Transcript Gamma-Ray Bursts and Puzzles of Core

Gamma-Ray Bursts and
Puzzles of CoreCollapse Supernovae
V. Sokolov, T. Fatkhullin , A. Moskvitin , T. N. Sokolova, V. Komarova,
A. J. Castro-Tirado , A. de Ugarte Postigo , J.Gorosabel , S. Guriy, M.Jelinek,
D. Branch, E. Sonbas , et al.
Discovery of relation between long-duration gamma-ray bursts (GRBs) and SNe is the
most important progress in this domain during recent 10 years. Now the search for SN
signs in photometry and spectra of GRB afterglows became the main observational
direction both for large ground-based telescopes and space platforms.

In particular, in the process of study, a new branch of observational cosmology has
arisen as a result of investigations of GRB host galaxies. The GRBs themselves are
already considered as a tool for studying processes of star-forming at cosmological
distances up to redshifts z~10.

Irrespective of specific models of this phenomenon, it might be said now that when
observing GRBs we observe the most distant SN explosions which, probably, are
ALWAYS connected to the relativistic collapse of massive stellar cores in very distant
galaxies. The connection is that GRBs may serve as a guideline to better understand the
SNe mechanism, and possibly solve the long-standing problem of the core-collapse SN
explosion, since in the GRBs we have additional information related to the core-collapse.

Outline
I would like to tell at first about works on GRB optical identifications fulfilled in
SAO RAS together with Alberto J Castro-Tirado team starting from 1998:
I. Massive star-forming rate and GRBs: the first stage of optical
identification and GRB host galaxies with massive star-forming.
II. Connection between long GRBs and massive stars: GRB/SNe and
puzzles of core-collapse supernovae (SN), the second stage of optical
identification:
1) SN signatures in GRB afterglows: photometry and spectroscopy
2) The shock-breakout effects in core-collapse SNe: The early spectra of XRF
060218/SN 2006aj and XRF 080109/SN 2008D
3) On asymmetry of the Type Ib and Ic SNe explosions
Discovery of the X-ray afterglow
In 1997 the first GRB counterpart at longer
wavelengths was detected thanks to BeppoSAX
satellite...
(Costa et al. 1998, Piro et al. 1998)
Photometric observation of GRB970508 in
SAO RAS
Photometry of optical transients
CCD images of the optical transient of
GRB970508 (Zeiss-1000 and BTA)
Light curves of the optical transient of
GRB970508 in B, V, Rc and Ic bands
(Zeiss-1000 and BTA)
Multi-wavelength observations of GRBs have
confirmed that a significant fraction of long GRBs
are associated with the collapse of short-lived
massive stars (Hjorth et al., 2003; Stanek et al.,
2003……).
Massive star-forming rate (SFR) and
GRBs
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Universe is transparent in γ-rays up to z ~10: observation of GRBs is a
powerful tool for studying physical conditions of environment and the
processes of birth and death of massive stars at red shifts up to 10 and even
more (at present, the red shift of the most distant GRB 090423, at redshift
z=8.26 -0.08 +0.07)
GRBs helps for studying stellar astrophysics, the interstellar and intergalactic
medium and high redshift Universe.
The GRB formation rate can be used as a potential tracer of the massive starforming rate (SFR) in the Universe.
Basic directions of the study of optical objects related to GRBs and main
questions that must be answered by observations and their interpretation can
be presented in the form of a scheme of
“Astronomy of GRBs in SAO RAS from 1998”:
Astronomy
of
γ-ray
bursts
with the 6-m telescope
from_1998
I. GRB host galaxies
The first stage of optical identification:
galaxies with massive star-forming
Fast localization, follow-up observations and measurement of red
shifts of GRBs have shown their relation to distant galaxies
located in sites of faded transients.
 The study of physical properties of host galaxies permits
determining the differences from usual galaxies (in the same CCD
fields like for GRB 070508) with massive star-forming, which
gives us a key to the understanding of conditions in which a GRB
progenitor object is born, evolves and dies.
