Galaxy ClustersGalaxy Clusters& &
NHXMNHXM
Silvano Molendi Silvano Molendi (IASF-Milano/INAF)(IASF-Milano/INAF)
Innovative GC science Innovative GC science with NHXMwith NHXM
Can we perform innovative studies of galaxy clusters with
NHXM?
High Energy Detector E > 10 High Energy Detector E > 10 keVkeV
• Measure thermal emission in
exceptional systems (i.e. massive
systems undergoing mergers)
• Explore with high sensitivity the
region beyond the thermal cutoff
Non-Thermal processes Non-Thermal processes
• Bulk of the emission is thermal, non-thermal mechanisms are potentially very important, provide clues on the physical process presiding over the formation and evolution of clusters.
• In some objects, evidence of non-thermal processes has been known for quite some time. Radio observations indicate that merging clusters are often the site of cluster-wide synchrotron emission (radio haloes & relics).
B field B field • B fields can be estimated through radio
measurements (Faraday rotation, minimum energy)
• Alternativelly from combination of radio and X-ray measurements.
• The latter rely on the detection of non-thermal emission at X-ray wavelengths (hard tails) attributed to IC scattering of microwave background photons by relativistic electrons.
• If the emission is not detected the upper limit on the X-ray flux converts to a lower limit on the B field
Detections/ULDetections/UL
Non-thermal emission results are "controversial"
Recent results from INTEGRAL and Suzaku are all UL, with one exception.
Inverse Compton Inverse Compton detections detections
From detailed simulations on a few systems
we found that
If IC reported from BeppoSAX and RXTE
detections are real:
detection and possibly spatial/spectral
characterization
If not:
tighter upper limit, detection maybe if
emission is concentrated
• Clusters form via merging of smaller mass concentrations.
• In the course of a merger, a significant fraction of the energy is dissipated by shocks and turbulence
• The bulk of the energy dissipated by shocks goes into heating ions.
• A small fraction of the energy may go into accelerating particles
• Typical shock velocities ~2000 km/s• Observationally shocks are difficult to
detect
Shocks in ICM
Shock in 1E0657
Markevitch+(07)
Best example of shock:
“Bullet Cluster”
Core of sub-structure already
gone through cluster
SX 100 ks simulation
vs = cs x M
ΔT/T ~ 4%ΔT/T ~ 4% ΔT/T ~ 10%ΔT/T ~ 10%
T ~ 25 T ~ 25 keVkeV
T ~ 10 T ~ 10 keVkeV
Δvs/vs ~17%
M measured from Chandra images, ΔM/M ~ 13%
Hard X-ray focusing mission
HPD FOV FL E range AeffHPD FOV FL E range Aeff FWHM m keV cm2@30keVFWHM m keV cm2@30keV
NuStar 40” 12’ 10 6-80 300 NuStar 40” 12’ 10 6-80 300 Astro-H 90” 9’ 12 0.1-80 300 Astro-H 90” 9’ 12 0.1-80 300 NHXM 20” 12’ 10 0.5-80 300NHXM 20” 12’ 10 0.5-80 300
To improve significantly wrt to competitors To improve significantly wrt to competitors
NHXM must devote attention to:NHXM must devote attention to: broad band calibrationbroad band calibration minimization and characterization of bkgminimization and characterization of bkg
Broad Band Calibration / Perseus Broad Band Calibration / Perseus hard tailhard tail
• Perseus hosts a mini radio halo • Detection of non-thermal emission
from Chandra data (Sanders & Fabian 05,07).
• Analysis of EPIC data using new calibrations and detailed treatment of bkg and systematics finds no evidence of non-thermal emission (SM & Gastaldello 09)
PerseusPerseus
The difference btwn Chandra and EPIC measures is due to a cross calibration issue between EPIC and ACIS
Caused by a problem Caused by a problem in the calibration of in the calibration of
the Chandra high the Chandra high energy effective areas energy effective areas recently identified by recently identified by Chandra calibrators Chandra calibrators
(David+07,(David+07,Marshall+08)Marshall+08)
ppnn
ACIS S3ACIS S3
PerseusPerseus
Caused by a problem Caused by a problem in the calibration of in the calibration of
the Chandra high the Chandra high energy effective areas energy effective areas recently identified by recently identified by Chandra calibrators Chandra calibrators
(David+07, (David+07, Marshall+08)Marshall+08)
A high quality calibration of the A high quality calibration of the instrumentation is very importantinstrumentation is very important
ACIS S3ACIS S3
ppnn
PerseusPerseus
Caused by a problem Caused by a problem in the calibration of in the calibration of
the Chandra high the Chandra high energy effective areas energy effective areas recently identified by recently identified by Chandra calibrators Chandra calibrators
(David+07, (David+07, Marshall+08)Marshall+08)
A high quality calibration of the A high quality calibration of the instrumentation is very importantinstrumentation is very important
ACIS S3ACIS S3
ppnn
Suzaku HXD vs BeppoSAX Suzaku HXD vs BeppoSAX PDSPDS
Suzaku/HXD sensitivity comparable to Beppo-SAX/PDS altough the bkg/EffArea ratio is
4-5 times smaller?
