Ben Stappers Jodrell Bank Centre for Astrophysics

University of Manchester -

with material from Petroff, Keane, Possenti, Thornton

FRBS IN A (LARGISH) NUTSHELL

RADIO TRANSIENTS• Searches for dispersed single pulses found repeating bursts in PMPS data

• RRATs – neutron stars with very sporadic detectable emission* • Also interested in highly dispersed single pulses; 2 possible examples • These searches then revealed an exciting new type of source!

* McLaughlin, et al. (2006)

Lorimer, et al. (2007) Keane, et al. (2012)

The “Lorimer burst”

DM = 375 cm-3 pc (15%) DM = 746 cm-3 pc (70%)

A POPULATION OF FAST RADIO BURSTS AT PARKES.• Four highly-dispersed single pulses in 24% of the high-latitude survey • DM = 944, 723, 1103, 553 cm-3 pc • Only 3-6% of the measured DM can be explained by MW – even lower than LB & KB (15%,70%) • None have been observed to repeat in follow up observations of many 10’s of hours.

FRB 110220

Thornton, Stappers et al 2013

ALSO SEEN AT ARECIBO & GBT(?) NOW

4

FRB 121102

• Galactic anticentre. (l=175,b=0.223) • DM (pc cm−3) 557.4 ± 2.0 • DMNE2001,max (pc cm−3) 188

Spitle

r et a

l. 201

4

POPULATION GROWING

5DM = 563 cm−3 pc, 16xNE2001

FRB 131104 - Ravi, Shannon, Jameson 2015 FRB011025 - Burke-Spoloar & Bannister 2014

DM = 790 cm−3 pc, 7xNE2001

FRB 140514 - Petroff et al 2015 +++ PKS bursts

DM = 780 cm−3 pc, 11xNE2001

EXTRAGALACTIC?

6

High DM values Scattering

Very precise cold plasma, ν-2, law. Scales close to ν-4 as expected

SOME CURRENT NUMBERS

7from numbers compiled by Keane.

INFERRING DISTANCE FROM APPARENT DM• Can model free electron density as fn. of redshift, z * • Contributions from host, IGM, MW, and intervening galaxy (possibly) • Deal in terms of delay across the observing band – not traditional DM

* Ioka (2003); Inoue (2004)

• How much dispersion from a host? • MW center maybe 700 cm-3 pc** • Likely much lower for source in an inclined

galactic disk • i = 60° DMhost ≈ 100 cm-3 pc

** Deneva, Cordes, & Lazio (2009)

TotalTIGMTHost

TMWDisp

ersiv

e Dela

y

Source Redshift

see Walker talk

i

~ 700 cm-3 pc

DMhost(i=60°) ~ 100 cm-3 pc

DMhost

iinter

DMinter

?

DMinter(iinter)

DMMW

DMMW(l, b)

DMIGM(z)

rest frame DMhost

ν ➔ν(1+z)

DISPERSION CONTRIBUTIONS

z = 0.81; Dcm = 2.8 Gpc z = 0.60; Dcm = 2.2 Gpc

RATES

• If • A) the intrinsic luminosity does not depend on distance and detectability depends only

on luminosity. • B) in a Euclidean universe then…

• The Lorimer burst had significantly higher fluence ~ 150 Jy ms and thus the rate of LBs should consequently be lower (225 sky-1 day-1) than measured here.

• Within significant uncertainties the LB and these FRBs are consistent with being from the same population of A) + B) objects

• Several experiments* (e.g. ATA, PALFA, VFASTR) have placed limits on this rate via non-detections: our result is consistent with the lack of detection by these searches.

• The large amount of on sky time means It should come as no surprise that Parkes has detected most of the FRBs to date

• Lots of caveats on the rates, small number of sources and recent developments suggest it may be a factor of 2-3 overestimated.

• See more of this in discussions in subsequent talks…..

Thornton, et al 2013

WHERE ARE THEY IN THE SKY

11From Petroff.

SKY DISTRIBUTION

12

Petro

ff et a

l. 201

4

Burke

-Spo

laor &

Ban

nister

2014

cosmological —- disagreement at 2.9 σ with low-lat rates

local/isotropic- —excluded at 3.6 σ

FRB events are simulated and the effects of dispersive smearing, interstellar scattering, and Tsky are also taken into account to estimate the effective S/N with which the pulse would be detected at Parkes radio telescope.

