Overview of Science with Astrosat

P.C.Agrawal UM-DAE Center for Excellence in Basic Sciences, Mumbai University Campus, Vidhyanagari,Mumbai

Talk at LAXPC Workshop at BF Hyderabad , December 15 , 2014 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

•IXAE on IRS-P3

• Launched on March 21, 1996 from SHAR • IXAE PPCs on top deck with remote sensing instruments • Stellar mode observations for about 2/3 months in a year • IXAE switched off after 5 yrs of operation due to depletion of fuel for pointing control

Quasi-regular Bursts from GRS 1915+105 observed with PPCs on IXAE (Paul et al. ApJ Lett ,1998) 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 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 2 0 0 cm at 20 keV, FOV =1 X 1 , 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) 2 array with a coded mask aperture having Aeff = 500 cm and medium spectral resolution (E/ΔE ≈ 20 to 30).

3. SXT : Soft X-ray Imaging Telescope using conical-foil mirrors with medium angular (~3' ) and spectral (E/ΔE ≈ 20 to 50) 2 resolution in 0.3-8 keV with A eff ≈ 200 cm at 1 keV. 4. SSM : Scanning Sky Monitor (SSM) using 3 PSPCs with 2 coded mask aperture , each with Aeff = 30 cm 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 FUV ----- 130 – 180 nm 28 arc min field NUV ------200 – 300 nm Visible ----- 320 – 550 nm

A Charged Particle Monitor (CPM) as an auxiliary instrument for the control and operation of the Astrosat Instruments.

• LAXPC has high detection efficiency up to ~ 80 keV ( > 50 % upto 70 keV) • Deep Detector (15 cm arranged in 5 layers each 3 cm deep vs 3.3 cm for the PCA on RXTE • Xenon filled at a pressure of 2 atmosphere

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. Au-plated SS wires under tension used for anodes.

A view of the LAXPC Instrument used for assessing the performance of LAXPCs in a Balloon flight launched on April 16,2008 from BF Hydearabad reaching a ceiling of 41 km (2.5 g/ cm -2 of residual atmosphere. It used 2 LAXPCs similar to Astrosat LAXPCs but with FOV of 3 deg X 3 deg. LAXPC A Count rates as a function of time. Increase in count rates in Cygnus X-1 observations can be clearly seen. 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 Thermoelectr ic Cooler to be used for the SXT CCD Data (CCD +TIFR Electronics)

Isolated pixels only 5.9 and 6.4 keV peaks

Resolution ~150 eV (2.5% at 6 keV)

Si escape peaks 3.70 and 4.15 keV

30 December 2014 16 CZT Module characterization Estimated Effective Areas of UVIT Effective area of Astro-H at different energies for the 4 instruments aboard (Takahashi et al. 2014) X-ray light curve and pulsations from NuStar J09551+6940.8 coincident with known ULX in M82 . (Pulsation P= 1.37 s , Orbital P= 2.51 days)

Bachetti et al. Nature, 2014 Study of High Energy Universe by X-ray and UV Observations All types of Galactic and Extragalactic objects are UV and X-ray sources Brightest Galactic Sources in UV and X-rays : 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 :

Intermediate –Mass Black Holes in galaxies AGNs ( Quasars, BL Lacs , Seyfert Galaxies ) : 7 9 Powered by massive ( 10 - 10 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 )

Cluster of Galaxies : Thermal emission Lx ~ 10 44 ~ 10 46 ergs per sec Detection and study of Non-Thermal Component

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 so far.

• Correlated UV , Optical and X-ray variations , measure time lags and do reverberation mapping.

• Broad band studies of X-ray binaries and Magnetic CVs is important for probing origin of components of emission

Multiwavelength light curves from intensive monitoring of the BL Lac object PKS 2155- 304 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. Size of emission region, Nature of X-ray source, orbital parameter , rotation rate of neutron star, Accretion Torque acting on it, idea about magnetic field etc • 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 . Accretion process , innermost stable orbit of matter in accretion disk • High Freq. QPOs studies put constraints on mass and spin of Black Holes.

