Radio and X-ray studies of transient objects:
Supernovae and Gamma Ray Bursts
Poonam Chandra
Jansky Postdoctoral Fellow
National Radio Astronomy Observatory
&
University of Virginia
Collaborators:
Roger Chevalier (Univ. Virginia)
Dale Frail (NRAO)
Alak Ray (Tata Inst. Fundamental Research)
Shri Kulkarni (Caltech)
Brad Cenko (Caltech)
Alicia Soderberg (Princeton)
Douglas Bock (CARMA)
Claes Fransson (Stockholm Observatory)
Nikolai Chugai (Moscow University)
Fate of Massive stars (> 8 solar)
mass)
8MΘ ≤ M ≤ 30MΘ
M ≥ 30MΘ
Supernova
Gamma Ray Burst
In universe 8 new
supernovae explode
every second.
21st Dec 2006
In universe, roughly 1
GRB is detected
everyday.
Two kinds of supernova explosions
Thermonuclear
Supernovae
Core collapse
Supernovae
•Type Ia
•Type II, Ib, Ic
•No remnant
remaining
•Neutron star or Black
hole remains
•Less massive
progenitor (4-8 MSolar)
•More massive
progenitor (> 8 MSolar)
•Found in elliptical and
Spiral galaxies
•Found only in Spiral
arms of the galaxy
(Young population of
stars)
Energy scales in various explosions
Chemical explosives
~10-6 MeV/atom
Nuclear explosives
~ 1MeV/nucleon
Novae explosions
few MeV/nucleon
Thermonuclear explosions
few MeV/nucleon
Core collapse supernovae
100 MeV/nucleon
Based on
optical spectra
Classification
H (Type II)
(Various typesIIn, IIP, IIL, IIb
etc.)
No H (Type I)
Si (Type Ia)
No Si (6150Ao)
He (Type Ib)
No He (Type Ic)
Crab
Tycho
Kepler
Cas A
Gamma-ray burst
They were discovered serendipitously
in the late 1960s by U.S. military
satellites which were on the look out
for Soviet nuclear testing in violation of
the atmospheric nuclear test ban
treaty. These satellites carried gamma
ray detectors since a nuclear explosion
produces gamma rays.
Gamma-ray bursts
Long-duration bursts:
Last more than 2 seconds.
Range anywhere from 2 seconds to a few hundreds of
seconds (several minutes) with an average duration time
of about 30 seconds.
Short-duration bursts:
Last less than 2 seconds.
Range from a few milliseconds to 2 seconds with an
average duration time of about 0.3 seconds (300
milliseconds).
GRB properties
Afterglows made study possible and
know about GRB
GRB are extragalactic explosions.
Associated with supernovae
They are collimated.
They involve formation of black hole at
the center.
If collimated, occur much more
frequently.
How explosive???
100,000,000,000,000,
000,000,000,000,000
Single Supernova
times
more energy
can In
shine
onebrighter
month as
than
theour
energy
inway
an
than
milky
much energy as
atmospheric
nuclear
having
sun will give in
bomb!!!!
100,000,000,000
1,000,000,000
stars.
years.
21st Dec 2006
How explosive???
Even 100 times
brighter
than times
a
Million trillion
supernova
as
bright as source
sun
Brightest
of Cosmic Gamma
Ray Photons
Calcium in our bones
Oxygen we breathe
Iron in our cars
This is my research interest.
Understanding the fate of massive
stars. Supernovae and Gamma
Ray Burst formation and
understand the underlying physics.
Environment around massive stars
Through interaction of
the ejecta with the
circumstellar medium.
Multiwaveband studies
are the most effective
way to do that.
Interaction of the ejected material from the
supernvae and GRBs with their surrounding
medium and study them in multiwavebands.
Circumstellar
matter
Density
Not to scale
Radius
SN/GRB explosion centre
Photosphere
Outgoing ejecta
Reverse shock shell
Contact discontinuity
Forward shock shell
SPACE TELESCOPES
Swift
XMM
RADIO TELESCOPES
Giant Meterwave Radio Telescope
GRB Missions
BATSE
BeppoSAX
Swift was launched in 2004
Current Projects I am working on:
Study of all newly exploded Type IIn
supernovae with the Very Large Array
(50 hours of VLA time).
•Dense Circumstellar Medium (CSM)
•Different stellar evolution and mass loss history
•Hybrid with many other classes of SNe
SN 2001em (Ic/IIn)
SN 2002ic (Ia/Iin)
•Brightest radio supernova Iin SN 2006gy
Radio Emission
in Supernovae
Radio emission is by 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:
absopriton by external medium
Information about mass loss rate.
2
 .

