event rate survey and background study of the...

Event Rate Survey and Background Study

of the NCT‟09 Flight Data

Jeng-Lun (Alan) Chiu

Institute of Astronomy, NTHU

2011/06/27 HEAG Group Meeting @ NTHU

Outline

< Introduction >

• Introduction & Current Status

• Overview of NCT‟09 Flight Data

< NCT’09 Detailed Data examination and System Check >

• Unexpected Increase of Event Rates & Hz-feature

• Variation of Event Rates

< Data Analysis >

• Spectrum Study of Flight Background

J.-L. Chiu (Institute of Astronomy, NTHU)

Introduction

&

Current Status

NCT – Instrument in 2009 Flight


Germanium Detector Array

Instrument Cradle

Instrument Gondola

Table 2. Summary of the NCT stratospheric balloon flights.

Launch Date Launch Location Primary Target Duration * GeDs References

June 01, 2005 Ft. Sumner, NM, USA Background (o) 5.5 / (t) 8.5 hrs 2 [8,9] **

May 17, 2009 Ft. Sumner, NM, USA Crab Nebula (o) 22 / (t) 38.5 hrs 10 [7,10,11]

April 29, 2010 Alice Springs, Australia Galactic Center Crashed / (e) 48-96 hrs 10 [7,12,13]

Note: * (o) = operational, (t) = total, (e) = expected durations ; ** NCT Taiwan team had not yet attended the collaboration before 2006.

Energy Range 0.2-10 MeV

Spectral Resolution 0.2-1% FWHM

Field of View (FoV) ~40º×70º FWHM

Angular Resolution ~5º FWHM (662 keV)

Effective Area * 5-18 cm2

Narrow Line Sensitivity (3σ) (1-2) ×10-5 γ cm-2 s-1

Continuum Sensitivity (3σ) (1/E) ×10-4 cm-2 s-1 MeV-1

100% Polarization Sensitivity 37 mCrab (0.2-0.5 MeV)

NCT – Characteristics & Flights

• NCT’05: Despite a failure of a servo system in the azimuthal pointing system, the

6-hour prototype flight allowed detailed characterization of the background at float

altitudes [J. D. Bowen, 2007], where observed background data were compared

with simulations at passing altitudes.

• NCT’09: The Crab Nebula was detected at a significance of 4σ in this flight [M. S.

Bandstra, 2011]. Figure (in next silde) shows the Crab image from 25 ks of data,

using 2-site events from 200–1500 keV. There are 49,000 photons in the back-

projection, where 700 are expected from the Crab. Five iterations of an image

reconstruction algorithm (i.e. MLEM) were applied to the image. It‟s the first

reported detection of an astrophysical source by a Compact Compton

Telescope (CCT). Besides, a very promising potential was also shown to detect

the Crab polarization [J.-S. Liang, 2010].

• Calibrations: Intensive ground calibrations from NCT’09 and NCT’10 (before

flight attempt) have been carried out and analyzed [J.-L. Chiu, 2010 ; E. C. Bellm,

2011] to give a better understanding of the detector response functions such as

the effective area and the polarization performance.

NCT – Scientific Results


NCT’09 Imaging – Crab Image (ep.02)

Methods to obtain Crab image (by Andreas Zoglauer): (1) Use only 2-site events (for some unknown reason 3+ are not working as good) (2) Use the Klein-Nishina-times-Photo-Absorption event reconstruction approach (the one we usually use for HEMI). (3) Use only events with Compton scatter angles maximum half as large as the distance down to the horizon (I do the

same for COMPTEL data)

The first reported detection of an astrophysical source by a CCT


NCT’09 Imaging – Significance of Crab Detection

(M. S. Bandstra, ApJ, in press (accepted June 1, 2011)) :

1. The Crab was detected at a significance of at least 4σ by NCT during the

2009 balloon flight.

2. Using image processing, the Crab appears in a Compton image made

from the data.

3. Examination of the spectrum and ARM histograms from the source are

consistent with the simulations of the Crab.

4. This result is the first significant detection of a celestial source by a CCT

and is an important step in establishing the viability of the compact Compton

telescope design for future space-based wide-survey instruments.