 The most distant host galaxies can be often observed only
photometrically. In these cases, such physical properties as SFR,
intrinsic extinction laws, ages, masses and metallicities can be
estimated only by modelling spectral energy distributions (SEDs)

Multi-color photometry and the Rc image of the GRB 980703 host galaxy field from BTA observations in July
1998. The comparison of energy distribution obtained from BVR cIc fluxes (with consideration for the shift in
the ultra-violet part of spectrum for z=0.966) of this galaxy with energy distribution in spectra of galaxies of
different Hubble types is shown. The FWHM of each filter for its λeff with consideration for its left shift for
z=0.966 are denoted by dotted horizontal segments with bars.
Comparison of modeled and observed fluxes in the filters B, V, Rc, Ic, J, H, K for the GRB 980703 host galaxy.
The dashed line denotes the model SED without data of JHK.
First 21 GRB hosts: The Hubble diagram for GRB host galaxies with known (before June 2002)
observable stellar magnitudes (or with upper R limits) and spectroscopic red shifts against the background of
results of the photometric measurement of z applied to galaxies from the Hubble Deep Field (HDF) by
Fernández et al. (1999). Circles denote the GRB host galaxies with the BTA photometry, asterisks are results
by other authors (HST, VLT). For the galaxy GRB 991208 first measurement of z = 0.706 and R = 24.35 were
made at the BTA. Points show location of HDF galaxies from results of deep observations with the Hubble
Space Telescope (HST), i.e. the diagram shows stellar magnitudes in the filter HDF F606W and corresponding
photometric red shifts of galaxies from the catalogue F606W. The observable R stellar magnitudes of host
galaxies are corrected for the Galactic extinction. Effects of observational selection are as follows: the
decrease of amount of measured spectroscopic z after z ≈ 1.2; the z values of host galaxies are mainly obtained
by spectra of brighter galaxies. With regard to these effects, the R distribution of z for GRB host galaxies well
follows the Hubble course for all other “normal” (non-peculiar) galaxies of the deep survey. (In this picture
one can see galaxies of large and small luminosities up to dwarfs for identical values of z.)
The main conclusion from the investigation of the GRB
hosts (in SAO RAS)
In point of fact, this is the first result of the GRB optical identification with
already known objects: GRBs are identified with ordinary (or the most
numerous in the Universe at any z) galaxies up to ~28 st. magnitudes and
more.
The GRB hosts should not be special, but normal, faint, star-forming galaxies
(the most abundant), detected at any z just because a GRB event has
occurred
(Djorgovski et al., 2001; Frail et al., 2002; Sokolov et al., 2001; Savaglio,
2006;).
The main conclusion resulting from the investigation of these galaxies is that
the GRB hosts do not differ in anything from other galaxies with close redshifts: neither in colours, nor in spectra, the massive SRFs (Sokolov et al.,
2001; Sokolov et al., 2001a), and the metallicities (Sokolov, 2002, The
Doctoral Thesis). It means that these are generally star-forming galaxies
(“ordinary” for their red shifts) constituting the base of all deep surveys.
There are multiple long lines of evidence that
long-duration (~ 1s-100s) GRBs are associated
with death of massive stars, occurring in regions
of active star massive formation embedded in
dense clouds of dust and gas (see Woosley &
Bloom, 2006 and many other references…).
Astronomy of γ-ray bursts
with the 6-m telescope from
1998
II. CC-SNe features
--
Photometric observation of GRB 970508
(z = 0.835)
Photometry of optical transients (GRB OTs)
Garcia et al. ApJ, 500, L105-L108 (1998)
Light curves of the optical transient of
GRB970508 in B, V, Rc and Ic bands
(Zharikov, Sokolov, Baryshev, A&A.,337, 356
Photometrical effects
Some GBRs have shown rebrightening and
flattening in their late optical afterglows, which have
been interpreted as emergence of the underlying SN
light curve.
