backend on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope. We find that one of the GBT-detected bursts has potentially associated emission in the CHIME band (400-800 MHz) but we detect no bursts in the LOFAR band (110-190 MHz), placing a limit of on the spectral index of broadband emission from the source. We also find that emission from the source is severely band-limited with burst bandwidths as low as ∼40 MHz. In addition, we place the strictest constraint on observable scattering of the source, <1.7 ms at 350 MHz, suggesting that the circumburst environment does not have strong scattering properties. Additionally, knowing that the circumburst environment is optically thin to free-free absorption at 300 MHz, we find evidence against the association of a hyper-compact H ii region or a young supernova remnant (age <50 yr) with the source.
Abstract
Fast radio burst (FRB) source FRB 20180916B exhibits a 16.33-day periodicity in its burst activity. It is as of yet unclear what proposed mechanism produces the activity, but polarization ...information is a key diagnostic. Here we report on the polarization properties of 44 bursts from FRB 20180916B detected between 2018 December and 2021 December by CHIME/FRB, the FRB project on the Canadian Hydrogen Intensity Mapping Experiment. In contrast to previous observations, we find significant variations in the Faraday rotation measure (RM) of FRB 20180916B. Over the 9-month period 2021 April and 2021 December we observe an apparent secular increase in RM of ∼50 rad m
−2
(a fractional change of over 40%) that is accompanied by a possible drift of the emitting band to lower frequencies. This interval displays very little variation in the dispersion measure (ΔDM ≲ 0.8 pc cm
−3
), which indicates that the observed RM evolution is likely produced from coherent changes in the Faraday-active medium’s magnetic field. Burst-to-burst RM variations appear unrelated to the activity cycle phase. The degree of linear polarization of our burst sample (≳80%) is consistent with the negligible depolarization expected for this source in the 400–800 MHz bandpass of CHIME. FRB 20180916B joins other repeating FRBs in displaying substantial RM evolution. This is consistent with the notion that repeater progenitors may be associated with young stellar populations by their preferential occupation of dynamic magnetized environments commonly found in supernova remnants, in pulsar wind nebulae, or near high-mass stellar companions.
Abstract
We report on the host association of FRB 20181030A, a repeating fast radio burst (FRB) with a low dispersion measure (103.5 pc cm
−3
) discovered by the CHIME/FRB Collaboration et al. Using ...baseband voltage data saved for its repeat bursts, we localize the FRB to a sky area of 5.3 arcmin
2
(90% confidence). Within the FRB localization region, we identify NGC 3252 as the most promising host with an estimated chance-coincidence probability <2.5 × 10
−3
. Moreover, we do not find any other galaxy with
M
r
< −15 AB mag within the localization region to the maximum estimated FRB redshift of 0.05. This rules out a dwarf host 5 times less luminous than any FRB host discovered to date. NGC 3252 is a star-forming spiral galaxy and at a distance of ≈20 Mpc, it is one of the closest FRB hosts discovered thus far. From our archival radio data search, we estimate a 3
σ
upper limit on the luminosity of a persistent compact radio source (source size < 0.3 kpc at 20 Mpc) at 3 GHz to be 2 × 10
26
erg s
−1
Hz
−1
, at least 1500 times smaller than that of the FRB 20121102A persistent radio source. We also argue that a population of young millisecond magnetars alone cannot explain the observed volumetric rate of repeating FRBs. Finally, FRB 20181030A is a promising source for constraining FRB emission models due to its proximity and we strongly encourage its multi-wavelength follow-up.
Abstract
Fast radio bursts (FRBs) display a confounding variety of burst properties and host-galaxy associations. Repeating FRBs offer insight into the FRB population by enabling spectral, temporal, ...and polarimetric properties to be tracked over time. Here, we report on the polarized observations of 12 repeating sources using multiyear monitoring with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) over 400–800 MHz. We observe significant rotation measure (RM) variations from many sources in our sample, including RM changes of several hundred radians per square meter over month timescales from FRBs 20181119A, 20190303A, and 20190417A, and more modest RM variability (ΔRM ≲ few tens of radians per square meter) from FRBs 20181030A, 20190208A, 20190213B, and 20190117A over equivalent timescales. Several repeaters display a frequency-dependent degree of linear polarization that is consistent with depolarization via scattering. Combining our measurements of RM variations with equivalent constraints on DM variability, we estimate the average line-of-sight magnetic field strength in the local environment of each repeater. In general, repeating FRBs display RM variations that are more prevalent and/or extreme than those seen from radio pulsars in the Milky Way and the Magellanic Clouds, suggesting repeating FRBs and pulsars occupy distinct magnetoionic environments.
