Simulating Athena with Sixte: The WFI and X-IFU instrument

Christian Kirsch & Maximilian Lorenz, Remeis Observatory& ECAP

Simulating Athena with Sixte:The WFI and X-IFU instrument

Sixte Workshop IFCA, Santander — February 2019

The Athena Mission

• to be launched to L2 in ∼2030 as the second ESA L-class mission• large consortium, members from Europe, US, and Japan

(> 200 members)• two instruments on board:• Wide Field Imager (WFI)• X-ray Integral Field Unit (X-IFU)

Christian Kirsch & Maximilian Lorenz, Remeis Observatory & ECAP 2

The Athena Instruments

WFI (Imager)

• high count-rate, moderate spectralresolution• large field of view

MPE

X-IFU (Calorimeter)

• for high-spectral resolutionimaging• calorimeter operating at 50 mKelvin

CNESChristian Kirsch & Maximilian Lorenz, Remeis Observatory & ECAP 3

The Wide Field Imager (WFI)

Large Detector Array and Fast Detector (35 mm defocused)

• DePFET activepixel technology(similar to CCDwith line-by-linereadout)• spectral resolution:≤ 170 @ 7keV• high count-rate

capabilities(10 Crab)• large FOV:

40′ × 40′


Example: The Galactic Center with Athena

5′

25

20

15

10

5

kcts

5′

10

8

6

4

2

kcts


Example: The Chandra Deep Field South with Athena

5′

30

25

20

15

10

5

kcts

5′

20

15

10

5

kcts


Example: The Chandra Deep Field South with Athena

A. Rau

dithering efficientlyremoves gaps be-tween the chips


WFI Effective Area

ARF (100µm Be filter)ARF (with filter)ARF (no filter)mirror area

520.50.2 101

10000

1000

100

Photon Energy [keV]

Are

a[cm

2]

thick Be filter⇒ removes photons below 2 keV


Different modii of the WFI (in SIXTE)

Name Size (rows× columns) time resolution defocusinglarge 512× 512 5018µs —w64 64× 512 627µs —w32 32× 512 314µs —w16 16× 512 157µs —

w64df 64× 512 627µs 35 mmfast 64× 64 80µs 35 mm

fastBe 64× 64 80µs 35 mm

• Large Detector Array and Fast Detector• Fast Detector defocused by default• Option for a thick Be filter


Defocusing of the Fast Chip

40mm35mm25mm10mm

543210

1

0.1

0.01

10-3

10-4

10-5

Radius [mm]

Surf

ace

brig

htne

ss[a

.u.]

10 mm10 mm10 mm10 mm10 mm 25 mm25 mm25 mm25 mm25 mm

35 mm35 mm35 mm35 mm35 mm 40 mm40 mm40 mm40 mm40 mm

⇒ defocusing distributes photons over larger area (35 mm is optimal)


Event Detection in SIXTE for the WFI

1

3 4

2

y

x

ccrd

d

=⇒

single quadrupletripledouble

patterns are recombined for each frame in the pattern analysis⇒ invalid patterns rejected


Pile-up in the WFI

energy pile-up pattern pile-up

pile-up events distort spectral shape


WFI DePFET read-out implementation in SIXTE

0

Inte

gra

tion f

act

or

t0 t1

Cle

ar

t0 t1 t3 t4t2

t3 t4t2

0

Exp. Readout Exposure

Misfits

If photon hits during the read out: measured charge is affected⇒ Energy E wrong (“Misfit”)

this is most relevant for window modes or the fast detector


Bright Sources with the WFI

fastBefastw64dfw16w32w64large

1010.10.0110-310-4

1

0.8

0.6

0.4

0.2

01010.10.0110-310-4

0.1

0.01

10-3

10-4

Flux [Crab]

Thr

ough

put

Flux [Crab]

Pile-upFraction

among

ValidE

vents

throughput: ratio of valid events to number of incident photons

• slightly better bright source performance with smaller mirror• fast chip allows to observe sources above 1 Crab• up to 10 Crab with Be filter possible


Summary: The WFI with Sixte

• DePFET technology: active pixels, no line shifts→ misfits if pixel is hitduring readout• observations possible up to a few Crab, plus a thick filter for even brigther

sources• large 40’ FoV made of 4 chips→ requires dithering• simulations possible for the full 4 chip LDA (athenawfisim), or only a

single chip (LD, or the 35 mm defocused FD) with runsixt


The X-ray Integral Field Unit (X-IFU)

• very high spectral resolution imaging (2.5 eV FWHM and a 5’ FoV)• 3168 TES (Transition Edge Sensor) pixels



Pixels are single Transition Edge Sensors, operated at 50 mK⇒ measure temperature increase of photon hitting the pixel

0.5350.530.5250.520.5150.51

1

0.8

0.6

0.4

0.2

0

time [sec]

signal/tempera

ture

[a.u.]

