Progenitor stars of supernovae

Poonam ChandraRoyal Military College of Canada

SUPERNOVAE

Energetic explosions in the universeEnergy emitted 1051 ergs (1029 times more than an atmospheric nuclear explosion)One SN explosion shines brighter than the host GalaxyIn universe few supernovae explosions every second

Core collapse Supernovae•Type II, Ib, Ic

•Neutron star or Black hole remains

•Found only in Spiral arms of the galaxy (Young population of stars)

Thermonuclear Supernovae•Type Ia

•No remnant remaining

•Found in elliptical and Spiral galaxies

Two kinds of supernova explosions

Supernovae

• Core collapse supernovae: explosion of a massive star in a red supergiant phase.– Progenitor star > 8 Msun.

• Thermonuclear supernovae: explosion of a carbon-oxygen white dwarf in a binary system.– Progenitor star 4-8 Msun in a binary.

Progenitors of supernovae

• Very few are known.• Require pre-explosion images.• The progenitor stars are much fainter than the

supernovae.• Most supernovae at far away distances.

Circumstellar interaction

• The most reliable way to get indirect information about the mass of the progenitor star and the conditions of the surrounding medium.

SN explosion centre

Photosphere

Outgoing ejecta

Reverse shock shell

Contact discontinuity

Forward shock shell

Radius

Den

sity

Circumstellar matter

Not to scale

Circumstellar Interaction

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.

• Radio emission from Supernovae: Synchrotron non-thermal emission of relativistic electrons in the presence of high magnetic field.

• X-ray emission from Supernovae: Both thermal and non-thermal emission from the region lying between optical and radio photospheres.

Interaction of SN ejecta with CSM gives rise to radio and X-ray emission

SN 1995N

A type IIn supernova

Discovered on 1995 May 5

Parent Galaxy MCG-02-38-017 (Distance=24 Mpc)

Excellent Case: SN 1995N

Chandra et al. 2009, ApJ, Chandra et al. 2005, ApJ

Radio and X-ray observations:

Radio observations: for 11 years

-Very Large Array (VLA)

-Giant Meterwave radio telescope (GMRT)

X-ray observations:-ROSAT HRI: Aug 1996, 1997

-ASCA: Jan 1998

-ChandraXO: March 2004

-XMM-Newton: 2005

Bremsstrahlung (kT=2.21 keV, NH=1.51 x 1021/cm2. )

Gaussians at 1.02 keV (N=0.34 +/- 0.19 x 10-5) and 0.87 keV (N=0.36 +/- 0.41 x 10-5)

NeXNeIX

Mass of the progenitor star

• If most of the Ne is in the Helium zone, close to C+O boundary then

2

1

51077.6

f

ne

f is the fraction of NeIX to Ne

Mass of the progenitorFor f = 0.1, ne = 2 x 106 cm-3, nNe = 600 cm-3

Corresponding Neon mass ~ 0.016 Msun.Compatible with 15-20 Msun progenitor star.

Radio light curves of SN 1995N

•How fast ejecta is decelerating? R~t-0.8, this also implies n=8 (m=(n-3)/(n-2) in R~t-m)

•What is the mass loss rate of the progenitor star?

Mass loss rate = ~10-4 Msun yr-1

• Red supergiant star on 15 Msun in a superwind phase

•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

32

3

2

2.

Rw TuM sff

Presence of a cool shell• Presence of a cool shell between the forward and

the reverse shock responsible for excessive absorption of the X-rays.

• NHα Mass loss rate

NH~ 1.5 x 1021 cm-2

• If reverse shock is in He layers close to C-O boundary (Fransson et al. 2002), then this implies reverse shock mass of ~0.002M-0.8M.

SN 2006X, Patat, Chandra, P. et al. 2008 and 2007, Science

•In Virgo cluster spiral Galaxy M100•Feb 4, 2006, 70 million light years away•Type Ia supernova

•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?

SN 2006X- Nature of progenitor?

How to investigate?

Search for signatures of the material tranferred to the accreting white dwarf. •Narrow emission lines •Radio emission •X-ray emission

Till date no detection.

ABSORPTION OF THE RADIATIONS COMING FROM SUPERNOVA DUE TO THE CIRCUMSTELLAR MEDIUM SURROUNDING SUPERNOVA.

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).

Na I D2 line

Na vs Ca

RESULTS

•Variability not due to line-of-sight geometric effects.

•Associated with the progenitor system.

•Ionization timescale τi < Recombination timescale τr . Increase in ionization fraction till maximum light. Recombination starts, ts.

Results• Estimate of Na I ionizing UV flux:

SUV 5 × 10 ∼ 50 photons s − 1

• This flux can ionize Na I up to ri 10∼ 18 cm.

• This and recombination time scale of ~10 days implies ne 10 ∼ 5 cm − 3 (ONLY PARTIALLY IONIZED HYDROGEN CAN PRODUCE SUCH HIGH NUMBER DENSITY OF ELECTRONS )

• Confinement: rH ≈ 10 16 cm

• When all Na II recombined, no evolution. Agree with results.

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 (8.46GHz) < 70 µJy. Mass loss rate ≤ 10 − 8M⊙ year − 1

CSM mass < 10 − 3 M⊙ Below detection limit.

Mass estimation

•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.

Nature of the progenitor star