S.Mereghetti - Simbol-X: The hard X-ray Universe in focus - Bologna -15/5/2007 1

Studying the Galactic Ridge Emission with SIMBOL-X

Sandro Mereghetti

IASF - Milano

S.Mereghetti - Simbol-X: The hard X-ray Universe in focus - Bologna -15/5/2007 2

Galactic Ridge X-ray Emission

• X-ray emission extending along the Galactic plane• Longitude extent ~ +/- 40 deg Inner Galaxy R ~ 4 kpc• Latitude extent ~ few deg small scale height ~100 pc• High peak at GC• Luminosity ~ 2 10^38 erg/s• Intense emission lines

S.Mereghetti - Simbol-X: The hard X-ray Universe in focus - Bologna -15/5/2007 3

S.Mereghetti - Simbol-X: The hard X-ray Universe in focus - Bologna -15/5/2007 4

• Double T NEI model• Soft component

kT~0.8 keV• Hard component

kT~7 keV

S.Mereghetti - Simbol-X: The hard X-ray Universe in focus - Bologna -15/5/2007 5

Valinia et al. 2000

S.Mereghetti - Simbol-X: The hard X-ray Universe in focus - Bologna -15/5/2007 6

Lebrun et al. 2004Nature

GRXE resolved by IBIS above 40 keV

20-40 keV

40-60 keV

60 – 120 keV

120-220 keV

S.Mereghetti - Simbol-X: The hard X-ray Universe in focus - Bologna -15/5/2007 7

S.Mereghetti - Simbol-X: The hard X-ray Universe in focus - Bologna -15/5/2007 8

Ebisawa et al. 2005

S.Mereghetti - Simbol-X: The hard X-ray Universe in focus - Bologna -15/5/2007 9

NO IMAGING

DISCRETE SOURCES ?

IMAGING DIFFUSE EMISSION

SIMBOL-X

S.Mereghetti - Simbol-X: The hard X-ray Universe in focus - Bologna -15/5/2007 10

Simbol-X contribution:

1. Population studies in hard X-rays

2. Mapping of emission lines

3. Imaging-spectroscopy at >10 keV with point sources removed

S.Mereghetti - Simbol-X: The hard X-ray Universe in focus - Bologna -15/5/2007 11

Several hundreds of pointings at low Galactic latitude

FoV = (0.1)^2 ~ 0.03 square deg Sky coverage ~ several square deg Sensitivity tens of Crabs

(100 x better than IBIS) ~ 10 sources/square

deg (2-10 keV)

1 ) Population studies

Highly absorbed HMRXB discovered by INTEGRAL

Tip of the iceberg ?

~100 serendipitous sources

..but how many in the 10-40 keV ?

S.Mereghetti - Simbol-X: The hard X-ray Universe in focus - Bologna -15/5/2007 12

2 ) Mapping of emission lines

Compare with XMM / EPIC :

Effective area larger than EPIC pn at E >~4-5 keV similar energy resolution similar angular resolution

much lower instrumental background

Anticoincidence systemSoft protons magnetic diverter

better modelling of continuum emission thanks to extended energy range

S.Mereghetti - Simbol-X: The hard X-ray Universe in focus - Bologna -15/5/2007 13

3 ) Spectroscopy above 10 keV

Done up to now only with collimated instruments

Difficult to correctly estimate point sources contribution

Deep pointings of selected regions in Galactic Plane can for the firsttime properly measure the GRXE spectrum

Also the spatial distribution, e.g. latitude dependence, can be directly measured

S.Mereghetti - Simbol-X: The hard X-ray Universe in focus - Bologna -15/5/2007 14

Simulation of 500 ks pointing with Simbol-X

spectrum of diffuse emission from 6 arcmin radius extraction region

S.Mereghetti - Simbol-X: The hard X-ray Universe in focus - Bologna -15/5/2007 15

S.Mereghetti - Simbol-X: The hard X-ray Universe in focus - Bologna -15/5/2007 16

3 ) Spectroscopy above 10 keV

Done up to now only with collimated instruments

Difficult to correctly estimate point sources contribution

Deep pointings of selected regions in Galactic Plane can for the firsttime properly measure the GRXE spectrum

Also the spatial distribution, e.g. latitude dependence, can be directly measured

CAVEAT: Accuracy depends ultimately on good knowledge of instrumental background

It is essential to control the systematics uncertainties

S.Mereghetti - Simbol-X: The hard X-ray Universe in focus - Bologna -15/5/2007 17

Formation flight can help:

Mirror field of view

detector

S.Mereghetti - Simbol-X: The hard X-ray Universe in focus - Bologna -15/5/2007 18

Formation flight can help:

detector

S.Mereghetti - Simbol-X: The hard X-ray Universe in focus - Bologna -15/5/2007 19

Formation flight can help:

detector

S.Mereghetti - Simbol-X: The hard X-ray Universe in focus - Bologna -15/5/2007 20

Formation flight can help:

detector

S.Mereghetti - Simbol-X: The hard X-ray Universe in focus - Bologna -15/5/2007 21

Formation flight can help:

Mirror field of view

detector

The external parts of the detection plane can monitor the instrumental background

S.Mereghetti - Simbol-X: The hard X-ray Universe in focus - Bologna -15/5/2007 22

Conclusions

• The spectral/imaging capabilities of SX will allow for the first time detailed studies of the GRXE above 10 keV

• It will be possible to determine the contribution of hard X-ray sources and verify if a hot plasma is really needed

• These studies have obvious implications on our understanding of the X-ray emission from the Galactic Center region

• Several dedicated long (~500 ks) pointings required in addition to results from “serendipitous” sources

• A small background level is not enough: It is essential to be able to reproduce its spatial and temporal variations