1. p no Bhaswati Bhattacharyya On behalf of GHRSS team
GHRSS survey and beyond : A SKA pathfinder interferometric survey
Bhaswati Bhattacharyya
On behalf of GHRSS team

2. p no
Team
University of Manchester: Bhaswati Bhattacharyya, Ben Stappers, Jayanta Roy, Mike Keith, Mateusz Malenta, Sally Cooper
National Centre for Radio Astrophysics: Jayaram Chengalur, Sanjay Kudale
West Virginia University: Maura MacLaughlin
National Radio Astronomy Observatory: Scott Ransom
Naval Research Laboratory: Paul Ray
Ref: Bhattacharyya et al. 2016, ApJ
Web page :

3. Prospects (1) PSR (4) RRAT (2) MSP GHRSS survey (3) FRB
1% known of ~105
Population study
Emission mechanism
Glitches
Profile state changes
Nulling, intermittency
(1) PSR
83 known of ~105
Emission process
Link with NS population
(4) RRAT
(2) MSP
GHRSS
survey
19 known,
Event rate 6x103 FRBs sky-1day-1
Cosmological origin
Probe of IGM
Spectral index of emission
(3) FRB
5% known of ~40,000
Test of gravity
Gravitational waves
Evolution

4. GHRSS Parameter space Similar to SKA1 Mid and Low Sky coverage
Survey parameters
GBT drift scan
GBNCC
GHRSS
Parameter space of GHRSS vs SKA
Frequency overlap with SKA1 Mid and Low
SKA: Frequency resolution~15 kHz, Time resolution~ 64 μs
Real-time compute need for SKA1~10 Peta-Ops (see Jayanta’s talk)
Single SKA beam cost similar to GHRSS (~10 Tera-Ops)

5. GHRSS sensitivity 10% of SKA1
Re-detection of known in-beam pulsars with expected SNR confirms sensitivity
Interfrometric vs cataloged flux density
Interferometric flux density within ± 50% of catalogue
Interferometric calibration
by Kudale and Chengalur
Discovery rate :12 pulsars in 1500 square degree
Areal discovery rate  one of the highest (GBNCC rate Stovall et al.)
affected by low number statistics?
Present status : 45% completed e confirmed

6. Pulsar discoveries
12 PSRs (1 MSP)

7. GHRSS features (1) High resolution mode (2) RFI mitigation
J (2.5x sensitivity gain)
Zero-DM RFI mitigation:
Integrated profile, phasogram of B1007−47
 Improvement of SNR a factor of 3
512 ch 61μs
Before
After
Pulse phase
Flux
Frequency (MHz)
2048 ch 61μs
Similar time, frequency resolution as SKA

8. GHRSS features Pulsars : Discover  Localise  Time Timing Residuals
Incoherent array
GHRSS features
Pulsars :
Discover  Localise  Time
Phased array
(3) Locatisation with gated imaging and timing
Enabling phased array observations
Timing Residuals
10’’ Localisation
Residuals
imaging by Chengalur and Roy
Time 
Time 
Convergence in timing with a priori arc-sec position
Pulsars discovered with SKA will have positions known up to 50’’

9. GHRSS features (4) Processing CPU vs GPU pipeline
p no
GHRSS features
(4) Processing
GHRSS survey data are concurrently processed by
Time-domain acceleration search on GPU cluster using ‘BIFORST’
(developed by Mateusz Malenta)
Frequency-domain acceleration search on CPU cluster (Hydrus, IBM) using PRESTO
NS-BH
NS-NS
NS-WD
CPU processing
GPU processing
CPU vs GPU pipeline
Acceleration parameter
4x increased for GPU
Dedispersion range increases
500 pc cm-3 to 2000 pc cm-3
Maximum acceleration (m/s2)
Orbital period (hr)

10. GHRSS features GPU Processing: A Cluster with 20 Nvidia GTX 980 GPUs
set up for GHRSS
GPU Manchester
Benchmark : 0.25 x of real time on GTX 980
(1 hr to process 15 min)
CPU pipeline:
192 core takes 10 hr to process 15 min
i.e. 100 times less efficient than GPU pipeline
(10x on performance X 10x for parameter space)

11. GHRSS features (5) Machine learning 500 (less RFI) Accuracy ~ 70%
Number of Candidates per GHRSS pointing
> 5000 (in presence of RFI)
Total number of candidates ~ 1 Million
Human investigation
Difficult
Solution : Machine Learning
(based on Weka software)
Developed by Lyon et al. 2016
Also applied to HTRU and LOFAR
very-fast-decision-tree on
Accuracy ~ 70%
 35 genuine detections, 100% hit rate
Trained with GHRSS detections + RFIs
Similar methodology as SKA candidate optimisation and machine learning
Credit : Rob Lyon

12. (FRB & RRAT) : No discoveries yet
Radio transients
(FRB & RRAT) : No discoveries yet
FRB detection for GHRSS survey completion (500 hrs on-source time)
 at 3 Jy-ms fluence (according to Champion et al. 2016)
GHRSS  FRB survey with Interferometer
Sensitivity for FRB searches
Simultaneous localisation &
identify the origin
Lorimer Burst
GHRSS Sensitivity 1.6 Jy for 10σ for 5ms
 parameter space of 4 known FRBs
Peak flux density (Jy)
Full 500 hrs of GHRSS survey probe
~30% of FRB parameter space.
Gives a non detection limit of < 2100 sky-1day-1
Pulse width (ms)

13. FRB Output of BIFORST pipeline with GPU
Searching for dispersed ( pc cm-3)
Bursts (1-100 ms) in quasi-realtime on GPU
Output of BIFORST pipeline with GPU
GHRSS on FRB parameter space
DM (pc cm-3)
DM (pc cm-3)
SNR
Candidate count
S min(Jy)
DM (pc cm-3)
Time (s)
Field of View X time (deg2 hr)
300 hrs of GHRSS survey cross single FRB detection line

14. GHRSS in uGMRT era
Parameter space

15. FRBs with uGMRT No FRB detected < 800 MHz
Low frequency search important
Sensitivity for FRB searches
GHRSS with uGMRT on FRB parameter space
Peak flux density (Jy)
S min(Jy)
Pulse width (ms)
Field of View X time (deg2 hr)
100 hrs of GHRSS with uGMRT cross single FRB detection line

16. Thank you
Thank you

17. GHRSS sensitivity GHRSS green GBNCC blue
Survey sensitivity
GHRSS green
GBNCC blue
HTRU magenta
Fermi-GMRTcyan
Solid line : 50 pc cm -3
Dashed line :100 pc cm-3
Pulsar period (ms)
Minimum detectable flux density (mJy)
Interferometric flux density within ± 50% of catalogued flux
Interferometric flux density (mJy)
Interferometric calibration
by Kudale and Chengalur
Catalogued flux density (mJy)
12 pulsars in 1500 square degree discovered in GHRSS survey
Areal discovery rate  one of the highest (GBNCC rate Stovall et al.)
affected by low number statistics?
Present status : 50% completed with some candidates to be confirmed
Related Publications:
Survey description and initial discoveries: Bhattacharyya et al. ApJ, 2016
`Biforst’ analysis pipeline and FRBs : Malenta, Bhattacharyya et al. (in preparation)

18. FRB
Event rates and fluence for different surveys

19. FRB
Events/sky/day
Frequency (MHz)
Parkes
VLA
GHRSS
GBT
Molonglo
LOFAR
MWA
No FRB detected < 800 MHz
Low frequency search important
Spectral index (α) from non-detection (w.r.t. Keane & Petroff 2015) :