1. Reflection components of NuSTAR Bkg: Spatial variation
Fabio Gastaldello
&
Silvano Molendi
(IASF-Milano/INAF)

2. What we know
Soft component clearly related to sun activity and present when the satellite is in sunshine: scattered solar X-rays
CXB also scattered: clear signature in the power-law component seen in Dark Earth

3. Goal (what we don’t know yet)
Spatial distribution of the reflected components and their dependance to parameters like sun angle and roll angle
What are the scattering elements in the spacecraft ?

4. Spatial variation of reflected solar component: method
Investigate the difference between period of observations taken in sunshine and periods of observations taken in no sunshine, when the spectra are different: relative low statistics require binning and stacking
Sunshine No sunshine

6. Spatial variation reflection:method
Detector A
1.6-5 keV
Sunshine – ratio_exposure * Nosunshine =
Reflection

7. Spatial variation reflection:method
Detector B
1.6-5 keV
Sunshine – ratio_exposure * Nosunshine =
Reflection

8. Spatial variation reflection:results
Cosmos 10-> January 2013
Detector A sun angle position angle 185
100% 29%
94% 8%
72% 25%
50% 35%

9. Spatial variation reflection:results
Cosmos 10-> January 2013
Detector B sun angle position angle 185
71% 21%
100% 12%
89% 31%
23% 48%

10. Spatial variation reflection:results
Cosmos 36-> April 2013
Detector A sun angle position angle 349
100% 25%
75% 18%
70% 27%
54% 38%

11. Spatial variation reflection:results
Cosmos 36-> April 2013
Detector B sun angle position angle 349
64% 54%
91% 29%
100% 35%
17% 112%

12. Spatial variation reflection:results
Cosmos 55-> May 2013
Detector A sun angle position angle 349

13. Spatial variation reflection:results
Cosmos 55-> May 2013
Detector A sun angle position angle 349
76% 29%
87% 10%
100% 22%
68% 35%

14. Spatial variation reflection:results
Cosmos 55-> May 2013
Detector B sun angle position angle 349
64% 33%
100% 10%
90% 23%
36% 37%

15. Spatial variation reflection:results
Cosmos 55->58 Detector A in a harder band
3-10 keV
49% 33%
76% 11%
100% 19%
64% 38%

16. Spatial variation reflection:results
Cosmos 55->58 Detector B 3-10 keV band
55% 33%
100% 17%
91% 24%
52% 36%

17. Spatial variation reflection:results
Analysis is complicated by different level of absorptions/redistributions between each detector B0 B1

18. Spatial variation reflection:results

19. Puzzle
Striking spectral difference between Detector A and B for some of the Cosmos fields (9-25, 39-44) in the soft solar component A B

20. Dependance on sun angle
ECDFS fields observed at 2 different epochs, December 2012 and March 2013, and different sun angles, in December and in March
Det A Dec 2012
Mar 2013
Det B Dec 2012
Mar 2013

21. Dependance on sun angle
Det B Dec 2012
Mar 2013
Det A Dec 2012
Mar 2013

22. Dependance on sun angle
The intensity of the reflected solar component is qualitatively affected by the sun angle, but a quantitative comparison with GOES tabular data is needed
ECFS MOS016

23. Dependance on sun angle
A sun angle < 90 seems not to reduce dramatically the solar component, as naively expected if the scatterer is only the aperture stop
ECFS MOS011

24. Spatial variation of reflected CXB
Stacking of ECDFS Dark Earth data in the 4-10 keV band where the reflected CXB is dominant
DETECTOR A PA 194
82% 23%
80% 30%
100% 21%
94% 13%

25. Spatial variation of reflected CXB
DETECTOR B PA 194
99% 24%
100% 12%
89% 18%
81% 28%

26. Spatial variation of reflected CXB
DETECTOR A PA 335
100% 16%
93% 11%
79% 19%
82% 29%

27. Spatial variation of reflected CXB
DETECTOR B PA 335
87% 16%
100% 11%
90% 17%
74% 24%

28. Summary
Soft solar component seems clearly connected to the level of solar activity when the satellite is in sunshine. It has a distinct, variable spatial pattern different from the aperture bkg and it’s complicated by different levels of absorption/redistribution between the detectors
Puzzle of the different spectral behavior between A and B seen in some observations (and not in others)
The reflected CXB component has a more uniform distribution on the detector

29. Future work
If possible more quantitative correlation with solar X-ray flux (need solar satellites data)
More investigation of same fields observed at different sun angles and ideally at the same level of solar activity
More Dark Earth data (better with no sunshine) to investigate spatial behavior of reflected CXB