1. Mysterious transient objects Poonam Chandra Royal Military Collage of Canada

2.  Universe has > 125 billion galaxies  Each galaxy has ~100 billion stars  Universe has > 125 billion galaxies  Each galaxy has ~100 billion stars

3. Astronomical time scales Age of Universe ~14 billion years Life time of stars ~ millions to billions of years Astronomical time scales Age of Universe ~14 billion years Life time of stars ~ millions to billions of years Some sources appear in the sky for few seconds to few months to few years…. Transient objects Observing, modeling and understanding these transient objects

4. SUPERNOVAE (SNe)  Few months to few years timescale  Massive explosions in the universe  Energy emitted 10 51 ergs (10 29 times more than an atmospheric nuclear explosion)  Shines brighter than the host Galaxy  As much energy in 1 month as sun in ~1 billion years  In universe 8 supernova explosions every second  Thermonuclear and gravitational collapse  Few months to few years timescale  Massive explosions in the universe  Energy emitted 10 51 ergs (10 29 times more than an atmospheric nuclear explosion)  Shines brighter than the host Galaxy  As much energy in 1 month as sun in ~1 billion years  In universe 8 supernova explosions every second  Thermonuclear and gravitational collapse

5. GAMMA-RAY BURSTS (GRBs)  Most luminous events in the universe since big bang  Flashes of gamma-rays from random directions in sky  Few milliseconds to few seconds timescale  Even 100 times more energetic than supernovae  Brightest sources of cosmic gamma-ray photons in the universe  In universe roughly 1 GRB is detected per day  Short duration ( 2sec)  Most luminous events in the universe since big bang  Flashes of gamma-rays from random directions in sky  Few milliseconds to few seconds timescale  Even 100 times more energetic than supernovae  Brightest sources of cosmic gamma-ray photons in the universe  In universe roughly 1 GRB is detected per day  Short duration ( 2sec)

6. Soft Gamma-Ray Repeaters (SGR)  Time scale of few days  Repeated flares in Soft Gamma Ray or hard X-ray band  Less energetic then supernovae and GRBs but Galactic  In 1/10 of a second as much energy as sun emits in 100,000 years continuously.  1000 times more bright than combining all the stars of Milky Way together.  Only handful of SGRs are known  Time scale of few days  Repeated flares in Soft Gamma Ray or hard X-ray band  Less energetic then supernovae and GRBs but Galactic  In 1/10 of a second as much energy as sun emits in 100,000 years continuously.  1000 times more bright than combining all the stars of Milky Way together.  Only handful of SGRs are known

7. Common origin: Massive stars

8. Nuclear reactions inside a star

9. 4-8 M sun : thermonuclear supernovae 4-8 Massive star: Burning until Carbon Makes Carbon-Oxygen white dwarf White Dwarf in binary companion accretes mass Mass reaches Chandrashekhar mass Core reaches ignition temperature for Carbon Merges with the binary, exceed Chandrasekhar mass Begins to collapse. Nuclear fusion sets Explosion by runaway reaction – Carbon detonation Nothing remains at the center Energy of 10 51 ergs comes out Standard candles, geometry of the Universe 4-8 Massive star: Burning until Carbon Makes Carbon-Oxygen white dwarf White Dwarf in binary companion accretes mass Mass reaches Chandrashekhar mass Core reaches ignition temperature for Carbon Merges with the binary, exceed Chandrasekhar mass Begins to collapse. Nuclear fusion sets Explosion by runaway reaction – Carbon detonation Nothing remains at the center Energy of 10 51 ergs comes out Standard candles, geometry of the Universe

10. Thermonuclear Supernovae

11. M >8 M sun : core collapse supernovae Burns until Iron core is form at the center No more burning Gravitational collapse First implosion (increasing density and temperature at the center) Core very hard (nuclear matter density) Implosion turns into explosion Neutron star remnant at the centre. Explosion with 10 53 ergs energy 99% in neutrinos and 1 % in ElectroMagnetic Scatter all heavy material required for life Burns until Iron core is form at the center No more burning Gravitational collapse First implosion (increasing density and temperature at the center) Core very hard (nuclear matter density) Implosion turns into explosion Neutron star remnant at the centre. Explosion with 10 53 ergs energy 99% in neutrinos and 1 % in ElectroMagnetic Scatter all heavy material required for life