So, a systematic study on the GRB afterglows with
this approach suggests that all long-duration GRBs are
associated with SNe
(A. Zeh, S. Klose, D.H. Hartmann 2004).
!
The flattening in late time GRB 970508
optical afterglow (z = 0.835)
The Type Ic SN in the light
curve of the optical transient
of GRB970508 ?
Or a Type IIn SN?
Type Ic SN?
Observing SN signatures in high-redshift GRBs
is difficult because of selection effects…
In spite of this challenge, some GRBs have
shown rebrightening and flattering in their late
optical afterglows, which have been interpreted
as emergency of the underlying SN lightcurve.
But fortunately…
A.Zeh, S.Klose,
D.Hartmann (2004)
jet + shock breakout?
z=0,169
The energetic SN- long GRB connection
2.2m
8.1m VLT
ESO
+ BUSCA
First hinted in GRB 980425/SN
1998bw (Galama et al. 1998)
GRB 030329 Multirrange campaing
leading to detect prominent CC-SN lines
in afterglow spectra (Stanek et al. 2003,
Hjorth et al. 2003, Sokolov et al. 2003): BTA
important result !
BTA & Zeiss-1000 & NOT: GRB 030329 OT, Sokolov et al., Bull.
Spec. Astrophys. Obs. 59, 5 and in Nuovo Cim. 28C (2005) 521-524
GRBs and SNe with spectroscopically
confirmed connection:
GRB 980425/SN 1998bw
(z=0.0085),
GRB 030329/SN 2003dh
(z=0.1687),
GRB 031203/SN 2003lw
(z=0.1055),
GRB/XRF 060218/SN2006aj (z=0.0335).
Searching for more pairs of GRBs (XRFs) and SNe in
future observations is very important for understanding
the nature of the GRB-SN connection, the nature of
GRBs, and
the mechanism of core-collapse SNe explosion.
The closer GRB has the more features of SN (from 2000)...
•
So, GRB may be the beginning of core-collapse SN explosion, and GRB is a
signal allowing us to catch a SN at the very begining of the exploding?
•
On puzzles of core-collapse SNe and the GRB-SN connections…
Finally, GRBs were identified with quite a
definite class of supernovae – the corecollapse supernovae or massive supernovae.
A new era in the study of
core-collapse supernovae.
Thanks to gamma-ray bursts, these
supernovae can be observed from the very
beginning.
Core-collapse SNe explosion observations have much longer
history than GRB observations. Therefore SNe events should
be much clearer than GRBs. But the explosion mechanism of
the CC-SNe and some important issues are not solved yet
(see e.g. Janka et al., 2007, Imshennik and Nadeshin 1987).
May be early spectroscopical observations of the CC-SNe
connected with or without GRBs is the key moment for the
understanding of explosion mechanism of core-collapse SNe
and other questions which are not properly solved yet.
Outline
I. Massive star-forming rate and GRBs: the first
stage of optical identification and GRB host galaxies
with massive star-forming.
II. Connection between long GRBs and massive
stars: GRB/SNe and puzzles of core-collapse
supernovae, the second stage of optical
identification:
1) SN signatures in GRB afterglows: photometry and
spectroscopy
2) The shock-breakout effects in core-collapse
SNe: the early spectra of XRF 060218/SN 2006aj and
XRF 080109/SN 2008D
3) On asymmetry of the Type Ib and Ic SNe explosions
Hydrogen and Helium in spectra of
Type Ib-c Core-Collapse
Supernovae SN 2006aj
and SN 2008D
E. Sonbas , A. Moskvitin , T. Fatkhullin , V. Sokolov, D. Branch, A. de Ugarte Postigo ,
A. J. Castro-Tirado , J.Gorosabel , S. B. Pandey, M.Jelinek, T. N. Sokolova
GRB/XRF 060218 and SN 2006aj
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Feb. 18.149, 2006 UT: Swift detected a peculiar GRB/XRF (Campana et al., 2006)
X-ray emission was prevailing in the GRB spectrum, the GRB is also classified as
XRF (X-Ray Flash)
redshift z=0.0331 (can be compared to GRB 030329/SN 2003dh, z=0.1683, Ic SN)
BTA spectra: details (~6200A) interpreted as hydrogen lines (sign of stellar-wind
envelope around a massive progenitor star of the γ-ray burst).
