The Mind Reels - West Virginia Universityaspen17.phys.wvu.edu/BurkeSpolaor.pdf · CHIME Parkes...

We know both too much, and not quite enough.

The Mind Reels S. Burke-SpolaorWest Virginia University

“Future surveys, strategies, and capabilities”

The Main FRB Questions

What makes FRBs?

How are FRBs made?

What can we use them for?

?

ASKAPEVN

HIRAX

DSA10

FRBs

HERA

Scientific things that are most important …?

Localization. [gateway to cosmology and progenitor identification]

Detection rates. [basic FRB statistics & diagnostics]

Broad frequency coverage.[constrains emission mechanism and location]

Polarization measurements. [constrains emission mechanism, location, and maybe progenitor classes]

Figure out the “Hessels bumps”. [understand the nature of our best-characterized burst]

Bizarre Burst Spectra

Conceptual search things that are important …?❖ What do we want to DO with FRBs?

❖ What is making them? [localization, detection rate].

❖ What can we do with them? [localization, detection rate].

❖ What are their average properties? [localization, detection rate].

❖ Telescope Design.

❖ Maximize science potential.

❖ Survey Strategy.

❖ “Look deep” vs “scan wide”. Specific target class searches?

❖ Multi-frequency follow-up.

❖ Rapidity of processing [follow-up and data triage].

❖ Follow-up studies.

1.

Telescope design:Detection rate vs. Localization

Localization

0

0.2

0.4

0.6

0.8

1

10 15 20 25 30

1 arcsec

[VLA]

10 arcsec

1 arcmin

10 arcmin

[Single-dish]FR

B121

102

host

Con

fiden

ce in

ass

ocia

tion

Host Magnitude

95% confidence in association

Constructed based on Bloom et al (2002)

Localization

0

0.2

0.4

0.6

0.8

1

10 15 20 25 30

1 arcsec

[VLA]

10 arcsec

1 arcmin

10 arcmin

[Single-dish]FR

B121

102

host

Con

fiden

ce in

ass

ocia

tion

Host Magnitude


Questions that need quantification:

What extra confidence does a DM-based redshift limit buy us?

Will confidence improve if “all” (say, the first 5) precisely localized FRBs all come

from galaxies with similar weird properties (e.g. dwarf with strong emission lines)?

NO!!!

Localization

0

0.2

0.4

0.6

0.8

1

10 15 20 25 30

1 arcsec

[VLA]

10 arcsec

1 arcmin

10 arcmin

[Single-dish]FR

B121

102

host

Con

fiden

ce in

ass

ocia

tion

Host Magnitude


Constructed based on Bloom et al (2002)

Comparing telescope designs

❖ Assumptions

❖ Dispersion index -2, scattering index -4.

❖ FRBs are a broadband phenomenon. (i.e. they have a spectral index, scattering, and DM effects)

❖ No free-free absorption effects explicitly.

Considering❖ Telescope parameters

❖ FRB parameters

❖ wintrinsic τscat <DMx>

❖ γ (lum func index) α (spectral index)

SEFD including medlat sky

f center frequency

B (actual) total bandwidth

b freq resolution

tsamp time sampling

Ω field of view

N number of elements

Observing duty cycle(Over a year, how many hours

searched on an average?)

Localization of 7σ event(effective error radius)

Our FRB science playing field.FRB detection and localization landscape, ~2018

Typi

cal L

ocal

izat

ion

(arc

seco

nds)

0.1

1

10

100

1000

FRB Detections Per Year1 10 100 1000

z=0.22

Note: Insufficient (or late-arriving) parameters for FAST, HERA, HIRAX, and LOFAR!Note2: LWA, eMerlin, and Arecibo (PALFA) aren’t within the axes.

FRB detection and localization landscape, ~2020

Typi

cal L

ocal

izat

ion

(arc

seco

nds)

0.1

1

10

100

1000


Our FRB science playing field.

