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High Energy Universe Viewed Through
Astrosat
P.C.Agrawal
Tata Institute of Fundamental Research, Mumbai
Talk at the Chandrayan Symposium at IMSc , Chennai ,
January 4 , 2011
ASTROSAT : A Broad Spectral Band Indian
Astronomy Satellite
An Indian National Space Observatory
A Collaborative Project of
Tata Institute of Fundamental Research (TIFR), Mumbai
ISRO Satellite Centre (ISAC), Bangalore
Indian Institute of Astrophysics (IIA), Bangalore
Inter-University Centre for Astronomy & Astrophysics, Pune.
Raman Research Institute, Bangalore
Canadian Space Agency, Canada
Leicester University, U.K.
With participation of
Many Indian Universities and research centres
Salient Features of Astrosat
•
Multi-wavelength observations with four co-aligned
instruments covering Visible, Near-UV, Far-UV, Soft X-ray
and Hard X-ray bands.
•
Broad Spectral coverage in X-rays from 0.5 keV to 100
keV for timing and spectral studies with 3 X-ray
instruments.
•
Large collecting area in 2-20 keV ( ≥ 6000 cm sq. ) for
timing studies in X-rays.
•
Largest area detector for hard X-ray studies ( ~ 5000
cm sq. at 50 keV ), important for studying high frequency
QPOs and non-thermal component in Black Hole sources.
•
High angular resolution telescopes ( ~ 2 arc sec ) in the
UV region. Two telescopes each of 38 cm aperture, one in
Visible and Near-UV and other in Far- UV with photon
counting detectors for high sensitivity observations.
•
• Soft X-ray Imaging Telescope and CZT Imager for
medium energy resolution spectral studies and
localization of Transients in soft and hard X-ray bands.
• A Scanning Sky X-ray Monitor to detect and monitor
Transients and known objects.
• High time resolution (10 µs ) and high count rate
capability ( 40 k Counts with PHA and 60 k Counts
without PHA ) with LAXPC instrument.
Astrosat Instruments
Four X-ray Astronomy Instruments and one Ultraviolet Instrument
With two Telescopes
1. LAXPC : Large Area X-ray Proportional Counters with Aeff ≈ 6000
cm2 at 20 keV, FOV =10 X 10, sensitive in 3-80 keV band with low
spectral resolution (E/ΔE ≈ 5 to 12) .
2. CZT Imager : X-ray detector CdZnTe (Cadmium-Zinc-Telluride)
array with a coded mask aperture having Aeff = 500 cm2 and
medium spectral resolution (E/ΔE ≈ 10 to 15 ).
3. SXT : Soft X-ray Imaging Telescope using conical-foil mirrors
with medium angular (~3' ) and spectral (E/ΔE ≈ 20 to 50)
resolution in 0.3-8 keV with A eff ≈ 200 cm2 at 1 keV.
4. SSM : Scanning Sky Monitor (SSM) using 3 PSPCs with
coded mask aperture , each with Aeff = 30 cm2 and energy
band of 2-20 keV.
5. UVIT : Ultraviolet Imaging Telescope (UVIT) has two
similar telescopes each with 38 cm aperture primary mirror
and photon counting imaging detectors covering
simultaneously near-uv , far-uv and visible bands.
A Charged Particle Monitor (CPM) as an auxiliary
instrument for the control and operation of the Astrosat
Instruments.
Instruments are technically complex and challenging, they are not commercially
available. In India the design and development of instruments have to be done in
house as expertise and experience available only with few persons.
Fabrication of flight hardware also mostly done in house only.
X-ray CCD mounted on Thermoelectric
Cooler to be used for the SXT
LAXPC X-ray detector Anode Assembly
with veto layer on 3 sides mounted on
the back plate. 60 Anode cells are
arranged in 5 layers to make the X-ray
detection volume. 37 Micron dia. Auplated SS wires under tension used for
anodes.
One LAXPC unit undergoing tests in Thermovac Chamber to simulate
space-like environment.
Soft X-ray Imaging
Telescope employs Xray Reflecting Optics
and an X-ray CCD to
record X-ray Image and
measure X-ray energy.