12. Core Collapse Supernovae

13. M > 30 M sun : Gamma Ray Bursts Forms black hole at the center Rapidly rotating massive star collapses into the black hole. Accretion disk around the black hole creates jets GRBs are collimated. All GRBs extragalactic Some GRBs associated with supernovae (GRB980425/SN1998bw, GRB030329/SN2003dh etc.) Dedicated instruments (BATSE, BeppoSax, Swift) These GRBs last for few seconds For longer duration in lower energy bands Forms black hole at the center Rapidly rotating massive star collapses into the black hole. Accretion disk around the black hole creates jets GRBs are collimated. All GRBs extragalactic Some GRBs associated with supernovae (GRB980425/SN1998bw, GRB030329/SN2003dh etc.) Dedicated instruments (BATSE, BeppoSax, Swift) These GRBs last for few seconds For longer duration in lower energy bands

14. Short Hard Bursts Neutron stars or black holes formed during end stages of massive stars Merger of two neutron stars or a black hole and a neutron star colliding Less energetic than collapsar GRBs Duration less than < 2 seconds. Neutron stars or black holes formed during end stages of massive stars Merger of two neutron stars or a black hole and a neutron star colliding Less energetic than collapsar GRBs Duration less than < 2 seconds.

15. Soft Gamma Ray Repeater When the neutron star in initial formation stages gains very high magnetic field It becomes a magnetar with 10 15 Gauss magnetic field Global rearrangement in its magnetic structures give SGRs Only Galactic sources with energies ~10 41-46 ergs When the neutron star in initial formation stages gains very high magnetic field It becomes a magnetar with 10 15 Gauss magnetic field Global rearrangement in its magnetic structures give SGRs Only Galactic sources with energies ~10 41-46 ergs

16. One common origin DEATH OF MASSIVE STARS How do massive stars die? How are these extreme conditions reached in these events? Does the known physical laws work in these extreme conditions? Why does small difference in initial conditions lead to such drastic differences? Does nature really need so much fine tuning? How do massive stars die? How are these extreme conditions reached in these events? Does the known physical laws work in these extreme conditions? Why does small difference in initial conditions lead to such drastic differences? Does nature really need so much fine tuning?

17. Specific problems: Shock velocity of typical SNe are ~1000 times the velocity of the (red supergiant) wind. Hence, SNe observed few years after explosion can probe the history of the progenitor star thousands of years back. Specific problems: Shock velocity of typical SNe are ~1000 times the velocity of the (red supergiant) wind. Hence, SNe observed few years after explosion can probe the history of the progenitor star thousands of years back. Interaction of the ejected material from the supernovae and GRBs with their surrounding medium and study them in multiwavebands.

18. SN/GRB explosion centre Photosphere Outgoing ejecta Reverse shock shell Contact discontinuity Forward shock shell SN/GRB explosion centre Photosphere Outgoing ejecta Reverse shock shell Contact discontinuity Forward shock shell Circumstellar environment 10 5 K 10 9 K 10 7 K

19. Radio emission is synchrotron emission due to energetic electrons in the presence of the high energy magnetic fields. Radio emission is absorbed either by free-free absorption from the circumstellar medium or synchrotron self absorption depending upon the mass loss rate, ejecta velocity and electron temperature, magnetic field. Both absorption mechanisms carry relevant information. Radio Emission

20. Free-free absorption: absorption by external medium Information about mass loss rate. Synchrotron self absorption: absorption by internal medium Information about magnetic field and the size.

21. X-ray emission from supernovae Thermal X-rays versus Non-thermal X-rays

22. Date of Explosion : 28 March 1993 Type : IIb Parent Galaxy :M81 Distance : 3.63 Mpc SN 1993J “Modeling the light curves of SN 1993J”, T. Nymark, P. Chandra, C. Fransson 2008, accepted for publication in A&A “X-rays from explosion site: 15 years of light curves of SN 1993J”, P. Chandra, et al. 2008, submitted to ApJ “Synchrotron aging and the radio spectrum of SN 1993J”, P. Chandra, A. Ray, S. Bhatnagar 2004 ApJ Letters 604, 97 “The late time radio emission from SN1993J at meter wavelengths”, P. Chandra, A. Ray, S. Bhatnagar 2004 ApJ Letters 604, 97

23. Understanding the physical mechanisms in the forward shocked shell from observations in low and high frequency radio bands with the GMRT and the VLA. Radio emission in a supernova arises due to synchrotron emission, which arises by the ACCELERATION OF ELECTRONS in presence of an ENHANCED MAGNETIC FIELD.