In [Bourke-Spolaor & Bannister 2014] isotropic local and cosmological distributions of sources are assumed

unscattered

scattered

WHAT ABOUT THE PERYTONS?• Swept frequency pulses – perytons* - have been seen at Parkes • Has been suggested that Lorimer burst is a peryton • Perytons are symmetrical in width and widths are W ~ 20 ms pulses • “DM” of the perytons peaks at 375 cm-3 pc with range 200—420 cm-3 pc • Found in all beams simultaneously: indicative of sidelobe detection or near field source. • “kinks” seen in dispersion sweep, i.e. not a pure power law. • Our narrow widths, wide spread of DMs, remarkable adherence to predictions of cold plasma

propagation – including scattering, single beam detections mean FRBs are not perytons • Low B values - 6 Perytons 0 FRBs! • Watch this space…..

* Burke-Spolaor, et al. (2011); Bagchi et al.(2012), Saint-Hilaire, Benz, Monstein2 2014, Petroff et al. 2015

Bleien Obs.Parkes

NON DETECTIONS

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LOFAR Pilot Survey

Coenen et al 2014

150 MHz, flat spectrum

New limits including LOFAR Single Station - Karastergiou et al. 2015 See also papers by Hassall et al 2013, Lorimer et al 2013 & Metzger et al. 2015 …. on limits and predictions.

VLA Fast Imaging

Law et al 2014

1.4 GHz, 166 hours

CURRENT SUMMARY

15

Given the so far observed parameters:

• Burst of ≈ millisecond duration

• Dispersion measure > 5-10 x the expected Milky Way contribution

• Dispersion delay = ν -2 : in two cases ν -2.003±0.006 and ν-2.000±0.006

• When measurable, scattering time follows ν -4.8±0.4 and ν -4.0±0.4

• Peak Flux density at 1.4 GHz ≈ 1 Jansky

• Rate ≈ 104 sky/day ≈ 10-3 MWgal/yr

Assuming extra-DM is mainly due to the IGM:

• Red-shift 0.2 < z < 1.3 (IGM from [Ioka 2003;Inoue 2004])

• Comoving distance 1 < D (Gpc) < 4

• Fluence 0.5 < F (Jy msec) < 8

• Isotropic luminosity 1038 < Liso (erg) < 1040

• Brightness temperature 1033 < T (K) < 1036

WHAT IS THE SOURCE OF FRBs?

WHAT IS THE SOURCE OF FRBs?

WHAT ARE THEY?

18

Kulkarni et al. 2014 provided a wide review of possibilities, from local radio interferences to high z cosmological sources

Suitable progenitor models are those which have an ultra-clean emitting region and, in addition, a low density circum-stellar medium so that external absorption is not significant. This means, almost always, that the free-free optical depth should not be large (for usual parameters, the plasma frequency is usually well below the GHz band)

Core Collapse SuperNovae (CCSN) [Thornton et al 2013] • energetics might work / environs not clean?

Binary White Dwarf merger to highly magnetic rapidly spinning White Dwarf [Kashiyama et al 2013]

• environs not clean enough?

Asteroid/Planet/WD magnetosphere interaction with the wind from a orbited pulsar/NS [Mottez & Zarka 2014]

• events should repeat with orbital period

Magnetar Giant Flares

19

• Energetic works (with 10-6 radio efficiency) and rate about right for Magnetars.

• Compatible with a clean enough environment [Kulkarni et al 14]

• Synchrotron maser mechanism from relativistic, magnetized shocks formed via the interaction of the magnetic pulse with the plasma within the nebula.

• A scattering tail appears when the medium is highly turbulent at the interface btw the plerion and star forming molecular clouds.

• Expected to be repeatable over decade-long timescale

• Also [Lyubarsky 2014] indicates that a strong detectable TeV ms-burst should be associated to these events and visible by Cerenkov detector up to ≈100 Mpc

Popov & Postnov 2007, Thornton et al 2013, Kulkarni et al 2014, Lu et al 2014

0 100 200 300 400Time, s

10

100

1000

10000

100000

Cou

nts/

0.5

s

GIANT FLARE FROM SGR1806-20 RHESSI DATA

COSMOLOGICAL PROBES

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The first measurement of the average density of the ionized component of the Inter Galactic Medium along 1000+ lines of sight.