    M uw T


2
ff
3
2
s
R 3
Synchrotron self absorption:
absorption by internal medium
Information about magnetic field and the size.

ssa

2.5 
1.5 
B
N
rel
Study of bright Target of
Opportunity supernovae with the
XMM-Newton ( 90 ks XMM time)
Our immediate goal is to understand the
role of mass loss in determining the
nature of supernovae and cause of
diversity among them.
X-ray emission from supernovae
Thermal X-rays
versus
Non-thermal X-rays
X-rays from the shocked shell
Inverse Compton scattering
(non-thermal)
X-rays from the clumps in the CSM
(thermal)
Goals:
•Locate the origin and mechanism of Xray production from the SN.
•Putting constraints on the processed gas
in the ejecta from imaging spectroscopy.
•Using our self-consistent multi-temp
hydrodynamic model for X-ray line
emission.
•Constrain the ejecta structure and density
profile from multiwaveband inputs.
Very Large Array hunting all the GRBs
(112 hours of VLA time) in radio band
•More than 200 GRBs observed by VLA
•Detection rate 1/6 GRBs.
•We send GCN circulars immediately.
GRBs in millimeter band with CARMA (48 hours
of VLA time)
Determination of Kinetic Energy
Understanding the physical mechanisms in shocked
shell from observations in low and high frequency radio
bands with the GMRT.
Radio emission in a supernova arises due to
synchrotron emission, which arises by the
ACCELERATION OF ELECTRONS
in presence of an
ENHANCED MAGNETIC FIELD.
Two specific papers, which I consider interesting
“Comprehensive analysis of a most energetic GRB 070125”,
Poonam Chandra, Brad Cenko, Dale Frail, Roger Chevalier,
Shri Kulkarni et al. 2008, Submitted to ApJ,
astro-ph/0802.2748.
“Synchrotron aging and the radio spectrum of SN 1993J”,
Poonam Chandra, Alak Ray, Sanjay Bhatnagar 2004
ApJ Letters 604, 97
SN 1993J
Date of Explosion :
28 March 1993
Type : IIb
Parent Galaxy :M81
Distance : 3.63 Mpc
235 MHz map of FOV of SN1993J
M82
M81
1993J
Flux density (mJy)
Composite radio spectrum on day 3200
 = 0.6
GMRT
VLA
Frequency (GHz)
Synchrotron Aging
Due to the efficient synchrotron
radiation, the electrons, in a
magnetic field, with high
energies are depleted.
.
4
dE
2
e


2
2
2

B sin E


4 7
3m c
 dt  Sync
b
Q(E)E-g
N(E)=kE-g
N(E)
steepening of spectral index from =(g-1)/2 to g/2 i.e. by 0.5
Ecut off
3e
2
 
B
sin

E
3 5
4

m
c
.
E
1
 2
bB t
Composite radio spectrum on day 3200
Flux density (mJy)
break =4 GHz
c2= 7.3
per 5 d.o.f.
17
R= 1.8x10 cm
B= 38±17 mG
 = 0.6
GMRT
VLA
Frequency (GHz)
c2= 0.1
per 3 d.o.f.
Synchrotron Aging in SN 1993J
Synchrotron losses
Adiabatic expansion
Diffusive Fermi acceleration
Energy losses due to adiabatic expansion
V
E
 dE 
 E


R
t
 dt  Adia
R
V
Ejecta velocity
Size of the SN
Energy gain due to diffusive Fermi acceleration
E EV
E(R / t)
 dE 





tc
20 
20 
 dt  Fermi
2
4( v1  v 2 )

3v
4 
tc 
v
 1
1 



 v1 v 2 
2
v1 Upstream velocity
v 2Downstream velocity
  Spatial diffusion
coefficient of the test
particles across
ambient magnetic
field
vParticle velocity
E
E