VLA(2020)

GBT 350MHz

CHIME

Parkes

VLA (2018)ASKAP

z=0.22

Molonglo 2DMeerKATDSA-10

FRB params:100us < wint < 3ms

0 < τscat (1GHz) < 3ms<DMx> = 400-800 pc/cc

-1.5 < γ < -0.5-1.0 < α < 2.0

MWA

Molonglo 1D

APERTIF


Typi

cal L

ocal

izat

ion

(arc

seco

nds)

0.1

1

10

100

1000



VLA(2020)

Molonglo 1DGBT 350MHz

CHIME

Parkes

VLA (2018)

z=0.22

Molonglo 2DMeerKAT

DSA-10

FRB params:0 < τscat (1GHz) < 3ms<DMx> = 400-800 pc/cc

-1.5 < γ < -0.5-1.0 < α < 2.0

MWA

ASKAP

wint = 100 us

APERTIF


Typi

cal L

ocal

izat

ion

(arc

seco

nds)

0.1

1

10

100

1000



VLA(2020)

GBT

CHIME

Parkes

VLA (2018)ASKAP

z=0.22



<DMx> = 400-800 pc/cc

-1.5 < γ < -0.5-1.0 < α < 2.0

MWA

Molonglo 1D

τscat (1GHz) = 3ms

APERTIF


Typi

cal L

ocal

izat

ion

(arc

seco

nds)

0.1

1

10

100

1000



VLA(2020)

GBT 350MHz

CHIME

Parkes

VLA (2018) ASKAP

z=0.22

Molonglo 2DMeerKAT

DSA-10

MWA

Molonglo 1D



-1.0 < α < 2.0

γ = -0.5

APERTIF


Typi

cal L

ocal

izat

ion

(arc

seco

nds)

0.1

1

10

100

1000



GBT 350MHz

CHIME

Parkes

VLA-S (2018)

ASKAP

z=0.22




-1.5 < γ < -0.5-1.0 < α < 2.0

MWA

Molonglo 1D

VLA-L(18)

VLA-C (2020)

VLA-X (2020)

VLA-L(20)

APERTIF


Typi

cal L

ocal

izat

ion

(arc

seco

nds)

0.1

1

10

100

1000



GBT 350MHz

CHIME

Parkes

VLA-S (2018)

ASKAP

z=0.22

Molonglo 2DMeerKAT

DSA-10



-1.0 < α < 2.0

MWA

Molonglo 1D

VLA-L(18)

γ = -1.5

VLA-C (2020)

VLA-X (2020)

VLA-L(20)

APERTIF


Typi

cal L

ocal

izat

ion

(arc

seco

nds)

0.1

1

10

100

1000



VLA-C

GBT

CHIME

Parkes

VLA-S

ASKAP

z=0.22

Molonglo MeerKAT

DSA-10



MWA

Molonglo 1D

VLA-L(18)

VLA-X

γ = -1.5α = 0.0

VLA-L(20)

APERTIF


Typi

cal L

ocal

izat

ion

(arc

seco

nds)

0.1

1

10

100

1000



VLA-C

G

CHIME

Parkes

VLA-S

ASKAP

z=0.22

M MeerKAT

DSA-10



M

Molonglo 1D

VLA-L(18)

VLA-X

γ = -1.5α = +2.0

VLA-L(20)

APERTIF


Typi

cal L

ocal

izat

ion

(arc

seco

nds)

0.1

1

10

100

1000



GBT 350MHz

CHIME

Parkes

VLA-S (2018)

ASKAP

z=0.22




-1.5 < γ < -0.5-1.0 < α < 2.0

MWA

Molonglo 1D

VLA-L(18)

VLA-C (2020)

VLA-X (2020)

VLA-L(20)

APERTIF

Lessons?❖ Different instruments have their merits.

❖ Optimal telescope still depends on too many unknowns.

❖ Molonglo2D, ASKAP: great if dNdS is flat. Still good if not.

