Overview of CZTI and results of the PV phase A R Rao Tata Institute of Fundamental Research, India (on behalf of CZTI team)

§  TIFR: Lead institute, overall instrument design & development §  VSSC: Electronic design, assembly and testing §  ISAC: Mechanical design, quality consultation & project management, science team §  IUCAA: Coded Mask design, analysis algorithm, calibration & Payload Operations §  PRL: Polarimetry algorithm & demonstration, calibration, response matrix §  SAC: Analysis software §  NCRA: Radio observations

AstroSat

Detector CdZnTe DetectorOptics 2-D coded Mask

Bandwidth 15 - 100 keV

Energy Resolution 6% @100 keV

Time resolution 20 microsec

Detector Proportional counter

Optics CollimatorBandwidth 3 - 80 keV

Energy Resolution 12% @ 22 keV

Time resolution 10 microsec

Effective area 8000 cm2

Detector X-Ray CCD at the focal planeOptics Conical foil ( Wolter-I) Mirrors

Bandwidth 0.3 - 8 keVEnergy

Resolution 2.34% @ 5.9 keV

Angular Resolution 2 arc min (HPD)

Detector Position sensitive Proportional Counter(3)

Optics 1-D coded MaskBandwidth 2.5 - 10 keV

Energy Resolution 25% @ 6 keV

DetectorPhoton-counting (Intensified)

CMOS imagers

Optics Twin Ritchie Chretian 2 mirror system

Bandwidth130-180 nm200-300 nm 320-550 nm

Angular Resolution 1.8 arc sec

2

3

Swift Integral

Above 80 keV: HEAO A4 : 22 sources (2 years) Swift/BAT : 86 sources (6 years) Integral/IBIS : 132 sources (11 years)

Salient Features Ø  Indirect imaging with coded aperture mask

§  Sources cast shadow on detector plane

§  Cross correlation of mask pattern with the shadow recovers source locations and flux

§  Simultaneous background measurement

Ø  Mask and shielding designed up to 100 keV

§  Hard X-ray monitoring above ~100 keV

CZT-Imager

Ø  Time tagged photon data with 20 �s accuracy

§  Allows Compton spectroscopy and polarimetry

Ø  Alpha-tagged detector for onboard calibration

Ø  Veto detector for efficient background rejection

Ø  Low inclination orbit

Ø  Absolute time correlation with onboard SPS

CAM assem bly

C olimatorhs g.as s embly

Calibration hsg. assem bly

Mother board assembly

Details of a Quadrant

Detector Box Assembly

Size - 484 x 484 x 600 mm Weight - 50 kg FOV – 4.8 x 4.8 Degree; 17 x 17 Degree; ~80 Degree Shield Material – Tantalum + Aluminum (Passive shielding)

Power- 50 Watts

Four Independent Quadrants

Radiator Alpha tag

CAM

6

Continuous time-tagged individual photon data (20 micro-sec)

Hard X-ray monitoring (above ~ 80 keV)

CZT-Imager Weight - 50 kg Size: 60 cm

Integral (2000 kg; 500 cm; 25.6°) Swift (1500 kg; 560 cm; 20°)

Low Inclination 6°

•  Individual photon data •  CZT : Energy (pulse height), pixel address,

Time of incidence (20 µs). •  Veto : Energy (pulse height), time of incidence. •  Alpha : time of incidence. •  Simultaneity: Interaction : nano-sec. Detectors : 1-2 µ s. Electronics : 4-5 µ s. Total : 20 µ s. Chance : < 0.2 % (calculation).

Diffuse Cosmic background Calibration source

<10 <100

Crab Nebula 100 Veto triggered events ~ 250

Maximum expected event rate 1000

CZTI Ground Calibration Individual pixel calibration

Ø  Spectral calibration:

§  At multiple temperatures using radio-active sources :

§  Gain, off-set; relative quantum efficiency.

Ø  Imaging test with sources at known distance (a few meters).

Ø  Individual photon data: §  time calibration, alpha / veto

calibration: by analysis

Ø  CZT response to mono-energetic photon is not Gaussian

Ø  CZTI consists of 16384 czt detector pixels each having different response

Ø  Need to characterize all pixels at different operating conditions

Ø  Model to predict energy dependant line shape

CZTI Line profile model Ø  Physics based model – effects of

§  Charge carriers trapping §  Charge sharing §  Escape peaks §  Compton scattering

Ø  Model implemented in ISIS §  Simultaneous fit to gain calibrated

spectra at three energies for all pixels at five temperature

Ø  Total ~80000 spectral fits §  Using PRL Vikram-100 HPC cluster

Ø  Proper Fitting ~90% of the pixels to obtain model parameters

§  Rest of the pixels flagged spectroscopicallly bad

Ø  Group pixels with similar parameters

Ø  Compute redistribution matrix for each group

§  All parameters and matrices stored in CALDB

CZTI Response Matrix

Ø  Final multi-pixel response matrix §  Weighted addition of response matrices for each pixel