• NCT gondola was supposed to be launched on April 29, 2010 from Alice Springs Airport for a „> 28-hour‟ flight, which could allow us at least a whole period of Galactic-center observation.

• However, it crashed during launch (ps. fortunately without hurting any person).

• The NCT instrument was recovered on April 29 and then shipping back to Berkeley on July 8, 2010.

• The cryostat was initially checked to be in a fine condition due to the protection of shields and cradle, while the rest of devices were damaged to different levels by visual inspection.

• Functionality tests were carried out to verify the status of the GeDs (ps. some need reprocessing), the BGO shields (ps. need further test for 4 of the 36 channels), and the readout electronics (ps. working fine, need minor replacements).

• A two volume set of investigation report was published by NASA on October 22, 2010. Several recommendations were made to the Balloon Program Office about the standard operating process, where some parts are arguable. More details can be checked in the report online ( http://www.nasa.gov/centers/goddard/business/foia/balloon_mishap.html ).

NCT - Current Status of the Project


• The instrument is planned to be reconstructed with a new configuration (with only 3 layers), which will enhance the efficiency of polarization measurement and hard X-ray imaging. The next balloon launch is planned for Spring 2013.

http://www.nasa.gov/centers/goddard/business/foia/balloon_mishap.html

Overview of NCT’09 Flight Data

Energy & Position Measurements

• Energy measurement: Unipolar shaper, 6μs time-to-peak

• Timing measurement: bipolar shaper, 170ns

• X and Y positions: determined by orthogonal strips

Strip pitch: 2 mm (0.25 mm gap)

• Z position: calculated by time difference between X & Y strips

Preliminary (depth) resolution: 0.6 mm

- +

Depth

eh

Edge-On View mirror

X

YZ


< Estimate of Loss and Rates >

• EvtID loss: Sum of the discontinuity on event ID assigned in each CC.

• Frame loss: Sum of the discontinuity on frame ID assigned by flight

computer for all frames but GCUHK.

• Frame/Transmission/Event rates are obtained by dividing relevant counters into increment of GCU/GPS time recorded in the flash disk. If

there’s any GCUHK frame-loss, rates will be over-estimated.

Event types:

-Total E0AE: events with SYNC word received. (may lose the rest) -Valid E0AE: events with SYNC word and group header. -Valid events: Number of events with either timing or ADC data.

-E&T event: Events with both ADC and time data.-LLD only event: Events with ADC data only.-FT only event: Events with time data only.

-No-data event: Events with no data but only headers.

“Event” means “trigger” due to “single interaction”

< Data Structure & Event types in GSE >

(Definitions)

Clock Increment History (UHF Clock)

07456

27772

29336

46184

65141

02552-0

256

4: 0

9-0

5-1

7 0

8-2

4-3

1

CC

4S

ys-e

rr (

3 C

C r

ese

ts)

18432-1

8448: 09-0

5-1

7 1

4-3

7-4

7

CC

4S

ys-e

rr (

4)

21400-2

142

4: 0

9-0

5-1

7 1

5-4

8-0

4

CC

4S

ys-e

rr (

5)

24904-2

492

4: 0

9-0

5-1

7 1

7-1

0-1

3

CC

4S

ys-e

rr (

5)

32520-3

253

2: 0

9-0

5-1

7 2

0-0

9-0

1

CC

0S

ys-e

rr (

3)

30732-3

074

4: 0

9-0

5-1

7 1

9-2

7-1

3

CC

2S

ys-e

rr (

3)

44832-4

485

6: 0

9-0

5-1

8 0

0-5

6-1

8

CC

4S

ys-e

rr (

5)

(~ 6

.6 h

r)

46191-4

868

7: <

09-0

5-1

8 0

7-1

4-1

5

Syste

m W

arm

-up

(3)

54

10

7: 0

9-0

5-1

8 0

9-2

0-2

8 (

1)

Re

bo

ot a

fte

r S

oft

-ve

to s

hie

ld m

ode

55

38

7: 0

9-0

5-1

8 0

9-5

0-2

2 (

1)

Re

bo

ot a

fte

r S

oft

-ve

to s

hie

ld m

od

e

61

83

7: 0

9-0

5-1

8 1

2-0

4-2

8 (

1)

Re

bo

ot fo

r p

ow

er

an

om

aly

20984-21440:

dGPS anomaly

3800:

