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THE SOXs MISSION

THE SOXs MISSION. Partha Chowdhury University of Calcutta West Bengal, India. Outline. Introduction to the Sun Solar Activity - Small and Large scale activity Characteristic properties of Solar activities during descending phase of cycle 23

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THE SOXs MISSION

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  1. THE SOXs MISSION ParthaChowdhury University of Calcutta West Bengal, India

  2. Outline • Introduction to the Sun • Solar Activity - Small and Large scale activity • Characteristic properties of Solar activities during descending phase of cycle 23 • SOXS Mission: Instrumentation and recent result on Periodicity of X-rays during descending phase of cycle 23 • Conclusions

  3. Overview of Solar StructureThe Sun is made mostly of HYDROGEN and HELIUM and a little admixture of heavy elements • Corona • Chromosphere • Photosphere • Convection Zone • Radiative Zone • Core

  4. 11-year sunspot cycle. • Center – Umbra: ~ 4500 K • Edge – Penumbra: ~ 5500 K • Photosphere: ~ 5800 K Sunspots Sunspots are dark (and cooler) regions on the surface of the Sun. They have a darker inner region (the Umbra) surrounded by a lighter ring (the Penumbra). Sunspots usually appear in groups that form over hours or days and last for days or weeks. The earliest sunspot observations indicated that the Sun rotates once in about 27 days.

  5. Sunspot Formation: Dynamo Model • a) Dipolar field at cycle minimum threads through a shallow layer below the surface. • b) Differential rotation shears out this poloidal field to produce a strong toroidal field (first at the mid-latitudes then progressively lower latitudes). • c) Buoyant fields erupt through the photosphere giving Hale’s polarity law and Joy’s Tilt. • d) Meridional flow away from the mid-latitudes gives reconnection at the poles and equator.

  6. The Sunspot Cycle ( large scale activity ) The average cycle lasts 131±14 months and has a smoothed sunspot number maximum of 114 ± 40.

  7. Sunspot properties during cycle 23 and ascending phase of cycle 24 : A comparison Solar cycle 23 (May,1996 – December, 2008) is abnormally long, having a prolonged minima of ~ 3 years and during 2007- 08, about 71% days were spotless. Cycle 24, started much later, progressing sluggishly. However, till now cycle 24 is ~ 40% weaker than cycle 23.

  8. Galactic cosmic rays attained its maximum value during 2008 – 2009 and sunspot number also reached a minimum value. Modulation of galactic cosmic rays was anomalous during descending phase of cycle 23. [ Chowdhury, Kudela and Dwivedi, Sol.Phys.2013]

  9. The Dynamo Prediction Choudhuri, Chatterjee, & Jiang (2007) used polar field strength of cycle minima in dynamo code with high diffusivity and predicted a weak cycle 24. Cycle 24 Prediction ~ 75 (SSN).

  10. SOXS onboard GSAT-2 • Details of SOXS Instrument • Solar X-Ray Spectrometer (SOXS) was flown onboard GSAT-2 Indian spacecraft on 8-May-2003. • SOXS employs Si and CZT semiconductor devices, which are extremely high resolution and low noise detectors. • Detector package is mounted on a Sun Pointing Mechanism with tracking accuracy better than 0.1 degree. • Pulse Height (PHA) measurements in 256 channels. • System Dead Time- 16 microseconds for Si Pin and 13 microseconds for CZT. • Energy window counters. • On board calibration using Cd109 Radio isotope. • System Health Parameters Monitoring. • Onboard selection for Background Rejection (LLD/Threshold). • In view of Temperature sensitivity of the detectors, observational interval is < 3 Hrs starting from 04:00 to 06:45 UT.