Ø  Keeping track of §  Mask open fraction and effective area of pixels §  Module wise energy thresholds

Ø  Two different versions of response matrices §  Mask weighted à for simultaneous background subtracted spectrum §  non mask weighted à for independent background spectrum

No.

of P

ixel

s

No.

of P

ixel

s N

o. o

f Pix

els

No.

of P

ixel

s

μτe μτh

σ r0

Key parameter for all pixels Simulated spectra

Ø  Launched on 28 September 2015 by PSLV C30

Ø  Day 5: CZTI PE switched on

Ø  Day 6: CZTI Quadrants switched on

Ø  Day 6-9: Suppressing noisy pixels, Adjusting module thresholds

Ø  Day 8: Veto HV on

Ø  Day 9: First target of Astrosat- Crab

Ø  Hot pixel check à continuous

Ø  Six months of Performance Verification (PV) phase

CZTI Inflight operations

12

Field Light Curve Field spectrum FFT Image

First look at the data

Ø  Observed count rate ~10 times more then expected Ø  Level-2 pipeline failed to process voluminous on-board data Ø  Level-0 to Level-1 processing chain failures Ø  Auxillary information was not proper

However Ø  Instrument header data was flawless. On-board electronics

working perfectly. HK parameters well behaved Ø  Event data (though at higher rate) present without any issues

Ø  Variance is much higher than expected

§  All events are not “independant”

§  There are “bunch” of events seem to be produced by single actual event

Ø  Large number of secondary photons or particles generated due to

§  interaction of one high energy particle anywhere in instrument / satellite

§  Many of these secondaries are recorded by independent detector pixels simultaneously.

Ø  Possible to identify by clever algorithm

è Advantage of having time tagged event information, unlike RT-2 or HEX experiments !!

Closer look at the data Ø  Genuine X-ray events (source or background) must follow Poisson

distribution, both temporally and spatially

Bunch cleaning Ø  Ignore Bunches à more

then 3 events within 20 µs Ø  Some post-bunch cleaning

Ø  Algorithm tracks the lost time and effective exposure for each pixel

Results §  Events reduced to ~20%

§  Event file size reduced from 10 Gb to less than 2 Gb!

§  Effective loss in exposure is 1-2%

§  300 particles are recorded as 4000 events!

§  Further filtering of flickering / noisy pixels

Bunch cleaning implemented onboard in Feb 16 by a software patch

Bunch Clean: Results

Crab Results First Image Later image (less artifacts)

Pulse profile

PI = 2.09

Spectrum

17

Mayukh Pahari / J S Yadav / Mithun

Powerlaw Index: 2.1

Powerlaw Norm free; (yet to be finalized).

Good �2

Ø  CZTI normalization is about half of what is expected §  Some issues in determining relative alignment

à both w.r.t other instruments and between four quadrants è About to be resolved

Crab: simultaneous fitting with LAXPC

Crab: Absolute Timing Ø  Crab spin down (36 ns/day)

detected clearly in one day observation

Ø  No measurable relative delay between quadrants

Ø  X-ray pulse known to lead radio pulse by ~300 µs (Integral)

Ø  CZTI pulse leads radio by ~490±150 µs

Ø  Absolute time accuracy: ~200 µs

Integral (Oct. 2015)

CZTI (folded with radio ephemeris)

Core Science Areas

�  Galactic Black Hole Binaries:  Spectro-temporal long term monitoring and understanding disk-jet    connection with simultaneous multi-wavelength data like GMRT etc.

�  Gamma-ray bursts: Investigate hard X-ray   spectro-polarimetric properties of very bright  GRBs and make follow up studies using GMRT etc.

�  Pulsars:  Search for hard X-ray counterparts for  Fermi-LAT pulsars.

�  Bright nearby AGN: Make spectro-temporal  long term monitoring to   understand the emission   mechanism.

Astrosat science: Cygnus X-1: black hole binary

Zdziarski+

GMRT

UVIT SXT

LAXPC CZTI Mt Abu

HCT TIRSPEC

HAGAR

CZTI Observations Cygnus X-1

Ø  Very good coverage of Cygnus X-1 state transition from soft to hard during last six months

Ø  First CZTI observation à peculiar ultra soft state, hard X-ray intensity ~150 mCrab

Ø  Simultaneous NuStar observations for Oct. / Nov. observations

Ø  Contemporaneous IR and GMRT observations available

Ø  CZTI data very valuable, once spectrum normalization issue is resolved

GRS 1915+105

Get Actual image

CZTI Observations GRS 1915+105

Cygnus X-3

Cygnus X-3

24

Astrosat

Fermi

Swift

Gamma-ray Bursts Astrosat: 650 km; 6° Fermi: 565 km 25°.6 Swift: 600 km 20°

Ø  CZTI has best sensitivity to GRBs in 150 to 400 keV energy range è Has been �lucky� with GRBs

Ø  First GRB on first day / first observation

Ø  Extremely useful for optimizing noise reduction and data cleaning

Ø  Next two GRBs after stabilization of data cleaning, pipeline etc.