Zheng et al 2014

He II reionization leads to a ∼ 8% jump in the differential DM across the He II reionization epoch. • likely need thousands of FRBs around z ∼ 2 − 3

The RM from IGM to z = 1 is only 6 rad m−2 for an IGM magnetic field of 10 nG. • tens of thousand of FRBs are needed to clearly

map out the redshift evolution of RM caused by the IGM magnetic field.

COSMOLOGICAL PROBES

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With a series of 100 to 1000’s independent z determination (from the identification of the source at other wavelengths), one could

• measure the missing baryonic matter in the Universe [e.g. through the investigations of galactic halos at 0.2-2 virial radii [MacQuinn 2014]]

• important parameter in galaxy formation and feedback models

• weigh baryons in the IGM [Deng & Zhang 2014] ; - > 50% baryons missing at z < 2 and most may reside at temperatures and densities that are difficult to detect with current methods

• constrain the EoS of the “dark energy” [Gao et al 2014; Zhou et al 2014] ;

• BUT there are issues with accuracy of the IGM model that is required.

• put limits to the existence of floating MACHO-like objects in the IGM via gravitational lensing (better with > 5 GHz observations) [Zheng et al. 2014]

Macquart et al. SKA Science book.

WHERE NEXT?• Definitely need to find more:

• Increase the population to understand the properties of the bursts • Distribution on the sky and how affected by local ISM properties • What is the luminosity distribution? Are they standard candles? • What is the source population? Only one? • Spectral properties in the radio • Higher redshifts etc….

• Rapid response to bursts - Petroff Talk • Follow up at other wavelengths (triggered/be-triggered) • Get host location, and even potentially location within host • Independent distance estimation. • More information to allow determination of source.

• IGM studies • Sufficiently large number of lines of sight to build IGM density model • Scattering in the IGM • Missing Baryons? • Ionisation properties and epochs. • Cosmological parameters…?

LOCALISATION - OBROCKA ET AL 2015

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Flux Density Ratio

Spectral index

FDR + SI

ONGOING AND UPCOMING FRB SEARCHES

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• HTRU-S - Champion Talk • SUPERB - New Search at Parkes - Hundreds of hours on sky (1.4 GHz) - Keane talk • PALFA - Ongoing search with Arecibo (1.4 GHz) • LOTAAS - LOFAR all sky survey (150 MHz) - Michilli Talk • LOFAR Single Station Search (150 MHz) - Karastergiou Talk • VLA Imaging surveys (1.4 GHz) • MWA - (100-200 MHz) • GHRSS - GMRT (350 MHz) - Bhattacharyya Talk • Various GBT searches (300 MHz) • Effelsberg - HTRU-N - Spitler Talk • Lovell Telescope (soon eMerlin)

• UTMOST — improved MOST (800 MHz) telescope - under construction • good detection rate, poor localisation — full funding pending

• CHIME — add transient capability to Hydrogen Intensity Mapping • if they can reach full capability lots of FRBs, but poor localisation - full funding pending.

MEERTRAP - FIND FRBS WITH MEERKAT

• Fully commensal beam-formed survey for fast transients including FRBs

• Large on sky team ensures many 10’s of FRBs will be found

• Use innovative techniques (Obrocka et al 2015) to localise transients (< arsceonds) rapidly

• Transient Buffers provide:

• Localisation to sub-arsecond to allow host-id even if no multi-lambda counterpart

• Ability to reprocess data to correct for beam effects on Flux and Polarisation

• Also can coherently dedisperse to get intrinsic width (some unresolved)

• Measure accurate positions for the bursts to enable their use as probes of the intergalactic medium and for testing cosmological models.

• Simultaneous optical through MeerLicht.

SQUARE KILOMETRE ARRAY

26Fender et al, Macquart et al. SKA Science book.

CONCLUSIONS • Discovered a new population of cosmologically interesting and useful radio sources • Parkes’ dedication to surveying means it is leading the way but other projects are coming online. • Detection of burst at Arecibo/GBT and clear distinction from Peryton’s confirming their status • Real-time detection, improved radio methods, and multi-wavelength follow-up may enable

identification of a host galaxy • Lots of exciting physics to be studied to do with the progenitors. • Exciting possibilities for studying the IGM and galaxy surroundings. • We are entering the era of real-time follow up of these bursts. • Next generation telescopes can revolutionise this field, and some already are

• MeerTRAP could find and precisely localise an extragalactic transient every few days on average.

• SKA will basically clean up!