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SSM onboard ASTROSAT Calibration and First Results

Explore the calibration and initial results of the SSM instrument onboard ASTROSAT, including the detection of transient sources and long-term time variability.

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SSM onboard ASTROSAT Calibration and First Results

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

  2. 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

  3. Instrument Details 5

  4. 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

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

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

  7. 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

  8. 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 .

  9. 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

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

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

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

  13. 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...

  14. Anode spectra

  15. Ground calibration

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

  17. 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

  18. Crab in FOV along with other sources (one of the FOVs) RA Dec cnt/s src-name (theta_x, theta_y) in SSM 52.7972 43.9031 2.19 gkper -11.62383 -43.82445 53.7498 53.1734 0.225 v0332+53 -2.23588 -49.95809 64.9252 55.9996 2.19 xtej0421+560 7.90293 -47.91637 65.4281 32.9075 0.225 groj0422+32 -8.99822 -28.92295 83.6332 22.0145 30 crab 0.72754 -11.44549 84.7272 26.3158 0.9 x0535+262 3.56415 -14.91754 94.2092 22.4708 2.19 ic443snr 9.96182 -7.93732 94.2805 9.1371 3.3 x0614+091 4.82040 4.50453 95.6852 -0.3457 0.225 x0620-003 2.36662 13.77493 104.61 -7.2638 0.6 x0656-072 8.24969 23.78644

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

  20. 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

  21. 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 1915+105

  22. β-Class variability

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

  24. Pulsations from binary pulsars Vela X1 241+/-0.8 s Cen X3 4.8+/- 0.25 s

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

  26. 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

  27. 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

  28. Thank you

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

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

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

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

  33. Performance Specs

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

  35. Spectrum

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

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

  38. 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.

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