Ø  Fourth GRB in direct FOV!!!

GRBs with CZTI

GRB 151006A

Earth Crab Crab

GRB151006A

Ø  GRB detected on first day of CZTI observation!!

Ø  Extremely helpful to stream line CZTI data analysis pipeline as well

Ø  Extensively studied combining data from Fermi-GBM and Swift-BAT

8 – 25 keV, GBM, BAT

25 – 50 keV, GBM, BAT

50 – 100 keV, GBM, BAT, CZTI

100 – 200 keV, GBM, CZTI Veto

200 – 500 keV, GBM-BGO, Veto

GRB 151006A

Ø  Peculiar GRB à peak energy ~ 2 MeV Ø  Joint spectral fitting with GBM, BAT,

CZTI and CZTI-Veto Ø  CZTI can also provide course localization

Other GRBs GRB 160131A GRB 160119A

GRB 160325A

GRB in CZTI FOV!!

GRB 160325A

X-ray polarimetry with CZT-Imager Ø  Significant Compton scattering

probability in 100 – 300 keV

Ø  CZTI can detect multi-pixel events

Ø  Based on Geant4 simulations

Ø  CZTI does have significant polarization capability Ø  beyond its spectroscopic

energy range Ø  Clear azimuthal modulation

Ø  Better then 10% MDP for 1 Crab source in 500 ks

X-ray polarimetry with CZTI: Experimental Confirmation

(Vadawale et al. 2015)

GRBs: Compton events light curve

GRB 151006A GRB 160119A

GRB 160131A Ø  Validation of the Compton events selection criteria

Ø  Firm demonstration of detection of Compton events from astrophysical source

Ø  Enables •  Compton spectroscopy •  Compton polarimetry

CZTI Polarimetry

Simulations for CZTI show that for 1 Crab source 20 % to 60 % polarization should be detected in ~100 to 20 ks

Ø  Four GRBs detected so far by CZTI

Ø  Total 14 observations of Crab

§  Exposure ranging from 7 ks to 100 ks

Ø  Total 8 observations of Cygnus X-1

§  Exposures ranging from 15 ks to ~80 ks

à  Accurate background subtraction is critical

à  Background modulation due to Earth albedo is declenation dependent

à  Need blank sky observations with similar DEC as source, results in relatively small exposure ~60 ks to 80 ks

GRBs: Polarization

GRB 151006A §  ~1.5 sigma detection of

azimuthal modulation §  Chance modulation probability

due to à unpolarized X-rays à 0.4 %

(worst case à 50 %)

GRB 160131A §  ~2.5 sigma detection of

azimuthal modulation §  Chance modulation probability

due to à §  unpolarized X-rays à

0.0013 % (worst case à 1.7 %) §  Communicated through a GCN

Degree of polarization require full mass model of S/C è under progress

GRB 151006A

GRB 160131A

ID@316, 55ks bkg1_42

ID@316, 55ks bkg2_276

ID@016, 19ks bkg1_42

I D @ 0 1 6 , 19ks

bkg2_276

Crab Polarization

Crab Polarization

Cygnus X-1 Polarization Very promising results… coming up soon

Results from 8 out 14 observations

Ø  Rest of observations under processing Ø  Next steps: Co-adding all observations, phase resolved polarimetry

Summary Ø  Astrosat-CZTI is working flawlessly

§  Excellent data for hard X-ray imaging, spectroscopy and polarimetry

§  Perfectly complimenting rest of the Astrosat instruments

Ø  Supplementary objectives è hard X-ray monitoring and hard X-ray polarimetry §  Better than expectations! §  Number of GRBs detected

§  Search EM counter part for LIGO events! §  X-ray polarimetric capability confirmed with Crab

observations §  Promising results on GRB polarimetry, with

sensitivity better then order of magnitude §  More results expected soon

Acknowledgements

CZTI Team Ø  TIFR: A. R. Rao, M. K. Hinger, A. P. K. Kutty, J. P. Malkar,

Milind Patil, Rakesh Khanna, Yash Bhargava, Vikas Chand, Debdutta Paul

Ø  IUCAA: Dipankar Bhattacharya, Varun Bhalerao, G. C. Dewangan, Ranjeev Misra, Ajay Vibhute, Vedant, Shrikant

Ø  PRL: Santosh Vadawale, Mithun N. P. S., Tanmoy Chattopadhyay

Ø  VSSC: S. Sreekumar, P. Vinod, Essy Samuel, Priya

Ø  SAC: Arvind Singh, Tanul

Astrosat Project Team

Astrosat Mission Team