document: on 9th october 2006 , @xcite reported k. itagaki s discovery of a possible supernova ( sn ) in ugc  4904 . 
   although the sn was discovered after the peak , an upper limit of the @xmath6 magnitude ( @xmath7 ) was obtained at @xmath820 days before the discovery @xcite . 
   interestingly , @xcite also reported that an optical transient had appeared in 2004 close to the position of sn  2006jc . 
   the transient was as faint as @xmath9 and its duration was as short as @xmath10 days . since the event was faint and short - lived , they speculated that the transient was a luminous blue variable ( lbv)-like event . 
   the spatial coincidence between the lbv - like event and sn  2006jc is confirmed by @xcite . because of such an intriguing association with the lbv - like event , many groups performed follow - up observations of sn  2006jc in various wavebands : x - ray , ultra violet ( uv ) , optical , infrared ( ir ) , and radio . 
   spectroscopic observations showed many broad features and strong narrow emission lines . according to the he detection , sn  2006jc 
   was classified as type ib @xcite . however , 
   strange spectral features and their evolutions were reported . 
   a bright blue continuum was prominent in the optical spectrum at early epochs @xcite . 
   such a bright blue continuum had also been observed in type ii sn  1988z @xcite , but the origin of this feature is still unclear . 
   as the blue continuum declined , the red wing brightened and the optical spectra showed `` u''-like shapes @xcite . 
   this is a distinguishing feature of sn  2006jc in contrast to the spectra of usual sne that have a peak in optical bands . 
   photometric observations in optical and ir bands were performed continuously . 
   the optical light curve ( lc ) showed a rapid decline from 50 days after the discovery , as in the case of sn  1999cq @xcite . at the same epoch , near infrared ( nir ) emissions brightened @xcite . 
   the nir brightness increased from @xmath11 days to @xmath12 days after the discovery and then declined @xcite . 
   the epoch of the nir brightening corresponds to that of the development of the red wing in the optical spectra @xcite . 
   the nir brightening , as well as the fact that the redder side of the he emission profile declined faster than the bluer side , has been interpreted as an evidence of an ongoing dust formation @xcite . additionally , on 29th april 2007 ( 200 days after the discovery ) , the _ akari _ satellite performed nir and mid - infrared ( mir ) photometric and spectroscopic observations @xcite and the _ magnum _ telescope obtained the nir photometries @xcite . 
   they report the formation of amorphous carbon dust : another piece of evidences of the dust formation . 
   x - ray and uv emissions have also been observed by the _ swift _ and _ chandra _ satellites @xcite . 
   x - ray observations were performed at seven epochs and showed a brightening from @xmath13 days to @xmath14 days after the discovery @xcite . 
   the x - ray detection suggests an interaction between the sn ejecta and the circumstellar matter ( csm ) . on the contrary 
   , the radio emission was not detected by very large array ( vla ) @xcite . 
   we present a sn explosion model of a wolf - rayet star that explains the bolometric and x - ray lcs . 
   hydrodynamics , nucleosynthesis , and lc synthesis calculations are performed assuming the spherical symmetry . in this study 
   , we assume the explosion date of sn  2006jc to be 15 days before the discovery ( @xmath15 ) and the energy source of the light to be the @xmath4ni-@xmath4co  decay . 
   the paper is organized as follows : in   [ sec : bol ] , we describe how we derive the bolometric lc from observations in the various wavebands , in   [ sec : presn ] , we briefly discuss the presupernova evolutionary properties of the progenitor star ; in   [ sec : hyd ] , hydrodynamical and nucleosynthesis calculations are described ; in   [ sec : lc ] , lc synthesis calculations are presented ; in   [ sec : csm ] , we calculate the x - ray emission due to the ejecta - csm interaction ; in   [ sec : conclude ] and   [ sec : discuss ] , conclusions and discussion are presented . 
   cc 20 & 370 + 21 & 340 + 24 & 250 + 27 & 180 + 28 & 170 + 33 & 110 + 36 & 87 + 38 & 75 + 39 & 70 + 40 & 66 + 42 & 58 + 44 & 53 + 47 & 44 + 49 & 40 + 53 & 36 + 58 & 28 + 60 & 27 + 62 & 25 + 64 & 23 + 65 & 22 + 70 & 15 + 77 & 6.3 + 79 & 4.8 + 81 & 4.0 + 89 & 2.2 + 92 & 2.1 + 103 & 1.0 + 119 & 0.36 + 138 & 0.23 + 195 & 0.15    the bolometric luminosities of sne are usually estimated from the integration over the optical and nir emission because the usual sne radiate dominantly in the optical and nir bands ( e.g. , @xcite ) . 
   however , the spectra of sn  2006jc show the bright red and blue wings @xcite , which implies that the emissions in uv and ir bands considerably contribute to the bolometric luminosity . 
   we construct the bolometric luminosity with the integration of the uv , optical , and ir photometries that are obtained with the _ hct _ 
   @xcite , _ azt-24 _ 
   @xcite , _ magnum _ 
   @xcite , and _ subaru _ telescopes @xcite and the _ swift _ @xcite and _ akari _ satellites @xcite . since the uv fluxes are available only at @xmath16 days @xcite , the uv luminosity is estimated from the optical luminosity at the other epoch . 
   available observations are shown in figure  [ fig : lcobsall ] . 
   details of optical observations will be presented in the forthcoming papers ( e.g. , @xcite ) . 
   we adopt a distance of 25.8mpc corresponding to a distance modulus of 32.05 @xcite and a reddening of @xmath17 @xcite . 
   the optical lcs were obtained with the _ hct _ and _ subaru _ telescopes @xcite . 
   we integrate the optical fluxes with a cubic spline interpolation from @xmath18 hz to @xmath19 hz . 
