Early Universe Gamma Ray Burst Detection

2004

Scientific Rationale

• The first generation of stars were very important for the conditions of the early Universe!

– Synthesis of heavy elements

– Reionization of the Universe

• In order to understand the Universe at this time, we have to understand the first generation of stars

Gamma Ray Bursts

GRBs are the brightest objects known in the Universe.

Detectable to redshifts of 20 or even more!

Gamma Ray Bursts

GRBs are the brightest objects known in the Universe.

Detectable to redshifts of 20 or even more!

Gamma Ray Bursts are unique probes of the death of these first stars !

Current Understanding

GRBs are emitted in the collapse of massive and fast spinning stars (hypernovae)

We expect the first stars to generate GRBs through a similar mechanism

Mission Objectives

• Primary objective

Detection of extremely high redshift Gamma Ray Bursts (GRBs) as a probe of the first generation of stars.

• Secondary objectives○ Properties of the intergalactic matter○ X-ray flashes of proto-stars○ Studies of extragalactic objects

Mission Objectives

Demands for primary objective

• Wide Field Camera (position)

• X-Ray (position, spectroscopy)

• Infrared (spectroscopy)

• Payload– Required Observations– Detectors

• Wide Field Camera• Pointing X-Ray Telescope• Near Infrared Telescope

• Mission Architecture– Mission Analysis– Spacecraft Engineering– Telemetry– Attitude Control

Mission Design Overview

Prompt emission: 0.1 –100 s with energy peak ~ 150 keV

Afterglow emission in X-ray and optical

Known GRBs

• Payload– Required Observations– Detectors

High-z GRBs

• Payload– Required Observations– Detectors

Lamb & Reichart 2000

• Peak emission shifted to X-ray energies

• UV lines shifted into the infrared (specifically Ly alpha)

• Time dilatation

Prompt emission fluxes

• Payload– Required Observations– Detectors

High-z GRBs

Energy bin

1-2 2-4 4-6 6-8 (keV)

0

0.5

1

Num

ber

of p

hoto

ns /

cm

2 /

s z = 10z = 20z = 30z = 30

• Payload– Required Observations– Detectors

Detectors

• We use 3 types of detectors:

1. Wide Field Cameras (WFC)

2.2. X- Ray Telescope (XPT)X- Ray Telescope (XPT)

3. Infrared Telescope (IT)

• Payload– Required Observations– Detectors

Wide Field Camera

• 4 wide field cameras:

Size

Mask

Detector

cm2 90 x 90

70 x 70

Height 167 cm

Spectral range

keV

0.1 - 15

15 - 100

FOV

4 x FOV

30° x 30°

60° x 60°

Coded MaskImaging deviceSize: 90 x 90 cm2Material: Tungsten IBIS mask

DEPFET type: Soft X-Ray detector

CdTe type: Hard X-Ray detector

• Payload– Required Observations– Detectors

X-Ray Pointing Telescope

• Telescope mirror:• Silicon pore optics • r = 28 cm, f = 5.5 m• Effective Area: 1400 cm2 @ 1.5 keV• FOV: 10 arcmin• Angular resolution: 5 arcsec ( 2 arcsec)

• Detector:• DEPFET • Size: 3.2 x 3.2 cm2 [640 x 640 pixels]• no active cooling

Pore structure optics

High spatial resolution + Spectroscopy

• Payload– Required Observations– Detectors

Near Infrared

NIR Telescope:• Diameter: 0.85 m• Weight: 50 kg• Height: 1.5 m

NIR Camera:• FOV: 10 x 10 arcmin• Sensitivity for R ~ 100: 26.8 mJy@10σ• Angular Resolution: ~0.3 arcsec• Rockwell Scientific HgCdTe

2048 x 2048 pixels• Passive cooling

Ritchey-Chrétien design

• Mission Architecture– Mission Analysis – Spacecraft Engineering– Telemetry– Atitude Control

Launcher

Soyuz-Fregat

Launch: spaceport in Korou

Cost: ~ 45M€

Total payload mass: 1500 kg

Fairing dimensions: 3.5m in diameter, 7m in height

• Mission Architecture– Mission Analysis – Spacecraft Engineering– Telemetry– Atitude Control

Orbit / Propulsion

http://wso.vilspa.esa.es/Conferences/Madrid_2003/Launchers_Russian_capabilities.pdf

Orbit:• halo-orbit around L2• excluding observational on the galactical

plane.

