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Page 1: Michael Garcia Jan 2011 AAS

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Michael GarciaJan 2011 AAS

Page 2: Michael Garcia Jan 2011 AAS

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Question:

What is absolute aspect requirement, What is absolute aspect requirement, both on-orbit and on-ground?both on-orbit and on-ground?

Driving Science Topic: IDs for deep(<10Driving Science Topic: IDs for deep(<10-17-17) ) fields, mainly AGN and galaxies, requires fields, mainly AGN and galaxies, requires final x-ray positions <1”final x-ray positions <1”

Difference from previous missions: deep Difference from previous missions: deep all-sky x-ray survey (ala eROSITA) likely in all-sky x-ray survey (ala eROSITA) likely in not-too-distant future (late 2012)not-too-distant future (late 2012)

17’x17’, 1Ms

IXO WFI

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Background CXO on-orbit astrometry <1’’, but CXO on-orbit astrometry <1’’, but

registration allows <0.2” positions in registration allows <0.2” positions in selected, well studiedselected, well studied fields (M31, Orion) fields (M31, Orion)

eROSITA will find ~10eROSITA will find ~1066 AGN with F AGN with Fxx > 1.5x10> 1.5x10-14-14 (0.5-2.0 keV) covering ~20,000 (0.5-2.0 keV) covering ~20,000 square degrees (expect optical/IR IDs, <1’’ square degrees (expect optical/IR IDs, <1’’ positions for ~all based on XMM-COSMOS positions for ~all based on XMM-COSMOS >99% ID rate, Brusa et al 2010)>99% ID rate, Brusa et al 2010)

Can we use these AGN to register future Can we use these AGN to register future (deeper) pointings, therefore relaxing on-(deeper) pointings, therefore relaxing on-orbit absolute astrometry requirements? orbit absolute astrometry requirements?

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On-Ground Registration How many x-ray/optical matches are How many x-ray/optical matches are

required, and what positional accuracy is required, and what positional accuracy is needed, in order to boot-strap from R’’ to needed, in order to boot-strap from R’’ to better than 1”?better than 1”?

Experience says ~4+ matches are needed. Experience says ~4+ matches are needed. One ‘outlier’ to the registration can be One ‘outlier’ to the registration can be tolerated, but two cannot. tolerated, but two cannot.

X-rayError

Circles,Radius R”

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Surface Densities (X-ray,Opt) 101066 eROSITA AGN/20,000 sq-deg (=wide, eROSITA AGN/20,000 sq-deg (=wide,

high latitude survey) means <4> AGN in high latitude survey) means <4> AGN in every WFI/FOV at 17’x17’ (every WFI/FOV at 17’x17’ (2 or more 91%, 2 or more 91%, 1 1 or more 98%)or more 98%)

From ChaMP: <r> = 20.0 for 1.5x10From ChaMP: <r> = 20.0 for 1.5x10-14-14 AGN, AGN, one sigma limit r<21.1one sigma limit r<21.1

From NOAO 4m MOSAIC fields for ChaMP: From NOAO 4m MOSAIC fields for ChaMP: Density of Density of ANYANY object at r<21.1 is 1.24/sq- object at r<21.1 is 1.24/sq-arcminarcmin

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Error Circle Size? Assume a 5’’ on-orbit error circle. Density Assume a 5’’ on-orbit error circle. Density

of r<21 objects yields 0.11 random of r<21 objects yields 0.11 random objects in 4 circles. objects in 4 circles.

Poisson probability of 0 or 1 random Poisson probability of 0 or 1 random match (=success!) is 99.5%. Random match (=success!) is 99.5%. Random match= many match= many outliers in registration. outliers in registration. [15’’ circle gives 25% failure rate][15’’ circle gives 25% failure rate]

Random matches (interlopers) rare even Random matches (interlopers) rare even with 5’’ absolute aspect. Surface density with 5’’ absolute aspect. Surface density of BG (eROSITA) AGN limiting factor, at 2 of BG (eROSITA) AGN limiting factor, at 2 or more 91% of time. or more 91% of time.

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Conclusion Ground processing (registration) can Ground processing (registration) can

reduce absolute position errors to <1’’, reduce absolute position errors to <1’’, which will be required for ID of fainter which will be required for ID of fainter (F(Fxx<10<10-14-14, r>21) AGN, r>21) AGN

On-orbit absolute positions of 5” are On-orbit absolute positions of 5” are sufficient. There will be 2 or more sufficient. There will be 2 or more eROSITA BG AGN 91% of the time (at high eROSITA BG AGN 91% of the time (at high latitude).latitude).

Similar approach studied in design of Similar approach studied in design of WFXT deep surveys, ie, Brusa et al 2010WFXT deep surveys, ie, Brusa et al 2010