   the optical luminosities ( @xmath20 ) are summarized in table  [ tab : uvopt ] and the lc is shown in figure  [ fig : lcobs ] . the optical lc declines 
   monotonically after the discovery . 
   the decline suddenly becomes rapid at @xmath21 days and the optical luminosity finally goes down to @xmath22ergs  s@xmath23  at @xmath24 days . 
   the x - ray lc obtained with the _ swift _ and _ chandra _ satellites @xcite shows that the x - ray luminosities , @xmath25 , are much fainter than the optical luminosities @xcite . 
   thus , the x - ray contribution to the bolometric luminosities is negligible . 
   however , the uv luminosity , @xmath26 , is comparable to the optical luminosity at @xmath16 days ( @xmath27ergs  s@xmath23  as estimated from the uvot observations , @xcite ) . 
   the uv luminosity is @xmath28 of the optical luminosity , i.e. , the total flux is @xmath29 times brighter than the optical flux ( fig . 
   [ fig : lcobs ] ) . 
   since the uv flux declined as the optical flux @xcite , we assume that @xmath30 at every epoch . although the blue wing declines with time and @xmath26 might be over - estimated at @xmath31 days @xcite , the bolometric luminosity ( @xmath32 ) should be reliable because the ir contribution dominates in the bolometric luminosity at such late epochs (   [ sec : irest ] ) . 
   ccccc 49 & 3.9 & 1580 & 2.9 & 9.0 + 57 & 12 & 1330 & 5.1 & 12 + 67 & 16 & 1340 & 6.6 & 15 + 70 & 19 & 1330 & 7.8 & 17 + 72 & 23 & 1300 & 8.9 & 19 + 77 & 27 & 1310 & 11 & 23 + 79 & 18 & 1400 & 9.1 & 21 + 127 & 46 & 1050 & 7.6 & 12 + 132 & 52 & 1010 & 7.2 & 11 + 154 & 17 & 1150 & 4.2 & 7.0 + 157 & 32 & 1010 & 4.5 & 6.6 + 159 & 75 & 900 & 6.7 & 8.7 + 160 & 26 & 1050 & 4.4 & 6.8 + 167 & 35 & 990 & 4.5 & 6.4 + 168 & 54 & 940 & 5.5 & 7.5 + 169 & 99 & 880 & 7.6 & 9.7 + 170 & 48 & 930 & 4.8 & 6.3 + 171 & 45 & 950 & 4.9 & 6.7 + 172 & 44 & 940 & 4.6 & 6.3 + 192 & 48 & 900 & 4.0 & 5.3 + 195 & 45 & 870 & 3.3 & 4.2 + 197 & 56 & 860 & 3.8 & 4.8 + 202 & 5.6 & 1190 & 1.5 & 2.7 + 215 & 28 & 870 & 2.1 & 2.7    the ir spectroscopy and photometries are obtained with the _ azt-24 _ and _ magnum _ telescopes ( nir photometries , @xcite ) and the _ akari _ satellite ( nir spectroscopy and mir photometries , @xcite ) . as indicated by the red wing in the optical spectra 
   , the ir emission considerably contributes to the bolometric luminosity of sn  2006jc . 
   the mir observation is available at @xmath33 days @xcite . 
   the ir luminosity integrated over @xmath34 hz is estimated from the nir and mir observations as @xmath35 ergs  s@xmath23 . 
   @xcite concluded that the ir emission is originated from amorphous carbon grains with two temperatures of @xmath36k and 320k . 
   the large difference between the two temperatures would imply that the origin of the hot carbon dust with @xmath36k is different from that of the warm carbon dust with @xmath37k . 
   the hot carbon dust is suggested to be newly formed in the sn ejecta and heated by the @xmath4ni-@xmath4co  decay by a dust formation calculation @xcite . on the other hand , the origin of the emission from the warm carbon dust 
   is suggested to be a sn light echo of the csm carbon dust ( @xcite ; see also @xcite ) . 
   therefore , we assume that the optical emission from sn  2006jc is absorbed and simultaneously re - emitted by the hot carbon dust and thus the luminosity emitted from the hot carbon dust should be included in the bolometric luminosity of sn  2006jc . according to the estimated temperatures and masses of the hot and warm carbon grains @xcite , the luminosities contributed by the hot and warm carbon grains are @xmath38 ergs  s@xmath23  and @xmath39 ergs  s@xmath23 , respectively . and 
   @xmath40 stems from that the h - band luminosity is slightly brighter than the luminosity emitted from the hot carbon dust @xcite . ]    for the epochs when the ir photometries at @xmath41 are unavailable , we estimate the contribution of the ir emission by fitting the jhk - band photometries with amorphous carbon emission .    from the kirchhoff s law , the thermal radiation from a spherical dust grain x with a uniform radius @xmath42 and temperature @xmath43 is given by @xmath44 , where @xmath45 is the absorption efficiency of the grain . 
   for the optically thin case , the observed emission from dust grains @xmath46 is written as @xmath47 where @xmath48 and @xmath6 denote the total number of the dust particles and the distance from the observer , respectively @xcite . in the followings , 
   we convolve the @xmath49-independent coefficients as an emission coefficient @xmath50 . applying the absorption efficiency for the amorphous carbon grain with @xmath51 
   , we derive the temperature of the hot carbon dust , @xmath52 , and @xmath53 to reproduce the jhk - band photometries .    to justify the above estimate 
   , we compare the estimate with the actual mir observation at @xmath33 days @xcite . 
   the fitting gives the temperature @xmath54 k and the emission coefficient @xmath55 for the hk - band photometries at @xmath33 days . 
   the luminosity integrated over @xmath56 is @xmath57 ergs  s@xmath23 . 
   the temperature and luminosity are roughly consistent with those of the hot carbon dust . 