1st GCU

Time

Reset

34052:

2nd

GCU

Time

Reset

58915:

3rd GCU

Time

Reset

46191:

2nd-day

system

turned

on (dT~5hr)

61837:

system

reboot for

power

anomaly (dT~380s)

1a 1d 2a 2e 2j 2p 2r 3a 3d 3g 3l 4c 4e 4g

18432-1

844

8: 0

9-0

5-1

7 1

4-3

7-4

7

CC

4S

ys-e

rr (

4)

32508-

32804:

Shield

off

32520-3

253

2: 0

9-0

5-1

7 2

0-0

9-0

1

CC

0S

ys-e

rr (

3)

4d

Clock Histories T(GCU-GPS) vs. ΔT(UHF Clock)

Unexpected Increase of Event

Rates

&

Hz-feature

• Q1: Why were the event rates in NCT‟09 much

higher than estimate from NCT‟05 to exceed the

transmission maximum? No-data events

• Q2: What caused the Hz-feature during NCT‟09

flight? Event loss during DAQ through GCU

Frame & Event Rate Histories

during NCT’09 Flight

< System – Event Loss >

Alan Chiu, 2011/03/10

Q1: Much higher event rates than

estimate from NCT’05?

< Calculation from NCT’05 by Mark >

1. Average rate per strip: D0: ~52 counts/sec ; D1: ~50 counts/sec

2. Average event rate per detector: ( flight_03.bin: from frame 140 to frame 40140. Elapsed time: 1231 seconds (+/- 3 seconds) )

- Number of 80-word data frames: 30791 frames,

25.0 frames/sec = 32 kbps.

- D0 events: 57466 events, 46.7 events/sec


< Calculation from NCT’09 by Eric >

3. 100-MB data files were stored in GCU-disk for about 1500s,

which is about 546 kbps.

~ 42.4 events/GeD/sec

Outline

Q1: Why exceeding the transmission maximum?

Q1

Transmission Rate HistoryA: Comparable transmission rates on valid & no-data events!

(All events)

TRValid-events = TRValid-SYNC -TRNo-data events

Almost all of the no-data events were originally LLD trigger only!

Q1

No-data events = Valid SYNC – Valid events

(384 kbps)

-Valid E0AE: events with SYNC word and group header. -Valid events: Number of events with either timing or ADC data. -No-data event: Events with no data but only headers.

Event Ratio History (Valid vs. No-data)

A: Higher no-data-event rate than valid event rate!

Revise DSP code!


Event Ratio History (relative to total-E0AE)

Q: What caused the difference?

~29.8%~30.2% ~30.7% ~29.9% ~29.8%

Consistent ratio of valid-events in “normal” epochs

~91.9%

A: Because junk events with system errors were compressed in data on

CC4, making no-data events as E&T events.

E&T events from CC4 ↑during this epoch

No-data events in CC4 ~0during this epoch

~29.4%

Q1

Event Rate History

Valid SYNC

Cause of No-data event in NCT’09

• Signature 1: Valid events were about 92% of total in soft-shield-veto mode, while they were about 30% in other normal epochs.

• Signature 2: Almost all of the no-data events were originally LLD trigger only!

1. In the current signal timing diagram, LLD signals will be a few μs later than Shield and Guard-ring Veto signals. (See diagram below)

2. Therefore, following unexpected trigger conditions happened in NCT’09 flight.

-Veto-rejected events can trigger CardCage DAQ again by LLD only trigger.

-Since the signal timing of those events were wrong, most of them were “no-data” events.

-There was very minor effect to CardCage DAQ. Livetime was always greater than 90%.

Shall we keep “LLD-only” trigger? If yes, a wait window (several μs) will be added in the trigger logic to avoid this condition.

Q1

(by CH Lin)

NCT’09 Result form Mark (2010/01/28) NCT’09 Result form Justin (2009/12/08)

Q: Periodically event loss somehow?

In flight data epoch 01 and 02

Ep.012540-2560: CCs reset

Event-loss peak offset

from Pfotzer

maximum ???

Mark’s result

Rates result

Q2: What caused the Hz-feature during NCT’09 flight?

Outline

Q2

ps. This epoch is found as the only epoch with almost no event loss!