  11. Detector and absorber specifications: The first space-borne solar astronomy experiment of India namely “Solar X-ray Spectrometer (SOXS)” (Jain et al., 2000, 2005, 2006, 2008) was successfully launched on 08 May 2003 onboard geostationary satellite (GSAT-2) of India. The SOXS is composed of two independent payloads viz. SOXS Low Energy Detector (SLD) Payload and SOXS High Energy Detector (SHD) Payload. The SOXS aims to study the solar flares by measuring the full disk integrated X-ray emission in the energy range of 4 keV to 10 MeV. The basic science aim of the SLD payload is to study the solar flares in the energy range of 4 to 56 keV with high spectral and temporal resolution. To meet these requirements, the SLD payload employs state-of-the-art solid state detectors, first time for a solar astronomy experiment, viz. Si PIN (4-25 keV), and Cadmium-Zinc-Telluride (4-56 keV). The Si detector provides sub-kev energy resolution and therefore can observe iron and iron-nickel line complex features that are visible only during solar flares. In view of 3.40 FOV, the detector package is mounted on a Sun Aspect System, for the first time, to get the uninterrupted observations in the geostationary orbit.

  12. Response Matrix: Figure 1: Effective area of Si detector as a function of energy Figure 2: Response of Si detector over its dynamic energy range.

  13. A correlation study between magnitude of flares observed by Si/ CZT detector (7-10 keV) and the GOES (1.6-12.4 keV) during the same interval of time of a given day for the period 01 July 2003 through 31 January 2007. The above study reveals the correlation better than 0.9 for both detectors.

  14. Figure 1a: Time series of daily X-ray index (DXI) in 6 - 7, 7 - 10, 10 - 20 and 4 -25 keV bands of SOXS Si detector for the period from 1 January 2004 to 31 December 2008.

  15. Figure 1b: Time series of daily X-ray index (DXI) in 10-20, 20-30 and 30- 56keV bands of SOXS CZT detector for the period from 1 January 2004 to 31 December 2008.

  16. Important Observations from SOXs counts • It may be noted from Figure 1 that the intensity of hard X-rays (>10keV) measured by CZT detector is larger than soft X-rays intensity detected by Si detector because of higher efficiency and larger effective area of the CZT detector relative to Si detector. • During 2004 to 2006, we find ~four sharp peaks in both soft and hard X-rays in consistence to Bai (2006) who reported a high flare activity in the early descending phase of cycle 23. • In Si detector the intensity of the peaks in X-ray flux in 6 -7 KeV, 7 – 10 keV , 10 – 20 KeV and 4 -25 KeV is almost 4 to 20 times higher than average DXI (X) of the given energy band. • But, in case of CZT detector we find the hard X-ray emission the flux hike is only 2 - 3 times., compared to average flux density .

  17. Periodicities in the X-ray emission from the solar corona AIMS: 1] For better understanding of the convection-zone-photosphere-corona coupling we should probe the periodic nature of the surface manifestations by differential rotation beneath the convection zone viz. the magnetic fields and solar activity one hand and the X-ray corona on the other hand. 2] The X-ray corona refers to different plasma temperature and density for different solar features, observed in different X-ray energy bands. The 6-7 and 7-10 keV energy bands in general refer to soft X-ray emission band and in particular for the emission of Fe-line and Fe/Ni-line features respectively during occurrence of solar flares. It has been recently observed by Jain et al., (2006b) and Gupta et al., (2008) that microflares also reveal Fe-line feature, and some microflares as well reveal even Fe/Ni-line feature. Thus, these two energy bands may be used as proxy to the occurrence of solar flares ranging from micro to macro size. 3] The plasma temperatures for the formation of Fe and Fe/Ni-line features are estimated to be 9 and 14 MK respectively by Jain et al., (2006a). Thus, any significant periodicity other than regular prominent periods if observed in these two bands may be referred to flare activity of all magnitude scales. 4] Thus it is crucial to measure the prominent periodicities in soft and hard X-ray bands to investigate the connection of the solar corona with solar activity caused by differential rotation beneath the convection zone.

  18. Results: • The time series of DXI in soft and hard X-Rays in different energy bands (6-7, 7-10, 10-20, 4-25 keV of Si and 10-20, 20-30 and 30-56 keV of CZT detector) reveals the prominent periodicities: 1.24 years, ~181, ~27, and ~13.5 days. • We report the 1.24-year period detected for the first time in the X-ray emission form the solar corona in wide energy band during the declining phase of sunspot cycle 23.The detection of 1.24 year periodicity in the X-ray corona suggests coupling of this outermost layer with the rotation of the innermost core. It is generally suggested that the 1.24-1.3 year periodicity is associated with variation in equatorial speed of the rotation in the convective zone, which is in anti-phase with an oscillation in the corresponding speed of rotation of the core, on the other side of the tachocline. We suggest that variation in equatorial speed of the solar rotation beneath convective zone and perhaps at the core level is also manifested in the coronal plasma, and suggests exploring the physical processes that couple the core to corona.

