Gamma-Ray Bursts and Puzzles of Core-

Collapse SupernovaeV. 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

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)

Photometry of optical transients

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

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 star-forming 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 BVRcI

c 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 λ

eff 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, I

c, 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 red-shifts: 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)

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)

Photometry of optical transients (GRB OTs)

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)

z=0,169

jet + shock breakout?

2.2m ESO2.2m ESO

The energetic SN- long GRB connection

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 !

8.1m VLT8.1m VLT2.2m + BUSCA2.2m + BUSCA

First hinted in GRB 980425/SN 1998bw (Galama et al. 1998)

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 core-collapse 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

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

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.

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.)

Nature, 442, p.1018 Mazzali et al.

VLT (8 m) and

Lick (3m) spectra

VLT (8m)

Lick (3m)

VLT (8m)

BTA Feb20.70

BTA Feb21.70

Black lines are fortheoretical spectra,color lines denotereal observations

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 prep.)

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.

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.)

SN 2006aj, UBVRIJ light curves (Sonbas et al., arXiv:0805.2657)

the end of the shock break-out phase

light curve of SN 1987Athe shock break-outphase

Imshennik & Nadyozhiin, UFN, 156, 261, (1988), fig.16

Nature, 364, 507, 1993 K.Nomoto et al.

The shockbreak-out

56Ni → 56Co → 56Fe → the radioactive heating

SN1993J

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.

Shematic model of asymmetric explosion of a GRB/SN progenitor

…a strongly non-spherical 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/0603297Leonard, Filippenko et al.

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 shock breaks out through the wind

The windenvelopeof size ~1013 cm

56Ni synthesizedbehind the shock wave

The popular conception of the relation between long-duration GRBs and core-collapse SNe (the picture from Woosley and Heger , 2006)

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

phot), all elements and their ions

equal to 33,000 km s-1 is shown by smooth lines differing only in the blue range of the spectrum at λ < 4000 Ǻ.

HI denotes the Hα PCyg profile at Vphot

= 33,000 km s-1. The model spectrum for the photosphere velocity

8000 km s-1 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

Sonbas et al., astro-ph/0805.2657

v ~ r

SN 2006aj/ GRB 060218, 2006 Feb. 20.7 UT, Δt = 2.55 d.The undetached case: v = 33,000 km s-1

TiII, CaII

FeIII, FeII

FeIII, FeII

HeI

SiII

OI

v ~ rCII

Hα

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 expansion of the detached HI layer equal to 24,000 km s

-1.

Sonbas et al., astro-ph/0805.2657

v ~ r

SN 2006aj/GRB 060218, 2006 Feb. 21.7 UT, Δt = 3.55 dThe 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 prep.)

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) 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

(2) 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 shock-breakout 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).

ApJ, 566, 1005-1017, 2002, D.Branch et al.

2008D

2006aj

The curve of the photosphere velocity fall

XRF 080109 / SN 2008D

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…

AsphericityThe 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 [astro ph] 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 stripped-envelope stars are aspherical explosions and that SNe accompanied by GRBs exhibit the highest degree of asphericity

Shematic model of asymmetric explosion of a GRB/SN progenitor

…a strongly non-spherical 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/0603297Leonard, Filippenko et al.

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 shock breaks out through the wind

The windenvelopeof size ~1013 cm

56Ni synthesizedbehind the shock wave

The popular conception of the relation between long-duration GRBs and core-collapse SNe (the picture from Woosley and Heger , 2006)

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 core-collapse SN explosion itself and GRB source.

The optical identification of GRBs is going on…

SUMMARY: There are direct and indirect observational evidences in favor There are direct and indirect observational evidences in favor of a physical relation between core-collapse SNe and long of a physical relation between core-collapse SNe and long GRBs. This relation was first justified by the fact that all GRB GRBs. This relation was first justified by the fact that all GRB host galaxies turned out to be ordinary (star-burst) galaxies host galaxies turned out to be ordinary (star-burst) galaxies with high rate of with high rate of massivemassive star-forming (Djorgovski et al., star-forming (Djorgovski et al., 2001; Frail et al., 2002; Sokolov et al., 2001; Savaglio 2006)2001; Frail et al., 2002; Sokolov et al., 2001; Savaglio 2006). . But if evident/indisputable spectral and photometric signs of But if evident/indisputable spectral and photometric signs of association between core-collapse SNe of the type Ib/c (and association between core-collapse SNe of the type Ib/c (and other types?) and GRBs were obtained in many cases, then, other types?) and GRBs were obtained in many cases, then, beside being a direct proof of relation between GRBs and beside being a direct proof of relation between GRBs and massivemassive stars, we could have a strong observational limitation stars, we could have a strong observational limitation of the gamma-ray beaming and, thus, of the gamma-ray beaming and, thus, we would have an we would have an OBSERVATIONAL estimation of the true total energy of GRB OBSERVATIONAL estimation of the true total energy of GRB sources.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.