(Please check details in 02-Rate-Variation)

(01) Pump-ON, GCU, GCU-sync, shield-off

(06) Pump-off, GCU, GCU-sync, shield-off

(02) Pump-ON, CCGSE, GCU-sync, shield-off

(05) Pump-off, CCGSE, GCU-sync, shield-off

Ground Hz-feature Survey – Loss Rate

No event loss with CCGSEEvent loss always relevant to frame loss. No GCU data to confirm event-loss only…

Q2

Shorter data range due to lots of data loss

No event and frame loss!




Result of Ground Hz-survey by Mark

☆

☆

☆

☆ : 30-minute data were also conducted.

☆

☆

☆

☆

☆ : data with plots shown in former pages.

Q: 1-sec feature appeared with GCU as DAQ?

Pump ON

Pump OFF

(05)

(06)

(02)

(01)

There are occasional peaks in the FFTsof each detector, but there aren't anyrepeated from detector-to-detector, sothey'reprobably just noise. ~Mark

Q2

Cause of Hz-feature in NCT’09

1. The overall event rate showed a periodic 1-second dip, likely due to how the flight computer was handling data packets when in the (unexpected) condition of constant UHF telemetry saturation.

2. The 1 Hz dip is related to the way the flight code handled non-event packets, but there is no easy explanation for the higher-order Hz features. The rate of counter frames, etc. were all 1, 4, or 10 seconds.

Conclusion: change the flight code so it drops all packets when the buffers are full, without prejudice for packet type.

Q2

by Eric Bellm

• No-data events, which were resulted from the failure in LLD-only re-triggers of original shield-veto-rejected events, occupied almost half of the band-width in data transmission to exceed the telemetry upper limit.

Revise DSP code.

• Valid-event ratios to all in “normal” epochs were consistent (~30%).

• Event and frame rates were also checked in ground Hz-feature survey. The result as well as Mark‟s and Justin‟s former studies indicate that “1-Hz feature may be due to periodic event loss caused by UHF telemetry saturation during DAQ process in flight computer”.

Revise flight code.

Summary

< Data Transmission Rates > (NCT’05: 32 kbps)

- All / Valid / No-data events: ~ (599±121) / (308±63) / (291±61) kbps

< Event Rates from all GeDs on the 2nd day (e.g. ep.4e) > (NCT’05: 42.4 /GeD)

- Valid SYNC + lost: ~ 1622±336 events/sec (100%) (no D0, h~39km)

- Estimate lost evt.: ~ 1± 6 events/sec (~ 0%)

- Valid events: ~ 482±101 events/sec (~30%) ( ~53.6 /GeD/sec)

(More in 02-Rate-Variation!)

Variation of Event Rates

• Q1: What is the cause of event-rate

variation? Variation of event loss

Altitude transition or electronics issue (?)

• Q2: What were the relevant data/event

rates in NCT’09? Summary (1)

Frame & Event Rate Histories

during NCT’09 Flight

< Rate Variation & NCT’09 Rates >

~ Alan Chiu, 2011/03/10

< Estimate of Loss and Rates >

• EvtID loss: Sum of the discontinuity on event ID assigned in each CC.

• Frame loss: Sum of the discontinuity on frame ID assigned by flight

computer for all frames but GCUHK.

• Frame/Transmission/Event rates are obtained by dividing relevant counters into increment of GCU/GPS time recorded in the flash disk. If

there’s any GCUHK frame-loss, rates will be over-estimated.

Event types:

-Total E0AE: events with SYNC word received. (may lose the rest) -Valid E0AE: events with SYNC word and group header. -Valid events: Number of events with either timing or ADC data.

-E&T event: Events with both ADC and time data.-LLD only event: Events with ADC data only.-FT only event: Events with time data only.

-No-data event: Events with no data but only headers.

“Event” means “trigger” due to “single interaction”

< Data Structure & Event types in GSE >

(Definitions)

Event Rate History(Valid Sync + Lost)

(2) With steady “valid-sync + lost” event rates

(3) Q2: What caused event loss varied to affect event rate?

Valid E0AE = Valid events + No-data eventsValid events = E&T + LLD-only + FT-only evt.

4e 4g2a

Why?

No record was found for it!