24. Giant Meterwave Radio Telescope, India Very Large Array, USA

25. On Day 3200…… GMRT+VLA spectrum GMRT VLA Synchrotron cooling break at 4 GHz Chandra, P. et al. 2004 Frequency FluxFlux

26. 1.5 years later…………. ~Day 3750 Synchrotron cooling break at ~ 5.5 GHz GMRT VLA Frequency FluxFlux

27. Synchrotron Aging Due to the efficient synchrotron radiation, the electrons, in a magnetic field, with high energies are depleted.

28. N(E) E N(E)=kE - . Q(E)  E -  steepening of spectral index from  =(  -1)/2 to  /2 i.e. by 0.5.

29. On day 3200 B=330 mG On day 3770 B=280 mG Magnetic Field follows 1/t decline trend Equipartition magnetic field~ 30 mG

30. Equipartition magnetic field is 10 times smaller than actual B, hence magnetic energy density is 4 order of magnitude higher than relativistic energy density

31. Diffusion acceleration coefficient  =(5.3 +/- 3.0) x 10 24 cm 2 s -1 Diffusion acceleration coefficient  =(5.3 +/- 3.0) x 10 24 cm 2 s -1

32. On Day 3200…… GMRT+VLA spectrum GMRT VLA Synchrotron cooling break at 4 GHz Chandra, P. et al. 2004 Frequency FluxFlux

33. X-ray studies of SN 1993J (Chandra et al 2008; Nymark, Chandra, Fransson 2008) X-ray studies of SN 1993J (Chandra et al 2008; Nymark, Chandra, Fransson 2008)  ROSAT  ASCA  Chandra  XMM-Newton  Swift X-ray telescopes

34. ROSAT Swift ASCA Chandra XMM

35. X-ray studies of SN 1993J (Chandra et al 2008; Nymark, Chandra, Fransson 2008) L ~ t -(0.8-1) : adia

36. L ~ t -1/(n-2) : rad. Density index ~ 12

38. X-ray spectrum of SN 1993J (Chandra et al 2008; Nymark, Chandra, Fransson 2008)

39. All the X-ray emission below 8 keV is coming from reverse shock. Reverse shock is adiabatic and clumpy. The clumps are producing slow moving radiative reverse shock. The ejecta density profile is Density ~ R -12 The reverse shock has travelled upto CNO zone in the ejecta. All the X-ray emission below 8 keV is coming from reverse shock. Reverse shock is adiabatic and clumpy. The clumps are producing slow moving radiative reverse shock. The ejecta density profile is Density ~ R -12 The reverse shock has travelled upto CNO zone in the ejecta.

40. SN 1995N in radio and X-ray bands (Chandra et al 2008, to appear in ApJ; Chandra, P. et al. 2005, ApJ) SN 1995N in radio and X-ray bands (Chandra et al 2008, to appear in ApJ; Chandra, P. et al. 2005, ApJ) SN 1995N A type IIn supernova Discovered on 1995 May 5 Parent Galaxy MCG-02-38-017 (Distance=24 Mpc)

41. Bremsstrahlung (kT=2.21 keV, N H =2.46 x 10 21 /cm 2. ) Gaussians at 1.03 keV (N=0.34 +/- 0.19 x 10 -5 ) and 0.87 keV (N=0.36 +/- 0.41 x 10 -5 ) NeX NeIX?

42. NeX NeIX 99.9% 90% 67% 99.9% 90% 67%

43. Constraining the progenitor mass Compatible with 15 solar mass progenitor star Luminosity of Neon X line Cascade factor Emissivity of neon X line Number density of neon is ~ 600 cm -3. Fraction of NeXI to total Neon

44. SN 1995N Chandra observations Total counts758 counts Temperature2.35 keV Absorption column Depth1.5 x 10 -21 cm -2 0.1-2.4 keV Unabsorbed flux0.6-1.0 x 10 -13 erg cm -2 s -1 0.5-7.0 keV Unabsorbed flux0.8-1.3 x 10 -13 erg cm -2 s -1 Luminosity (0.1-10 keV)2 x 10 40 erg s -1

