1. Anti-Correlated Lags in Compact Stellar X-ray Sources Dr. Kandulapati Sriram Collaborators: Prof A. R. Rao (TIFR) Dr. Vivek Kumar Agrawal (ISRO/TIFR). Dr. Ranjeev Misra (IUCAA)

2. The Work is based on published papers by our group 1. Anticorrelated Hard X-Ray Time Lag in GRS 1915+105: Evidence for a Truncated Accretion Disk Choudhury, M., Rao, A. R., Dasgupta, S., Pendharkar, J., Sriram, K., & Agrawal, V. K. 2005, ApJ 2. Anticorrelated Hard X-Ray Time Lags in Galactic Black Hole Sources Sriram, K., Agrawal, V. K., Pendharkar, Jayant, & Rao, A. R., 2007, ApJ 3. Energy-dependent Time Lags in the Seyfert 1 Galaxy NGC 4593 Sriram, K.; Agrawal, V. K.; Rao, A. R., 2009, ApJ 4. A truncated accretion disk in the galactic black hole candidate source H1743-322 Sriram, K.; Agrawal, V. K.; Rao, A. R., 2009, RAA And some other work carried out at KASI

3. Overview A. Introduction 1. Mass transfer and Disk formation 2. SS disk and Why ADAF? 3. Basic X-ray continuum models B. About 1. RXTE Satellites 2. X-ray spectral states in GBHs 3.VH/SPL/IM state and possible geometry C. Method, Application & Results 1. CCF 2. ACL in GBHS, NS 3. physical interpretation and Results D. Conclusion

4. Mass Transfer in Binary Stars In a binary system, each star controls a finite region of space, bounded by the Roche Lobes (or Roche surfaces). Matter can flow over from one star to another through the Inner Lagrange Point L1. Lagrange points = points of stability, where matter can remain without being pulled towards one of the stars.

5. Accretion from stellar wind Accretion through Roche lobe outflow Two mechanisms of mass transfer in a binary system

6. How Disk forms? Jet disk L1 Accretion in LMXB is due Roche Lobe Overflow As secondary star evolves it fill up its Roche lobe (equipotential surface) Mass transfer take place from Lagrange point L1

7. Formation of disk.. Low AM High AM Matter passing through L1 has AM forms an elliptical orbit around primary For continues stream of matter, form a ring to sink in the gravitational potential of primary, it loses AM matter slowly spiral inwards in circular orbit and forms an accretion disk

8. How does disk heats up? Two main process responsible for heating up the disk 1. Gravitational Binding energy : Matter goes in -----> decrease in GBE results in hot disk 2. Viscous Dissipation: Friction between two layer----transport the AM outside—heat up the disk 3. Because of heating---->~disk temp. goes to 10 7-8 K (X-ray band)

9. Black Body approximation SS Disk For steady geometrically thin (h<<r) and optically thick disk Each ring “dR” loses GΩ'dR of mechanical energy into heat energy (G is torque) for upper and lower face of disk D(R)=9/8* νΣ GM/R 3 (D(R)=rate / unit surface area ν- kinematic viscosity Σ-surface density)‏ changing νΣ in terms of M dot and R, we get D(R)=3GMM dot / 8ΠR 3 [1-(R*/R) 1/2 ] Total rate at which energy is dissipated 3GMM dot /2ΠR 2 [1-(R*/R) 1/2 ] Emitted spectrum σ T 4 =D(R)---> T= (3GMM dot / 8ΠR 3 σ) 1/4

10. Multi BB components in Disk Standard accretion disk spectrum looks like super-positon of blackbody spectra multi-color disk-blackbody approximation works (diskbb in xspec) Each disk annuli is responsible for obs. Disk temperature

11. Problems.. SS disks are ideal and occasionally seen Remedy: ADAF, radiative inefficient (developed by Narayan and collaborators) Most probable model to explain the low luminous episodes in X-ray binaries

12. Why Is the Flow Advection-dominated? Radiation comes primarily from electrons At low, ion-electron (Coulomb) coupling is weak Plasma becomes two-temperature --- heat energy is locked up in the ions and advected to the center Radiative efficiency of electrons is also low, so electrons also advect their energy Very hot, optically thin gas. Quasi-spherical. Non-blackbody spectrum (Shapiro, Lightman & Eardley 1976; Ichimaru 1977; Bisnovatyi–Kogan & Lovelace 1997; Quataert 1998; Gruzinov 1998; Quataert & Gruzinov 1998 ; Blackman 1998; Medvedev 2000 ) Too Many changes in disk theory to explain observations, ADIOS, CDAF, slim disk model etc.