• numerical solution of differential equations for T (t), I(t) (Irwin & Hilton,2005),

CdTdt

= −Pb + PJ + P + Noise and LdIdt

= V − IRL − IR(T , I) + Noise

• linear resistance, R(T , I;α, β); noise: Johnson of circuit, bath, excess noise• input parameters: C, Gb, n, α, β, m, R0, T0, Tb, Lcrit

pulses with smaller separation yield lower energy resolution⇒ Event Grading depending on the source flux




0.5350.530.5250.520.5150.51

1

0.8

0.6

0.4

0.2

0

time [sec]

signal/tempera

ture

[a.u.]

• numerical solution of differential equations for T (t), I(t) (Irwin & Hilton,2005),

CdTdt

= −Pb + PJ + P + Noise and LdIdt

= V − IRL − IR(T , I) + Noise

• linear resistance, R(T , I;α, β); noise: Johnson of circuit, bath, excess noise• input parameters: C, Gb, n, α, β, m, R0, T0, Tb, Lcrit





0.5350.530.5250.520.5150.51

1

0.8

0.6

0.4

0.2

0

time [sec]

signal/tempera

ture

[a.u.]



X-IFU Implementation in the end-to-end simulator SIXTE

xifupipeline:• full detector array• full imaging implemented• fast detection simulation using

response matrices (workssimilar to CCD-typesimulations)

⇒ science simulations

tessim/sirena• Simulation of TES physics

and pulse reconstruction• Slower than xifupipeline,

but much better physics• pixel interaction (crosstalk)⇒ Input for xifupipeline

⇒ physics-based tessim results converted to be used in the fast andgeneral xifupipeline simulation (event grading, crosstalk, . . . )


X-IFU Implementation in the end-to-end simulator SIXTE

xifupipeline:• full detector array• full imaging implemented• fast detection simulation using

response matrices (workssimilar to CCD-typesimulations)

⇒ science simulations

tessim/sirena• Simulation of TES physics

and pulse reconstruction• Slower than xifupipeline,

but much better physics• pixel interaction (crosstalk)⇒ Input for xifupipeline

⇒ physics-based tessim results converted to be used in the fast andgeneral xifupipeline simulation (event grading, crosstalk, . . . )


Example: SIXTE X-IFU simulation of a Galaxy Cluster

520.5 101

10-12

10-13

10-14

0.950.900.85

10-13

10-14

1′

520.5 101

10-12

10-13

10-14

0.950.900.85

10-13

10-14

Energy [keV]

νF

ν[erg

/cm

2/s]

Energy [keV]

νF

ν[erg

/cm

2/s]

SIXTE describing, simulating, and analyzing complicated sourcesX-IFU spatially resolved high-resolution spectroscopy


Performance at High Countrates (grading effect only)

defocusing of the Athena optics allows observations up to 1 Crab

High resolutionTotal throughput25 mm35 mm

High res goal (10 mCrab)

Broa

dban

d th

roug

hput

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Source flux [mCrab]1 10 100 1000

No filter100 µm Be filter25 mm defocus35 mm defocus

7 eV

thro

ughp

ut in

the

5-8

keV

band

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Source flux [mCrab]1 10 100 1000

Grade ∆t since previous pulse ∆t until next pulse Energy res.(1) High res. > 7.9 ms > 45.3 ms 2.5 eV

(2) Medium res. > 7.9 ms > 2.3 ms 3 eV(3) Limited res. > 7.9 ms > 1.0 ms 7 eV

(4) Low res. > 7.9 ms – ∼ 30 eV


Crosstalk in SIXTE

unintended transmission of information between signal channels

Different types of crosstalk:• thermal coupling of two pixels (physical neighbors)• electrical coupling due to multiplexed readout (frequency neighbors)• non-linear amplification of the read-out SQUID

→ implemented in SIXTE

crosstalk effect on events is predictable


How does Crosstalk affect X-IFU Events?

simulation of a narrow emission line (1 Crab)

Ext < 4 eVExt < 0.2 eVall events

6.426.416.46.396.38

7×105

6×105

5×105

4×105

3×105

2×105

1×105

0

Energy [keV]

Flux[X

-IFU

Counts

/keV]

1000100101

5.5

5

4.5

4

3.5

3

2.5

Flux [mCrab]

Energ

yReso

lution

(Ext<

4eV)[eV]

⇒ remove events which are strongly effected by crosstalk

trade-off between energy resolution and throughput⇒ 10 eVresolution with 50% throughput @ 1 Crab


Summary: The X-IFU with Sixte

• 3168 TES pixels in a hexagonal shape• 5’ FoV• higher flux (>10mCrab) reduces energy resolution and throughput• science simulations with xifupipeline, taking the most important TES

physics effects into account• physics input to the simulation pipeline by tessim


Documents

Simulating Athena with Sixte: The WFI and X-IFU instrument