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Gamma-Ray Bursts and Puzzles of Core- Collapse Supernovae V. Sokolov, T. Fatkhullin, A. Moskvitin, T. N. Sokolova, V. Komarova, A. J. Castro-Tirado, A.

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Presentation on theme: "Gamma-Ray Bursts and Puzzles of Core- Collapse Supernovae V. Sokolov, T. Fatkhullin, A. Moskvitin, T. N. Sokolova, V. Komarova, A. J. Castro-Tirado, A."— Presentation transcript:

1 Gamma-Ray Bursts and Puzzles of Core- Collapse 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.

2 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.

3 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 /SN 2006aj and XRF /SN 2008D 3) On asymmetry of the Type Ib and Ic SNe explosions

4 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)

5 Photometric observation of GRB in SAO RAS CCD images of the optical transient of GRB (Zeiss-1000 and BTA) Light curves of the optical transient of GRB in B, V, Rc and Ic bands (Zeiss-1000 and BTA) Photometry of optical transients

6 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……).

7 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 , at redshift z= )‏ 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”:

8 Astronomy of γ-ray bursts with the 6-m telescope from_1998 I. GRB host galaxies

9 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 ) 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)

10 Multi-color photometry and the R c image of the GRB host galaxy field from BTA observations in July The comparison of energy distribution obtained from BVR c I 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.

11 Comparison of modeled and observed fluxes in the filters B, V, R c, I c, J, H, K for the GRB host galaxy. The dashed line denotes the model SED without data of JHK.

12 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 first measurement of z = and R = 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.)‏

13 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.

14 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…).

15 Astronomy of γ-ray bursts with the 6-m telescope from 1998 II. CC-SNe features -- 

16 Photometric observation of GRB (z = 0.835) Garcia et al. ApJ, 500, L105-L108 (1998) Light curves of the optical transient of GRB in B, V, Rc and Ic bands (Zharikov, Sokolov, Baryshev, A&A.,337, 356) Photometry of optical transients (GRB OTs)

17 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).

18 !

19 The flattening in late time GRB optical afterglow (z = 0.835) The Type Ic SN in the light curve of the optical transient of GRB ? Or a Type IIn SN? Type Ic SN?

20 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…

21 A.Zeh, S.Klose, D.Hartmann (2004) z=0,169 jet + shock breakout?

22 2.2m ESO The energetic SN- long GRB connection GRB 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 VLT 2.2m + BUSCA First hinted in GRB /SN 1998bw (Galama et al. 1998)

23 BTA & Zeiss-1000 & NOT: GRB OT, Sokolov et al., Bull. Spec. Astrophys. Obs. 59, 5 and in Nuovo Cim. 28C (2005)

24 GRBs and SNe with spectroscopically confirmed connection: GRB /SN 1998bw (z=0.0085), GRB /SN 2003dh (z=0.1687), GRB /SN 2003lw (z=0.1055), GRB/XRF /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.

25 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…

26 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.

27 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.

28 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 /SN 2006aj and XRF /SN 2008D 3) On asymmetry of the Type Ib and Ic SNe explosions

29 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

30 GRB/XRF and SN 2006aj Feb , 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= (can be compared to GRB /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).

31 The early spectra of GRB OT before Feb 23 T first Sp is a time after GRB 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. ( ), obtained with the low S/N ratio at the FLWO 1.5m telescope 3.97 days after the burst. TelescopeT first Sp astro-ph/GCN Circ. MDM (2.4m)1.95 days ( UT) (Mirabal et al.) BTA (6m)2.55 days (20.70 UT)Fatkhullin et al ESO VLT (8m)2.89 days ( UT) (Pian et al.) BTA (6m)3.55 days (21.70 UT)Fatkhullin et al NOT (2.56m)3.78 days (Sollerman et al.) ESO Lick (3m)4.01 days ( UT) (Pian et al.) ESO VLT (8m)4.876 days ( UT) (Pian et al.)

32 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 for theoretical spectra, color lines denote real observations

33 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.)‏

34 So, we have the moment of the changing of the radiation mechanism for the SN: Our optical spectra of XRF / 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.

35 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: )‏ the end of the shock break-out phase

36 light curve of SN 1987A the shock break-out phase Imshennik & Nadyozhiin, UFN, 156, 261, (1988), fig.16

37 Nature, 364, 507, 1993 K.Nomoto et al. The shock break-out 56 Ni → 56 Co → 56 Fe → the radioactive heating SN1993J

38 According the (formal) definition, the Type Ic and Ib supernovae don't have conspicuous lines of H in its optical spectra...

39 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.

40 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/ Leonard, 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 wind envelope of size ~10 13 cm 56 Ni synthesized behind the shock wave The popular conception of the relation between long-duration GRBs and core-collapse SNe (the picture from Woosley and Heger, 2006)

41 The SN 2006aj spectrum in rest wavelengths obtained with BTA in 2.55 days after XRF/GRB 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 V phot = 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 and in astro-ph/ http://www.nhn.ou.edu/~parrent/synow.html Sonbas et al., astro- ph/ v ~ r

42 SN 2006aj/ GRB , 2006 Feb UT, Δt = 2.55 d. The undetached case: v = 33,000 km s -1 TiII, CaII FeIII, FeII HeI SiII OI v ~ r CII HαHα

43 The SN 2006aj spectrum (rest wavelength) obtained with BTA in 3.55 days after XRF/GRB 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/ v ~ r

44 SN 2006aj/GRB , 2006 Feb UT, Δt = 3.55 d The detached case: km s -1 ≤ V ≤ km s -1 v ~ r

45 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 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).

46 Considering all early observations with other telescopes (ESO VLT, NOT, ESO Lick, and ESO VLT for 2006 Feb ) 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.)‏

47 Results. In the early spectra of the optical afterglow of the X-ray burst XRF/ /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.

48 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 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 ) 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).

49 ApJ, 566, , 2002, D.Branch et al. 2008D 2006aj The curve of the photosphere velocity fall

50 XRF / 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 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: ) and Mojaz et al., 2008 (arXiv: v1). 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 as interaction between the SN shock and the wind envelope around the SN 2006aj/XRF 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).

51 Sp of SN 2008D, Jan. 16. andSYNOW modelling.

52 Spectrum of SN 2008D, Feb, 6. and SYNOW modelling.

53 Evolution of photosphere velocities Fig.22 from Branch, D. et al. 2002, ApJ, 566, 1005

54 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…

55 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 ) 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 /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.

56 arXiv: v3 [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 stripped- envelope stars are aspherical explosions and that SNe accompanied by GRBs exhibit the highest degree of asphericity

57 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/ Leonard, 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 wind envelope of size ~10 13 cm 56 Ni synthesized behind the shock wave The popular conception of the relation between long-duration GRBs and core-collapse SNe (the picture from Woosley and Heger, 2006)

58 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 /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…

59 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 star- forming (Djorgovski et al., 2001; Frail et al., 2002; Sokolov et al., 2001; Savaglio 2006). 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 star- forming (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.

60 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)?

61 Thank you.


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