A SEARCH FOR FAST RADIO BURSTS WITH THE GBNCC SURVEY PRAGYA CHAWLA - - PowerPoint PPT Presentation

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A SEARCH FOR FAST RADIO BURSTS WITH THE GBNCC SURVEY PRAGYA CHAWLA - - PowerPoint PPT Presentation

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A SEARCH FOR FAST RADIO BURSTS WITH THE GBNCC SURVEY PRAGYA CHAWLA McGill University (On Behalf of the GBNCC Collaboration) P. Chawla 1 , V. M. Kaspi 1 , A. Josephy 1 , K. M. Rajwade 2 , D. R. Lorimer 2,3 , A. M. Archibald 4 , M. E. DeCesar 5 ,

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A SEARCH FOR FAST RADIO BURSTS WITH THE GBNCC SURVEY

PRAGYA CHAWLA McGill University (On Behalf of the GBNCC Collaboration)

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2 Pragya Chawla, McGill University December 9, 2016

  • 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 University 2Department of Physics and Astronomy, West Virginia University 3National Radio Astronomy Observatory, Green Bank 4ASTRON, the Netherlands Institute for Radio Astronomy 5Department of Physics, Lafayette College 6Anton Pannekoek Institute for Astronomy, University of Amsterdam 7Department of Physics, University of Wisconsin-Milwaukee 8Astro Space Center, Lebedev Physical Institute, Russian Academy of Sciences 9Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester 10National Radio Astronomy Observatory, Charlottesville 11New York University, Abu Dhabi 12Department of Physics and Astronomy, University of British Columbia 13National Radio Astronomy Observatory, Socorro

2017, ApJ, Submitted

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3 Pragya Chawla, McGill University December 9, 2016

FAST RADIO BURSTS

  • Millisecond-duration events
  • 1.4 DMMW < DM < 35 DMMW
  • Origin unknown, likely

extragalactic

  • 18 FRBs discovered till date in

the freq. range of 700 – 1500 MHz.

  • Scattering, spectral index and

free-free absorption could be possible reasons for non- detection at low frequencies.

DM = ׬

𝟏 𝒆 𝒐𝒇 ⅆ𝒎

𝐮𝐭𝐝𝐛𝐮𝐮 ∝ 𝛏−𝟓.𝟓

Thornton et al. 2013

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4 Pragya Chawla, McGill University December 9, 2016

FAST RADIO BURSTS

  • Millisecond-duration events
  • 1.4 DMMW < DM < 35 DMMW
  • Origin unknown, likely

extragalactic

  • 18 FRBs discovered till date in

the freq. range of 700 – 1500 MHz.

  • Scattering, spectral index and

free-free absorption could be possible reasons for non- detection at low frequencies.

DMMW Contours Based on NE2001 Model (Cordes & Lazio 2002)

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5 Pragya Chawla, McGill University December 9, 2016

FAST RADIO BURSTS

  • Millisecond-duration events
  • 1.4 DMMW < DM < 35 DMMW
  • Origin unknown, likely

extragalactic

  • 18 FRBs discovered till date in

the freq. range of 700 – 1500 MHz.

  • Scattering, spectral index and

free-free absorption could be possible reasons for non- detection at low frequencies.

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6 Pragya Chawla, McGill University December 9, 2016

THE GBNCC PULSAR SURVEY

  • Operates at 350 MHz with a

bandwidth of 100 MHz.

  • The analysis pipeline (Stovall et al.

2014) based on PRESTO (Ransom 2001) includes:

  • RFI Removal
  • Dedispersion
  • Single Pulse Search
  • Dispersion delays are corrected

for by dedispersing the data at a large number of trial DMs.

  • Single pulses are searched for by

convolving the dedispersed time series with boxcars of varying duration.

An Example Plot Generated by the Analysis Pipeline

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7 Pragya Chawla, McGill University December 9, 2016

THE GBNCC PULSAR SURVEY

  • 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

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8 Pragya Chawla, McGill University December 9, 2016

THE GBNCC PULSAR SURVEY

  • 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

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9 Pragya Chawla, McGill University December 9, 2016

THE GBNCC PULSAR SURVEY

  • Selected pointings with at least
  • ne pulse with S/N > 10.
  • 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

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10 Pragya Chawla, McGill University December 9, 2016

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.

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11 Pragya Chawla, McGill University December 9, 2016

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)
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12 Pragya Chawla, McGill University December 9, 2016

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-GHz flux density distribution (γ = 0.8, 1.2 or 1.5) Scale distribution to 350 MHz by sampling α from a normal distribution (σ = 0.5) Compute 350-MHz FRB rate above S = 0.63 Jy from the resulting distribution

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13 Generate 1.4-GHz flux density distribution Scale distribution to 350 MHz by sampling α from a normal distribution Assign tscatt drawn from a lognormal distribution to each detectable FRB (S > 0.65 Jy) Is tscatt for all FRBs > 100 ms? Increase mean of lognormal 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,

SCATTERING

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14 Pragya Chawla, McGill University December 9, 2016

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.

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15 Pragya Chawla, McGill University December 9, 2016

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.

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16 Pragya Chawla, McGill University December 9, 2016

PREDICTING FRB DETECTION RATES FOR OTHER SURVEYS

  • Limits on bursts per

hour arise because

  • f range of spectral

indices considered (αlim < α < +2).

  • No free-free

absorption assumed.

γ = 0.8

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17 Pragya Chawla, McGill University December 9, 2016

PREDICTING FRB DETECTION RATES FOR OTHER SURVEYS

  • 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 = 1.2

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18 Pragya Chawla, McGill University December 9, 2016

  • CHIME bandwidth

divided into 4 parts centered at 450, 550, 650 and 750 MHz.

  • For γ = 1.5,

simulations predict detection of 1-60 bursts a day for the freq. range

  • f 400-500 MHz.
  • For 700-800 MHz,

simulations predict 5-42 bursts a day.

PREDICTING FRB DETECTION RATES FOR CHIME

γ = 1.5

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19 Pragya Chawla, McGill University December 9, 2016

SUMMARY

  • No FRBs above a S/N of 10 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.