The early spectra of GRB 060218 OT before Feb 23
Telescope
Tfirst Sp
astro-ph/GCN Circ.
MDM (2.4m)
1.95 days (20.097 UT)
0603686 (Mirabal et al.)
BTA (6m)
2.55 days (20.70 UT)
Fatkhullin et al. 2006
ESO VLT (8m)
2.89 days (21.041 UT)
0603530 (Pian et al.)
BTA (6m)
3.55 days (21.70 UT)
Fatkhullin et al. 2006
NOT (2.56m)
3.78 days
0603495 (Sollerman et al.)
ESO Lick (3m)
4.01 days (22.159 UT)
0603530 (Pian et al.)
ESO VLT (8m)
4.876 days (23.026 UT)
0603530 (Pian et al.)
Tfirst Sp is a time after GRB 060218
These are spectra with the high S/N ratio. The 6100A absorption (trough) reaches the
maximal depth and width at the moment UT Feb ~ 23.
Here we do not take into account the early spectrum of their paper Modjaz et al.
(0603377), obtained with the low S/N ratio at the FLWO 1.5m telescope 3.97 days after
the burst.
Nature,
442, p.1018
Mazzali et al.
VLT (8m)
Lick (3m)
VLT (8m)
VLT (8 m)
and
Lick (3m)
spectra
Black lines are for
theoretical spectra,
color lines denote
real observations
BTA Feb20.70
BTA Feb21.70

Analysis of early spectra (BTA + ESO Lick, ESO VLT, NOT) before 2006
Feb. 23 UT: evolution of optical spectra of the Type Ic core-collapse
supernova SN 2006aj during transition from the short phase related to the
shock breakout to outer layers of the stellar-wind envelope to spectra of the
phase of increasing brightness corresponding to radioactive heating. Signs of
hydrogen in spectra of the GRB afterglow were detected for the first time.
Jelinek et al. (in
So, we have the moment of the changing of the radiation
mechanism for the SN:
Our optical spectra of XRF 060218 / SN 2006aj obtained in
2.55 and 3.55 days after the beginning of the SN explosion,
i.e. when contribution of the thermal component of radiation of
the shock was still determining, which is also indicated by
strong blue excesses in our spectra.
But, as it is seen from the UBVR light curve, in 5 days the
GRB afterglow has been already noticeably reddening, which
is related to the change of the mechanism of the SN radiation
by this time, when the classical (radioactive/non-thermal)
phase of the SN explosion begins.
SN 2006aj, UBVRIJ light curves
(Sonbas et al., arXiv:0805.2657)
the end of the shock
break-out phase
The light curves showed non-monotonic behaviour with two maxima.
(The same first maximum was observed in SN1987A and SN1993J
and attributed to shock break-out.)
light curve of SN 1987A
the shock
break-out
phase
Imshennik & Nadyozhiin, UFN, 156, 261, (1988), fig.16
Nature, 364, 507, 1993
K.Nomoto et al.
SN1993J
The shock
break-out
→ 56Co → 56Fe
→ the radioactive heating
56Ni
According the (formal) definition, the Type Ic and Ib supernovae don't
have conspicuous lines of H in its optical spectra ...

The signs of hydrogen in spectra of Type Ib and Ic (Ib-c) SNe are not a new:
evolution of the blueshifted Hα line were already found (using SYNOW code)
in the analysis of a time series of optical spectra for usual CC-SNe with type
Ic and Ib (Branch et al., 2001, 2002, Elmhamdi et al., 2006, …).