  19. Results : • The 13.5 days periodicity is a result of 180° appositively directed longitudes. • ~ 27 day periodicity refers to the solar rotation, which is most prominent due to all the active centers or exciters hotspot are very close to the equator particularly during the declining phase of the solar cycle. • Detection of ~181 days period from SOXS X-ray coronal data in all energy bands in general with 99.99% confidence and greater than 5 level and in 20-30 and 30-56 keV in particular suggests strongly that it is associated to the flare activity, and in order to trigger flare activity significant magnetic flux should be available in the corona. Thus, it appears that change in rotation rate causes up flow of magnetic flux with a periodicity of ~ 181 days. • Our discovery of 31 days periodicity observed in all the energy bands suggests that many sunspot regions did not approach close to equator during declining phase of cycle 23. This indicates that the length of the declining phase of cycle 23 should be longer which is in agreement to sunspot observations that report decay phase to be ~8 years.

  20. Reasons of different solar X –ray periodicities • Several mechanisms have been put forward to explain the origin of these periodicities, especially ~150 days. • Bai and Cliver (1990) : Clock model of period 25.5 The physics behind this ‘clock mechanism’ is still unknown( Bai,2003). • On the other hand, another explanation proposed that periodic emergence of magnetic flux which triggers the destabilization of active regions having strong magnetic fields where the reconnection between old and new magnetic flux takes place is the cause of Rieger type periodicities (Oliver et al. 1998; Ballester et al.1999). • As a possible mechanism of periodic emergence of magnetic flux Lou (2000) and Sturrock (2004) suggested that Rieger-type periodicities are related to physical properties of Rossby type waves or r-modes (Papaloizou & Pringle 1978; ). Lou (2000) pointed out that such waves can give rise to detectable features such as surface elevation in the photosphere. Using solar limb data Kuhn et al. (2000) have reported the detection of a regular structure of 100m “hills” spaced uniformly on solar surface with a characteristic separation of 90000 km through Michelson Doppler Imager (MDI) on board SOHO and interpreted as surface manifestation of Rossby waves, or r-mode signatures.

  21. The r–modes are retrograde waves which can be classified by spherical harmonic indices (l, m, n) where l, m and n respectively are degree, azimuthal and radial order. In the rotating frame of a rigidly rotating fluid sphere, a co-rotating observer would find oscillations at the frequencies ν ≈ ( 2mνs) / l (l+1)…….. Here, νs is the sidereal rotation frequency of the Sun. Lou (2000) have shown that the periodicities due to Rossby–waves are : • Pr ≈ PΘ [m/2 + 0.172{(2n+1)/m}] days • where PΘ = 2π/ΩΘ = Sun’s sidereal rotation period of ~ 25.1 days for equatorially trapped mixed Rossby–Poincare waves. • For m= 15 ,P = ~182 days and for m= 36 , P= 452.15 days • Source of this periods might be external : • Effect of the planetary tidal forces ? • Gravitational lensing ?

  22. Future Missions • Next Generation SOXS is under discussions. • We plan Solar X-ray Spectroscopy covering energy range • from 1-100 keV. • b) We propose to use three detectors viz. • 1. SDD small area for 1-15 keV – to study line emission. • 2. SDD large area for 10-30 keV – to study thermal regime • 3. CdTe large area for 20-100 keV – to study thermal+ non-thermal regimes. • 2. Plasma analyzer experiments for Planetary Exploration: • Solar Wind and Energetic Particle spectrometer • Plasma and Current Experiment • 3. Simultaneous observations in X-ray, optical (H-alpha) and • radio waveband are planned from next year.

  23. Conclusions • We have detected significant periods ~ 13.5, ~ 27, ~ 181 days and ~1.24 yr. period in coronal X-ray data during descending phase of cycle 23 • Detection of ~ 1.2 yr. periodicity is in contradiction with results of NSO group who argued about the cease of this period in convection zone after 2001. • From coronal X-ray data , we have delivered a possible explanation about the extended length of cycle 23.

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