CZT Imager on Astrosat
For Hard X-ray
Spectroscopy and Imaging
Sectional View of the
Two Telescope
configuration of the
Ultra Violet Imaging
Telescope (UVIT) for the
Astrosat mission
UVIT Characteristics
Two similar coaligned telescopes
Primary Mirror aperture
:
Secondary
38 cms
14 cms
Focal length
:
503 cms
f/ratio
:
13
Configuration
:
RC with focal plane corrector
90% energy
:
≈ 1”
Corrected field
:
0°.5
Passband:
Channel I
120-180 nm
Channel II
180 – 300 nm
Optical
350-650 nm
Detector :
Photon counting system
CPM with appropriate read out
for getting X & Y
40 mm x 40 m
Pixel resolution
Material of Mirror :
:
25 μ
Zerodur with Al + MgF2
Input Window
Components
in each
Detector
300 V (nom)
and -50V,
switched
Photocathode
Front Gap
MCP Front
1000V (max)
MCP Intermediate
Intensifier
MCP Output
1700V (max)
Rear Gap
Anode
(DM)
5000V (nom)
Output Window
Fiber Optic
Taper
Fibre Optic
Taper
Imaging area : ~ 40 mm f
QE :> ~5% in band centre
Pos. res. < 100 mm
Exposure : 10-1000 mSec
Frame rate : > 20 Hz
Gain : 2000 – 20,000 e-/g
Safety : electronic gating
High Voltage
supplies
(HVU)
Static Drain
CCD
CCD/CMOS
(Need High Voltage Power Supplies;
up to 8000 V)
ASTROSAT Top Deck Layout
SXT
UVIT
LAXPC
CZT
SSM
Artist’s View of the Astrosat Multiwavelength
Observatory
Study of High Energy Universe by X-ray and UV
Observations
All types of Galactic and Extragalactic objects
are UV and X-ray sources
Galactic Sources :
Compact Stars in Accreting X-ray Binaries :
Neutron Stars { Both have high luminosity in X-rays
Black Holes { and are also visible in UV
White dwarfs ( Bright UV objects as T is high)
Supernova Remnants :
About 200 SNRs in our galaxy .
Shock heated gas (T ~ 10 5 - 10 7 ) emits UV and
X- rays
Extragalactic Sources :
AGNs ( Quasars, BL Lacs , Seyfert Galaxies ) :
Powered by massive ( 10 7- 10 9 M O ) accreting Black
Holes in their nuclei
Accretion Disks Around BHs emit UV and X-rays . There is
excess UV from AGNs (called UV Bump )
Star Burst Galaxies and Star Forming Regions :
Nurseries of young stars and pre-main sequence stars
that are copious UV and X-ray sources
Astrosat Science Objectives
Multiwavelength Observations
•
ASTROSAT will be a powerful mission for Multiwavelength
studies of various types of sources using 5 co-aligned telescopes
covering broad X-ray , near- UV , far- UV and Optical bands.
•
AGNs will be prime targets for this as only a small number of bright
AGNs studied in campaign mode so far.
•
Correlated UV , Optical and X-ray variations , measure time lags
and do reverberation mapping.
•
Construct energy distribution curves of AGNs over 5 decades in
energy
Images of the Active
Galaxy Nucleus of
NGC 4303 (M61) in
Optical,UV and Xray bands. The bright
central object is
likely to be a
Massive Black Hole
of 100 million Solar
mass producing
energy by accretion
of matter.
Light Curves of quasar 3C 273 over 20 year period in
different spectral bands
Fig. 2. Examples of light curves from the
3C 273 database for the last 23 years of
observations, at 5 GHz, 37 GHz, 0.8 mm,
in the K band, in the V band, at 5 keV and
in the 20–70 keV range (this latter rebinned
to 1-month bins).
The data during strong synchrotron flares
(Flag = 1) are indicated in grey (red in the
electronic version) for the optical and IR
data sets.
( From S. Soldi et al. A&A, 486, 411425,2008 )
Multiwavelength light curves from intensive monitoring of the BL Lac object PKS 2155304 in 1991 November (Edelson et al. 1995). X-ray data are from the Rosat PSPC; UV
data are from the IUE SWP (short wavelength) and LWP (long-wavelength)
spectrographs; optical data are from the FES monitor on IUE. The emission is closely
correlated at all wavelengths, and the X-rays lead the UV by ~ 2-3 hours.