(1) Q2: Cause of the event-rate variation?

Outline

Q1

(b). Very little (~0) event loss

here!!

~2380: Pfotzer maximum

61619-62109: System Reboot

46191-48819: System on

(a). Red epochwith significant variation

Relevant System Records

Altitude History (Enlarged)

46191: 2nd-day system turned

on (dT~5hr)

09-0

5-1

7 1

0-1

9-5

4 (C

ST

)

09-0

5-1

801

-27-1

5 (C

ST

)

09-0

5-18

-06-

32-1

5 (C

ST

)

09-0

5-1

813

-15-3

4 (C

ST

)

09-0

5-1

707

-32-5

1 (C

ST

)

09-0

5-1

7 1

8-1

7-3

8 (C

ST

)

09-0

5-1

7 1

8-5

4-2

3 (C

ST

)

09-0

5-1

715

-21-3

2 (C

ST

)

09-0

5-1

716

-34-4

6 (C

ST

)

09-0

5-1

7 1

9-2

2-57

(CST

)

Red epoch: Is event-loss coincidence with altitude transition? Or...?

32508-32804: Shield off

18424-18444: Rate raised

18432-18448: 09-05-17 14-37-47CC4 Sys-err (4)

61837: system

reboot for power

anomaly (dT~380s)

55387: 09-05-18 09-50-22 (1)Reboot after Soft-veto shield mode

Q1

4e2a

Q2: What were the relevant

data/event rates NCT’09?

< Calculation from NCT’05 by Mark >

1. Average rate per strip: D0: ~52 counts/sec ; D1: ~50 counts/sec

2. Average event rate per detector: ( flight_03.bin: from frame 140 to frame 40140. Elapsed time: 1231 seconds (+/- 3 seconds) )

- Number of 80-word data frames: 30791 frames,

25.0 frames/sec = 32 kbps.



< Calculation from NCT’09 by Eric >

3. 100-MB data files were stored in GCU-disk for about 1500s,

which is about 546 kbps.

~ 42.4 events/GeD/sec

Outline

Were rates in NCT’09 similar with those in NCT’05?

Q1

Transmission Rate History

(All events)


[ Ep.2a ]<Total> 570 ±72<Valid> 287 ±36

<NoDat>283 ±38(kbps)

[Ep.2e-p ]<Total> 610 ±90<Valid> 317 ±45


[ Ep.3g ]<Total> 463 ±54<Valid> 271 ±44


[ Ep.3l ]<Total> 438 ±108<Valid> 228 ±51


[ Ep.4c ]<Total> 549 ±80<Valid> 281 ±37


[ Ep.4e ]<Total> 599 ±121<Valid> 308 ±63


TRValid-events = TRValid-SYNC -TRNo-data events

[ Ep.4g ]<Total> 445 ±48<Valid> 229 ±24


53787-54103, 54347-55387:

Soft-veto Shield

32508-32804: Shield off

~2380: Pfotzer

maximum

61619-62109: System Reboot

46191-48819: System on

18424-18444: Rate raised

18432-18448: 09-05-17 14-37-47CC4 Sys-err (4)

Relevant System Records

Q2

Event Ratio History (Valid vs. No-data)

Consistent ratio of valid-events in “normal” epochs

Event Ratio History (relative to total-E0AE)

~29.8%~30.2% ~30.7% ~29.9% ~29.8%

~91.9%

Long-term CC4 system-error epoch

E&T events from CC4 ↑during this epoch

No-data events in CC4 ~0during this epoch

~29.4%

Event Rate History

Valid SYNC


Q2

Event Rate History(Valid Sync + Lost)

Steady “valid-sync + lost” event rates

Ep.04e can be a reliable standard for rate estimate in other epoch


4e 4g

Very little event loss

here!!

[ Ep.4e ]<VE0AE+L>

1622 ±336<Valid-Evt>

482 ±101(Hz)

(~30% here)

2a

[ Ep.2a ]<VE0AE+L>

1929 ±225<Valid-Evt>

478 ± 64(Hz)

(~25% here)

Why?

No record was found for it!

