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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 - PowerPoint PPT Presentation
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THE SOXs MISSION
Partha ChowdhuryUniversity 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
SOXS Mission: Instrumentation and recent result on Periodicity of X-rays during descending phase of cycle 23
Conclusions
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
SunspotsSunspots 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.
• 11-year sunspot cycle. • Center – Umbra: ~ 4500 K• Edge – Penumbra: ~ 5500
K• Photosphere: ~ 5800 K
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.
The Sunspot Cycle ( large scale activity )
The average cycle lasts 131±14 months and has a smoothed sunspot number maximum of 114 ± 40.
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.
-70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70700
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
0.7
0.75
0.80.8
Time lag ( months ) ---------------------->
Nor
mal
ized
CC
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SSN vs Oulu GCRs for descending phase of cycle 23 ( 1.1.2003 - 31.12.2008 )
1996.5 1997.5 1998.5 1999.5 2000.5 2001.5 2002.5 2003.5 2004.5 2005.5 2006.5 2007.5 2008.5200920095400
5600
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6800
Time ( years ) ------------->
Gal
actic
cos
mic
ray
inte
nsity
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----->
(a ) Oulu cosmic ray counts for cycle 23
1996.5 1997.5 1998.5 1999.5 2000.5 2001.5 2002.5 2003.5 2004.5 2005.5 2006.5 2007.5 2008.5200920090
20
40
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80
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120
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Time ( years ) --------------->
Suns
pot n
umbe
r --
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->
(b) Sunspot number for cycle 23Galactic 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]
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).
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.
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 3.4 0 FOV, the detector package is mounted on a Sun Aspect System, for the first time, to get the uninterrupted observations in the geostationary orbit.
S.No. Parameter Detector-Si Detector-CZT
1. Detector Thickness (cm) 0.03 0.2
2. Al Thickness (micron) 50+20 100+20
3. Be Thickness (micron) 25.4 (1mil) 254 (10mil)
4. Kp Thickness (micron) 150 150
5. Geometric Area (cm2) 0.091 0.18
Detector and absorber specifications:
Figure 1: Effective area of Si detector as a function of energy Figure 2: Response of Si detector over its dynamic energy range.
Response Matrix:
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.
2004 2004.5 2005 2005.5 2006 2006.5 2007 2007.5 2008 2008.5 2009
101
102
103
Time ( year ) ------------->
log
[ DX
I ( c
ount
s / s
ec )
] ---
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->
Coronal X- ray intensity measuredby SOXS Si pin at 6 - 7 KeV
2004 2004.5 2005 2005.5 2006 2006.5 2007 2007.5 2008 2008.5 2009
101
102
103
Time ( year ) ----------->
log
[ D
XI (
cou
nts/
sec
) ]
------
------
->
X -ray intensity measuredby SOXS Si pin at 7 - 10 KeV
2004 2004.5 2005 2005.5 2006 2006.5 2007 2007.5 2008 2008.5 2009
101
102
Time ( years ) ---------->
log
[ D
XI (
coun
ts /
sec
) ]
-----
------
--->
Coronal X - ray intensitymeasured by SOXS Si pin at10 - 20 KeV
2004 2004.5 2005 2005.5 2006 2006.5 2007 2007.5 2008 2008.5 20090
250
500
750
1000
1250
1500
1750
2000
2250
25002500
Time ( year ) ---------------->
DXI
( co
unts
/ se
c ) ]
----
------
----->
Coronal X -ray intensity measured
by SOXS Si pin at 4 - 25 KeV
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.
