Mysterious transient objects Poonam Chandra Royal Military Collage

Mysterious transient objects Poonam Chandra Royal Military Collage of Canada

ØUniverse has > 125 billion galaxies ØEach galaxy has ~100 billion stars

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

SUPERNOVAE (SNe) ØFew months to few years timescale ØMassive explosions in the universe ØEnergy emitted 1051 ergs (1029 times more than an atmospheric nuclear explosion) ØShines brighter than the host Galaxy ØAs much energy in 1 month as sun in ~1 billion years ØIn universe 8 supernova explosions every second Ø Thermonuclear and gravitational collapse

GAMMA-RAY BURSTS (GRBs) ØMost luminous events in the universe since big bang ØFlashes of gamma-rays from random directions in sky ØFew milliseconds to few seconds timescale ØEven 100 times more energetic than supernovae ØBrightest sources of cosmic gamma-ray photons in the universe ØIn universe roughly 1 GRB is detected per day ØShort duration (< 2 sec) and long duration (> 2 sec)

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

Common origin: Massive stars

Nuclear reactions inside a star

4 -8 Msun : 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 1051 ergs comes out • Standard candles, geometry of the Universe

Thermonuclear Supernovae

M >8 Msun : 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 1053 ergs energy • 99% in neutrinos and 1 % in Electro. Magnetic • Scatter all heavy material required for life

Core Collapse Supernovae

M > 30 Msun : 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 (GRB 980425/SN 1998 bw, GRB 030329/SN 2003 dh etc. ) • Dedicated instruments (BATSE, Beppo. Sax, Swift) • These GRBs last for few seconds • For longer duration in lower energy bands

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.

Soft Gamma Ray Repeater • When the neutron star in initial formation stages gains very high magnetic field • It becomes a magnetar with 1015 Gauss magnetic field • Global rearrangement in its magnetic structures give SGRs • Only Galactic sources with energies ~1041 -46 ergs

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?

Specific problems: Interaction of the ejected material from the supernovae and GRBs with their surrounding medium and study them in multiwavebands. 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.

105 K 107 K Circumstellar environment 109 K SN/GRB explosion centre Photosphere Outgoing ejecta Reverse shock shell Contact discontinuity Forward shock shell

Radio Emission 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.

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.

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

Date of Explosion : 28 March 1993 SN 1993 J Type : IIb Parent Galaxy : M 81 Distance : 3. 63 Mpc “X-rays from explosion site: 15 years of light curves of SN 1993 J”, P. Chandra, et al. 2008, submitted to Ap. J “Modeling the light curves of SN 1993 J”, T. Nymark, P. Chandra, C. Fransson 2008, accepted for publication in A&A “Synchrotron aging and the radio spectrum of SN 1993 J”, P. Chandra, A. Ray, S. Bhatnagar 2004 Ap. J Letters 604, 97 “The late time radio emission from SN 1993 J at meter wavelengths”, P. Chandra, A. Ray, S. Bhatnagar 2004 Ap. J Letters 604, 97

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.

Giant Meterwave Radio Telescope, India Very Large Array, USA

On Day 3200…… GMRT+VLA spectrum Chandra, P. et al. 2004 F l u x Synchrotron cooling break at 4 GHz GMRT VLA Frequency

1. 5 years later…………. ~Day 3750 Synchrotron cooling break at F l u x ~5. 5 GMRT VLA Frequency GHz

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

. Q(E) E-g N(E)=k. E-g N(E) steepening of spectral index from a=(g-1)/2 to g/2 i. e. by 0. 5 . E

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

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

Diffusion acceleration coefficient k=(5. 3 +/- 3. 0) x 1024 cm 2 s-1

On Day 3200…… GMRT+VLA spectrum Chandra, P. et al. 2004 F l u x Synchrotron cooling break at 4 GHz GMRT VLA Frequency

X-ray studies of SN 1993 J (Chandra et al 2008; Nymark, Chandra, Fransson 2008) X-ray telescopes ØROSAT ØASCA ØChandra ØXMM-Newton ØSwift

ROSAT ASCA Swift XMM Chandra

X-ray studies of SN 1993 J (Chandra et al 2008; Nymark, Chandra, Fransson 2008) L ~ t-(0. 8 -1): adia

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

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

CONCLUSIONS • All the X-ray emission below 8 ke. V 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.

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

Bremsstrahlung (k. T=2. 21 ke. V, NH=2. 46 x 1021/cm 2. ) Gaussians at 1. 03 ke. V (N=0. 34 +/- 0. 19 x 10 -5) and 0. 87 ke. V (N=0. 36 +/- 0. 41 x 10 -5) Ne. X Ne. IX?

