the frb population: observations and theoryaspen17.phys.wvu.edu/petroff.pdf · the frb population:...

The FRB Population: Observations and Theory

Dr. Emily Petroff ASTRON

Aspen Winter Conference on FRBs 12 February, 2017

@ebpetroff www.ebpetroff.com

http://www.ebpetroff.com

What do we talk about when we talk about “population”

• 26 known FRB sources

• 18 published, 8 unpublished

• Out of ~1000s occurring every day

• Properties of the observed population

• What do they tell us about FRBs?

• How these can constrain theory?

• Sources that live at the edges

Emily Petroff, Aspen Winter Conference 2017

Observational basics• What do we measure?

• DM • pulse width • S/N*, (flux, fluence) • scatter broadening • DM index • scattering index • spectral index* • polarization • rotation measure Thornton et al.(2013)

*these depend heavily on where the FRB is located in the primary beam


Observations guiding theory• From these parameters we want:

• Progenitors! • Emission region size • Energetics • Distances, redshifts • Emission mechanism • Local density + B field • Host galaxy • IGM information • Galactic effects • Brightness distribution

?


Outline• Observational constraints on theory from specific

FRBs:

• and what these bursts can teach us re: physical properties of FRBs

• A new way to view the population - FRBCAT and new plotting tools

• Discussion


re: Progenitors A repeating FRB!

• FRB 121102

• 100+ pulses seen

• Same DM to within a few %

• Pulses with varying width/structure

• Detected from 5 GHz - 1.4 GHz

• Localized to a host galaxy (z~0.19273(8))

Emily Petroff, Aspen Winter Conference 2017Spitler et al. 2016

re: Progenitors• Limits:

• Extragalactic!!

• Non-cataclysmic progenitor

• Energy ~ 1038 erg

• Associated with stable radio source

• Located in dwarf galaxy


Chatterjee et al. 2017

re: Progenitors• No other FRBs seen to repeat

• Best constraints from FRB 131104 in 170 hours, FRB 140514/110220: >50 Hours

• Multiple progenitors?

• No robust evidence for two progenitors based on any other observed parameters

• BUT there are differences between FRB 121102 and many others in the population: width, frequency structure

• Different behavior at different source ages?

• Observational reasons: unlucky observing times, Parkes sensitivity, caught the brightest pulses in the pulse energy distribution


re: Emission region size• Light travel time

• Example: Crab nano-shot pulses 2 ns = 0.6 m light travel time

• Narrowest bursts give us this constraint

• FRB 150807: 0.35 ms = 105 km

• Many other FRB pulses unresolved in width when taking scattering time into account

FRB 150807; Ravi et al. 2016


re: Redshift• Looking at the FRB DM excess

• z ≤ DMexcess/1200

• Very basic, lots of assumptions, for IGM after He re-ionization (z < 3)

• No precise relation, but some indication of path of FRB

• Constrain bounds of population with both high and low DM FRBs Ioka 2003


re: Redshift• Using DM as an indicator for

distance:

• 0.05 < z < 2.1

• Heavily depends on density of progenitor region and models for DM-redshift relation

• Most FRBs still have DMs between 500 and 1,000 pc/cm3


re: Emission mechanism• First polarization results suggest coherent emission

(but we probably knew that already)FRB 140514

FRB 110523

FRB 150807 FRB 150418


re: Local magnetic field• FRB 110523

• High fractional linear polarization

• RM much higher than estimated foreground

• Ordered magnetic field local to progenitor or in host galaxy

• FRB 150807

• High fractional linear polarization

• Low RM consistent with estimates of Galactic foreground

• No ordered magnetic field in addition to Galactic contribution

• Two conflicting pictures

RM may give greatest insights into local environment!Emily Petroff, Aspen Winter Conference 2017

re: Galactic effectsHTRU

intHTRU high RRATs

FRB follow

upSUPERB P574 Total N FRBs

0 - 19.5 1157 402 483 0 700 281 3024 3

19.5 - 42 0 942 28 50 1115 10 2145 5

42 - 90 0 982 39 60 907 9 1998 8

See Shivani’s talk for more on this!Emily Petroff, Aspen Winter Conference 2017

re: Galactic effects• Growing number of detections in the Galactic Plane

• It can take 3x or 4x the observing to find an FRB in the plane

• Possible explanation: scintillation boosting in Galactic halo (Macquart & Johnston 2015)

• could have huge implications for measured vs intrinsic values (flux, spectral index)

• Models must take this into account


re: Brightness distribution

• No immediately obvious correlation between DM and S/N

• No evidence in data for standard candles

DMS/

N


Bringing it all together• Each of these parameters gives us one angle of

information

• Need to combine all angles to get a fuller picture of the physics behind FRBs

• Only a handful of measurements for each parameter with such a small population of FRBs

• Fortunately that’s about to change…


The big bright future


FRBCAT: A population tool

Petroff et al. (2016)http://www.astronomy.swin.edu.au/pulsar/frbcat/

@FRBCatalogue


FRBCAT: A population tool

• Expanding the functionality of the catalogue

• What features would you like to see? What functionality?

• Feedback welcome!

A quick demo!


Discussion Questions• What if FRBs arise from multiple populations?

• What will the most constraining parameters be for theorists going forward?

• How do we describe and name this growing population?

• Tradeoffs of two different types of experiments to find FRBs: High volume, poor localization

vs. Rare detections, precise localization

• Other discussion points?


the frb population: observations and theoryaspen17.phys.wvu.edu/petroff.pdf · the frb population:...

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