....
RXTERXTE
Beppo-SAX/PDSBeppo-SAX/PDS
Suzaku/HXDSuzaku/HXD
PDSPDS twin rocking twin rocking collimators allowed collimators allowed a simultaneous a simultaneous measure of source measure of source and bkg.and bkg.HXDHXD relies on a relies on a background model background model based on bkg based on bkg measures which are measures which are not simultaneous not simultaneous with sou measures.with sou measures.
SuzakuSuzaku
....
RXTERXTE
Beppo-SAX/PDSBeppo-SAX/PDS
Suzaku/HXDSuzaku/HXD
Keeping your background low is important.Keeping your background low is important.
Knowing to a high precision the intensity and Knowing to a high precision the intensity and shape of your background is also very important.shape of your background is also very important.
PDSPDS twin rocking twin rocking collimators allowed collimators allowed a simultaneous a simultaneous measure of source measure of source and bkg.and bkg.HXDHXD relies on a relies on a background model background model based on bkg based on bkg measures which are measures which are not simultaneous not simultaneous with sou measures.with sou measures.
Low Energy Detector 0.5-10 Low Energy Detector 0.5-10 keVkeV
• Explore with unprecedented
sensitivity low surface brightness
regions
• For all missions flown thus far the
instrumental background has been the
major obstacle precluding measures of
low sb regions
Instrumental BackgroundInstrumental Background
pn measured bkg comparable to SX LED expected bkg with AC off
Hall et al. (08)
Instrumental BackgroundInstrumental Background
Hall et al. (08)
pn measured bkg comparable to SX LED expected bkg with AC off
this is what happens when you turn the AC on
From SX to NHXMFrom SX to NHXM
• The major contribution to the instrumental bkg comes form p+ induced events.
• On LEO p+ are about 1/3 than on high orbit.
• We expect a factor of 3 or so reduction in instrumental background
• Place identical detector on both orbits
XMM MOS vs Swift MOSXMM MOS vs Swift MOS
• The major contribution to ins bkg
comes form p+ induced events.
• On LEO p+ are about 1/3 than on high
orbit.
• We expect a factor of 3 or so reduction
in ins background
Hall et al. (08b)
Dead time much less of a problem on LEODead time much less of a problem on LEO
Sensitivity to low SB Sensitivity to low SB emissiomemissiom
• Depends upon:
• SB of source ~ Eff.Area
• SB of background (area in angular
units)
• Figure of merit Eff.Area/SBbkg
• Compare Eff.Area/SBbkg for different
experiments with Eff.Area/SBbkg for
LED
Sensitivity to low SB Sensitivity to low SB emissionemission
---------------------LED/EPIC MOS | 5.4LED/EPIC pn | 2.8---------------------LED/Swift XRT | 1.2---------------------LED/Suzaku FI | 1.2LED/Suzaku BI | 1.6
Eff.Area 333cm2
Sensitivity to low SB Sensitivity to low SB emissionemission
-----------------------------LED/EPIC MOS | 5.4 7.9 LED/EPIC pn | 2.8 4.1 -----------------------------LED/Swift XRT | 1.2 1.7 -----------------------------LED/Suzaku FI | 1.2 1.7 LED/Suzaku BI | 1.6 2.4
Eff.Area Eff.Area 333cm2 500cm2
Sensitivity to low SB Sensitivity to low SB emissionemission
-------------------------------------LED/EPIC MOS | 5.4 7.9 19.7LED/EPIC pn | 2.8 4.1 10.3-------------------------------------LED/Swift XRT | 1.2 1.7 4.3-------------------------------------LED/Suzaku FI | 1.2 1.7 4.3LED/Suzaku BI | 1.6 2.4 6.0
Eff.Area Eff.Area Eff.Area 333cm2 500cm2 500cm2 +LEO (2.5)
Sensitivity to low SB Sensitivity to low SB emissionemission
LED has the potential to become the
most sensitive experiment to low SB
emission ever flown!
Provided we:
• Invest time and resources in BKG
related activities
• Increase effective areas in 2-10 keV
range
RecomendationsRecomendations We need a systemic approach to:
1.Background issue, SX heritage
2.Broad band calibration
Both recomendations are vital to study
of galaxy clusters and much of the
NHXM science!
A few examplesA few examples
In any broad band study of extragalactic
sources the spectrum in the hard band
will include a significant background
component!
A 15% cross calibration error btwn low
and high energy ranges can result in
errors of order unity in estimates of
secondary components (e.g. reflection
bump, cluster hard tails etc.)
SummarySummary Both High Energy Detector and Low Energy
Detector can provide important contributions to Cluster science
1. HED Non-thermal emission, thermal
emission in hot systems 2. LED Low surface brightness regions
To achieve these goals we need to devote particular attention to:
1. broad band calibration of LED + HED system
2. mininimmization and characterization of the bkg