1. Transients and Robotic Triggering at 15 GHz with AMI
Gamma-ray Bursts (GRBs)
ESO
Gemma Anderson
ICRAR-Curtin University
7 July 2016
Focus on triggering of high energy events – particularly GRBs

2. ICRAR-Curtin – science & engineering
‘I’m from ICRAR-Curtin, we are currently a group of  60 astronomers and engineers; our focus is R&D towards SKA including working with its precursor telescopes and data’.
Accretion physics group
Gemma Anderson, Transient triggering with AMI (ASA 2016)

3. Radio Transients All require robotic triggering! X-ray Binaries
Gamma-ray Bursts
Supernovae
Tidal disruption Events
Flare Stars
Radio sky is extremely dynamic place – transients
Study shocks and particle acceleration, probe magnetic fields and ISM from radio follow-up
Difficult to get prompt response – when most interesting and dynamic physics occurring
Require robotic triggering
Each of these transients could have their own talk so today:
Focus on GRBs
All require robotic triggering!
Gemma Anderson, Transient triggering with AMI (ASA 2016)

4. Robotic Transient Triggering
Test bed for SKA
Prompt GRB follow-up
Test Fireball model - REVERSE shock
Unbiased population
Scientific payoff of interrupting observing programs for transients
Benefits of simultaneous multi-wavelength observation
Fireball model describes the production of the GRB afterglow as the shock propogates into the ISM
Predicts a reveres shock that progates back into post-shock eject, creates more prompt emission like optical flashes and radio flares
Gemma Anderson, Transient triggering with AMI (ASA 2016)

5. GRB radio robotic triggering
Cambridge: 1990’s
151 MHz, BATSE GRBs
Mt Pleasant
2.3 GHz, 5 Swift GRBs
Parkes 12m dish
1.4 GHz
9 Swift GRBs
Lots of robotic optical and X-ray follow-up
Radio is rare
Cambridge Low Frequency Synthesis Telescope
Clearly there is a need to further explore this parameter space – particularly at higher frequencies
MWA
MHz
Swift & Fermi GRBs
Gemma Anderson, Transient triggering with AMI (ASA 2016)

6. AMI Transient Program Arcminute Microkelvin Imager (AMI) – Large Array
15.7 GHz, 5’ primary beam, ~30’’ resolution
Rapid Response Mode
Swift trigger
On target <5 mins
Follow-up 24hrs, 3, 7, 10 days
RMS μJy
>150 GRBs
Flare stars, XRBs, magnetars
Gemma Anderson, Transient triggering with AMI (ASA 2016)

7. Radio Emission from GRBs
First 15 years: Chandra & Frail (2012)
2995 flux densities and limits, days post-burst
30% radio GRBs
Sensitivity, not intrinsic
Radio follow-up of GRBs is biased!
3σ upper limits
Put AMI in context
Put AMI program into context
Does NOT include robotic triggers mentioned before
Put AMI radio observations in context
19 years of GRB radio detections
Summary first 15 years
Rarity radio telescopes
Prior knowledge
Detections
Chandra & Frail (2012)
Gemma Anderson, Transient triggering with AMI (ASA 2016)

8. Earliest Radio Observations of GRBs
C&F: 304 GRBs
AMI: 139 GRBs
C&F: 304 GRBs
AMI: 139 GRBs
MWA: 16 GRBs
Other: 17 GRBs
42 observed within first our post-burst
Zoom in further its 40 GRBs within the first 36 mins post-burst => in first 14 years only ONE obs within 37 mins, in 3 years we have observed 40!!!
First time true constraining the early time radio properties of GRBs with a significant number of events
Project allow us to constrain radio properties of GRBs at extremely early times
Gemma Anderson, Transient triggering with AMI (ASA 2016)

9. AMI Observations GRB 130427A One of earliest radio detection of LGRB
AMI detection of the radio REVERSE SHOCK (rare!)
Reverse
Compared Perley et al. (2013) model
Say all the stuff about how fast we were on target and the VLA observations!
First detection of radio peak in GRB reverse shock!
Forward
Anderson et al. (2014), MNRAS, 440, 2059
Gemma Anderson, Transient triggering with AMI (ASA 2016)

10. AMI GRB Catalogue < 1hr to ~90 days post-burst
90.2 days AMI observing time
13 (12 Swift) radio GRBs
5 AMI discovered GRBs!
AMI detection: 15%
UNBIASED: ~ mJy
Increased known radio GRBs by 50% within 1.5 yrs
This program allowed us to probe a unique parameter space and explore strategies for the SKA
This experiment was uniquely possible with AMI and could not have been conducted on any other facility that are highly oversubscribed
Anderson et al. in prep
Gemma Anderson, Transient triggering with AMI (ASA 2016)

11. AMI GRB Catalogue Anderson et al. in prep 7 known 5 unknown
3 candidates
4 steady sources
Anderson et al. in prep
Gemma Anderson, Transient triggering with AMI (ASA 2016)

12. Conclusions AMI: longest running GRB robotic radio follow-up
>150 GRBs
Early radio detection
First detection reverse shock peak
5 new radio GRBs (increase 50% over 1.5 years)
15% detection ( mJy)
Importance robotic triggering
Explore SKA strategies
This program allowed us to probe a unique parameter space and explore strategies for the SKA
This experiment was uniquely possible with AMI and could not have been conducted on any other facility that are highly oversubscribed
Gemma Anderson, Transient triggering with AMI (ASA 2016)

13. AMI Detection of DG CVn – flaring from a rapidly rotating M dwarf (24/04/2014)
AMI observing <6 mins
Quiescence in 4 days (2-3mJy)
First radio flare associated γ-ray flare star
Magnetic reconnection induces radio flaring: GYROSYNCHRTRON
Reached 100mJy before dropping to quiescent level 2-3 mJy
Particles accelerated during flaring process
flare event encompasses a host of physical processes, including particle acceleration and plasma heating, and involves all layers of the stellar atmosphere
Gyrosynchrotron radiation while they are trapped in the magnetic flaring coronal loop.
time-scale of the event relates to the time-scales for the acceleration of electrons, their injection into the coronal loop, and the trapping time
DG CVn binary sep ~0.2 arcsec, distance 18 pc, age ~30 Myr, detected in past radio surveys at few mJy
Fender et al. (2015)
Gemma Anderson, Transient triggering with AMI (ASA 2016)

14. LMXB V404 Cyg outburst – 15 June 2015
26 yrs quiescence
AMI observing <2 hrs
Bright radio flare >2.5 Jy!
×1000 charge in variability!
Monitor daily, sometimes for up to 8 hours with AMI, for the next ~3 weeks
AMI/ALARRM team
Fender et al. in prep
Gemma Anderson, Transient triggering with AMI (ASA 2016)

15. AMI GRBs Catalogue 139 (132 Swift) AMI observed GRBs ~871 observations
<1 hr to ~90 days post-burst
90.2 days worth of observing time
Not including weather affected ~20% observations
12 (11 Swift) confirmed AMI detected GRBs
GRB A
GRB A
GRB A (discovered Fermi)
GRB A (Fermi LAT detected)
GRB A
GRB A
GRB A (Dark Burst)
5 radio GRBs discovered with AMI!
4 strong radio GRB candidates
4 coincident steady sources (host galaxies)
7 known
5 unknown
3 candidates
4 steady sources
Gemma Anderson, Transient triggering with AMI (ASA 2016)