Propulsion System:

• Correct the flight trajectory to L2

• Keeping around the L2

• Offloading of the reaction-wheels

• Propellant: hydrazine

• Mission Architecture– Mission Analysis – Spacecraft Engineering– Telemetry– Atitude Control

AccomodationS

UN

Solar arraysWide field of view camerasInfrared telescopeX-Ray telescopeStar trackerService Module

3.24 m

3 m 2 m

• Mission Architecture– Mission Analysis – Spacecraft Engineering– Telemetry– Atitude Control

Accomodation

3D Plot and Rotation

• Mission Architecture– Mission Analysis – Spacecraft Engineering– Telemetry– Atitude Control

Mass estimates

Payload mass: 550 kg

Spacecraft bus dry mass: 776 kg

Propellant mass: 50 kg

Total mass: 1376 kgLow mass spacecraft

Smaller launcher

Cheaper mission

Very exciting science for very low cost!

• Mission Architecture– Mission Analysis – Spacecraft Engineering– Telemetry– Atitude Control

Power

• Solar Arrays: Highly efficient Multijunction GaInP/GaAs

• Efficiency: 19 %

• Area: 12 m²

• Power (avg.): 700 W

• Battery for peak power and backup

• Mission Architecture– Mission Analysis – Spacecraft Engineering– Telemetry– Atitude Control

Thermal Control

Instruments Temperature:• IR: ~50K• Hard X: ~253K

Payload Module

Service Module

IR (2 m²)

X-Ray (0.01 m²)

Sum = 9 m²

Passive cooling by black painting

• Mission Architecture– Mission Analysis – Spacecraft Engineering– Telemetry– Attitude Control

Telemetry: Overall Data Rate

• Diffuse X- Ray background Large amount of data from the WFC

Detailed calculations for 1 WFC:Expected number of counts: 7600 photon/sData / photon: X-Ray energy + (x,y) position

4 WFC: 900 kbits/sX-Ray telescope: 100 kbits/sIR telescope: 2 kbits/sHousekeeping: 2kbits/sTotal data rate: 1 Mbit/s

30 bits/photon

For 1 WFC: 7600 x 30 = 225 kbits/s

• Including all the instruments:

• Mission Architecture– Mission Analysis – Spacecraft Engineering– Telemetry– Attitude Control

Telemetry: Communication

• Continuous data transmission through a high gain antenna

• Quasi real time ground data processing [15 s delay]

• Medium gain antenna for minor transmissions or emergency situation

• On board data storage: few Gbits

• Realistic scenario in 10 years [assuming improvements in antenna technology]

• Mission Architecture– Mission Analysis – Spacecraft Engineering– Telemetry– Attitude Control

Attitude Control

4 reaction wheels:• 3 orthogonal [necessary for 3D pointing]• 1 in a plane tilted with an angle of 45° to the

other ones [as a fail safe]

but... why reaction wheels?• Monopropellant trusters require extra fuel

and are less accurate in pointing• Control of the angular position and rotation

Technical details:• Angular speed: 1° in 2 sec Whole field of view in only 1 minute!•Weight: 4 x 7 kg = 28 kg

example of reaction wheel

Observational Strategy

WFC

XPT

Ground stationIR

Earth telescopes

evtl. repointing

e.g. VLT, ...

po

intin

g

~ 60 s position ~ 1"spectrum

spectrum

position ~ 5"spectrum

follow-up observations

every 1ms

~ 100s

Estimated Costs Payload:

15 MEuro Spacecraft bus:

41 MEuro Program level:

7 MEuro Ground Equipment:

5 MEuro Launch:

45 MEuro

Total estimated cost (without operation costs): ~ 113 Meuro

• 3 years Mission (possible extension)

• Spacecraft designed for 10 years lifetime

• Areas where X-RED is improving on SWIFT:

– X-Ray sensitivity below 10 keV – important for high z detections

– Same area, same sky coverage, but lower background

– IR telescope for follow-up observation

– Continous observations from L2

Why X-RED?

vs.

Early Universe Gamma Ray Burst Detection

Why X-RED?

Early Universe Gamma Ray Burst Detection

• Areas where X-RED is improving on SWIFT:

– X-Ray sensitivity below 10 keV – important for high z detections

– Same area, same sky coverage, but lower background

– IR telescope for follow-up observation

– Continous observations from L2

Conclusions• High redshift GRBs (z = 10-30) are detectable with

• IR-Spectroscopy allows to measure the redshift of these GRBs

• In a 3 year mission we estimate to detect 10 GRBs with z>10

will place constraints on the formation of the first generation of stars and hence on the evolution of the Early Universe.

Red Team

Science

Payload Mission