Analysis of NuSTAR Bkg Analysis of NuSTAR Bkg

Fabio Gastaldello Fabio Gastaldello &&

Silvano Molendi Silvano Molendi (IASF-Milano/INAF)(IASF-Milano/INAF)

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GoalGoal

Provide description of recent findings following 2 week stay at

Caltech

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Data Data Blank fields from COSMOS and ECDFS NuSTAR

surveys

• 64 COSMOS fields• 16 ECDFS fields

• COSMOS fields short DE passages, few ks Sun angle 130+ deg

• ECDFS 15-17 ks DE Sun angle 70+ deg

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Data Data Blank fields from COSMOS and

ECDFS NuSTAR surveys- Sky ELV > 3- Bright Earth BE < -5- Dark Earth (BE > 5)&&(ELV <-5)

Energy band 1.8keV<E< 3.5keV

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Data Data Blank fields from COSMOS and

ECDFS NuSTAR surveys

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Data Data Blank fields from COSMOS and

ECDFS NuSTAR surveys

- Sunshine - No sunshine

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Sun Sun

Rise clearly associated to sunshine Modulation over longer timescales

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Spectra Spectra Blank fields from COSMOS and ECDFS NuSTAR surveys

30+ COSMOS fields16 ECDFS fields

COSMOS fields short DE observation few ksECDFS longer 15-17 ks

- Sky ELV > 3- Sky and nosunshine - Sky and sunshine 8

What could it be? What could it be?

• Compton Scattering of solar light from elements in the satellite affording a direct view of the detectors

• Aperture stops by construction have direct line of sight to the detectors.

• Back-scattering off aperture stops one of the major contributors, if sun angle is larger than 90

Reflected Solar X-rays

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Scattering elements Scattering elements Other scattering elements also present

Sun angle ~70deg

ECDFS observations feature significantly weaker contamination.Many observations are effectively contamination-free.Plausible explanation aperture stops provide most significant contribution for Sun Angle > 90,For smaller angles other elements provide some scattering surface.Needs to be verified through analysis of more fields.

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ImplicationsImplications• Presence of contamination in an observation

can be easily assesed by comparing sunshine with no-sunshine spectra

• Most of the time contamination, if present, is restricted to E<6-7 keV

• In a few instances can extend up to 15 keV.

• In these rare cases filtering against sunshine will remove contaminating component

• More complex strategies can be implemented to minimize data loss.

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Dark Earth Spectra Dark Earth Spectra

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Dark Earth Spectra Dark Earth Spectra

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Dark Earth Dark Earth is not so dark! is not so dark!

During «quiescent» periods DE spectra feature a component which is consistent with being a rescaled version of the aperture background seen during SKY observations.

Scaling factor is ~ 2

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Dark Earth Dark Earth is not so dark! is not so dark!

During «quiescent» periods DE spectra feature a component which is consistent with being a rescaled version of the aperture background seen during SKY observations.

Scaling factor is ~ 2Most likely explanation is Compton backscattering

of the CXB.

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Exploring BKG Exploring BKG phenomenology phenomenology cr[4-20keV] full FOV unit A

In ECDFS fields In COSMOS fields mean stdev mean stdev DEARTH 8.21e-2 0.41e-2 1.05e-1 0.54e-1Sky 2.00e-1 0.10e-1 2.15e-1 0.51e-1Ratio 0.410 0.025 0.489 0.220

When Solar contamination is modest ratio of Sky/DEarth cr is well constrained 6%

In COSMOS ratio is far less constrained, however can be reduced to ~6% by excluding sunshine data

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Future Work Future Work

• Reduction of more fields to verfiy dependence on sun angle

• More analysis: stacking spectra image analysis etc.

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