9 research outputs found
Non-detection of CHIME/FRB sources with the Arecibo Observatory
In this work, we present follow-up observations of two known repeating fast
radio bursts (FRBs) and seven non-repeating FRBs with complex morphology
discovered with CHIME/FRB. These observations were conducted with the Arecibo
Observatory 327 MHz receiver. We detected no additional bursts from these
sources, nor did CHIME/FRB detect any additional bursts from these sources
during our follow-up program. Based on these non-detections, we provide
constraints on the repetition rate, for all nine sources. We calculate
repetition rates using both a Poisson distribution of repetition and the
Weibull distribution of repetition presented by Oppermann et al. (2018). For
both distributions, we find repetition upper limits of the order for all sources. These rates are much lower
than those recently published for notable repeating FRBs like FRB 20121102A and
FRB 20201124A, suggesting the possibility of a low-repetition sub-population.Comment: 12 pages, 4 figures, 5 tables; submitted to Ap
Comprehensive Bayesian analysis of FRB-like bursts from SGR 1935+2154 observed by CHIME/FRB
The bright millisecond-duration radio burst from the Galactic magnetar SGR
1935+2154 in 2020 April was a landmark event, demonstrating that at least some
fast radio burst (FRB) sources could be magnetars. The two-component burst was
temporally coincident with peaks observed within a contemporaneous short X-ray
burst envelope, marking the first instance where FRB-like bursts were observed
to coincide with X-ray counterparts. In this study, we detail five new radio
burst detections from SGR 1935+2154, observed by the CHIME/FRB instrument
between October 2020 and December 2022. We develop a fast and efficient
Bayesian inference pipeline that incorporates state-of-the-art Markov chain
Monte Carlo techniques and use it to model the intensity data of these bursts
under a flexible burst model. We revisit the 2020 April burst and corroborate
that both the radio sub-components lead the corresponding peaks in their
high-energy counterparts. For a burst observed in 2022 October, we find that
our estimated radio pulse arrival time is contemporaneous with a short X-ray
burst detected by GECAM and HEBS, and Konus-Wind and is consistent with the
arrival time of a radio burst detected by GBT. We present flux and fluence
estimates for all five bursts, employing an improved estimator for bursts
detected in the side-lobes. We also present upper limits on radio emission for
X-ray emission sources which were within CHIME/FRB's field-of-view at trigger
time. Finally, we present our exposure and sensitivity analysis and estimate
the Poisson rate for FRB-like events from SGR 1935+2154 to be
events/day above a fluence of
during the interval from 28 August 2018 to 1 December 2022, although we note
this was measured during a time of great X-ray activity from the source.Comment: 22 pages, 6 figures, 4 tables. To be submitted to Ap
A fast radio burst localized at detection to a galactic disk using very long baseline interferometry
Fast radio bursts (FRBs) are millisecond-duration, luminous radio transients
of extragalactic origin. These events have been used to trace the baryonic
structure of the Universe using their dispersion measure (DM) assuming that the
contribution from host galaxies can be reliably estimated. However,
contributions from the immediate environment of an FRB may dominate the
observed DM, thus making redshift estimates challenging without a robust host
galaxy association. Furthermore, while at least one Galactic burst has been
associated with a magnetar, other localized FRBs argue against magnetars as the
sole progenitor model. Precise localization within the host galaxy can
discriminate between progenitor models, a major goal of the field. Until now,
localizations on this spatial scale have only been carried out in follow-up
observations of repeating sources. Here we demonstrate the localization of FRB
20210603A with very long baseline interferometry (VLBI) on two baselines, using
data collected only at the time of detection. We localize the burst to SDSS
J004105.82+211331.9, an edge-on galaxy at , and detect recent
star formation in the kiloparsec-scale vicinity of the burst. The edge-on
inclination of the host galaxy allows for a unique comparison between the line
of sight towards the FRB and lines of sight towards known Galactic pulsars. The
DM, Faraday rotation measure (RM), and scattering suggest a progenitor
coincident with the host galactic plane, strengthening the link between the
environment of FRB 20210603A and the disk of its host galaxy. Single-pulse VLBI
localizations of FRBs to within their host galaxies, following the one
presented here, will further constrain the origins and host environments of
one-off FRBs.Comment: 40 pages, 13 figures, submitted. Fixed typo in abstrac
CHIME/FRB Discovery of 25 Repeating Fast Radio Burst Sources
We present the discovery of 25 new repeating fast radio burst (FRB) sources
found among CHIME/FRB events detected between 2019 September 30 and 2021 May 1.