   the agreement indicates that the fitting gives a good estimate of the ir emission due to the hot carbon dust . 
   we note that the estimate can not account for the emission from the warm carbon dust . 
   table  [ tab : nirbb ] summarizes the emission coefficient , temperature , estimated luminosity at @xmath58 hz , and luminosity emitted below @xmath59 hz . 
   the dust temperature roughly declines from @xmath60k at @xmath61 days to @xmath62k at @xmath33 days . 
   this is consistent with a picture that the hot carbon dust was formed in the sn ejecta and cooled down gradually @xcite . 
   the ir lc is shown in figure  [ fig : lcobs ] . 
   the estimated luminosity at @xmath58 hz evolves as the jhk lcs , and thus the ir lc brightens at @xmath63 days and declines at @xmath64 days . 
   since there is no nir data at @xmath65 days , the bolometric lc can not be estimated at this epoch . 
   the bolometric luminosity is derived from the summation of @xmath26 , @xmath20 , and @xmath66 and summarized in table  [ tab : bol ] , where @xmath67 is applied . 
   cc 49 & 81 + 51 & 81 + 53 & 75 + 58 & 64 + 60 & 61 + 62 & 59 + 65 & 55 + 66 & 54 + 70 & 45 + 77 & 33 + 79 & 29 + 119 & 14 + 138 & 10 + 195 & 4.7 
   the presupernova model has been extracted from a set of models already presented by @xcite and computed with the latest release of the stellar evolutionary code franec ( 5.050218 ) . since all the features of this code 
   have been already presented , we will address here only the main points . 
   the interaction between convection and local nuclear burning has been taken into account by coupling together and solving simultaneously the set of equations governing the chemical evolution due to the nuclear reactions and those describing the convective mixing . 
   more specifically , the convective mixing has been treated by means of a diffusion equation where the diffusion coefficient is computed by the use of the mixing - length theory . 
   the nuclear network is the same as that adopted in @xcite , but the nuclear cross sections have been updated whenever possible ( see table 1 in @xcite ) . 
   a moderate amount of overshooting of 0.2 @xmath68 has been included into the calculation only on the top of the convective core during core h burning . 
   mass loss has been taken into account following the prescriptions of @xcite for the blue supergiant phase ( @xmath69k ) , @xcite for the red supergiant phase ( @xmath70k ) , @xcite for the wnl wolf - rayet phase and @xcite during the wne / wco wolf - rayet phases . 
   we adopt the following correspondence of the models to the various wr phases according to the surface abundances , as suggested by @xcite : wnl ( @xmath71 ) , wne ( @xmath72 and @xmath73 ) , wnc ( @xmath74 ) and wco ( @xmath75 ) . 
   ( hereafter , c / n and c / o denote the number ratios . )    the x - ray emission , as well as the early bright blue continuum and the narrow lines , clearly indicates an interaction between the sn ejecta and the csm , i.e. , the existence of a dense csm . 
   furthermore , the ir spectral energy distribution may be explained by the formation of amorphous carbon grains in the sn ejecta and the csm ( @xcite , see also @xcite ) . since the c - rich environment ( i.e. , @xmath76 ) is required to form carbon dust ( e.g. , @xcite ) 
   , the ir observations suggest that the sn ejecta and csm contain a c - rich layer . 
   this suggests that the progenitor star of sn  2006jc is a wco wolf - rayet star with a c - rich envelope and csm ( figs . 
   [ fig : modpresn]a-[fig : modpresn]d ) . 
   lr + @xmath77 [ myr ] & 4.64 + @xmath78 [ @xmath79 & 25.80 + @xmath80 [ @xmath79 & 35.40 + @xmath81 [ myr ] & 4.16 + @xmath82 [ @xmath79 & 10.01 +   + @xmath83 [ myr ] & 0.46 + @xmath84 [ @xmath79 & 12.56 + @xmath80 [ @xmath79 & 7.04 + @xmath85 [ @xmath79 & 18.80 + @xmath86 & 0.28 + @xmath87 [ myr ] & 0.07 + @xmath88 [ myr ] ( @xmath89 ) & 0.11 ( 0.77 ) + @xmath90 [ myr ] ( @xmath89 ) & 0.054 ( 0.44 ) + @xmath91 [ myr ] ( @xmath89 ) & 0.21 ( 0.31 ) +   + @xmath92 [ yr ] & 1.25(+4 ) + @xmath93 [ @xmath79 & 16.52 + @xmath94 [ @xmath79 & 4.83 + @xmath95 [ @xmath79 & 1.50 + @xmath96 [ @xmath79 & 6.88 + @xmath97 [ cm ] & 3.08(+10 ) + @xmath98 ( int .- ext . ) 
   [ @xmath79 & 5.262 - 6.648 + @xmath99 ( int .- ext . ) 
   [ @xmath79 & 2.736 - 4.097 + @xmath100 [ yr ] & 1.10(+5 ) + @xmath101 [ yr ] & 5.43(+4 ) + @xmath102 [ yr ] & 2.21(+5 ) + @xmath103 [ yr ] & 3.86(+5 )    inspection of all the presupernova models available in @xcite indicates that only massive models , i.e. , @xmath104 , fulfill the requirements from the ir observation and become wco stars . moreover , these are the only stars in which the chemical compositions of the mantle and csm are dominated mainly by c with a smaller amount of o ( fig .  [ 
   fig : modpresn]cd ) .    in stars with initial masses smaller than @xmath105 , 
   the mass of the he convective core increases or remains constant during the core he burning phase . at core he exhaustion , a sharp discontinuity of he abundance is produced at the outer edge of the co core . 
   then , the co core begins to contract to ignite the next nuclear fuel while he burning shifts to a shell inducing a formation of a convective zone . 
   the he convective shell forms beyond the he discontinuity at the outer edge of the co core . 
   hence its chemical composition is dominated by he [ @xmath46(he)@xmath106 . because of the short lifetime of the advanced burning stages , only a small amount of he is burned inside the shell before the presupernova stage ( figs . 
