Probing the violent Universe
with gravitational waves
Eric Howell
1. The GRB-GW Connection
2. Probing GRBs through GWs
3. GRBs – open questions
4. EM follow-up at low latency
long-soft LGRB
>2s
short-hard SGRB
< 2s
Gamma-ray bursts (GRBs)
 10keV-GeV photons
 1051-1054 ergs in few seconds
 γ-rays - ultra-relativistic energy flow converted to radiation
SGRB/GW connection
SGRBs linked to compact binary mergers - neutron star
mergers (BNS) and NS/BH mergers
Evidence includes:
 Dynamical timescale of disks consistent with short
duration of bursts
 Lack of associated SNe
 Offsets of GRB locations from their
hosts galaxies (few kpc)
 Kilonova - faint optical transient
– decay of neutron rich ejector
GRB Satellites
Fermi (2008-)
GBM (keV-30 MeV); 70% sky
LAT (0.02-300 GeV) ; 20% sky;
240 GRBs/yr (40s SGRBs)
Swift (late 2004-)
BAT: 15-150 KeV; 10% sky
>1000 GRBs (13% SGRBs)
Complex triggering
1. The GRB-GW Connection
2. Probing GRBs through GWs
3. GRBs – open questions
4. EM follow-up at low latency
What can GWs tell us?
 Conclusive proof of a binary merger origin
 The cleanest view of the inner engines of GRBs
 Constraints on the distance (if no redshift) and GW emissions
associated with GRBs (based on the aLIGO horizon)
 Coincident detections can initiate archival searches in GRB data
 Combining GW and EM data – clues to the evolutionary history and
progenitor pathways of the sources
 Probe the cosmological distance ladder - redshifts (EM) combined
with luminosity distances (GW)
GRB triggered searchs
SGRBs - Compact binary coalescence search –matched filtering
5s
off-source
modelled signal
1s
on-source
off-source
GRB TRIGGER
SGRBs + LGRBs - Burst search – time-frequency domain
600s
unmodelled signal
off-source
60s or T90
on-source
off-source
GRB TRIGGER
RAVEN = Rapid VOEvent Coincidence Monitor;
STAMP = longer duration signals (10-1000s)
GRB-plateaus = GW emissions associated with X-ray plateaus
BNS Merger Rates
 Calculate Swift SBRB rate from a well verified redshift sample
 Factor out detector selection bias to obtain intrinsic sGRB
rate (not beam corrected) ~ 10yr-1Gpc-3 *
 This results in an a BNS rate of between (600-1800) yr-1Gpc-3 a –
an aLIGO detection rate – (1 – 800 )yr-1
* See Coward, Howell, Piran et al., MNRAS 2012
1. The GRB-GW Connection
2. Probing GRBs through GWs
3. GRBs – open questions
4. EM follow-up at low latency
Fermi and GW150914





Weak 1s sub-threshold event within 0.4s - FAP of 0.2%
Stella mass BBHs – clean systems – little accretion expected
Properties - weak SGRB (spectra, lightcurve, duration); lum 1049erg/s
INTEGRAL SPI ACS - omnidirectional above 75keV – no detections
O2 should provide the answer – 10s of BBH events expected
BBHs - Friday 2.00pm David Blair; 2:30 Paul Lasky
Plateaus and Extended Emissions
X-ray plateaus (60% SGRBs)
Extended emissions (~20% SGRBs)
GRB 060614
Rowlinson 2010, 2013
Long lived GW emission?
Corsi & Meszaros 2009
Lasky & Glampedakis, 2016
Re-brightening after prompt
Norris, 2011
Gompertz et al, 2013
Low-luminosity GRBs
LL-GRBs - Luminosities < classical L-GRBs
Lower z : Rate densities > ~100 yr-1Gpc-3classical L-GRBs
Spectroscopically confirmed GRB-SNe
GRB
Redshift
GRB Type
980425
0.0085 (35 Mpc)
LL-GRB
030329
0.1685
L-GRB
031203
0.1055
LL-GRB
060218
0.334
LL-GRB
100316D
0.0591
LL-GRB
120422A
0.283
LL-GRB
130427A
0.597
L-GRB
130702A
0.145
L-GRB (Fermi)
060505
0.089
LL-GRB ? No SN
Howell & Coward, MNRAS, 428, 167, 2013
Swift
1. The GRB-GW Connection
2. Probing GRBs through GWs
3. GRBs – open questions
4. EM follow-up at low latency
Australian GW follow-up
At least 13 facilities/collaborations with Australian involvement
have signed MoUs for O2
Hunting Gravitational Waves with Multi-Messenger Counterparts: Australia’s Role.