The sources were found using a new clustering algorithm that looks for multiple
events co-located on the sky having similar dispersion measures (DMs). The new
repeaters have DMs ranging from 220 pc cm to 1700 pc
cm, and include sources having exhibited as few as two bursts to as many
as twelve. We report a statistically significant difference in both the DM and
extragalactic DM (eDM) distributions between repeating and apparently
nonrepeating sources, with repeaters having lower mean DM and eDM, and we
discuss the implications. We find no clear bimodality between the repetition
rates of repeaters and upper limits on repetition from apparently nonrepeating
sources after correcting for sensitivity and exposure effects, although some
active repeating sources stand out as anomalous. We measure the repeater
fraction and find that it tends to an equilibrium of % over
our exposure thus far. We also report on 14 more sources which are promising
repeating FRB candidates and which merit follow-up observations for
confirmation.Comment: Submitted to ApJ. Comments are welcome and follow-up observations are
encouraged
Water and Nitrogen Dynamics in Drip Fertigated Tomato for Water of Different Qualities under Polyhouse Conditions
Water and NO3-N dynamics in the soil during the growing season is an important tool in improving the nitrogen management and environmental protection. HYDRUS-2D has been widely used to predict the water and NO3-N distribution in the soil. The objective of this study was to simulate the water and NO3-N distribution in the soil under drip fertigated tomato irrigated with different water qualities under polyhouse conditions. Field data were collected on spatial and temporal distribution of water and available NO3-N during growing season. The model was calibrated for the hydraulic conductivity and parameters were used for the validation of the model. The model performance in simulating the water and NO3-N was evaluated by using coefficient of determination (R2), root mean square error (RMSE), index of agreement and Nash–Sutcliffe model efficiency (NSE). For both calibration and validation, the higher values of R2 from 0.70 to 0.99 for water distribution and 0.70 to 0.96 for NO3-N distribution showed that observed and predicted values are highly correlated. The value of RMSE ranges from 0.004 to 0.0016 for water and 0.002-0.006 for NO3-N distribution. The index of agreement value varied from 0.86-0.98 for water distribution and 0.89-0.99 for NO3-N distribution. The values of NSE (nearer to 1) i.e. 0.17 to 0.98 for water distribution and -0.09 to 0.94 for NO3-N distribution show that HYDRUS-2D was predicting with good accuracy. From these results, it can be concluded that the model performs well for predicting the water and NO3-N distribution in the tomato crop irrigated with different water qualities under polyhouse conditions
Discovery and characterization of novel CYP1B1 inhibitors based on heterocyclic chalcones: Overcoming cisplatin resistance in CYP1B1-overexpressing lines
© 2017 Elsevier Masson SAS The structure of alpha-napthoflavone (ANF), a potent inhibitor of CYP1A1 and CYP1B1, mimics the structure of chalcones. Two potent CYP1B1 inhibitors 7k (DMU2105) and 6j (DMU2139) have been identified from two series of synthetic pyridylchalcones. They inhibit human CYP1B1 enzyme bound to yeast-derived microsomes (Sacchrosomes™) with IC 50 values of 10 and 9nM, respectively, and show a very high level of selectivity towards CYP1B1 with respect to the IC 50 values obtained with CYP1A1, CYP1A2, CYP3A4, CYP2D6, CYP2C9 and CYP2C19 Sacchrosomes™. Both compounds also potently inhibit CYP1B1 expressed within ‘live’ recombinant yeast and human HEK293 kidney cells with IC 50 values of 63, 65, and 4, 4nM, respectively. Furthermore, the synthesized pyridylchalcones possess better solubility and lipophilicity values than ANF. Both compounds overcome cisplatin–resistance in HEK293 and A2780cells which results from CYP1B1 overexpression. These potent cell-permeable and water-soluble CYP1B1 inhibitors are likely to have useful roles in the treatment of cancer, glaucoma, ischemia and obesity