 2 2
2 2
1
dE / dt Total ( R t / 20  ) E  bB E  t E
For
 t
and
B  B0 / t
(Fransson & Bjornsson,
1998, ApJ, 509, 861)
Break frequency
.
 break
.
 R
1 / 2
1/ 2 
B 
t
 2t 
 20 

3
0
2
2
Magnetic field independent of equipartition
assumption & taking into account adiabatic
energy losses and diffusive Fermi
acceleration energy gain
B=330 mG
U rel
B
U
. mag
( 2g 13)

4
6
 8.5 10  5.0 10
(Chevalier, 1998, ApJ, 499, 810)
4
ISM magnetic field is few microGauss.
Shock wave will compress magnetic field
at most by a factor of 4, still few 10s of
microGauss. Hence magnetic field inside
the forward shock is highly enhanced,
most probably due to instabilities
Equipartition magnetic field is 10 times
smaller than actual B, hence magnetic energy
density is 4 order of magnitude higher than
relativistic energy density
Jet Break puzzle in Swift era
XRAY :JET BREAK
Thanks to Swift-XRT
team
Optical i’ band
JET BREAK
Optical R band
JET BREAK
GRB 070125
•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: Epeak =980+/-300 keV and
•Fluence (30keV-10MeV) =1.5 x 10-4 erg cm-1
•Konus-Wind: Epeak=367+/-~60 keV and
•fluence (20keV-10MeV)= 1.74 x 10-4 erg cm-1
•Redshift z=1.5477, Eiso = 1054 erg
GCN
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
GRB 070125
POONAM
CHANDRA
Jansky Fellow,
Radio light curves
Optical and X-ray light curves
•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.
F
F
IC
IC
 Fmax
IC



IC 

 c 
1 / 2

IC  
 Fmax 
IC 


m


;
p/2
IC
c
 
 mIC


IC 


c


IC
m
1 / 2
;  
IC
m
1/ 8
F
F
F
IC
IC
IC
 t 
 0.0079
 Jy; 2.8  t  3.7
 2.8d 
 t 
 0.0082

 3.7d 
1 / 2
 t 
 0.0066

 3.7d 
 2.4
Jy; 3.7  t  5.7
Jy; t  5.7
CONCLUSIONS: GRB070125
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
  
 src  2.25

 10GHz 
6/5
 Dscr 


 kpc 


SM
 3.5 20 / 3

kpc 
 10 m
    vISS 
 6.7 10 
 
-1 
 10GHz   50 km s 
6/5
t diff
1
4
1
3 / 5
as


SM
 3.5 20 / 3

kpc 
 10 m
(Goodman 1997)
Size of the
17
Fireball
R  5.7 10 cm
3 / 5
s
THANKS!!!!
Boltzmann Equation in the
presence of continuous injection

N
  dE 
g

 N   qE

t E  dt total 
 E g
N ( E , t )   (g 1)
/(g  1)
E
E  Ebreak
E  Ebreak
Form of synchrotron spectral distribution
  (g 1) / 2
I   g / 2

   break
   break
Kardashev, 1962, Sov. Astr. 6, 317
Self-similar solutions
Equations of conservations in Lagrangian co-ordinates for
the spherically symmetric adiabatic gas dynamics are
r
v
t
  4 3 
1
r 

M  3


v
GM
2 P
 4r

t
M
r2
To find similarity solution, we substitute velocity, density and pressure
into the spherically symmetric adiabatic gas dynamics equations
r
A
v  U ( )  1 m U ( )
t
t
b 2m
  n t G ( )
A
b 2m r 2
b  2 m  2 (1 m ) 2
P nt
( )  n  2 t
 ( )
2
A
t
A
where
r
 m
At
This reduces the partial differential equations to
G '
U  m   U '3U  2m  0
G
G '
  U ' (U  m)   '2  U (U  1)  0
G
G '
 '
(g  1)(U  m) 
(U  m)  2(U  1)  (g  1)2m  0
G

where
( )
 ( ) 
G ( )
and
n3
m
n2
g 1
A
G0 02
g 1
b
a 
1
n2
Hugoniot conditions
g 1
Gi 
g 1
g  1  2m
Ui 
g 1
(g  1)2(1  m) 2
i 
(g  1) 2
2m
U0 
g 1
(g  1)
0 
(g  1) 2