   [ fig : modpresn]ab ) . 
   such a behavior is typical for stars in which the he core mass remains roughly constant during core he burning ( e.g. , @xcite ) .    in stars with initial masses greater than @xmath105 , on the contrary , 
   the mass loss is efficient enough ( @xmath107 ) to uncover the he core and they reduce progressively their mass during the core he burning phase . 
   the star enters the wne wolf - rayet stage and its subsequent evolution is governed by the actual size of the he core . 
   in particular , as the he core progressively reduces due to the mass loss , the star tends to behave as an initially - lower mass star , i.e. , essentially reduces its central temperature . 
   this induces the he convective core to shrink progressively in mass as well , leaving a layer with a variable chemical composition that reflects the central abundances at various stages during core he burning . 
   when the stellar mass is reduced below the maximum extension of the he convective core , the products of core he burning appear on the surface and the star becomes a wco wolf - rayet star . 
   at core he exhaustion , he burning shifts to a shell inducing the formation of the convective shell . 
   the convective shell forms in the region with variable chemical composition . as a consequence , at variance with what happens in stars with @xmath108 , in these stars 
   , the chemical composition of the convective shell becomes a mixture of the central he burning products . 
   hence it is mainly composed of c , o and he ( figs . 
   [ fig : modpresn]cd ) .    since all the models above @xmath109 have a similar presupernova structure , we selected a @xmath109 star as representative of a typical star becoming a wco wolf - rayet star 
   . the mass at the presupernova stage ( @xmath96 ) is @xmath110 because of the strong mass loss . 
   we underline that the @xmath111-@xmath96 relation is highly uncertain because it strongly depends on many details of the stellar evolution ( e.g. , the mass loss , overshooting , rotation , and metallicity , see @xcite ) . 
   for this reason , for the purpose of this study , we mainly focus on a wco progenitor with @xmath112 @xmath113 , without paying much emphasis on @xmath111 . 
   a detailed discussion of the presupernova evolution during all the nuclear burning stages is beyond the purpose of this paper . 
   hence we report here in table  [ tab : presn ] some key properties during the h , he , and advanced burning stages . 
   in particular , for the h burning stage we report the following quantities : the h burning lifetime ( @xmath77 ) , the maximum extension of the convective core ( @xmath78 ) , the total mass ( @xmath80 ) at core h exhaustion , the time spent as an o - type star ( @xmath81 ) and the he core mass ( @xmath82 ) at h exhaustion . here 
   , we assume that the temperature of the o - type stars is @xmath114 . 
   for the he burning phase we report the following quantities : the he burning lifetime ( @xmath83 ) , the maximum size of the he convective core ( @xmath84 ) , @xmath80 at core he exhaustion , the maximum depth of the convective envelope ( @xmath85 ) , the central @xmath115 mass fraction at core he exhaustion [ @xmath86 ] , the time spent at the red side ( @xmath117 ) of the hr diagram ( @xmath87 ) , and the wnl , wne , and wco lifetimes ( @xmath88 , @xmath90 , and @xmath91 , respectively ) - in parenthesis the central he mass fraction [ @xmath89 ] when the star enters the wnl , wne and wco phases . for the advanced burning stage we report the following key quantities : the time until the explosion ( @xmath92 ) , the maximum size of the he core [ @xmath93 ] , the maximum size of the co core [ @xmath94 ] , the masses of the iron core ( @xmath95 ) and the star ( @xmath96 ) and the radius of the star ( @xmath97 ) at the presupernova stage , the final extension in mass of the he convective shell [ @xmath121 and of the convective c shell [ @xmath122 , and the total lifetimes during the wnl [ @xmath100 ] , wne [ @xmath101 ] , wco [ @xmath102 ] , and wr [ @xmath103 , where @xmath126 phases . 
   figures [ fig : hr40 ] and [ fig:40pre2 ] show the evolutionary path in the hr diagram and the temperature and density profiles at the presupernova stage . 
   the sn explosion and explosive nucleosynthesis are calculated for the progenitor star with @xmath110 . 
   we apply various explosion energies ( @xmath127 ) for the sn explosion calculations ( e.g. , @xcite ) . 
   the hydrodynamical calculation is performed by means of a spherical lagrangian hydrodynamics code with a piecewise parabolic method ( ppm , @xcite ) including nuclear energy production from the @xmath128-network . 
   the equation of state takes account of the gas , radiation , @xmath129-@xmath130 pair @xcite , coulomb interactions between ions and electrons , and phase transition @xcite . 
   after the hydrodynamical calculations , nucleosynthesis is calculated as a post - processing with a reaction network that includes 280 isotopes up to @xmath131br ( see table  1 in @xcite ) . 
   since the explosion mechanism of a core - collapse sn for a massive star with an iron core is still an unsolved problem ( e.g. , @xcite ) , we initiate the sn explosion as a thermal bomb . 
   although there are various ways to simulate the explosion ( e.g. , a kinetic piston , @xcite ) , it is suggested that the explosive nucleosynthesis does not depend sensitively on the way how the explosion energy is deposited @xcite . 
   we set an inner reflective boundary at @xmath132 and @xmath133  km within the iron core and elevate temperatures at the inner boundary .    in the spherical symmetry case , for any given progenitor model , 
   hydrodynamics and nucleosynthesis are determined by the explosion energy . during the sn explosion , a shock propagates outward inducing local compression and heating , triggering explosive nucleosynthesis . behind the shock front 
   the matter is accelerated and starts moving outward . however , 
   if the progenitor has a deep gravitational potential and the explosion energy is low , the inner layers begin to fall back due to the gravitational attraction . a more compact star and a lower explosion energy leads a larger amount of fallback . 