❖ VLA: strong probe of rising-spectrum FRBs. Observing NOW! Sensitivity likely to improve over next few years.

❖ APERTIF: don’t stop at a fixed survey!

❖ DSA-10 stand the FRB rate knob tests.

❖ Caveat: not yet on sky. Will it float?

❖ 10 dishes operational mid-2017.

❖ Future: possible expansion.

❖ CHIME: can’t slow it down.

How can other telescopes improve localization?❖ Outriggers.

❖ Too expensive? Worth it for CHIME?

❖ Trigger other (bigger) telescope at lower frequency?

❖ Europe: LOFAR.

❖ Australia: MWA.

❖ USA: LWA-OV, LWA-NM, LOFASM, VLA-Pband.

❖ Clever beam-forming techniques.

2.

Survey Strategies

Targeting Fields: Maximum Return

upcoming observations

Our limits with FRB-SFR

correlation

Realfast limits if no FRB-SFR correlation

Burke-Spolaor et al. in prep

Champion+15 rate

Thornton+13 rate

95% confidence limit

50% confidence limit

95% confidencelimits

Targeting Fields: Maximum Return

A great field selection will have multi-wavelength reference images (and spectra?).

NGC2146

Slow-sampled

Other considerations…

❖ Optical/multi-f *coordination*.

❖ Triggering real-time, low-frequency FRB observation.

❖ Wait for CHIME or attempt it now?

❖ Deep/lengthy repeater searches.

❖ “Scan wide” to map the sky distribution.

3.

Upcoming FRB science:Understanding FRB Progenitors

Radio: Evidence of FRB progenitor(s)❖ Specific progenitors

❖ DM, RM, polarization, τscat, fscint measurements.

❖ The Hessels spectral features.

❖ Host galaxy studies of localized FRBs.

❖ Counterparts/afterglows.

❖ Evidence for multiple populations

❖ Conclusive evidence for cataclysm (afterglow or LIGO).

❖ Statistical evidence.

Host Galaxy Analysis❖ Hogg & Fruchter (1999): 11 localized GRBs.

❖ Already inferred 2 progenitor populations!

❖ Used host distributions and simple rate vs. z models.

❖ Bloom et al. (2002): 20 localized long GRBs.

❖ Offsets and association with UV light.

❖ Implication: association with star formation but NOT NS-NS merger.

STIS/Clear HST

2.0"

9 kpc

GRB 990705

Fig. 2p

GRB 990712

STIS/Clear HST

3 kpc1.0"

Fig. 2q

1130

use the GRB redshifts (and, below, host magnitudes) com-piled in the review by Kulkarni et al. (2000). The resultingphysical projected distribution is depicted in Figure 3 andgiven in Table 2. The median projected physical offset of the20GRBs in the sample is 1.31 kpc or 1.10 kpc including onlythose 15 GRBs for which a redshift was measured. The min-imum offset found is just 91 ! 90 pc from the host center(GRB 970508).

6.3. Host-normalized Projected Offset

If GRBs were to arise from massive stars we would thenexpect that the distribution of GRB offsets would follow thedistribution of the light of their hosts. As can be seen in Fig-ure 2, qualitatively this appears to be the case since almostall localizations fall on or near the detectable light of agalaxy.

The next step in the analysis is to study the offsets, butnormalized by the half-light radius of the host. This stepthen allows us to consider all the offsets in a uniform man-ner. The half-light radius, Rhalf, is estimated directly fromSTIS images with sufficiently high signal-to-noise ratio, andin the remaining cases we use the empirical half-lightradius–magnitude relation of Odewahn et al. (1996); we usethe dereddened R-band magnitudes found in the GRB hostsummaries from Djorgovski et al. (2002b) and Sokolov etal. (2001). Table 3 shows the angular offsets and the effectiveradius used for scaling. Where the empirical half-lightradius–magnitude relation is used, we assign an uncertaintyof 30% toRhalf.