99. 9% 90% 67% Ne. X 99. 9% 90% 67% Ne. IX

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

SN 1995 N Chandra observations Total counts 758 counts Temperature 2. 35 ke. V Absorption column Depth 1. 5 x 10 -21 cm-2 0. 1 -2. 4 ke. V Unabsorbed flux 0. 6 -1. 0 x 10 -13 erg cm-2 s-1 0. 5 -7. 0 ke. V Unabsorbed flux 0. 8 -1. 3 x 10 -13 erg cm-2 s-1 Luminosity (0. 1 -10 ke. V) 2 x 1040 erg s-1

• 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 Msun yr-1 • Density structure Density ~ R-8. 5 • Density and temperature of the reverse shock Forward shock: T=2. 4 x 108 K, Density=3. 3 x 105 cm-3 Reverse shock: T=0. 9 x 107 K, Density= 2 x 106 cm-3

SN 2006 X, 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?

Observations of SN 2006 X: • Observations with 8. 2 m 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 Chandra. XO on day ∼ 10 (Immler, ATel 751, 2006).

Na I D 2 line

Na vs Ca

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: SUV ∼ 5 × 10 50 photons s − 1 • This flux can ionize Na I up to ri ∼ 1018 cm. • This implies ne ∼ 10 5 cm − 3 (ONLY PARTIALLY IONIZED HYDROGEN CAN PRODUCE SUCH HIGH NUMBER DENSITY OF ELECTRONS ) • Confinement: r. H ≈ 10 16 cm • Ionization timescale τi < Recombination timescale τr. Increase in ionization fraction till maximum light. Recombination star ts. • When all Na II recombined, no evolution. Agree with results.

Mass estimation From spectroscopic data: Na I column density N (Na I) ≈ 1012 cm − 1 log(Na/H)= − 6. 3. For complete recombination, M (H) ≤ 3 × 10− 4 ⊙ M. From radio: 3 − σ upper limit on flux density F (8. 46 GHz) < 70 µJy. Mass loss rate ≤ 10 − 8 ⊙ M year − 1 CSM mass < 10 − 3 ⊙ M Below detection limit.

Nature of the progenitor star • CSM expansion velocity ∼ 50 − 100 km s − 1. • For R ∼ 1016 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.

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

GRB 070125: Chandra et al. 2008 Ap. J • 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=4 min • RHESSI: Epeak =980+/-300 ke. V and • Fluence (30 ke. V-10 Me. V) =1. 5 x 10 -4 erg cm-1 • Konus-Wind: Epeak=367+/-~60 ke. V and • fluence (20 ke. V-10 Me. V)= 1. 74 x 10 -4 erg cm-1 • Redshift z=1. 5477, Eiso = 1054 erg GCN 6028, 6102, 6071, 6049, 6047, 6041, 6096, 6030, 6039, 6064, 6042

GRB 070125: observations Observed by Swift-XRT, Swift-UVOT, P 60, SARA 0. 9 m, Lick 3 m, Keck/LRIS, TNT 0. 8 m, Prompt, VLT, GMRT, WSRT, VLA , IRAM Follow up Observatiions: • P 60 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

D N A B B F R E O G V A NG IO RA I W D E I L A T T E R F L I U OD ST W M M E S T N I H 5 G I 2 POONAM CHANDRA 1 R Jansky Fellow, NRAO B 070 University of Virginia

• 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.

CONCLUSIONS: GRB 070125 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.

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

(Goodman 1997) Size of the Fireball

SGR 1806 -20, Cameron, Chandra et. al. Nature 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) 13 th July 2005 Poonam Chandra

27 th December 2004 at 4: 30: 26. 65 pm EST 13 th July 2005 Poonam Chandra Courtesy: NASA

Precursor Spike Tail Duration 1 sec 0. 2 sec 382 sec Temp 15 ke. V 175 ke. V 3 -100 ke. V Fluence 1. 8 x 10 -4 (erg/cm 2) 1. 36 Energy (ergs) 1. 8 x 1046 1. 2 x 1044 13 th July 2005 2. 4 x 1042 Poonam Chandra 4. 6 x 10 -3

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. 13 th July 2005 Poonam Chandra

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

Source HI absorption spectrum 13 th July 2005 Poonam Chandra

SGR 1806 -20 21 cm HI spectrum 100 13 th July 2005 Flux density (Jy) d (kpc) Flux density (Jy) Brightness temp (K) 80 - 60 40 20 Lower limit d=6. 4 kpc 0. 08 0. 04 0 10 20 Upper limit d=9. 8 kpc 0. 8 0. 6 0. 4 0. 2 -50 0 50 100 150 Poonam Chandra Velocity (km/s)

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

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