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

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

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 ?

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

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

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

Spatial variation reflection:results Cosmos 10->25 3-13 January 2013 Detector A sun angle 131-141 position angle 185 100% 29% 94% 8% 72% 25% 50% 35%

Spatial variation reflection:results Cosmos 10->25 3-13 January 2013 Detector B sun angle 131-141 position angle 185 71% 21% 100% 12% 89% 31% 23% 48%

Spatial variation reflection:results Cosmos 36->44 4-10 April 2013 Detector A sun angle 136-130 position angle 349 100% 25% 75% 18% 70% 27% 54% 38%

Spatial variation reflection:results Cosmos 36->44 4-10 April 2013 Detector B sun angle 136-130 position angle 349 64% 54% 91% 29% 100% 35% 17% 112%

Spatial variation reflection:results Cosmos 55->58 12-14 May 2013 Detector A sun angle 99-97 position angle 349

Spatial variation reflection:results Cosmos 55->58 12-14 May 2013 Detector A sun angle 99-97 position angle 349 76% 29% 87% 10% 100% 22% 68% 35%

Spatial variation reflection:results Cosmos 55->58 12-14 May 2013 Detector B sun angle 99-97 position angle 349 64% 33% 100% 10% 90% 23% 36% 37%

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

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

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

Spatial variation reflection:results

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

Dependance on sun angle ECDFS fields observed at 2 different epochs, December 2012 and March 2013, and different sun angles, 122-128 in December and 52-60 in March Det A Dec 2012 Mar 2013 Det B Dec 2012 Mar 2013

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

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

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

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%

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

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

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

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

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