The SNe Ic and Ic usually are modeled in terms of the gravitational collapse of
massive and bare carbon-oxygen cores which stripped envelope before
collapse, and, apparently, signs of this envelope must be present always in
spectra of these SNe as hydrogen lines.
The popular conception of the relation between long-duration GRBs and core-collapse SNe
(the picture from Woosley and Heger , 2006)
Shematic model of asymmetric explosion of a GRB/SN progenitor
…a strongly nonspherical explosion may
be a generic feature of
core-collapse
supernovae of all types.
…Though while it is not
clear that the same
mechanism that
generates the GRB is
also responsible for
exploding the star.
astro-ph/0603297
Leonard, Filippenko et al.
The shock
breaks out
through the wind
The wind
envelope
of size ~1013 cm
56Ni
synthesized
behind the
shock wave
Though the phenomenon (GRB) is unusual, but the object-source (SN) is not too unique.
The closer a GRB is, the more features of a SN.
Sonbas et al., astroph/0805.2657
v~r
The SN 2006aj spectrum in rest wavelengths obtained with BTA in 2.55 days
after XRF/GRB 060218 corrected for galactic extinction. The fitting by synthetic (SYNOW: D.Branch et al.,
2001, A.Elmhamdi et al., 2006) spectra with the velocity of the photosphere (V ), all elements and their ions
phot
-1
equal to 33,000 km s is shown by smooth lines differing only in the blue range of the spectrum at λ < 4000 Ǻ.
-1
HI denotes the Hα PCyg profile at V
= 33,000 km s . The model spectrum for the photosphere velocity
phot
-1
8000 km s is shown for example by the dashed line as an example of the Hα PCyg profile. More information
about the SYNOW code see in http://www.nhn.ou.edu/~parrent/synow.html and in astro-ph/0805.2657
SN 2006aj/ GRB 060218, 2006 Feb. 20.7 UT, Δt = 2.55 d.
The undetached case: v = 33,000 km s-1
FeIII, FeII
FeIII, FeII
TiII, CaII
Hα
HeI
SiII
v~r
CII
OI
Sonbas et al., astro-ph/0805.2657
v~r
The SN 2006aj spectrum (rest wavelength) obtained with BTA in 3.55 days after XRF/GRB 060218 and
corrected for galactic extinction. Synthetic spectra are shown by smooth lines. Locations of spectral lines of
some ions and blends of their lines are shown in those parts of the spectrum where contribution of this ion into
the spectrum is essential for given model parameters. The black line is the synthetic spectrum with parameters
from Table 3 at which the absorption with minimum about 6100 Ǻ is described by suppressing influence of HI
for “the detached case”. This is a strongly blue-shifted part (trough) of the Hα PCyg profile at the velocity of
-1
expansion of the detached HI layer equal to 24,000 km s .
SN 2006aj/GRB 060218, 2006 Feb. 21.7 UT, Δt = 3.55 d
The detached case: 18000 km s-1 ≤ V ≤ 24000 km s-1
v~r
These HI features (the troughs at ≈ 6100Å ) can be related
to an envelope which usually arises around a massive
progenitor star due to stellar wind.
The same envelope was observed during the XRF/GRB
060218 burst itself as a powerful black-body component
in spectrum (the shock-breakout effect).
The identification of our early spectra for SN 2006aj is also
confirmed by observations and interpretation of spectra
with the SYNOW code for other “usual” core-collapse
supernovae of the Ic and Ib types (Branch et al. 2006;
Branch et al. 2002; Elmhamdi et al. 2006).

Considering all early observations with other telescopes (ESO
VLT, NOT, ESO Lick, and ESO VLT for 2006 Feb. 23.026) one
may speak that we observe evolution of the optical spectra of the
core-collapse supernova SN 2006aj – a transition from the
shock-breakout phase to spectra of the phase of luminosity
increase corresponding to radioactive heating.