Abstract
We present timing solutions for 12 pulsars discovered in the Green Bank North Celestial Cap 350 MHz pulsar survey, including six millisecond pulsars (MSPs), a double neutron star (DNS) ...system, and a pulsar orbiting a massive white dwarf companion. Timing solutions presented here include 350 and 820 MHz Green Bank Telescope data from initial confirmation and follow-up, as well as a dedicated timing campaign spanning 1 ryr PSR J1122−3546 is an isolated MSP, PSRs J1221−0633 and J1317−0157 are MSPs in black widow systems and regularly exhibit eclipses, and PSRs J2022+2534 and J2039−3616 are MSPs that can be timed with high precision and have been included in pulsar timing array experiments seeking to detect low-frequency gravitational waves. PSRs J1221−0633 and J2039−3616 have Fermi Large Area Telescope gamma-ray counterparts and also exhibit significant gamma-ray pulsations. We measure proper motions for three of the MSPs in this sample and estimate their space velocities, which are typical compared to those of other MSPs. We have detected the advance of periastron for PSR J1018−1523 and therefore measure the total mass of the DNS system,
m
tot
= 2.3 ± 0.3
M
⊙
. Long-term pulsar timing with data spanning more than 1 yr is critical for classifying recycled pulsars, carrying out detailed astrometry studies, and shedding light on the wealth of information in these systems post-discovery.
Determination of potentially-reversible factors contributing to exertional dyspnea remains an unmet clinical need in chronic thromboembolic pulmonary hypertension (CTEPH). Therefore, we aimed to ...evaluate the influence of inspiratory muscle weakness (IMW) on exercise capacity and dyspnea during effort in patients with CTEPH. We performed a prospective cross-sectional study that included thirty-nine consecutive patients with CTEPH (48 ± 15 yrs, 61% female) confirmed by right heart catheterization that underwent an incremental cardiopulmonary exercise test, 6-minute walk test and maximum inspiratory pressure (MIP) measurement. MIP < 70%pred was found in 46% of patients. On a multiple linear regression analysis, MIP was independently associated with 6MWD and Formula: see text. Patients with MIP < 70% presented greater Formula: see text than those with MIP ≥ 70%. Additionally, they also presented stronger sensations of dyspnea throughout exercise, even when adjusted for ventilation. At rest and at different levels of exercise, mean inspiratory flow (VT/TI) was significantly higher in patients with MIP < 70%. In conclusion, IMW is associated with a rapid increase of dyspnea, higher inspiratory load and poor exercise capacity in patients with CTEPH.
MYC locus rearrangements-often complex combinations of translocations, insertions, deletions and inversions-in multiple myeloma (MM) were thought to be a late progression event, which often did not ...involve immunoglobulin genes. Yet, germinal center activation of MYC expression has been reported to cause progression to MM in an MGUS (monoclonal gammopathy of undetermined significance)-prone mouse strain. Although previously detected in 16% of MM, we find MYC rearrangements in nearly 50% of MM, including smoldering MM, and they are heterogeneous in some cases. Rearrangements reposition MYC near a limited number of genes associated with conventional enhancers, but mostly with super-enhancers (e.g., IGH, IGL, IGK, NSMCE2, TXNDC5, FAM46C, FOXO3, IGJ, PRDM1). MYC rearrangements are associated with a significant increase of MYC expression that is monoallelic, but MM tumors lacking a rearrangement have biallelic MYC expression at significantly higher levels than in MGUS. We also have shown that germinal center activation of MYC does not cause MM in a mouse strain that rarely develops spontaneous MGUS. It appears that increased MYC expression at the MGUS/MM transition usually is biallelic, but sometimes can be monoallelic if there is an MYC rearrangement. Our data suggest that MYC rearrangements, regardless of when they occur during MM pathogenesis, provide one event that contributes to tumor autonomy.
Abstract
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 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 (simulated based on the NE2001 model) 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 that 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 may inhabit environments with more extreme properties than those inferred for pulsars in the Milky Way.
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