   the fallback has a deep implication on the sn nucleosynthesis because it decreases the matter ejection , especially , of the inner core ( e.g. , @xmath4ni ) . 
   figure  [ fig : vrho ] shows density structures at 100 s after the explosions when homologously expanding structures are reached ( @xmath134 ) . 
   we find that the fallback takes place for the model with @xmath135 but not for the models with @xmath136 , 10 , and 20 . 
   figure  [ fig : escape ] shows a comparison between the escape velocity and the ejecta velocity for the model with @xmath135 and demonstrates that the matter below @xmath137 will fall back . on the other hand , in the models with @xmath136 , 10 , and 20 , the matter above the inner boundary will be ejected . 
   the abundance distributions after the explosions are shown in figures  [ fig : abn]a-[fig : abn]d . in every model , @xmath138ni 
   is synthesized in the innermost layer ( @xmath139 ) due to the low electron fraction . 
   thus , we can estimate the maximum amounts of synthesized @xmath4ni  for given energies . 
   the @xmath4ni - rich layer extending to @xmath140 [ where @xmath141 and @xmath142si - rich layer extending to @xmath143 [ where @xmath144 expand farther in the models with higher @xmath145 because the temperature achieved is higher in the outer layer for higher @xmath145 . @xmath146 and @xmath147 for each model are summarized in table  [ tab : abn ] . 
   ccccc 1 & 1.8 & 2.1 &  &  + 5 & 2.1 & 2.5 & 0.5 & 1.8 + 10 & 2.3 & 2.7 & 0.6 & 2.0 + 20 & 2.5 & 3.0 & 0.7 & 2.3    @xmath4ni  is synthesized at @xmath148 . since @xmath149 in the model with @xmath135 , 
   the model is likely not to eject @xmath4ni . on the other hand , the models with @xmath136 , 10 , and 20 
   can eject all synthesized @xmath4ni  because the fallback does not occur . 
   the total amounts of synthesized @xmath4ni  for the models with @xmath136 , 10 , and 20 are summarized in table  [ tab : abn ] . 
   the energy source of the lc of sn  2006jc is still under debate . 
   the possible sources include the @xmath4ni-@xmath4co  decay like type i sne and the ejecta - csm interaction like type iin sne . however , both scenarios have the following problems . in the case of the @xmath4ni-@xmath4co  decay , 
   the @xmath150-ray photon and positron emitted from the @xmath4ni-@xmath4co  decay are absorbed by the sn ejecta and the absorbed energy is thermalized . 
   thus , the spectra would show a blackbody - like continuum as normal type i sne do . however 
   , the spectra of sn  2006jc do not resemble those of normal type i sne but show a bright blue continuum in early epochs @xcite . in the case of the ejecta - csm interaction , the kinetic energy 
   is transformed to an x - ray emission via bremsstrahlung radiation , and then converted to uv , optical , and ir emissions . 
   thus , it is difficult to explain that the x - ray luminosity is much fainter than the optical luminosity unless the optical depth for the x - ray emission is much higher than that for the optical emission . 
   another problem with the ejecta - csm interaction model is that the x - ray lc is not synchronized with the bolometric lc . 
   in addition , the lc powered by the ejecta - csm interaction usually has a long - term plateau ( e.g. , sn  1997cy , @xcite ) . 
   thus , we assume that the lc is powered by the @xmath4ni-@xmath4co  decay . 
   the bolometric lc of sn  2006jc is constructed from the uv , optical , and ir observations as described in 
   [ sec : bol ] . 
   the estimated peak bolometric magnitude of sn  2006jc is @xmath151 , being as bright as sn  2006aj ( e.g. , @xcite ) . 
   thus , it is speculated that the ejected amount of @xmath4ni  [ @xmath152 is similar to sn  2006aj , i.e. , @xmath153 @xcite . according to   [ sec : hyd ] , 
   the models with @xmath136 , 10 , and 20 can eject a large enough amount of @xmath4ni , while the @xmath4ni  production of the model with @xmath135 is too small .    the spherical explosion models with @xmath136 , 10 , and 20 yield too much @xmath154 because of no fallback . however , no fallback is a consequence of the assumption of the spherical symmetry . 
   the fallback takes place in an aspherical explosion even with a high explosion energy and thus the aspherical explosion may well decrease @xmath154 and increase the central remnant mass @xmath155 ( @xcite ) . therefore , assuming that aspherical fallback takes place in the high - energy models with @xmath136 , 10 , and 20 , we estimate the amount of fallback to yield @xmath153 and then the ejected masses for the models as @xmath156 . as a result 
   , the sets of @xmath155 , @xmath157 and @xmath145 are derived to be ( @xmath158 , @xmath159 , @xmath160 ) @xmath161 ( 1.8 , 5.1 , 5 ) , ( 2.0 , 4.9 , 10 ) , and ( 2.3 , 4.6 , 20 ) .    applying the homologous density structures of the models ( fig . 