13. Basic Continuum models Two kind spectral components In BHB 1. Soft X-ray component ( few eV to ~ 1 keV) Thermal in nature, black body radiation No census of BB component Each radii in disk emits a BB spectrum know MCD model

14. Conti.. 2. Hard X-ray Component – Not exactly known in terms of physical location, exact mechanism (thermal,non- thermal, processes) etc. –Spectral domain is vast (few keV to GeV) –Many possible Mechanism »Thermal Comptonization »Non thermal Comptonization »Syncrhoton »Bremmstrulung

15. The Comptonization Process Discovered by A.H. Compton in 1923 gain/loss of energy of a photon after collision with an electron If electron at rest: Compton Inverse Compton For non-stationary electron:

16. Thermal Comptonization mean relative energy gain per collision mean number of scatterings ➨ Compton parameter for E < kT, unsaturated Compt. for E ≳ kT T soft T c,  Hot phase = corona Comptonization on a thermal plasma of electrons characterized by a temp. T and optical depth τ Cold phase = acc. disc For E~KT saturated Comptonization

17. Non-thermal Comptonizaton Comptonization by a non-thermal distribution of electrons For electron with large Lorentz factor ➥ very efficient energy transfert ⇒ Possible non-thermal electrons are from jets close to X-ray binaries

18. Disk Corona Geometries.. slab, sandwich sphere+disk geometry patchy

19. RXTE Satellite PCA Energy range: 2 - 60 keV Energy resolution: < 18% at 6 keV Time resolution: 1 microsec Spatial resolution: 1 degree Detectors: 5 proportional counters Collecting area: 6500 square cm HEXTE Energy range 15-200 keV Time resolution min 32 sec 4 NaI/CsI Scintillation counter Area : 1600 sq. cm All Sky Monitor (ASM) Remarkable temporal resolution and covers spectrum domain of 2.5-200 keV

20. COSPAR Workshop, Udaipur 2003 Unfolding Spectrum: the Basic Problem Suppose we observe D(I) counts in channel I (of N) from some source. Then : D(I) = T ∫ R(I,E) A(E) S(E) dE T is the observation length (in seconds) R(I,E) is the probability of an incoming photon of energy E being registered in channel I (dimensionless) A(E) is the energy-dependent effective area of the telescope and detector system (in cm 2 ) S(E) is the source flux at the front of the telescope (in photons/cm 2 /s/keV

21. COSPAR Workshop, Udaipur 2003 Conti.. D(I) = T ∫ R(I,E) A(E) S(E) dE We assume that T, A(E) and R(I,E) are known and want to solve this integral equation for S(E). We can divide the energy range of interest into M bins and turn this into a matrix equation : D i = T ∑ R ij A j S j where S j is now the flux in photons/cm 2 /s in energy bin J. We want to find S j.

22. COSPAR Workshop, Udaipur 2003 Conti.. D i = T ∑ R ij A j S j The obvious tempting solution is to calculate the inverse of R ij, premultiply both sides and rearrange : (1/T A j ) ∑ (R ij ) -1 D i = S j This does not work ! The S j derived in this way are very sensitive to slight changes in the data D i. This is a great method for amplifying noise.

23. COSPAR Workshop, Udaipur 2003 Mathematical Methods In mathematics the integral is known as a Fredholm equation of the first kind. Tikhonov showed that such equations can be solved using “regularization” - applying prior knowledge to damp the noise. A familiar example is maximum entropy but there are a host of others. Some of these have been tried on X-ray spectra - none have had any impact on the field.

24. COSPAR Workshop, Udaipur 2003 Define Model Calculate Model Convolve with detector response Compare to data Change model parameters Solution: Forward-fitting algorithm The aim of the forward-fitting is then to obtain the best-fit and confidence ranges of these parameters.