Comparison of the NUV UVW1 and X-ray (0.6–10 keV) light curves over the 160 days of
Swift observations of Black Hole source XTE J1817-330. The NUV flux most closely
tracks the X-ray power-law emission and does not track the total X-ray flux or the X-ray
disk flux (ApJ,666,1129,2007
Astrosat Sience Goals
High resolution timing studies :
Periodic and chaotic variability, Evolution of pulse and
orbital periods in X-ray binaries, Accreting Millisec Pulsars
and AXPs.
•
• Detection and measurements of of low and high
frequency QPOs in soft and hard X-ray bands in Black
Hole and other X-ray Binaries .
High Freq. QPOs studies put constraints on mass and
spin of Black Holes.
Periodicities in Accreting X-ray Binaries (Neutron Star and Black Hole
Systems)
P(spin) ~ msec to ~ 1000 sec , P (orbital) ~ 14 min to 100 days
P (QPOs) ~ 0.1 Hz to ~ 1000 Hz , P (Flicker) ~ 100 ms to 10 mins
P(Precession or disc warping) ~ 10 days to `300 days ( found in some XRBs
e.g. Her X-1 ~ 35 days, Cyg X-1 ~ 300 days)
Sub-second Intensity Variations in the Micro-quasar GRS 1915+105
with the Indian X-ray Astronomy Experiment (IXAE) on IRS-P3 .
Period vs. Period derivative Diagram for all known Pulsars
Red Stars are Magnetars
Big Red Star is the new Magnetar SGR 0418+5729 ( N. Rea et al.,Science,330, 944,
2010 )
Giant flares from SGRs
LF ~ 1045-1047 erg
SGR 1900+14 – Aug. 1998
Hurley et al. 1999
SGR 1806-20 – Dec. 2004
Palmer et al. 2005
Recent result
•
Detection of QPOs above 10 keV in Black Hole and
Neutron star binaries is an unexplored area. QPOs
above 10 keV detected so far only in 3 BH Binaries.
kHz QPOs above 10 keV reported so far only in GRO
J1655-40.
•
Do AGNs show Bimodal states similar to that of
Stellar- mass Black Holes ? Repeated observations of
AGNs required to answer this.
•
Search QPOs in AGNs. Reports of a few detections
so far.
QPOs detected in two ULXs (Strohmayer & Mushotzky 03; Strohmayer et al. 07)
M82 X-1: 􀈞QPO = 54-166 mHz
NGC5408 X-1: 􀈞QPO = 20 mHz
Properties (rms, coherence, noise, variability)similar to Type C QPOs in BHBs
(0.1-15 Hz). Extrapolating correlations known to exist for BH binaries and
assuming that
QPO scales inversely to MBH (Mucciarelli et al. 06; Strohmayer et al. 07):
QPOs detected in XMM-Newton light curve of Narrow-line
Seyfert 1 RE J10.34+396. QPO Period= 3733 s
M Gierliński et al. Nature 455, 369-371
(2008) doi:10.1038/nature07277
High-frequency QPOs seen in
several BHBs occur in pairs
with the frequency ratio of 3:28.
These frequencies appear to
be stable and are regarded as a
signature of strong gravity in
the vicinity of a rotating black
hole18. A tentative frequencymass relation, f 0 = 931
(M/M☼)-1 Hz, can be derived
from three objects. Here f 0 is the
fundamental frequency of the
pair, i.e. the observed
frequencies are 2f0 and 3f0 (the
fundamental
is not seen). This relation yields
the black hole mass
in RE J1034+396 of 6.9×10e6 or
1.0×10e7 M☼, depending on
whether the observed periodicity
corresponds to 2f0 or 3f0,
Astrosat Science Goals
Broad band Spectral measurements :
•
Spectra of the continuum emission from all
classes of UV and X-ray sources
•
Emission and absorption features with medium
energy resolution capability in 0.3 – 100 keV
spectral band with 3 co-aligned X-ray instruments.
•
Understand the Complex Multi-component energy
Spectra of galactic and extragalactic Black Hole
sources to understand the origin of radiation from
various processes.
