378 research outputs found
Regional CO2 fluxes estimated over North America for 2004 using a geostatistical inverse model
This article was submitted without an abstract, please refer to the full-text PDF file.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65108/2/ees9_6_042016.pd
A sample of low energy bursts from FRB 121102
We present 41 bursts from the first repeating fast radio burst discovered
(FRB 121102). A deep search has allowed us to probe unprecedentedly low burst
energies during two consecutive observations (separated by one day) using the
Arecibo telescope at 1.4 GHz. The bursts are generally detected in less than a
third of the 580-MHz observing bandwidth, demonstrating that narrow-band FRB
signals may be more common than previously thought. We show that the bursts are
likely faint versions of previously reported multi-component bursts. There is a
striking lack of bursts detected below 1.35 GHz and simultaneous VLA
observations at 3 GHz did not detect any of the 41 bursts, but did detect one
that was not seen with Arecibo, suggesting preferred radio emission frequencies
that vary with epoch. A power law approximation of the cumulative distribution
of burst energies yields an index that is much steeper than the
previously reported value of . The discrepancy may be evidence for a
more complex energy distribution. We place constraints on the possibility that
the associated persistent radio source is generated by the emission of many
faint bursts ( ms). We do not see a connection between burst
fluence and wait time. The distribution of wait times follows a log-normal
distribution centered around s; however, some bursts have wait times
below 1 s and as short as 26 ms, which is consistent with previous reports of a
bimodal distribution. We caution against exclusively integrating over the full
observing band during FRB searches, because this can lower signal-to-noise.Comment: Accepted version. 16 pages, 7 figures, 1 tabl
LOFAR observations of gravitational wave merger events: O3 results and O4 strategy
The electromagnetic counterparts to gravitational wave (GW) merger events
hold immense scientific value, but are difficult to detect due to the typically
large localisation errors associated with GW events. The Low-Frequency Array
(LOFAR) is an attractive GW follow-up instrument owing to its high sensitivity,
large instantaneous field of view, and ability to automatically trigger on
events to probe potential prompt emission within minutes. Here, we report on
144-MHz LOFAR radio observations of three GW merger events containing at least
one neutron star that were detected during the third GW observing run.
Specifically, we probe 9 and 16 per cent of the location probability density
maps of S190426c and S200213t, respectively, and place limits at the location
of an interesting optical transient (PS19hgw/AT2019wxt) found within the
localisation map of S191213g. While these GW events are not particularly
significant, we use multi-epoch LOFAR data to devise a sensitive wide-field GW
follow-up strategy to be used in future GW observing runs. In particular, we
improve on our previously published strategy by implementing direction
dependent calibration and mosaicing, resulting in nearly an order of magnitude
increase in sensitivity and more uniform coverage. We achieve a uniform
sensitivity of Jy across a single instantaneous LOFAR
pointing's 21 deg core, and a median sensitivity of 1.1 mJy when
including the full 89 deg hexagonal beam pattern. We also place the
deepest transient surface density limits yet on of order month timescales for
surveys between 60--340 MHz (0.017 deg above mJy and 0.073
deg above mJy).Comment: Replaced with accepted version for publication in MNRA
Global monthly averaged CO 2 fluxes recovered using a geostatistical inverse modeling approach: 1. Results using atmospheric measurements
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94622/1/jgrd14633.pd
Searching for the spectral depolarisation of ASKAP one-off FRB sources
Fast Radio Bursts (FRBs) are extragalactic transients of (sub-)millisecond duration that show wide-ranging spectral, temporal, and polarimetric properties. The polarimetric analysis of FRBs can be used to probe intervening media, study the emission mechanism, and test possible progenitor models. In particular, low-frequency depolarization of FRBs can identify dense, turbulent, magnetized, ionized plasma thought to be near the FRB progenitor. An ensemble of repeating FRBs has shown low-frequency depolarization. The depolarization is quantified by the parameter σRM, which correlates with proxies for both the turbulence and mean magnetic field strength of the putative plasma. However, while many non-repeating FRBs show comparable scattering (and hence inferred turbulence) to repeating FRBs, it is unclear whether their surrounding environments are comparable to those of repeating FRBs. To test this, we analyse the spectro-polarimetric properties of five one-off FRBs and one repeating FRB, detected and localized by the Australian Square Kilometer Array Pathfinder. We search for evidence of depolarization due to σRM and consider models where the depolarization is intrinsic to the source. We find no evidence (for or against) the sample showing spectral depolarization. Under the assumption that FRBs have multipath propagation-induced depolarization, the correlation between our constraint on and RM is consistent with repeating FRBs only if the values of σRM are much smaller than our upper limits. Additionally, the correlation between the constraints on σRM and τs is inconsistent with repeating FRBs. The observations provide further evidence for differences in the typical environments and sources of one-off and repeating FRBs
Constraining a neutron star merger origin for localized fast radio bursts
What the progenitors of fast radio bursts (FRBs) are, and whether there are
multiple types of progenitors are open questions. The advent of localized FRBs
with host galaxy redshifts allows the various emission models to be directly
tested for the first time. Given the recent localizations of two non-repeating
FRBs (FRB 180924 and FRB 190523), we discuss a selection of FRB emission models
and demonstrate how we can place constraints on key model parameters like the
magnetic field strength and age of the putative FRB-emitting neutron star. In
particular, we focus on models related to compact binary merger events
involving at least one neutron star, motivated by commonalities between the
host galaxies of the FRBs and the hosts of such merger events/short gamma-ray
bursts (SGRBs). We rule out the possibility that either FRB was produced during
the final inspiral stage of a merging binary system. Where possible, we predict
the light curve of electromagnetic emission associated with a given model and
use it to recommend multi-wavelength follow-up strategies that may help confirm
or rule out models for future FRBs. In addition, we conduct a targeted
sub-threshold search in Fermi Gamma-ray Burst Monitor data for potential SGRB
candidates associated with either FRB, and show what a non-detection means for
relevant models. The methodology presented in this study may be easily applied
to future localized FRBs, and adapted to sources with possibly core-collapse
supernova progenitors, to help constrain potential models for the FRB
population at large.Comment: MNRAS accepted version. Published in MNRAS, 12 pages, 6 figure
The utility of continuous atmospheric measurements for identifying biospheric CO 2 flux variability
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95026/1/jgrd16859.pd
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