a search for fast radio bursts with the gbncc …

A SEARCH FOR FAST RADIO BURSTS WITH THE GBNCC SURVEYPRAGYA CHAWLAMcGill University(On Behalf of the GBNCC Collaboration)

2Pragya Chawla, McGill University February 12, 2017

P. Chawla1, V. M. Kaspi1, A. Josephy1, K. M. Rajwade2, D. R. Lorimer2,3, A. M. Archibald4, M. E. DeCesar5, J. W. T. Hessels4,6, D. L. Kaplan7, C. Karako-Argaman1, V. I. Kondratiev4,8, L. Levin9,

R. S. Lynch3, M. A. McLaughlin2, S. M. Ransom10, M. S. E. Roberts11, I. H. Stairs12, K. Stovall13, J. K. Swiggum7 and J. van

Leeuwen4,6

1Department of Physics & McGill Space Institute, McGill University2Department of Physics and Astronomy, West Virginia University

3National Radio Astronomy Observatory, Green Bank4ASTRON, the Netherlands Institute for Radio Astronomy

5Department of Physics, Lafayette College6Anton Pannekoek Institute for Astronomy, University of Amsterdam

7Department of Physics, University of Wisconsin-Milwaukee8Astro Space Center, Lebedev Physical Institute, Russian Academy of Sciences

9Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester10National Radio Astronomy Observatory, Charlottesville

11New York University, Abu Dhabi12Department of Physics and Astronomy, University of British Columbia

13National Radio Astronomy Observatory, Socorro

2017, ApJ, Submitted, arXiv:1701.07457


LOW-FREQUENCY SEARCHES FOR FRBs

• All known FRBs have been detected at frequencies > 700 MHz.

• Scattering, spectral index and free-free absorption could be possible reasons for non-detection at low frequencies.

• Low-frequency surveys with LOFAR, MWA and Arecibohave not resulted in any detections.


THE GBNCC PULSAR SURVEY

• Operates at 350 MHz with a bandwidth of 100 MHz.

• Conducted using the 100-m diameter Green Bank Telescope.

• The analysis pipeline (Stovall et al. 2014) based on PRESTO(Ransom 2001) includes:

• RFI Removal

• Dedispersion

• Single Pulse Search

GBNCC Survey Parameters

Sampling Time 81.92 μs

Integration Time 120 s

Gain 2 K/Jy

System Temperature 23 K

Bandwidth 100 MHz

Number of Freq. Channels

4096

Channel Bandwidth 0.0244 MHz

θFWHM 36 arcmin

Sky Coverage δ > -40°


SURVEY OBSERVATIONS

• Maximum DM for FRB search = 3000 pc cm-3 (for 45000 pointings).

• 17000 pointings searched to a DM of 500 pc cm-3 have maximum Galactic DM along LOS < 100 pc cm-3.

• Total observing time for all pointings = 84 days.

GBNCC Pointings Searched to DM = 3000 pc cm-3


SURVEY OBSERVATIONS

• Maximum DM for FRB search = 3000 pc cm-3 (for 45000 pointings).

• 17000 pointings searched to a DM of 500 pc cm-3 have maximum Galactic DM along LOS < 100 pc cm-3.

• Total observing time for all pointings = 84 days.

GBNCC Pointings Searched to DM = 500 pc cm-3


THE SEARCH FOR FRBs

• Single pulse events at DM > 2 DMMW were processed with the grouping and rating algorithm, RRATtrap.

• RRATtrap (Karako-Argaman et al. 2015) was developed to detect Rotating RAdio Transients (RRATs).

• Enabled discovery of 10 new RRATs in GBNCC data.

• RRATtrap output was inspected and no FRBs were detected.

All GBNCC Pointings Searched for FRBs


CALCULATION OF FRB RATE

• Assuming Poisson statistics, field of view = 0.41 sq. deg for the GBT beam and a threshold flux density of 0.63 Jy for a pulse of intrinsic width = 5 ms.

• We place a 95% confidence upper limit on FRB rate = 3.6 x 103 FRBs sky-1 day-1

at 350 MHz.


CONSTRAINING SPECTRAL INDICES OF FRBs

• Assuming a power-law flux density model for FRBs:

• Varying the index γ of the log N–log S function of the FRB population (γ = 0.8, 1.2 and 1.5) such that:

• Performing Monte Carlo simulations of FRB flux density distribution consistent with the 1.4-GHz rate estimate reported for the Parkes surveys by Crawford et al. (2016) (3.3 x 103 FRBs sky-1 day-1)


ABSENCE OF SCATTERING AND FREE-FREE ABSORPTION

γ αlim

0.8 +0.19

1.2 +0.28

1.5 +0.35

For constraining spectral index, αlim,

computed 350-MHz FRB rate = 95% confidence GBNCC upper limit

Generate 1.4-GHzflux densitydistribution

(γ = 0.8, 1.2 or 1.5)

Scale distribution to350 MHz by sampling

α from a normaldistribution (σ = 0.5)

Compute 350-MHzFRB rate above

S = 0.63 Jy from theresulting distribution


SCATTERING

Generate 1.4-GHzflux density

distribution

Scale distribution to350 MHz by sampling

α from a normaldistribution

Assign tscatt drawn froma lognormal distributionto each detectable FRB

(S > 0.65 Jy)

Is tscatt forall FRBs

> 100 ms?

Increase mean oflognormal dist.

FALSE

Mean scattering time for spectral index α =

mean of lognormal dist.

TRUE

γ αlim

0.8 -0.9

1.2 -0.6

1.5 -0.3

Given the observed range of scattering times and FRB rate, R, at 1.4 GHz,


PREDICTING FRB DETECTION RATES FOR OTHER SURVEYS

• Based on flux density distribution consistent with 1.4-GHz rate estimate for Parkes surveys.

• Distribution scaled to each survey’s center freq. by sampling α from a normal distribution.

• Scattering time for each FRB drawn from a lognormal distribution.



• Based on flux density distribution consistent with 1.4-GHz rate estimate for Parkes surveys.

• Distribution scaled to each survey’s center freq. by sampling α from a normal distribution.

• Scattering time for each FRB drawn from a lognormal distribution.

γ = 1.5



• Limits on bursts per hour arise because of range of spectral indices considered (αlim < α < +2).

• No free-free absorption assumed.

γ = 1.5



• Predictions consistent with upper limits reported for FRB searches with MWA (Tingay et al. 2015, Rowlinson et al. 2016), LOFAR(Coenen et al. 2014, Karastergiou et al. 2016), AO327(Deneva et al. 2016) and UTMOST (Caleb et al. 2016).

γ = 1.5


SUMMARY

• No FRBs were detected in GBNCC pointings amounting to a total observing time of 84 days.

• We place a 95% confidence upper limit on the FRB rate of 3.6 x 103

FRBs sky-1 day-1 above 0.63 Jy at 350 MHz.

• Non-detection with GBNCC is consistent with 1.4-GHz rate estimate for α > +0.35 in the absence of scattering and free-free absorption and α > -0.3 in the presence of scattering, for γ = 1.5.

• We predict CHIME to detect 3-54 bursts per day assuming the Crawford et al. rate estimate, for γ = 1.5.

a search for fast radio bursts with the gbncc …

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