   [ fig : vrho ] ) , we synthesize bolometric lcs for the models with @xmath136 , 10 , and 20 using the lte radiation hydrodynamics code and the gray @xmath150-ray transfer code @xcite . in the radiative transfer calculation , 
   the electron scattering is calculated for the ionization states solved by the saha equation and the rosseland mean opacity is approximated with an empirical relation to the electron - scattering opacity @xcite . 
   the peak width ( @xmath162 ) of the sn lc depends on the ejected mass @xmath157 , explosion energy @xmath145 , opacity @xmath163 , density structure , and @xmath4nidistribution , as @xmath164 @xcite , where @xmath165 represents the effects of the density structure and the @xmath4ni  distribution . here , we assume for sake of simplicity a uniform mixing of @xmath4ni  in the sn ejecta . 
   also , the density structures after the sn explosions with various @xmath145 are analogous . 
   thus , the dependence on @xmath165 is negligible and we investigate the lc properties depending on @xmath163 , @xmath157 and @xmath145 . 
   the synthetic lcs obtained for the models with ( @xmath159 , @xmath160 ) @xmath161 ( 5.1 , 5 ) , ( 4.9 , 10 ) , and ( 4.6 , 20 ) are shown in figure  [ fig : lc ] . 
   figure  [ fig : lc ] also shows the multicolor and bolometric lcs of sn  2006jc . 
   the period of sn  2006jc is divided into four epochs depending on the available observations : ( 1 ) uv and optical photometries at @xmath166 days , ( 2 ) optical and nir photometries at @xmath63 days , ( 3 ) optical photometry at @xmath65 days , and ( 4 ) optical , nir , and mir photometries and nir spectroscopy at @xmath64 days . 
   \(1 ) at @xmath166 days , the ir contributions to the bolometric luminosity may well be small because the ir contribution is only @xmath167 at @xmath168 days . thus , the peak bolometric luminosity derived from the uv and optical fluxes is reliable (   [ sec : optest ] ) . 
   if the bolometric lc peaked at the discovery , the peak luminosity is reproduced by the @xmath4ni-@xmath4co  decay of @xmath169 . the rapid decline 
   after the peak prefers such high - energy models as ( @xmath159 , @xmath160 ) = ( 4.9 ,  10 ) and ( 4.6 ,  20 ) . 
   \(2 ) at @xmath63 days , the ir contribution to the bolometric luminosity increases from @xmath167 at @xmath61 days to @xmath170 at @xmath171 days . 
   the contribution of @xmath172 to @xmath173 changes from @xmath174 at @xmath61 days to @xmath175 at @xmath171 days . at this epoch , 
   the optical and ir emissions contribute to the bolometric luminosities . combining the ir brightening and the optical decline , the bolometric lc including @xmath26 ( @xmath176 ) declines slowly . 
   such a slow decline is consistent with the models of ( @xmath159 , @xmath160 ) = ( 4.9 ,  10 ) and ( 4.6 ,  20 ) . 
   \(3 ) at @xmath65 days , nir photometries are not available . 
   the decline of the optical luminosity at this epoch is more rapid than at @xmath177 days . 
   such a rapid decline of the optical lc can not be reproduced by the @xmath4ni-@xmath4co  decay . 
   however , the bolometric lc may well decline more slowly than the optical lc because the ir emission dominates in the bolometric luminosity . 
   \(4 ) at @xmath64 days , nir photometries are available continuously and optical photometries are available at @xmath178 days @xcite . 
   the contribution of the optical emission to the bolometric luminosities is negligible ( @xmath179 at @xmath178 days ) . at this epoch , 
   the contribution of @xmath172 to the total luminosity increases from @xmath180 at @xmath181 days to @xmath28 at @xmath33 days . 
   the estimated ir luminosity is consistent with the luminosity emitted from the hot carbon dust at @xmath33 days (   [ sec : irest ] ) . 
   since the dust temperature decreases with time , the ratio of the mir luminosities to the nir luminosities becomes larger with time . 
   therefore , the amorphous carbon emission model reasonably estimates the ir luminosity due to the hot carbon dust at @xmath182 days . 
   the model with @xmath183 , @xmath184 , and @xmath169 reproduces well the lc decline at @xmath64 days and the ir luminosities due to the hot carbon dust at @xmath33 days days was presented by @xcite . 
   they estimated the total luminosity and the dust temperature as @xmath185ergs  s@xmath23  and @xmath186  k , respectively . 
   our model with @xmath183 , @xmath184 , and @xmath169 predicted the luminosity of @xmath187ergs  s@xmath23and the dust temperature of @xmath188  k @xcite at @xmath189 days , which are lower than the observations . 
   this suggests that the observed ir emissions at @xmath190 days may originate not only from the newly - formed dust in the sn ejecta heated by the @xmath4ni-@xmath4co  decay but also from the light echo of the csm dust . ] . 
   therefore , we conclude that the hypernova - like sn explosion model with @xmath183 , @xmath184 , and @xmath169 is the most preferable model among the exploded models of a wco wolf - rayet star with @xmath110 . 
   x - rays from sn  2006jc were detected by the _ swift _ and _ chandra _ satellites @xcite . 
   the x - ray detection indicates that the expanding sn ejecta collides with the csm . 
   we calculate x - ray emission from the ejecta - csm interaction for the sn model with ( @xmath159 , @xmath160 ) @xmath161 ( 4.9 , 10 ) , and estimate the csm density structure on the basis of a comparison with the observed x - ray lc ( e.g. , @xcite ) . 
   the observed x - ray luminosities estimated with the distance of @xmath191 mpc in @xcite are scaled using @xmath192 mpc . 
   we adopt a csm density profile characterized by a power - law of @xmath193 and assume that the interaction starts at a distance @xmath194 cm . 
   the parameters @xmath195 , @xmath196 , and @xmath197 are determined so that the ejecta - csm interaction reproduces the observed x - ray lc . 
   the interaction generates reverse and forward shock waves in the sn ejecta and csm , respectively . 
   both regions are heated by the shock waves and emit x - rays . 
   in such a compact star , because the density in the shocked sn ejecta is higher than that in the shocked csm , the emitted x - rays from the shocked sn ejecta are more luminous than those from the shocked csm ( fig . 