•
Measuring non-thermal spectral component in
Accreting NS and BH Binaries,SNRs and AGNs
Energy Spectra of Black Hole Binary Cyg X-1 and Neutron
Star Binary 4U 1705-44 ( Astro-ph 0909.2572 by Gilfanov)
Energy Spectrum of SNR
Cas A in o.5-100 keV
X-ray measurements above
20 keV crucial for detecting
Non-thermal spectral
component in X-ray binaries,
SNRs, AGNs and Cluster of
Galaxies.
Average Spectrum of Intermediate
Polars . Best fit kT ~ 20 keV
Energy
Spectrum of
Seyfert 1
Galaxy IGR
07597 – 3842
from Integral
and Chandra/
XMM-Newton
data.
Molina et.al.
MNRAS (2009)
Microquasar GRS 1915+105
A & A,494,229,2009
Power Law index = 1.6, Cut off Energy= 70 keV
Energy Spectra of Magnetars
measured with instruments
onboard Suzaku in 0.8-70 keV.
A Blackbody thermal
component with kT ~ 0.5-1 keV
and a power law component
with photon index ~ 0.4-1.7 fit
the spectra well ( Enoto T. et al.
Astro-ph 1009.2810 ).
Astrosat Science Goals
•
Measure Magnetic Field of Neutron Stars in X-ray Binaries
From detection and energy of Cyclotron lines in the X-ray spectra of
Pulsars. Cyclotron absorption lines in ~ 12 – 60 keV detected in the X-ray
spectra of ~ 20 X-ray Pulsars
B ~ ( 2-8 ) 10 12 Gauss
• High resolution ( ≤ 2 arc sec ) UV imaging studies of Star Burst Galaxies,
Nornmal Galaxies ,AGNs, Hot stars, SNRs etc.
•
Deep UV survey of selected regions of sky
•
X-ray scans of Galactic Plane and Center for detection of new transients
and other variable sources
•
X-ray Monitoring of Sky for detection of Transients, Bursts and Flaring
activity and studies of persistent sources
Luminosity (3–50 keV) dependence of the fundamental cyclotron resonance energies in binary
X-ray pulsars, using Gaussian absorption modeling. The other data points for A0535+262
refer to Wilson & Finger (2005; LX = 1.1 × 1037 ergs s-1), Kretschmar et al. (2005; 0.4 × 1037),
Grove et al. (1995; 3.6 × 1037, assuming 110 keV as the second harmonic), and Kendziorra et
al. (1994; 3.8 × 1037). The results on 4U 0115+63 and X0331+53, both assuming a distance of
7 kpc, are from Nakajima et al. (2006) and Nakajima (2006), respectively.
Simulation of Cyclotron Lines from Pulsar 4U0115+63
Ultraviolet image of Galaxy M 33 with Galex. Credit:
NASA/JPL-Caltech/GALEX
Astrosat Mission Characteristics
• Pointing accuracy of about 1 arc sec.
• Three axes stabilized well proven satellite bus using 3
gyros and 2 star trackers for attitude control by reaction
wheel system with a Magnetic torquer
• Mission life of at least 5 years. Circular orbit of 600 km
altitude and inclination of ≤ 8°.
• Launch by well proven Indian Polar Satellite Launch
Vehicle (PSLV) from Satish Dhawan Launch Center at
Shriharikota (India).
•
Conclusions
• Astrosat will enable timing observations with 10 µs
accuracy in a broad spectral band of 3-80 keV with
LAXPCs of A ~ 6000 cm -2 in. 3-20 and ~ 5000 cm-2
in 20-60 keV bands. Largest area ever used for hard
X-ray studies.
• Medium energy resolution capability of CZT for
accurate spectra and detection of cyclotron features.
• SXT for imaging and spectral studies for 0.3-8 keV
band.
• Simultaneous observations with co-aligned 3 X-ray
Instruments covering 0.3-100 keV region to
construct spectra of sources.
Obtain multifrequency spectra covering Visible, UV , Soft
X-ray and Hard X-ray regions for a variety of sources.
UV studies and deep UV survey of selected regions and
sources with UVIT to a limit of m ~ 21st magnitude.
Detection and monitoring of transient and persistent Xray sources with SSM.