Q2

Event rate (excluding reset zone): ~ 1903 ±239 Hz @ Ep.02 ~ 1958 ±259 Hz @ Ep.03 ~ 1650 ±291 Hz @ Ep.04

Ep.02 Ep.03 Ep.04

Event Rate History (Valid Events) While shield off, E&Tevent rate ↑, LLD-only event rate ↓

[ Ep.2a ]<Valid> 478 ±64<E&T> 252 ±34<LLD>225 ±31

(Hz)

[Ep.2e-p ]<Valid> 505 ±79<E&T> 268 ±42 <LLD>237 ±38

(Hz)

[ Ep.4e ]<Valid> 482 ±101<E&T> 276 ±58<LLD>206 ±44

(Hz)

[ Ep.4g ]<Valid> 359 ±40<E&T> 204 ±23<LLD>154 ±18

(Hz)

[ Ep.4c ]<Valid> 446 ±73<E&T> 257 ±42<LLD>189 ±31

(Hz)

[ Ep.3g ]<Valid> 481 ±88<E&T> 251 ±98<LLD>155 ±26

(Hz)

[ Ep.3l ]<Valid> 367 ±103<E&T> 199 ±56<LLD>167 ±47

(Hz)

[ Soft-Veto Mode 02]<Valid> 1515 ±268<E&T> 1411 ±251<LLD> 95 ±17 (Hz)


Q2

< Data Transmission Rates > (NCT’05: 32 kbps)

- All / Valid / No-data events: ~ (599±121) / (308±63) / (291±61) kbps

< Event Rates from all GeDs on the 2nd day (e.g. ep.4e) > (cf: NCT’05: 42.4 /GeD)

- Valid SYNC + lost: ~ 1622±336 events/sec (100%) (no D0, h~39km)

- Estimate lost evt.: ~ 1± 6 events/sec (~ 0%)

- Valid events: ~ 482±101 events/sec (~30%) ( ~53.6 /GeD)

- E&T events: ~ 276± 58 events/sec (~17%)

- LLD-only events: ~ 206± 44 events/sec (~13%)

< Event Rates from all GeDs on the 1st day (e.g. Ep.2a) >

- Valid SYNC + lost: ~ 1929±225 events/sec (~119%) (+D0, h~35km)

( original counts can be estimated following the above ratio in ep.4e)

- Valid events: (~ 478± 64) events/sec 579 ( ~57.9 /GeD)

< LV0&LV1 Trigger Rates >

- D1, D8-D9 (outer): ~ (40±6)(ep.02), (45±21)(ep.03), (39±6)(ep.04) triggers/sec

- D2-D7 (inner): ~ (30±5)(ep.02), (32±19)(ep.03), (28±5)(ep.04) triggers/sec

< Shield Rates >

- (15472±214) / (16017±288) / (15327±248) Hz @ ep.02 / 03 / 04

Summary (1) – NCT’09 Rates

Because of consistent valid-event rate (~30%) in ep.2a

Q2

Outline

• Features in data/event rates during NCT‟09 flight were surveyed in

details. (more in 03-supplement)

• Event loss rates varied during flight in different epochs.

• Rates concerning data-events in NCT‟09 were checked and then briefly

summarized in previous page.

• Valid-event ratios to all in “normal” epochs were consistent (~30%).

• “Valid-sync + lost” event rates were steady at float.

• Very little event-loss may enable ep.04e to be a reliable standard for rate

estimate in other epoch, if considering steady total-event rates.

< Discussion >

• Was variation during the red epoch due to altitude transition? Or system

problem?

• What caused very little event loss on ep.4e?

Summary (2) – Results

Spectrum Study

of

Flight Background

Spectrum Study of Flight Background

• Moltivation:

- Improved background model for future balloon experiments

- Cosmic Background

• Method for the Flight Background Study

• NCT‟05 Result

• NCT‟09 – Corrections & Current Status

- Preliminary results – Flight Spectrum

- Count Rate Corrections

- Examination in epoch 1

- Event distribution about vetoed photons by shields


Method for the Flight Background Study

• “Monte Carlo Simulations” (with detailed “NCT Mass Model”) were performed with MGGPOD, a superset of the GEANT3-based MGEANT (version 3.1) containing additional code and scripts for the simulation of proton and neutron induced activation.

• The approach was to simulate particle intensities averaged over the flight trajectory for each of the flight segments for the observing times given.