E. J. Howell, A. Rowlinson, D. M. Coward, P. D. Lasky, D. L. Kaplan, E. Thrane, G. Rowell,
D. K. Galloway, F. Yuan, R. Dodson, T. Murphy, G. C. Hill, I. Andreoni, L. Spitler, and A.
Horton, 2015, PASA 32, e046
D-W-F - Thursday
3.00pm Igor Andreoni
MM-GW follow-up talks on Friday:
2.45pm Evert Rol: GOTO
3.00pm David Coward: Optical
3.15pm Tara Murphy: Radio
MM pathways and end products
Chu, Howell, Rowlinson et al., MNRAS 459, 121, 2016
Chirping waveform
 A GW signal can be detected 40s before merger
 Possible for maybe 2% ~1/yr aLIGO [Sathyaprakash 2015]
 But GW localisation improves with accumulated SNR
Low-latency follow-up
 40s pre-merger; 1s reaction; latency - 182 deg2 error region (50%)
 LIGO – Virgo – KAGRA – LIGO-I – AIGO (factor 2 over LVKI)
Chu, Howell, Rowlinson et al., MNRAS 459, 121, 2016
Clear need for a wide-FoV X-ray instrument like ISS-Lobster with a large FoV (30 deg2) and
good localisation (arcmin) see Camp et al. (2013) Exp Astron 36:505
Low-latency follow-up
Capturing the electromagnetic counterparts of binary neutron star
mergers through low latency gravitational wave triggers
Q. Chu, E. J. Howell, A. Rowlinson, H. Gao, B. Zhang, S. J. Tingay, M.
Boer, and L. Wen, 2016, MNRAS, 459, 121
astro-ph:1509.06876
Fast response electromagnetic follow-ups from low latency
GW triggers
E. J. Howell, Q. Chu, A. Rowlinson, H. Gao, B. Zhang, S. J.
Tingay, M. Boer and L. Wen, 2016, JPCS, 716, 1
astro-ph:1603.04120
Conclusions
 GRBs - still many outstanding questions
 A rich synergy between GWs & GRBs
 BNS data will allow us to explore the connection
 One or a handful of coincident events would
produce breakthrough science
 It’s a very exciting time to be an astronomer
“Many a true word is spoken in jest” The Cook's Tale, Geoffrey Chaucer, 1390
EXTRA SLIDES
EM Facilities
Australian GW follow-up
74 LSC partner astronomers
D-W-F - Thursday
3.00pm Igor Andreoni
MM-GW follow-up talks on Friday:
2.45pm Evert Rol: GOTO
3.00pm David Coward: Optical
3.15pm Tara Murphy: Radio
Australian involvement now includes Huntsman and Deeper-Wider-Faster
EM Low-latency
follow-up prospects
follow-up - LHV
 40s pre-merger; 40s reaction latency; LIGO – Virgo
 1000 deg2 error region (50% case)
Initial advanced detector network with 40s reaction latency
Low-latency EM Follow-up
 Simulate a population of detected binary neutron
star mergers (BNSs)
 Determine error regions at different times before
merger for different detector networks
 For a range of reaction latencies look at the
capability of EM facilities for fast response (goal:
capture early emission)
 Don’t consider: Rates, tiling strategies,
galaxy catalogues ….
Simulating the GW detector response
 See also Cannon et al. (2012) ApJ,
748,136
 Hsin-Yu Chens talk
Multi-messenger Pathways
Chu, Howell, Rowlinson et al., MNRAS 459, 121, 2016
Flux Estimations at 200 Mpc
 Use GRB 130603B observations – the most well observed SGRB
– extrapolate light curves – convert fluxes to 200 Mpc
 No energy injection: GRB 050509B
 Energy injection from unstable magnetar: – GRB 080905A
GRB 130603B
Low latency simulated results
NETWORK
50% error region
40s before merger
50% error region
50% error region 50% error region
10s before merger 1s before merger @ merger
LHV
1000 deg2
269 deg2
79 deg2
18 deg2
LHVJIA
183 deg2
61 deg2
18 deg2
4.3 deg2
Detection
40s before merger
LHV
40s reaction latency
1000 deg2
LHVJIA
1s reaction latency
183 deg2
Low latency performance
40s before merger
LHV
1000 deg2
40s reaction latency
LHVJIA
183 deg2
1s reaction latency
Reaction latencies
PROCESS
S6-VSR2/VSR3
ER5/ER6
OPTIMISTIC
Date acquisition, calibration &
distribution
1 min
~10s
0(1)s
Trigger generation
2~7 mins
~40s
0(1)s
Follow-up preparation
2~3 mins
~60s
0(1)s
Human vetting
20~30 mins
N/A
0s
GWs and CTA
 SGRB 1051 erg @ 300 Mpc
 Survey mode (~1000deg2)
observation of 1000 s
 Assume synchrotron emission
 tstart = time after merger
 ToO within 30s (LSTs fastest – 180
deg slew in ~20s )
Detection
 100 GeV – require tstart <50s for 1000 deg2 error region
 100 GeV – require tstart <200s for 200 deg2 error region
 Sub TeV photons @ aLIGO/AdV range not effected by EBL
(EBL models : Stecker, Malkan & Scully 2006; Dominguez et al. 2011)
Bartos, I. et al., MNRAS, (2014), 443, 738-749
Low-luminosity GRBs
- ~100 yr-1Gpc-3
- GRB 980425 – 36Mpc
Howell & Coward, 2013
Kilonova - observations
 NS/NS mergers create significant quantities of neutron-rich
radioactive species
 Radioactive decay produces a fain transient - kilonova
NIR kilonova models
Light curves:
X-ray -Optical -NIR -HST observation
Optical kilonova model
Kilonova - observations
Optical
NIR
 NS/NS mergers create significant quantities of neutron-rich radioactive species
 Radioactive decay produces a fain transient called a kilonova
 Kilonova should appear in the near-infrared spectral range (due to the high optical
opacity created by these heavy r-process elements ) within days
 Possibly the predominant source of stable r-process elements in the Universe - Gold.
