Analysis of NuSTAR Bkg

Analysis of NuSTAR Bkg Analysis of NuSTAR Bkg

Fabio Gastaldello Fabio Gastaldello &&

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

1

GoalGoal

Provide description of recent findings following 2 week stay at

Caltech

2

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

3

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

4

Data Data Blank fields from COSMOS and

ECDFS NuSTAR surveys

5

Data Data Blank fields from COSMOS and

ECDFS NuSTAR surveys

- Sunshine - No sunshine

6

Sun Sun

Rise clearly associated to sunshine Modulation over longer timescales

7

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

9

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.

10

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.

11

Dark Earth Spectra Dark Earth Spectra

12

Dark Earth Spectra Dark Earth Spectra

13

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

14

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.

15

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

16

Future Work Future Work

• Reduction of more fields to verfiy dependence on sun angle

• More analysis: stacking spectra image analysis etc.

17