• Each of the modeled background particle components includes a reference from which a depth-dependent component spectrum was taken.

• Cosmic particles are assumed to be simply absorbed or scattered out of the beam with an effective mass absorption coefficient, α (90 g cm−2 for protons and 36.6 g cm−2 for electrons/positrons; α is energy dependent for photons).

• Source functions for atmospheric photons were integrated along all lines of sight in the model atmosphere, with scattering and absorption accounted for.

• Source spectra were then corrected for the effects of solar modulation and the geomagnetic field.

• Activation due to the protons and neutrons has been simulated with two radi ation histories for each component. For a given flight segment, both prompt and in situ buildup and decay were modeled, after which radioactive decay was simulated in the remaining segments after propagating all the preceding cooldown periods through to the segments in question.

• Results are then filtered through an instrument response model.


[15]. B. Rossi, 1952

[41]. J. C. Ling, 1975

[70]. T. Mizuno, 2004

[71]. J. C. Ling, 1971

[72]. T. W. Armstrong, 1973

[73]. R. R. Daniel, 1974

[74]. M. Boezio, 2000

[76]. J. I. Trombka, 1973

[77]. J. I. Trombka, 1977ISOU (direction dependent intensity)

ISOT (isotropic intensity)

NCT’05 Flight Spectra (simulation vs. observation)

(a) 580 g/cm2 – 380 g/cm2 ; (b) 380 g/cm2 – 250 g/cm2

(c) 250 g/cm2 – 190 g/cm2 ; (d) 190 g/cm2 – 150 g/cm2

(a) 150 g/cm2 – 120 g/cm2 ; (b) 120 g/cm2 – 90 g/cm2

(c) 90 g/cm2 – 60 g/cm2 ; (d) 60 g/cm2 – 30 g/cm2

(a) 30 g/cm2 – 5 g/cm2 ; (b) 5 g/cm2 to float altitude

NCT’09 Flight Spectrum (simulation vs. obsevation)


<Simulation:>Spectral lines from

atmospheric neutrons & protons correspond to most

lines from data.

< Discussion > 1. Simulation model, which was built couple decades ago, need to be verified. 2. More background data from NCT flight (i.e. in other epochs) and calibrationsneed to be analyzed. 3. NCT data may help to build a better model for future balloon experiments.

<Simulation:>More counts (~1.5x) in

low-energy part

<Simulation:>Lower counts (<0.5x)from 511-keV line.

1. Spectral lines were fit and identified.

2. Obvious 511-keV line (FWHM=7.5 keV).

3. The rest of spectral lines were mainly related to theactivation.

Simulation vs. Data

Line-identification

(Simulation consulting J. D. Bowen, 2009, N. Gehrels,1985)

Spectra (02 vs. 03 vs. 04) (Raw)

Spectra (02 vs. 03 vs. 04) (After Loss Correction)

Spectra by epochs (Raw)

Spectra by epochs (After Loss Correction)

BTW, inflight energy calibrations is needed…

Spectra concerning SE (Raw)

Spectra concerning SE (After 2 corrections)

Spectra (02 vs. 03 vs. 04) (After 2 corrections)

Spectra (02 vs. 03 vs. 04) (After Loss Correction)

Event Ratios for the Count Rate Corrections

Count Rate vs. Altitude (Whole Flight)

Atmospheric Depth

(A. M. Hillas, 1985 ; D. Heck, 1998)

US Standard Atmosphere (S. J. Sciutto, 2002)

Some Depth-dependent Parameters in NCT’09

13.7 km

18.1 km

Count Rate vs. Altitude (ep.01)

Count Rate vs. Livetime (Whole Flight)

16.95 km17.64 km

Count Rate vs. Altitude (ep.01)

Next Step

< Observation >

• Divide data from epoch 1 into segments corresponding to the regions at different atmospheric depths.

• Carry out count rate corrections for data in epoch 1.

• Compare spectra among sub-epochs.

< Simulation >

• Conduct simulations for epoch 1 against the corresponding atmospheric depths.

• Carry out the activation simulations throughout the flight.

• Complete simulations with the rest of components.

• Consider the contribution from Crab Nebula.

Improve the background model & obtain the cosmic background


Thank You

event rate survey and background study of the...

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