The median of the distribution of normalized offsets is0.976 (Table 3). That this number is close to unity suggests astrong correlation of GRB locations with the light of thehost galaxies. The same strong correlation can be graphi-

cally seen in Figure 4, where we find that half the galaxies lieinside the half-light radius, and the remaining lie outside thehalf-light radius. We remark that the effective wavelength ofthe STIS bandpass and the ground-based R band corre-sponds to that of the rest-frame UV, and thus GRBs appearto be traced quite faithfully by the UV light, which mainlyarises from the youngest and thus massive stars. We willexamine the distribution in the context of massive-star pro-genitors more closely in x 7.2.

6.4. Accounting for the Uncertainties in theOffset Measurements

A simple way to compare the normalized offsets with theexpectations of various progenitor models (see x 7) isthrough the histogram of the offsets. However, because ofthe small number of offsets, the usual binned histogram isnot very informative. In addition, the binned histogramimplicitly assumes that the observables can be representedby !-functions, and this is not appropriate for our case, inwhich several offsets are comparable to the measurementuncertainty.

To this end we have developed a method to construct aprobability histogram (PH) that takes into account theerrors on the measurements. Simply put, we treat each mea-surement as a probability distribution of offset (rather thana !-function) and create a smooth histogram by summingover all GRB probability distributions. Specifically, foreach offset i we create an individual PH distribution func-tion, pi(r)dr, representing the probability of observing ahost-normalized offset r for that burst. The integral ofpi(r)dr is normalized to unity. The total PH is then con-structed as p(r)dr =

Pipi(r)dr and plotted as a shaded

region curve in Figure 5; see Appendix B for further details.

Fig. 4aFig. 4b

Fig. 4.—Host-normalized offset distribution. The dimensionless offsets are the observed offsets (X0, Y0) normalized by the host half-light radius (Rhalf) ofthe presumed host galaxy. See text for an explanation of how the half-light radius is found. The 1 " error bars reflect the uncertainties in the offset measurementand in the half-light radius. As expected if GRBs occur where stars are formed, there are 10GRBs (plus 1998bw/GRB 980425) inside and 10 GRBs outside thehalf-light radius of their host. All GRBs outside one half-light radius (circle; left) are labeled. All GRBs observed to be internal to one half-light radius arelabeled (right).

1138 BLOOM, KULKARNI, & DJORGOVSKI Vol. 123GRB 990506

STIS/Clear HST

12 kpc2.0"

Fig. 2n

GRB 990510

STIS/Clear HST

3 kpc0.5"

Fig. 2o

1129

GRB 990123

STIS/Clear HST

3 kpc1.0"

Fig. 2l

✕

GRB 990308

STIS/Clear HST

2.0

"

Fig. 2m

1128

Host Galaxy analysis

Milky Way

Image credits: Gemini/S. Tendulkar/B. Marcote/J. Hessels

Gemini i-bandGemini r-band

Gemini z-band EVN+Gemini

0.3 arcsec

EVN position

Tendulkar et al. (2017)Tendulkar et al. (2017)Marcote et al. (2017)

Answering current questions❖ Are there many repeaters/are all FRBs repeaters?

❖ Sensitive telescopes [Arecibo, FAST], APERTIF and CHIME will rule.

❖ What are the average observed properties [DM, pol, etc]?❖ All discoveries will contribute, APERTIF and CHIME will rule.

❖ Bandwidth/spectrum of FRBs?

❖ Keep going VLA, LOFAR, MWA, GMRT, GBT-lo, etc.

❖ Coordinated radio searching.

❖ Where/what/how do FRBs come from?

❖ Host galaxy studies

❖ Keep going interferometers!

Discussion❖ Are we doing all we should?

❖ What is the BEST (most effective) FRB telescope design?

❖ Yet uncertain.

❖ Optimize ARCSECOND LOCALIZATION * DETECTION RATE.

❖ We have limited resources (money) for a single science.

❖ When will/will it be worth building an FRB instrument?

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