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Casey Law edited untitled.tex
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\section{Summary}
We report on the state of observing for the VLA FRB project, also known as 13B-409 and 14A-425. In the first 76 hours was observed under an approved DDT proposal and detected no events. Comparing our rate constraint to published rates revealed inconsistencies that led to an overestimate of the FRB rate. We discuss an improved rate estimate and the chance of detecting an FRB under program 14A-425, approved at priority C to bring the total observing time to 147 hours. Raising the priority of 14A-425 will help us complete observing and improve our chances of making the first interferometric detection of an FRB.
\section{Current Status}
Observations took place between late September 2013 and mid January
2014. 2014 (see Table \ref{fields}). The array was in CnB configuration for the first 10 hours observed, was being reconfigured during the next 10 hours of observing, and was in B configuration for the final 56 hours observed. We observed for a total of 76 hours and were on our target fields for 63.3 hours for an observing efficiency of 83\%.
\begin{table}
\caption{Survey Fields}
...
\label{fields}
\end{table}
Our analysis shows that we can exclude the presence All 63.3 hours of
astrophysical transients time on
timescales of 5 milliseconds and below. Here we use data quality metrics extragalctic fields has been searched for transients with dispersion measures from 0 to
measure the effective survey time and sensitivity.
We measured data quality 3000 pc cm$^{-3}$ at
regular intervals throughout the search. Image quality was measured by the standard deviation of pixel value and was found to have a roughly Gaussian distribution with a
long tail due to sporadic interference or bad calibration. Overall, roughly 1\% timescale of
images had noise that was more than twice 5 ms. Figure \ref{snrhist} shows the
median image noise. Our flux-calibrated observations have a median image noise typical SNR histogram of
12--14 mJy, as expected candidates greater than $6.5\sigma$, which are saved for
5-ms, L -band images made analysis. Nearly all candidates are consistent with
data thermal noise. Fewer than 10 candidates deviated slightly from
26 good antennas and 230 MHz of bandwidth. To include variance in the
thermal noise
measurements, we define a 96\% completeness for a $1\sigma$ image sensitivity distribution and were inspected in detail. All of
15 mJy these candidates were found to be affected by RFI or
an $8\sigma$ flux limit of 120 mJy. were highly sensitive to flagging or imaging parameters.
Our
tests show analysis shows that
we can exclude the
transient search pipeline reached the nominal sensitivity to dispersed pulses in 96\% presence of
the 63 hours astrophysical transients on
target fields. That allows us to use our nondetection to constrain timescales of 5 milliseconds and below. We measured data quality at regular intervals throughout the
FRB rate. Figure \ref{rate_pub} summarizes search and found that roughly 1\% of images had noise that was more than twice the
published FRB event rates median image noise. Our flux-calibrated observations have a median image noise of 12--14 mJy, as expected for 5-ms, L-band images made with data from 26 good antennas and
230 MHz of bandwidth. To include variance in the
VLA rate noise measurements, we define a 96\% completeness for a $1\sigma$ image sensitivity of 15 mJy or an $8\sigma$ flux limit
to FRBs shorter than our integration time of
5 ms. 120 mJy. Observations of pulsar B0355+54 at a range of offset positions shows that our end-to-end sensitivity scales as expected for the VLA primary beam gain pattern.
Constructing Figure \ref{rate_pub}
revealed summarizes the published FRB event rates and the VLA rate limit to FRBs shorter than our integration time of 5 ms. In constructing this figure, we discovered that the sensitivity of
most published surveys are defined
hetergeneously. inconsistently. \citet{2014arXiv1404.2934S} calculate the mean beam gain within the FWHM. \citet{2007Sci...318..777L} use the measured fluence of their detection to define a fluence limit.
\citet{BSB} do not quantify a fluence limit, but it can be inferred from the significance of their detection. Finally, \citet{2013Sci...341...53T} don't report a fluence limit at all, but instead measure the mean fluence of all detections.