46. How fast ejecta is decelerating? R~t -0.8 What is the mass loss rate of the progenitor star? M/t = 6 x 10 -5 M sun yr -1 Density structure Density ~ R -8.5 Density and temperature of the reverse shock Forward shock: T=2.4 x 10 8 K, Density=3.3 x 10 5 cm -3 Reverse shock: T=0.9 x 10 7 K, Density= 2 x 10 6 cm -3 How fast ejecta is decelerating? R~t -0.8 What is the mass loss rate of the progenitor star? M/t = 6 x 10 -5 M sun yr -1 Density structure Density ~ R -8.5 Density and temperature of the reverse shock Forward shock: T=2.4 x 10 8 K, Density=3.3 x 10 5 cm -3 Reverse shock: T=0.9 x 10 7 K, Density= 2 x 10 6 cm -3

47. SN 2006X, Patat, Chandra, P. et al. 2007, Science Type Ia supernova (Thermonuclear supernova) True nature of progenitor star system? What serves as a companion star? How to detect signatures of the binary system? Single degenerate or double degenerate system? Type Ia supernova (Thermonuclear supernova) True nature of progenitor star system? What serves as a companion star? How to detect signatures of the binary system? Single degenerate or double degenerate system?

48. Observations of SN 2006X: Observations with 8.2m VLT on day -2, +14, +61, +121 Observations with Keck on day +105 Observations with VLA on day ∼ 400 (Chandra et al. ATel 2007). Observations with VLA on day ∼ 2 (Stockdale, ATel 729, 2006). Observations with ChandraXO on day ∼ 10 (Immler, ATel 751, 2006).

49. Na I D 2 line

50. Na vs Ca

51. RESULTS First ever supernova followed regularly till 4 months. Variability not due to line-of-sight geometric effects. Associated with the progenitor system. Estimate of Na I ionizing flux: S UV ∼ 5 × 10 50 photons s − 1 This flux can ionize Na I up to r i ∼ 10 18 cm. This implies n e ∼ 10 5 cm − 3 (ONLY PARTIALLY IONIZED HYDROGEN CAN PRODUCE SUCH HIGH NUMBER DENSITY OF ELECTRONS ) First ever supernova followed regularly till 4 months. Variability not due to line-of-sight geometric effects. Associated with the progenitor system. Estimate of Na I ionizing flux: S UV ∼ 5 × 10 50 photons s − 1 This flux can ionize Na I up to r i ∼ 10 18 cm. This implies n e ∼ 10 5 cm − 3 (ONLY PARTIALLY IONIZED HYDROGEN CAN PRODUCE SUCH HIGH NUMBER DENSITY OF ELECTRONS ) Confinement: r H ≈ 10 16 cm Ionization timescale τ i < Recombination timescale τ r. Increase in ionization fraction till maximum light. Recombination star t s. When all Na II recombined, no evolution. Agree with results. Confinement: r H ≈ 10 16 cm Ionization timescale τ i < Recombination timescale τ r. Increase in ionization fraction till maximum light. Recombination star t s. When all Na II recombined, no evolution. Agree with results.

52. Mass estimation

53. CSM expansion velocity ∼ 50 − 100 km s − 1. For R ∼ 10 16 cm, material ejected ∼ 50 year before! Double-degenerate system not possible. Not enough mass. Single degenerate. Favorable. Not main sequence stars or compact Helium stars. High velocity required. Compatible with Early red giant phase stars. Possibility of successive novae ejection. CSM expansion velocity ∼ 50 − 100 km s − 1. For R ∼ 10 16 cm, material ejected ∼ 50 year before! Double-degenerate system not possible. Not enough mass. Single degenerate. Favorable. Not main sequence stars or compact Helium stars. High velocity required. Compatible with Early red giant phase stars. Possibility of successive novae ejection. Nature of the progenitor star

54. COLLABORATORS Claes Fransson (Stockholm Obs) Tanya Nymark (Stockholm Obs) Roger Chevalier (UVA) Dale Frail (NRAO) Alak Ray (TIFR) Shri Kulkarni (Caltech) Brad Cenko (Caltech) Kurt Weiler (NRL) Christopher Stockdale (Marquette) …and …. more