Jelinek et al. (in
Results. In the early spectra of the optical afterglow of the X-ray
burst XRF/060218 /SN 2006aj we detected the following
spectral features:
(1)
(2)
Hα PCyg profile for velocities of ~33,000 km s-1 - a broad and
almost unnoticeable/small oscillation of continuum in the range
of ≈5600 – 6600 Å for rest wavelengths at the first epoch, and
a part/remnant of Hα PСyg profile in absorption blue-shifted by
24,000km s-1 - a broad spectral feature with a minimum/trough
at ≈ 6100 Å (rest wavelength) for the second epoch.
These HI features (at ≈ 6100Å )can be related to an envelope which usually arises
around a massive progenitor star due to stellar wind.
The same envelope was observed during the XRF/GRB 060218 burst itself as a
powerful black-body component in spectrum (the shock-breakout effect).
Considering all early observations with other telescopes (ESO VLT, NOT, ESO Lick, and
ESO VLT for 2006 Feb. 23.026) one may speak that we observe evolution of the optical
spectra of the core-collapse supernova SN 2006aj – a transition from the shockbreakout phase to spectra of the phase of luminosity increase corresponding to
radioactive heating.
The identification of our early spectra for SN 2006aj is also
confirmed by observations and interpretation of spectra
with the SYNOW code for other “usual” core-collapse
supernovae of the Ic and Ib types (Branch et al. 2006;
Branch et al. 2002; Elmhamdi et al. 2006).
The curve of the photosphere velocity fall
2006aj
2008D
ApJ, 566, 1005-1017, 2002, D.Branch et al.
XRF 080109 / SN 2008D
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We studied the core-collapse Type Ibc SN 2008D which exploded on Jan 9.56,
2008 and was identified with a bright X-ray transient XRF 080109 discovered
by Swift/XRT in the nearby galaxy NGC 2770 (the distance 27 Mpc).
On Jan.16 and Feb.6, 2 spectra of this object were taken with BTA (the
wavelength range 3700А-7500А).
Our spectra was also compared to the spectra from papers Soderberg et al., 2008
(arXiv:0802.1712) and Mojaz et al., 2008 (arXiv:0805.2201v1).
Physical conditions in the envelope of this SN were modeled with the
parametrized SYNOW code.
If interpretation of the thermal component in the spectrum of GRB/XRF 060218
as interaction between the SN shock and the wind envelope around the
SN 2006aj/XRF 060218 progenitor star will be confirmed by observations of
afterglow of other bursts, then it will give a new impulse to development of the
theory of GRBs themselves and of the core-collapse SNe (see E.Waxman et al.
papers) .
Sp of SN 2008D, Jan. 16. andSYNOW modelling.
Spectrum of SN 2008D, Feb, 6. and SYNOW modelling.
Evolution of photosphere velocities
Fig.22 from Branch, D. et al.
2002, ApJ, 566, 1005
Asphericity in core-collapse SN explosion:
The fact that in the case of usual and nearby SNe the explosion does not begin
with a GRB is naturally explained by an asymmetric, axial-symmetric or
bipolar (with formation of jets) explosion of the core-collapse SNe. Now one of
the popular conceptions proceeds from the idea that in the case of flashes of the
XRF type an observer is out of the beam in which the most γ-ray radiation is
concentrated for one reason or another…
Asphericity
The farther is an observer from the SN explosion axis, the more
of X-ray radiation and the less γ-ray quanta are in the spectrum of
the flash – GRBs transform to X-ray Rich GRBs (like GRB 030329)
and become X-ray Flashes. When observing at an angle close to
90º to the SN explosion axis, no GRB is seen; one observes only
an XRF (X-ray Flash like XRF 080109/SN 2008D) and then a
powerful UV flash caused by interaction in the shock an the
envelope surrounding the pre-SN as was in the case of SN 1993J.
