Ericson Lopez

Observatorio Astronomico de QuitoQuito,Ecuador

UN/ESA/NASA/JAXA Workshop on Basic Space Science and IHY 2007, Daejeon, Korea

Are GRBs events the most violent events in the Universe?

Quito Astronomical Observatory

• Founded in 1873• Latitude:

0º12'53.70''• Longitude:

78º30'9.20'' • Altitude:

2 818,05 m

ASTRONOMICAL HERITAGE

Instrumentos de paso

focal distance 200cm, lens: 162mm.

Focal distance: 319cmlens: 238mm

Big Telescopes

1. Review of Gamma Ray Bursts2. Fireball model for GRBs3. Some Fundamental Problems4. Relativistic Kinematic5. Relativistic Model6. Conclusions

Outline of Talk:

Quick Review

• 1967- Discovery by American military Vela satellite of GRBs1973 – Declassified for scientific communityEnd of 1970s – `Konus’ experiments onboard Russian Veneras(E.P.Mazets et al)

• 1991-2000 – `BATSE’ (CGRO) era. Largest homogeneous data (a few thousands) on GRBs. Debates on galactic vs extragalactic origin

• 1997-… Afterglow era. Discovery of afterglows in X-ray (BeppoSAX, 1997), optical, radio. Triumph of cosmological model for (long) GRB origin. Multivawelength GRB astronomy

• 1998 – possible association of GRB980425 with nearby peculiar type Ic SN1998bw. Start of hypernova era (?)

History of GRBs:

General propertiesObserved:

• Duration: 0.1-1000 s• Fluence: S~10^-7--10^-3 erg/cm2• Spectrum: nonthermal, 10keV-100 MeV• Variability: high, 1-10 ms• Rate: 1 per day• Location: z=0.17-4.5,• Associated events: X-ray (~100%),

optical (~70%), radio (~50%) afterglows

F(t)~t-α α~1-2+ Environment signatures: transient

X-ray em./abs. lines, metal rich material

Derived (for long GRBs only!):

• Isotropic energy release Eγ=4πdl^2/(1+z) ~10^51 -10^54 erg (but 980425 ~10^48)• Evidence for jets from afterglow

breaks θj~0.01-0.1• Points to ‘standard’ energy

release ΔE~10^50-10^51erg equally shared in kinetic energy and radiation

• Photon energy correlations vFν~Eiso

• Association with SN Ib/c

BATSE rate ~1 per dayNo repetions, full isotropy

Light Curve: GRB 990123

BATSE Evidence for Cosmological Origin of GRBs

Classes of Gamma Ray Bursts

1. (Classical) Long-duration GRBs

2. Short-hard class of GRBs

3. X-ray rich/X-ray flashes

4. Low Luminosity GRBs

Soft Gamma Repeaters (SGRs)

The problem of the high opacity for all photons about the pair-creation threshold. Fireball model by Piran (1993).

FIREBALL MODEL FOR GRBs

The optical thickness problem

Rees & Meszaros (1992, 1994…) Recent review: Piran 2004

Internal shocks GRB itself

External shock in ISM X-ray, optical, radio emission of the GRB `afterglow”

Initial interaction of GRB ejecta Reverse shock propagating inward and

decelerating fireball ejecta.

Fireball Model

G1

G2

ISM

INTERNALSHOCK

g-RAYS

EXTERNALSHOCK

X-RAYS

OPTICALRADIO20 km

1-6 AU

1000-2000 AU

How the energy escape the compact region?

How to produce 1054 erg?

FUNDAMENTAL PROBLEMS

RELATIVISTIC KINEMATICS

• To resolve this fundamental problem of opacity…

• In this context, we analyze the problem of large opacity as a relativistic illusion

• Causes by the emitting plasma of gamma-rays, which is moving relativistically as a whole.

Relativistic Plasma Motion

• Models involving the relativistic bulk motion of the of gamma-ray emitting plasma match the theory with high-energy photons observed to escape in the GRB events.

• Krolik & Pier (1991) remarkable and clearly exposed the potential of relativistic bulk motion of the emitting plasma in order to provide an elegant solution to the problem of large opacity.

Doppler Aberration * We propose further

considerations which must be taken into account in the relativistic moving models for GRBs.

The moving plasma is considered as relativistic fluid

The main physical parameters of the emitting material, must be reduced or boosted by a suitable potency of the Doppler Lorentz factor: 1)]cos1([ --G D

factorDoppler

Relativistic Boosting

)1( zD

D

tdzdt

)1(

Source size from temporal variability:

Spherical blob in comoving frame

rb=r´b G

Doppler Factor

arccos

1)]1([ --G D

Variability timescale implies maximum emission region size scale

2j

G(x)

And, now we must pay attention in deducing the corrected relationfor transformed Flux density expression.

Then, for the observer, the radiation is not more isotropic.

Flux Distribution

No evidence for anisotropy in GRB directions (Meegan et al. 1992)

This work is attempting to give a contributionin understanding the physics and origin of GRBs events, incorporing the relativistic motion of the jets and their geometry into the physical models.

Usual model:

Therefore, for a moving source, the observed monochromatic flux density F is related to the Flux density in the commoving frame by:

Relativistic model:

TOTAL FLUX:

RELATIVISTIC MODEL• In most of the proposed models the isotropic radiation can not provide

the release of energy necessary for the appearance of a cosmological GRB.

• Radiation must be affected by the Lorentz boosting factor . Therefore, we are detecting in the earth frame a flux F enhanced by:

From here, we are available to obtain the total energy released by the source and computed at the observed frame:

And the total intrinsic energy of the source at its rest frame can be derived from the previous relation:

the true energy released in a GRB event

Constrains on the GRBs energy• Considering that GRBs are located at distances around of :

• Computing the energy released by the source for several probable values of observed fluxes and Doppler factor.

• In the same way, we works also with sources located at a more far distance, around:

Energy released

We found that for all cases, the involved energy in a GRB event is appreciable less that the huge energy (10^52 ergs/cm2 s)

required in an isotropic model.

We note that a GRB can be pretty transparent formildly cosmological distance (r ~ 1 GPc) and for

mildly relativistic Lorentz factor (Γ ~ 300).

→

→

CONCLUSIONS• We evidenced the fact that the energy released in a gamma-

ray event could be over estimated, if the emission is considered isotropic.

• The observations carried out on these explosive events suggest us that anisotropic models are also a good alternative and maybe a more realistic sugesstion.

• We can process thinking in a relativistic beaming, where the observer see only a limited portion of emitted radiation.

• Then the true gamma-ray energy is smaller than the isotropic energy under the consideration of relativistic beaming which makes the observed radiation to be anisotropic.

MAIN CONCLUSIONS

• Therefore, the GRB events are not necessarily associated with the formation of stellar black holes or SN.

• The values present in these paper are more compatible with the energies involved in AGNs events, where a fraction of a solar mass per year can be accelerated to , leading to

powers of ergs/sec.

THANK YOU FOR YOUR KIND ATTENTION