55. Detected by inter-Planetary Network of GRB detectors Triangulated by Odyssey, Suzaku, Integral RHESII, Konus-Wind observed Swift was slewing, BAT marginal detection at t=4min RHESSI: E peak =980+/-300 keV and Fluence (30keV-10MeV) =1.5 x 10 -4 erg cm -1 Konus-Wind: E peak =367+/-~60 keV and fluence (20keV-10MeV)= 1.74 x 10 -4 erg cm -1 Redshift z=1.5477, E iso = 10 54 erg GCN 6028,6102,6071,6049,6047,6041,6096,6030,6039,6064,6042 GRB 070125: Chandra et al. 2008 ApJ

56. GRB 070125: observations Observed by Swift-XRT, Swift-UVOT, P60, SARA 0.9m, Lick 3m, Keck/LRIS, TNT 0.8m, Prompt, VLT, GMRT, WSRT, VLA, IRAM Follow up Observatiions: P60 observations until day ~25 (Swift-XRT followed it until day 14) Chandra observations on day ~39 Submm observations until day ~15 VLA observations until day ~280

58. 070125 MULTIWAVEBAND MODELING OF BRIGHTEST RADIO GRB 070125 IN SWIFT ERA POONAM CHANDRA Jansky Fellow, NRAO University of Virginia

59. Synchrotron emission Corrections to Inverse Compton Inverse Compton important in X-rays only IC important throughout the evolution Role of IC in GRB Light curve only the synchrotron model for the GRB afterglow and derive various parameters spectrum due to IC scattering has the same shape as that of the synchrotron model.

63. Inverse Compton Scattering flattens the X-ray light curve, at least in some GRBs. Jet break in X-ray may get delayed beyond Swift observations. It may be a major cause for the absence of jet break in X-ray bands. CONCLUSIONS: GRB070125

64. Radio scintillation detection 8 hours observation with VLA in 8 GHz Mapped every 20 minutes

65. Size of the Fireball (Goodman 1997)

66. 13 th July 2005Poonam Chandra SGR 1806-20 Giant flare on Dec 27, 2004 Detected by INTEGRAL, RHESSI, Wind Spacecraft, SWIFT, GMRT, VLA, ATCA etc. 80,000 counts/sec (RHESSI) SGR 1806-20 Giant flare on Dec 27, 2004 Detected by INTEGRAL, RHESSI, Wind Spacecraft, SWIFT, GMRT, VLA, ATCA etc. 80,000 counts/sec (RHESSI) SGR 1806-20, Cameron, Chandra et. al. Nature

67. 13 th July 2005Poonam Chandra 27 th December 2004 at 4:30:26.65 pm EST Courtesy: NASA

68. 13 th July 2005Poonam Chandra PrecursorSpikeTail Duration1 sec0.2 sec382 sec Temp15 keV175 keV3-100 keV Fluence (erg/cm 2 ) 1.8x10 -4 1.364.6x10 -3 Energy (ergs) 2.4x10 42 1.8x10 46 1.2x10 44

69. 13 th July 2005Poonam Chandra GMRT observations of SGR 1806-20 From January 4, 2005 to February 24, 2005 Initially very frequently, almost everyday Snapshots, 40-60 minutes. Mostly in 240 and 610 MHz and in 1060 MHz at some occasions.

71. 13 th July 2005Poonam Chandra Distance estimation of SGR 1806-20 from the HI absorption spectra HI emission spectrum

72. 13 th July 2005Poonam Chandra Source HI absorption spectrum

73. 13 th July 2005Poonam Chandra SGR 1806-20 Flux density (Jy) d (kpc) Flux density (Jy) Brightness temp (K) 100 20 40 60 80 Velocity (km/s) - -50 0 50 100 150 0.2 0 0.4 0.6 0.8 0.08 0.04 20 10 Lower limit d=6.4 kpc Upper limit d=9.8 kpc 21cm HI spectrum

74. 13 th July 2005Poonam Chandra Association with the heavy mass cluster and Luminous Blue Variable? What kind of stars produce magnetars which forms SGRs?

75. COLLABORATORS Claes Fransson (Stockholm Obs) Tanya Nymark (Stockholm Obs) Roger Chevalier (UVA) Dale Frail (NRAO) Alak Ray (TIFR) Shri Kulkarni (Caltech) Brad Cenko (Caltech) Bryan Cameron (Caltech) …and …. more