Thus, if an SN is observed close to the explosion
equator (and this situation is the most probable) and if
there is a sufficiently dense stellar-wind envelope around
a massive collapsing star cores, then only the shock
breakout effect is to be observed in X-ray and in optical.
arXiv:0801.1100v3 [astroph] 19 Mar 2008
Asphericity in Supernova Explosions
from Late-Time Spectroscopy
Keiichi Maeda, Koji Kawabata, Paolo A. Mazzali, Masaomi Tanaka, Stefano Valenti, Ken'ichi Nomoto,
Takashi Hattori , Jinsong Deng, Elena Pian, Stefan Taubenberger, Masanori Iye, Thomas Matheson,
Alexei V. Filippenko, Kentaro Aoki, George Kosugi, Youichi Ohyama, Toshiyuki Sasaki,
and Tadafumi Takata
Abstract. Core-collapse supernovae (CC-SNe) are the explosions that announce the
death of massive stars. Some CC-SNe are linked to long-duration gamma-ray bursts
(GRBs) and are highly aspherical. One important question is to what extent asphericity is
common to all CC-SNe. Here we present late-time spectra for a number of CC-SNe from
stripped-envelope stars, and use them to explore any asphericity generated in the inner
part of the exploding star, near the site of collapse. A range of oxygen emission-line
profiles is observed, including a high incidence of double-peaked profiles, a distinct
signature of an aspherical explosion. Our results suggest that all CC-SNe from strippedenvelope stars are aspherical explosions and that SNe accompanied by GRBs exhibit the
highest degree of asphericity
The popular conception of the relation between long-duration GRBs and core-collapse SNe
(the picture from Woosley and Heger , 2006)
Shematic model of asymmetric explosion of a GRB/SN progenitor
…a strongly nonspherical explosion may
be a generic feature of
core-collapse
supernovae of all types.
…Though while it is not
clear that the same
mechanism that
generates the GRB is
also responsible for
exploding the star.
astro-ph/0603297
Leonard, Filippenko et al.
The shock
breaks out
through the wind
The wind
envelope
of size ~1013 cm
56Ni
synthesized
behind the
shock wave
Though the phenomenon (GRB) is unusual, but the object-source (SN) is not too unique.
The closer a GRB is, the more features of a SN.
The second stage of optical identification:
GRBs and core-collapse SNe




The late-time light curve of several GRBs can be explained by the presence of a
SN similar to the CC-SN 1998bw but at the redshifts < 1. May be most GRB
afterglows should be accompanied by a supernova (SN) as already supported by
the GRB031203/SN2003lw, GRB 030329/2003dh and GRB060218/2006aj
results.
Moreover, the SN shock-breakout (Campana et al, 2006) in
GRB/XRF060218/SN2006aj afterglow suggest that H-lines should be
observable in the early GRB/SN spectrum if taken in the first hours/days
following the GRB, if the photosphere temperature of the SN shock becomes
sufficiently low and the H density over the photosphere is sufficiently high…
May be the study of GRBs is a new phase of investigation of core-collapse SNe,
but from the very beginning of this remarkable event: early spectral observations
turn out to be very important for understanding of the mechanism of both corecollapse SN explosion itself and GRB source.
The optical identification of GRBs is going on…
SUMMARY:
There are direct and indirect observational evidences in favor of a
physical relation between core-collapse SNe and long GRBs. This
relation was first justified by the fact that all GRB host galaxies turned
out to be ordinary (star-burst) galaxies with high rate of massive starforming (Djorgovski et al., 2001; Frail et al., 2002; Sokolov et al.,
2001; Savaglio 2006).
But if evident/indisputable spectral and photometric signs of
association between core-collapse SNe of the type Ib/c (and other
types?) and GRBs were obtained in many cases, then, beside being a
direct proof of relation between GRBs and massive stars, we could
have a strong observational limitation of the gamma-ray beaming and,
thus, we would have an OBSERVATIONAL estimation of the true total
energy of GRB sources.
If GRBs are the most distant
explosions of CC-SNe: What are
the redshift limit at which GRBs
can be observed?
What are the redshift at which there are no
more core-collapse supernovae (CC-SNe)?
Thank you.