1. SSM onboard ASTROSAT Calibration and First Results
SAG, SMG, ISRO Satellite Centre, Bangalore
IUCAA, Pune
VSSC, Trivandrum
M. C. Ramadevi
IACHEC, IUCAA, Mar., 1st, 2016

3. scan almost 50% of the sky in one full rotation of the platform in 6 hours
Step and Stare mode (10 min at every 10 deg)
Sensitivity of ~30 mCrab in 10 min

5. Instrument Details Detector
1D position sensitive gas proportional counter
Coded Mask
1D coded mask
Gas mixture
(75% P % 800 torr
Anode
Carbon coated Quartz (25 mic dia)
Cathode
Gold coated Tungsten (75 mic dia)
Anode High Voltage
1500 Volts
Window
Aluminized Mylar (50 mic) 5 5

6. Science Objectives
Detect and locate transient sources
Long-term time variability
Transient Alert generation
Catalog
scan almost 50% of the sky in one full rotation of the platform once in every 6 hours
Step and Stare mode (10 min at every 10 deg)
Sensitivity of 30 mCrab in 10 min

7. SSM – Crab observations
Imaging aspects
Sensitivity
Collimator response
Spectral
Timing

8. Xray sky
Earth occult
SAA
SSM Powered ON
Oct 12, 2015

11. Crab in SSM FOV
(First orbit of SSM observations onboard – Oct 12, 2015)
Angular resolution – expected 12 arcmin - Observed - Confined within a pixel
(12 arcmin X 2.5 deg)
sub-pixel imaging – aiming at finer resolution

12. Sub-pixel imaging
(First orbit of SSM observations onboard – Oct 12, 2015)
Sub-pixel imaging for localising the source better
additional peaks – probably due to statistics of the data from single orbit.
Need to co-add many orbits for sub-pixel imaging in order to get rid of the spurious peaks .

13. Crab in SSM 1, 2, 3 FOV
- Crab at the expected locations in all three units
- Observed at various positions in FOVs of each unit
- spurious peaks are observed
- fine tuning of calibration constants
- Careful data selection

14. PV Phase : Second slot Crab observations (Nov, 2015)
PV Phase :First slot Crab observations (Oct 2015)
Crab counts extracted from Sky Image

15. SSM Crab Obs - Collimator Response
Crab at different positions in SSM's Field of View +

16. Crab at different positions in SSM's FOV
- analysis is underway.

17. Crab spectrum SSM observations with Crab as the strong source in FOV
Large FOV (100 X 22 sq-deg) and background is significantly high
Other source contributions
Position of the Crab in the FOV also to be considered - collimator response
An Optimistic attempt...

18. Anode spectra

19. Ground calibration

20. Crab spectra in first three PV phases observations
Black – Oct. 12Th , 2015
Red – Nov 6th, 2015
Green – Jan 15th, 2016

21. Crab in FOV and Faint field spectra
In Black - Crab spectrum with other unresolved sources + bkgd
- FOV: 100 X 22 sq deg
In Red – Faint field observations – considered bkgd

22. Crab in FOV along with other sources (one of the FOVs)
RA Dec cnt/s src-name (theta_x, theta_y) in SSM
gkper v
xtej
groj
crab x
ic443snr x x x

23. Crab-FOV spectrum (black) and simulated Crab spectrum

24. Observed Crab spectrum – other source contributions and background to be removed (100 X 22 sq-deg)
Choice of orbits with common FOVs with sources present in FOVs of Crab obs
Diffuse X-ray Background spectra needs to be known
Band-wise imaging – source flux extraction in different energy bands - spectral fitting for the source needs to be done

25. SSM – GRS 1915+105 Black Hole source Observations; Oct 15, 2015
Astronomer's Telegram ATel#8185 generated on the above detection of variability in GRS

26. β-Class variability

27. SSM Observations of a binary pulsar 4U0115+63
Observed on October 26, 2015

28. Pulsations from binary pulsars
Vela X1
241+/-0.8 s
Cen X3
4.8+/ s

29. From Oct 12, 2015 to Dec 10, 2015

30. Current status Operational since Oct 12th, 2015 Instrument in PV phase
Initial results are very encouraging
More detailed analysis for every calibration aspect of the instrument is underway
Looking forward to interesting discoveries and dedicated Xray sky survey with SSM

31. ToO Observations with ASTROSAT
-> Optimal planning required – being worked out
-> How fast we can do it
-> And make the best use of ASTROSAT capabilities to study these sources

32. Thank you

33. PV Phase :First slot Crab observations
PV Phase : Second slot Crab observations

34. SSM Observations of GRS 1915+105 – orbit 00248 Spectral Variability

35. SSM – Indication of a M - class S olar Flare
SSM light curve
on 16th October 2015

36. Nov. 4, 2015
3:25 UT
Oct. 16, 2015
6:10 UT

37. Performance Specs Parameter Expected Specs Observed Specs Remarks
Angular Resolution
12 arcmin X 2.5 deg
FWZM of per pixel:
10 arcmin X 2.5 deg
Will definitely be better with sub-pixel imaging
Hardness Ratio (Gain indicator and Spectral parameter)
0.9 +/ (for Crab)
(Can vary with other sources in FOV)
0.5 to 0.8 (With all sources in FOV + Sky background)
Extracting events with respect to different sources needs to be done. Removal of background needs to be done
Sensitivity
25 mCrab at 10 min integration time
Yet to be estimated. However, imaging at finer timebins with 1Crab source was tried.
Yet to be estimated from faint fields
Effective Area
11 sq cm at 2.5 keV
53 sq cm at 5 keV
First order estimate of counts from Crab indicate the expected value
Yet to be estimated

38. Xray sky
Earth occult
SAA
SSM Powered ON
Oct 12, 2015

39. Spectrum

40. SSM – GRS 1915+105 Black Hole source Observations Oct 15, 2015
GRS at (theta_x, theta_y): (1,20) in SSM3 FOV

41. SSM – GRS 1915+105; Black Hole source Observations; Oct 15, 2015 – SSM Sky Image
GRS at (-1,-25) in SSM1 FOV
GRS at (-1,-25) in SSM1 FOV along with other sources

42. SSM as an indicator of SAA entry
SSM detectors show signatures of SAA entry promptly with an increase in veto count rates. This has been used by LAXPC team to set/optimize the timings for SAA entry/exit accordingly with the existing time-tagged mode of operation.
It is being planned to use this parameter of SSM for indication of SAA entry, as a back-up plan for the existing time-tagged mode of SAA entry-exit operations by mission.
In this context SSM team is working out the procedure for Event-Based-Command for SAA entry with SSM parameter along with Controls and Mission team.