Tanvir et al., 2013, Nature, 500, 547
GeV emissions in Fermi GRBs
Long GRB 080916C
8-20keV
Short GRB 090510
8-260keV
20-250keV
260keV
–5MeV
200keV–5MeV
All LAT
> 10MeV
> 1 GeV
> 100MeV
> 1 GeV
GeV emission:
 delayed onset GeV wrt MeV emission
 GeV longer lived than MeV emission
 evident in both long and short duration Fermi GRBs
 GRB 160625B – photons up to 15 GeV
Detection Rates
Epoch
Duration
BNS Range
BNS Detections
GW-GRB Detections
FERMI
SWIFT
O1 2015-16 4m
40-80 Mpc
0.004-3 (<1)
3x10-4 – 0.06
10-5 – 0.003
O2 2016-17 6m
80-120 Mpc
0.006-20 (5)
0.01-0.3
10-4 – 0.03
O3 2017-18 9m
120-170 Mpc 0.04-100 (20)
0.003-1.5
10-4 – 0.1
2019+
per yr
200 Mpc
0.2-200 (40)
0.02-3
0.01-0.2
2022+
per yr
200 Mpc
0.4-200 (40)
0.03-6
0.02-0.3
 If 20% of SGRBs are BH/NSs the joint detection rates are doubled
 Fermi numbers allow for untriggered blind search pipeline
- doubles sensitivity (Connaughton at al., 2016); close ≠ bright
See for example Clark et al 2015; B. Patricelli et al, 2016
GRB-GW Search Timescales
< All Sky/ All time
< Triggered
DQ = data quality; RAVEN = Rapid VOEvent Coincidence Monitor; CBC = Coalescing Binary
Compact object; GCN = GRB Coordinates Network
O1 GRBs and future plans
Fermi 51
Swift 27
 FOR O2
•
•
For all GRBs, we will provide the state of the GW detectors (via GCN Notice/Circular)
For GRBs coincident with GW signal candidates (either found by RAVEN or online analysis), w
will provide full sequence of LV Alerts
•
After a non-detection, we will provide exclusion distance for all short and “interesting” long
GRBs (through GCN Circular)
Log Z – Log T to separate different GRB
populations L-GRBs + SL-GRBs
L-GRBs
+
SL-GRBs
Howell & Coward, MNRAS, 428, 167, 2013
Other outstanding Questions
X-ray plateaus
Extended
emissions
GRB 060614
GeV emissions in Fermi GRBs
8-260keV
260keV
–5MeV
All LAT
> 100MeV
Low-luminosity GRBs
> 1 GeV
Short GRB 090510
- delayed onset GeV wrt MeV
- GeV longer lived
- GRB 160625B – photons to 15 GeV
Rowlinson et al. , 2013; Gompertz et al, 2013; Lasky et al , 2014 ; Lasky & Glampedakis, 2016
Fermi GRBs
Fermi GBM – 8-30 MeV
- 4x10-8 erg s-1cm-2
- almost all sky
Fermi LAT – 0.02-300 GeV
6x10-9 erg s-1cm-2
2.4pi sr
~250 GRBs/yr detected by GBM
> 40 GRBs detected by LAT in first 4 yrs
> 10GeV photons detected
(EGRET detected > 100MeV photons)
Expected Detection Rates
Plausible – 20/yr
aLIGO
LIGO
Extra components observed in both long
and short GRBs
Long GRB 090926A
Short GRB 090510
I) Band function
II) Pseudo-Thermal
III) Hard power law component
MeV – synchrotron
GeV - ?
Simulating the GW detector response
 Simulate 200,000 sources based on distributions of 7
free parameters
RA, DEC, polarization angle
Orbit inclination angle, dL, m1, m2 (neglect spins)
 Sky localisation error regions – Wen & Chen (2010)
formula – geometric expression based on FIM
 Calculate for extended detector networks including
Japan, India, Aus: HLV, LHJ, LHVI, LHVA, LHVJI, LHVJIA
 A total of 1009 detections were generated