   [ fig : lx ] ) . 
   figure  [ fig : lx ] shows the synthesized x - ray lc for @xmath198 g @xmath199 and @xmath200 for @xmath201 cm and @xmath202 for @xmath203 cm , i.e. , for a flat ( inside ) and steep ( outside ) csm density profile of @xmath204 g @xmath199 for @xmath201 cm and @xmath205 g @xmath199 for @xmath203 cm . 
   the total mass of the csm is @xmath206 to reproduce the peak of the observed x - ray lc and the subsequent decline . 
   the density , velocity , and temperature structures and their evolutions are shown in figures  [ fig : csm]abc . 
   the velocity of the reverse shock is @xmath207 km  s@xmath23 . 
   the reverse shock reaches @xmath208 from the outer edge of the sn ejecta at @xmath209 days and heats up the swept - up sn ejecta . 
   the temperature behind the reverse shock is higher than @xmath210 k where dust can not newly form and the dust formed in the sn ejecta is destroyed @xcite . 
   our calculation does not show the formation of a cooling shell . 
   this is because the csm interaction is so weak to emit x - ray of @xmath211 ergs  s@xmath23 . 
   if the bolometric luminosity is powered by the csm interaction , i.e. , if the csm interaction emits as high luminosity as @xmath212 ergs  s@xmath23 , the cooling shell might form and thus the dust formation might be possible . 
   further detailed studies , however , are required to confirm the dust formation behind the reverse shock . 
   such a flat density profile of the inner csm implies that the stellar wind was not steady because the steady wind should form the csm of @xmath213 . 
   this circumstellar environment might have been formed by a variable mass - loss rate @xmath214 and/or a variable wind velocity @xmath215 . 
   for example , assuming that the stellar wind blew with a constant @xmath216 km s@xmath23 for two years before the explosion , the mass - loss rate must have changed from @xmath217 to @xmath218 @xmath219 yr@xmath23 in two years . 
   such a drastic change of the mass - loss rate and/or the wind velocity is consistent with the fact that the progenitor of sn  2006jc was surrounded by the matter ejected by the lbv - like event two years before the explosion . 
   we present a theoretical model for sn  2006jc whose properties are summarized as follows . 
   \(1 ) * wco progenitor and dust formation * : the progenitor is a wco wolf - rayet star whose total mass has been reduced from @xmath220 to as small as @xmath110 . 
   the wco star model has a thick c - rich envelope and csm . 
   this is consistent with the formation of amorphous carbon grains in the sn ejecta and the csm suggested by _ akari _ 
   observations @xcite . 
   @xcite have calculated dust formation in the wco star explosion model and shown that carbon dust is formed in the c - rich layer at @xmath168 days . 
   this is much earlier than the dust formation after @xmath221 yr in type ii sne ( sne  ii ) , because of the much smaller @xmath157 in the wco star than sne  ii . according to the models in @xcite , 
   the stars with @xmath104 typically become wco stars to form a thick c - rich layer and csm . this limiting mass , however , is still uncertain and strongly depends on many details of the stellar evolution . 
   the early dust formation in the sn ejecta and the csm suggests that the progenitor of sn  2006jc is a massive star becoming a wco wolf - rayet star . 
   \(2 ) * explosion and bolometric light curve * : the multicolor lcs of sn  2006jc show peculiar evolutions , e.g. , a rapid decline of the optical lc and brightening of the ir lc . 
   these can be interpreted as an ongoing dust formation . assuming the absorbed optical light is re - emitted in the ir band , the bolometric lc is constructed as a summation of @xmath26 ( @xmath176 ) , @xmath20 , and @xmath66 . 
   by calculating the hydrodynamics , nucleosynthesis , and the bolometric lc for the sn explosion with the various explosion energies , @xmath135 , 5 , 10 , and 20 , we find that the hypernova - like sn explosion model with @xmath183 , @xmath184 , and @xmath169 best reproduces the bolometric lc of sn  2006jc with the radioactive decays . 
   also , the temperature evolution of the carbon dust heated by the @xmath4ni-@xmath4co  decay reasonably well explains the ir observations for @xmath222 days @xcite . 
   \(3 ) * csm interaction and x - ray light curve * : applying the model with @xmath183 and @xmath184 , we calculate the ejecta - csm interaction and the resultant x - ray lc . 
   we derive the csm density structure to reproduce the x - ray lc of sn  2006jc as @xmath204 g @xmath199 for @xmath201 cm and @xmath205 g @xmath199 for @xmath203 cm . 
   the flat density distribution in the inner csm indicates a drastic change of the mass - loss rate and/or the wind velocity that is consistent with the lbv - like event two years before the explosion . 
   * lbv connection * : our model does not take into account the lbv - like event that occurred two years before the explosion . 
   the first reason is that the mechanism of the outburst is still unclear . 
   the second reason is that , at least in the framework of the current understanding of standard stellar evolution , the envelope of a massive star practically freezes out after core he exhaustion ( i.e. , about 10000 years before the explosion ) due to the more rapid evolution of the core than the envelope . 
   in addition , it is interesting to note that , and this is a confirmation of the theoretical expectation , there is no observational evidence that any wolf - rayet star has ever undergone such a luminous outburst @xcite . 
   hence , there is no specific reason to associate the occurrence of a lbv - like outburst to the presupernova evolution . 
   future studies on the mechanism of the outburst are required to firmly conclude the origin of the lbv - like outburst . 
   it would be possible that a possible binary companion star could undergo the lbv - like outburst . 