25. Basic Spectral states in GBHs Soft State, thermalBB Hard State, thermal Comp. or Non-thermal IM state/VHS/SPL Cyg X-1 Figure is taken from Zdziarski et al. 2002 Soft State, Non-thermal

26. Three-state classification Remillard & McClintock 2006 In this classification the luminosity is not used as one of parameters.

27. VH state, special spectral state.. GRO J1655–40 Most often brightest state among all Steep unbroken (X-ray to gamma-ray) PL ( ≥ 2.4-2.8), no evidence for high- energy cutoff transitions between TD and LH states usually pass through SPL state essentially radio-quiet; though sometimes shows impulsive jets QPOs in 0.1–30 Hz range and HFQPO are also found in this state Both soft (disk) and hard (Compton cloud/corona) component dominates

28. Disk and jet connection (Fender et al. 2004, Remillard, McClintock astro-ph/0606352) The model for systems with radio jets LS – low/hard state HS – high/soft state VHS/IS –very high and intermediate states The shown data are for the source GX 339-4.

29. Typical outburst of BH source

30. QPO propagation during an Outburst

31. 26 March 2008Truncated disc and X-ray spectral states 31 Spectral states – moving truncation radius Lh/LsLh/Ls hard state soft state

32. Possible generalized geometry of AD LH- large truncation of accretion disk VHS/SPL/IM- less truncation of disk High state/Thermal dominated disk: No truncation

33. More about SPL state.. Steep Power-Law (SPL)‏/VHS/IM ⌂ physical origin still an outstanding problem ⌂ spectrum extends to ~1MeV, may be higher ⌂ possible physical model:  Inverse Compton scattering for a radiation mechanism  Perhaps scattering occurs in a thermal corona below 100 keV and non thermal corona at high energies.  Disk is observationally found to be truncated at ~10-30 Rs  PL gets stronger and steeper as disk luminosity and radius decrease, while keeping high temperature

34. Possible geometrical configuration of VH state Disk, seed soft photons Corona, Compton cloud, thermal Comptonized hard photons How can we detect these signatures in a short time of few kiloseconds instead of waiting for whole long outbusrt of typical duration few days to few 100 days????

35. Method: Cross-correlation Method To understand the disk Geometry, we use three different ways 1.Cross-Correlation 2. Model independent & dependent Spectral study 3. QPO analysis Cross correlation is a standard method of estimating the degree to which two time series are correlated. ALL the data used belongs to SPL/VH/IM state

36. CCF? Two series are highly correlated, with no lag, then CCF peak points to Zero In anti-correlation, CCF peak shift to the -tive side.

37. First such source to show lags is Cyg X-3 First source in which ACL was detected was Cyg X- 3 Brightest X-ray source in Radio band Orbital period ~4.8 hrs no optical counterpart has been found no information on Compact object strong evidence of jetlike structures Spectral studies reflects typical BH spectrum Choudhury & Rao 2004, ApJL

38. GRS 1915+105 Harbours Most massive BH (~14 solar mass)‏ Orbital period~33 days (largest among GBHs)‏ LMXB, secondary is K/MIII type star Show relativistic jet Highly variable X-ray source among all the BH distance 6~10kpc Chi state Choudhury et al. 2005, ApJ

39. H1743-322, Sriram et al. 2009, RAA XTE J1550-564, Sriram et al. ApJ, 2007

40. First Neutron stars source to show ACL Lei et al. 2008, ApJL Cyg X-2

41. GX 339-4, first BH source to show AC soft lag Sriram, Rao & Choi submitted to ApJ

42. ACL for GX339-4 using RXTE and INTEGRAL

43. Various Timescale is Accretion disk Viscous timescale : t v ~R/v r Dynamical time scale : t φ ~1/Ω k (QPO ???) Deviation in vertical structure timescale : t z ~t φ Thermal time scale : t th ~M -2 t v Compton cooling timescale: t cool = 10 −6 × R 3 7 Ṁ −1 17 m −1 10 T 8 t cool <~ t φ ~ t z < t th << t v (for complete derivation of Compton cooling time scale see Sriram et al. 2009, RAA)

44. Typical timescales in different size BH TimescaleGBHsULXsSMBH ViscousFew days - weeks ~ Few 10's years Few thousand to million years Dynamical0.1-100's Hz Few milli Hz Few hours QPO in AGN (Gierlinski et al. 2009, Nature) Compton cooling Few milli- micro sec Few 10's sec Few 100's-1000's sec (see Sriram et al. 2009, ApJ)