2004 2004.5 2005 2005.5 2006 2006.5 2007 2007.5 2008 2008.5 20090
50
100
150
200
250
300
350
400
450
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Time ( year ) ------------->
DXI ( counts / sec ) ------------------->
Coronal X - ray intensity measured
by SOXS CZT pin at 10 - 20 KeV
2004 2004.5 2005 2005.5 2006 2006.5 2007 2007.5 2008 2008.5 20090
100
200
300
400
500
600
700
800
900
Time ( year ) --------------->
DXI
( co
unts
/ se
c )
------
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-->
Coronal X -ray intensity measured
by SOXS CZT pin at 20 - 30 KeV
2004 2004.5 2005 2005.5 2006 2006.5 2007 2007.5 2008 2008.5 20090
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
Time ( year ) ------------->
DXI
( co
unts
/ se
c )
------
------
->
Coronal X -ray intensity measured
by SOXS CZT pin at 30 - 60 KeV
Figure 1b: Time series of daily X-ray index (DXI) in 10-20, 20-30 and 30- 56 keV bands of SOXS CZT detector for the period from 1 January 2004 to 31 December 2008.
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 .
Periodicities in the X-ray emission from the solar coronaAIMS: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.
10 90 170 250 330 410 490 570 6507007000
5
10
15
20
25
30
35
40
45
50
55
6060
log Period ( in days ) --------------->
Power ------------->
Scargle periodogram of SOXS Si data ( 6 - 7 KeV ) for 2004 - 08
50%90%
95%
~27d
~14d
~181d ~227d
~303d
~95d
~76d
~57d~48d~38d~31d~16d
99.99%
~454 d
~121d
10 80 150 220 290 360 430 500 570 6407000
5
10
15
20
25
30
35
40
45
log Period ( in days ) --------------->
Power ---------------->
Scargle Periodogram of SOXS Si data ( 7 - 10 KeV ) for 2004 - 2008
50%
90%
95%
99.99%
~27d
~14d
~227d
~121d~57d
~48d~38d~16d
~31d
~76d
~96 d
~181d
~454d
~303d
10 80 150 220 290 360 430 500 570 6407000
5
10
15
20
25
30
35
40
45
log Period ( in days ) --------------->
Power ---------------->
Scargle Periodogram of SOXS Si data ( 7 - 10 KeV ) for 2004 - 2008
50%
90%
95%
99.99%
~27d
~14d
~227d
~121d~57d
~48d~38d~16d
~31d
~76d
~96 d
~181d
~454d
~303d
10 90 170 250 330 410 490 570 6507007000
10
20
30
40
50
60
log Period ( in days ) -------------->
Power --------------->
Scargle periodogram of SOXS Si data ( 4 - 25 KeV ) for 2004 - 08
50%90%95%
99.99%
~181d
~454d
~303d~227d~130d
~96d
~76d~67d~57d
~42d~31d
~27d
~13.5d
~36d
10 90 170 250 330 410 490 570 6507007000
5
10
15
20
25
30
35
40
45
50
55
6060
log Period ( in days ) --------------->
Power
----
------
--->
Scargle periodogram of SOXS CZT data ( 10 - 20 KeV ) for 2004 - 08
50%90%
95%
99.99%
~27d
~41d
~181d
~454d
~129d~227d
~96d
~66d~57d~37d
~13.5d
10 90 170 250 330 410 490 570 6507007000
10
20
30
40
50
60
log Period ( in days ) ---------->
Pow
er --
------
->
Scargle periodogram of SOXS CZT data ( 20 - 30 KeV ) for 2004 - 08
50%90%
95%
99.99%
~181d
~454d
~130d~96d
~67d~57d
~47d
~36d~31d
~26d
~13.5d
~227d
10 90 170 250 330 410 490 570 6507007000
5
10
15
20
25
30
35
40
45
50
55
log Period ( in days ) ------------>
Pow
er
------
------
--->
Scargle periodogram of SOXS CZT data ( 30 - 60 KeV ) for 2004 - 08
50%90%
95%
~26d
~31d~36d
~41d
~181d
~130d
~67d
~454d
~13.5d
~227d
99.99% ~96d
~57d
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.
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.
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.
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 :
(1)Effect of the planetary tidal forces ?
(2)Gravitational lensing ?
Future Missions
1. Next Generation SOXS is under discussions. a) 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 regime3. 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.
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.