   * fallback * : according to our hydrodynamics and nucleosynthesis calculations , in the spherically symmetric models with @xmath223 , the fallback does not take place and thus the amount of synthesized @xmath4ni  is much larger than @xmath169 which is required to power the lc of sn  2006jc (   [ sec:56ni ] ) . in the aspherical explosions 
   , however , the fallback takes place even for @xmath223 . in this paper 
   , we assume the fallback even for the models with @xmath223 and derive the amount of fallback to yield the appropriate amount of @xmath4ni . to justify the above assumption 
   , we calculate an aspherical explosion induced by a jet with an opening angle of @xmath224 and an energy deposition rate of @xmath225 @xcite . 
   the jet - induced model realizes an explosion with @xmath226 , @xmath227 , and @xmath228 that is consistent with the adopted model . 
   we note that an aspherical radiative transfer calculation is required to confirm that the jet - induced explosion model can reproduce the lc of sn  2006jc .    * light curve models * : the model with @xmath183 , @xmath184 , and @xmath169 is not an unique model to reproduce the bolometric lc of sn  2006jc . in the case of usual sne 
   , the velocities of the absorption lines can disentangle the degeneracy of @xmath157 and @xmath145 by means of the comparison with the photospheric velocities ( e.g. , @xcite ) . 
   however , the spectra of sn  2006jc are dominated by he emission lines and the nature is unclear . 
   thus we can not fully resolve the degeneracy . since the lc shape is proportional to @xmath229 , the model with a larger @xmath157 requires a higher @xmath145 . 
   an explosion of the progenitor star with a larger @xmath96 reproduces the lc of sn  2006jc with a higher @xmath145 and the x - ray lc with a lower csm density . on the other hand , an explosion of the progenitor star with a smaller @xmath96 reproduces the lc with a lower @xmath145 , e.g. , 
   an explosion with @xmath230 and @xmath135 can explain the lc shape of sn  2006jc . 
   however , such low @xmath145 explosions suppress explosive nucleosynthesis and enhance the fallback . as a result 
   , the @xmath4niproduction is reduced for a small @xmath96 . 
   if the lc of sn  2006jc is powered by the @xmath4ni-@xmath4co  decay , the bright peak indicates a larger amount of @xmath4ni  production ( @xmath231 ) than a normal sn [ @xmath232 , e.g. , sn  1987a , @xcite ] . 
   therefore , sn  2006jc is likely a more energetic explosion than a normal sn with @xmath233 . 
   * dust formation * : we assume that the energy source of the lc of sn  2006jc is the @xmath4ni-@xmath4co  decay . this consistently explains the formation of carbon dust at the early epoch ( @xmath168days ) and the dust temperature at @xmath24days @xcite . in this scenario , however , the origin of the bright blue continuum remains an unsolved problem ( e.g. , @xcite ) . 
   such a spectrum might be explained by the ejecta - csm interaction . in this scenario , 
   however , the fine tunings are required to reproduce the bolometric lc ; most of the x - rays are absorbed and converted to the optical luminosity , which only a small fraction of the x - rays are emitted with changing the fraction from @xmath234 at @xmath235 days to @xmath236 at @xmath237 days . moreover , 
   the formation of carbon dust with two temperatures would not be explained . 
   since both scenarios are inconclusive so far , further investigations may give important implications on the emission mechanism of sn  2006jc . 
   we would like to thank a.  arkharov , n.  efimova , a.  di   paola , c.  corsi , e.  di  carlo , and m.  dolci for providing us the data of the jhk - band photometries . 
   we also would like to thank s. immler for the preprint on the swift observations . 
   thanks the support from the 21st century coe program ( quest ) of jsps ( japan society for the promotion of science ) for his stay in the university of tokyo and the hospitality of the department of astronomy . 
   , d.k.s . , and t.p.p . 
   are supported by the jsps - insa ( indian national science academy ) exchange programme . 
   m.t . are supported through the jsps research fellowship for young scientists . 
   this work has been supported in part by world premier international research center initiative ( wpi initiative ) , mext , japan , and by the grant - in - aid for scientific research of the jsps ( 10041110 , 10304014 , 11740120 , 12640233 , 14047206 , 14253001 , 14540223 , 16740106 , 18104003 , 18540231 , 20540226 ) and mext ( 19047004 , 20040004 , 20041005 , 07ce2002 ) . 
   holland , s. , et  al . 
   2007 , `` supernova 1987a : 20 years after : supernovae and gamma - ray bursters '' , ed . 
   s. immler , k.w . 
   weiler , and r. mccray ( aip : new york ) , in press . 
   the poster paper is available at http://astrophysics.gsfc.nasa.gov/conferences/supernova1987a/holland_poster.pdf .
summary: we present a theoretical model for type ib supernova ( sn )  2006jc . 
   we calculate the evolution of the progenitor star , hydrodynamics and nucleosynthesis of the sn explosion , and the sn bolometric light curve ( lc ) . 
   the synthetic bolometric lc is compared with the observed bolometric lc constructed by integrating the uv , optical , near - infrared ( nir ) , and mid - infrared ( mir ) fluxes . 
   the progenitor is assumed to be as massive as @xmath0 on the zero - age main - sequence . 
   the star undergoes extensive mass loss to reduce its mass down to as small as @xmath1 , thus becoming a wco wolf - rayet star . 
   the wco star model has a thick carbon - rich layer , in which amorphous carbon grains can be formed . 
   this could explain the nir brightening and the dust feature seen in the mir spectrum . 
   we suggest that the progenitor of sn  2006jc is a wco wolf - rayet star having undergone strong mass loss and such massive stars are the important sites of dust formation . 
   we derive the parameters of the explosion model in order to reproduce the bolometric lc of sn  2006jc by the radioactive decays : the ejecta mass @xmath2 , hypernova - like explosion energy @xmath3 ergs , and ejected @xmath4ni  mass @xmath5 . 
   we also calculate the circumstellar interaction and find that a csm with a flat density structure is required to reproduce the x - ray lc of sn  2006jc . 
   this suggests a drastic change of the mass - loss rate and/or the wind velocity that is consistent with the past luminous blue variable ( lbv)-like event .