45. Truncation radius assuming that they indicate small viscous delays α is the viscosity parameter in units of 0.01, M is the mass of the compact object in solar mass units, R is the radial location in the accretion disk in units of 10 7 cm, and Mdot is the mass accretion rate in units of 10 18 g s -1 Taking α = 1, M = 10, and Mdot= 3, we get R ~ 7 for a viscous timescale of 1000 s. Thus ~25 Schwarzschild radius. Similar dimension for truncation radius is observed in SPL state using QPO frequency (see Done et al. 2007)

46. QPO changes??? GRS 1915+105, Choudhury et al. 2005 XTE J1550-564 Sriram et al. 2007, ApJ

47. For source H1743-322

48. For GX 339-4 QPO changes

49. Spectral changes Model independent changes GRS 1915+105 Cyg X-3

50. XTE J1550-564

51. For H1743-322

52. GX 339-4 spectral changes Spectral Ratio

53. Spectral changes More importance is given to know the change in spectral parameters. spectral fitting was carried for H1743-322, XTE J1550-564, GRS 1915+105 (all of them were in VHS or SPL state) Spectra were obtained from initial and final part of the Lc, for the resp. sources for which QPO shift was found Model used : Smedge(Diskbb+Gaussian+ThComp+PL)‏ PL index =2.2 and Gaussian Line=6.4 keV were fixed

54. Simultaneous Spectral fitting –Data is not sufficient to know which parameter is changing –Fitted the initial and final part spectra simultaneously –all the parameters tied to the initial spectrum –Initially the χ2 was very high –Nthcomp of two parts allowed to vary independently(χ2 improved). –Then Ndisk and kTin were allowed to vary one by one –continued the process no considerable improvement was observed in the fit –Suggest that Normalisation and disk parameters significantly varied between these two parts.

55. Most important result is change in disk and Corona flux (unit: 10 -9 ergs/cm 2 /sec) during lag in different source XTE J1550-564 flux A B -------- soft 20.9 22 hard 56.5 52.5 _______________ _ 2 nd Obsev. flux A B -------- soft 17.3 23.2 hard 52.5 42 H1743 A1 B1 A2 B2 A3 B3 A4 B4 -332 Soft7.90 7.41 61.10 100.20 119.1 84.10 4.3 3.9 Hard 41.17 46.50 10.1 8.10 12.6 10 3.9 5.6 GRS 1915+105 A B Soft8.5 6.2 Hard 11.4 22.0 For GRS 1915+105, we found electron temperature is changed by ~4 keV Sriram et al. 2007, ApJ

56. GX 339 -4 unfolded residual with same model used for A section spectrum

57. Physical Interpretation of temporal and spectral delays of VH state In GBHs Disk, seed soft photons Corona, Compton cloud, thermal Comptonized hard photons As Disk goes in, Soft photons increases and cools the cororna and hard photons decreases

58. Conclusion Still the Hard X-ray source location in accretion process in BH, NS and CV is poorly know. Cross-Correlation method is one of the powerful tool to constrain the physical location in accretion disk (BH, NH)/ column (polar). Similar kind of work can be extended to other BHs, NSs, CVs inorder to constrain the geometrical and physical regions in the accretion processes

59. Conclusion Still the Hard X-ray source location in accretion process in BH, NS and CV is poorly known. Cross-Correlation method is one of the powerful tool to constrain the physical location in accretion disk (BH, NH)/ column (polar) or IPs Similar kind of work can be extended to other BHs, NSs, CVs inorder to constrain the geometrical and physical regions in the accretion processes.

60. Work carried out at KASI during Dec 16-till Now X-ray Work Anti-Correlated soft lags in Intermediate state of BH source GX 339-4 (Sriram, Rao & Choi submitted to ApJ) XMM-Newton observation of a cataclysmic variable candidate: AX J1853.3- 0128 (Hui, Sriram & Choi planning to submit in ApJ) Optical Work Photometric study of Contact binary systems in omega Centauri (Sriram et al., submitted to Ap&SS) Photometric study of W Uma type variable in LMC (Shanti, Sriram and Vivekananda Rao submitted to RAA)