Dependence of NS Spin-up rate on X-ray flux (Bildsten et al. 1997) Spin period evolution of GX 1+4 (Gonzalez-Galan et al. A&A 2011) LMXB with disk fed accretion, P= 7.66 sec

Spin-up/ Spin-down transition in disk accreting NS in the X- ray Binary 4U 1626-67 (Camero-Arranz et al. ApJ,708, 2010) Light Curve of LMXB Transient Aql X-1 can be explained by Propeller effect (Campana 2014) High Frequency QPOs in BH X-ray Binaries from PCA on RXTE QPOs in black hole transient XTE J1817- 330 (Roy et al. MNRAS 2011). Panel (a) 2-8 keV (b) 8-14 keV and (c) 15- 25 keV QPOs detected in XMM-Newton light curve of Narrow-line Seyfert 1 RE J10.34+396. QPO Period= 3733 s High-frequency QPOs seen in several BHBs occur in pairs with the frequency ratio of 3:2. 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 frequency- mass relation, f 0 = 931 (M/M☼)-1 Hz, can be derived from three objects. This relation yields the black hole M Gierliński et al. Nature 455, mass in RE J1034+396 of 6.9×10e6 369-371 (2008) or 1.0×10e7 M☼, depending doi:10.1038/nature07277 on whether the observed periodicity corresponds to 2f0 or 3f0, Relation between QPO Frequency and BH Mass (Zhou et al. ApJ Lett, 2014)

The solid line denotes the relation, f (Hz) = 1862(MBH/M⊙)−1 derived from three X-ray binaries (Remillard & McClintock 2006). The long-dashed line denotes the relation, f (Hz) =2030.8(MBH/M⊙)−1 for a model of 3:2 resonance and spin parameter a = 0.996; the dotted-dashed line denotes the relation, f (Hz) =3068.9(MBH/M⊙)−1 for a model of 3:1 resonance and spin parameter a = 0.996; dotted line denotes the Kepler frequency for a non-spinning Schwarzschild black hole at the innermost stable circular orbit. 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

Astrosat Science Goals

Broad band Spectral measurements :

• Black Body and Thermal Components usually dominant in most sources below a few keV.

• Non-thermal emission prominent in BH Binaries and AGNs above 10 keV.

RXTE-PCA Energy Spectrum of HMXB A 0535+26 during quiescence (Rothschild et al. ApJ,2013) Energy Spectra of Black Hole Binary Cyg X-1 and Neutron Star Binary 4U 1705-44 ( Astro-ph 0909.2572 by Gilfanov et.al. ) Spectrum of BH Binary GX 339-4 in hard state with Swift-XRT (0.8- 8keV),RXTE-PCA (3.6 – 25 keV) and RXT-HEXTE (17 – 240 keV) (a) Observed spectrum (b) Spectrum fitted with a thermal component, a reflection component and in iron emission line (Tomsick et al. ApJ. 2006) Astrosat Science Goals • Detection and profiles of Cyclotron Resonance Absorption Features in the spectra of X-ray Pulsars

Cyclotron features deteted so far in ~ 23 pulsars range in 10 keV ( ) to 78 keV ( ) • 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

P (spin) ---4.37 s , P (orbit) ---- 34.7 days Cyclotron line at 26 keV, harmonics at ~50 and ~ 73 keV L (x) anticorrelated with line energy

Energy spectrum of the accreting pulsar in V 0332+53 at two intensity levels measured with the INTEGRAL. Two Cyclotron lines are clearly seen (Tsygankov et al. MNRAS, 371,2006) Centroid Energy of phase averaged Cyclotron line from Her X-1 since its discovery (Staubert et al. A&A, 2014) Astrosat Mission Characteristics • 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 • Pointing accuracy of about 1 arc sec. • 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). • Mass of satellite 1548 kg including 870 kg mass of science payloads. • Data stored onboard in a 120 Gbits Solid State Recorder already proven in an earlier mission. • Data transmission by two X-band carriers at rate of 105 Mbits per sec.

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. • 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 ( 21 mag or better) 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 with LAXPC instrument.

Allocation of Observing Time and Data Sharing Policy

• Performance Verification Phase (First 6 months) All Observations by Instrument Teams • Guaranteed Time for Instrument Teams ( Next 6 months) • First Year of Regular Observations in Pointed Mode 35% Time for Indian Astronomers, 5% GT for CSA , 3% GT for Leicester University, 5% TOO, 2% TBD, 50% GT for Instrument Teams • Second Year of Regular Observations in PM 45% Time for Indian Astronomers on Competitive basis. 10% Any International Astronomer on Competitive basis. 30% GT for Instrument Teams, 5% GT for CSA, 3& GT for LU , 5% TOO, 2% TBD •

Allocation of Observing Time and Data Sharing Policy

•Third Year Onwards 5% GT for CSA, 3% GT for LU , No Guaranteed time for Instrument teams.

• All Science Data in a National Space Science Data Archival Centre for ISRO after a TBD period (12 months except PV and GT data) accessible to any one in the world.