* Astronomy

Members Login
Username 
 
Password 
    Remember Me  
Post Info TOPIC: Supernova 2008D


L

Posts: 131433
Date:
XRT 080109
Permalink  
 


Title: SN 2008D: A Wolf-Rayet explosion through a thick wind
Author: Gilad Svirski, Ehud Nakar

Supernova (SN) 2008D/XRT 080109 is considered to be the only direct detection of a shock breakout from a regular SN to date. While a breakout interpretation was favored by several papers, inconsistencies remain between the observations and current SN shock breakout theory. Most notably, the duration of the luminous X-ray pulse is considerably longer than expected for a spherical breakout through the surface of a type Ibc SN progenitor, and the X-ray radiation features, mainly its flat spectrum and its luminosity evolution, are enigmatic. We apply a recently developed theoretical model for the observed radiation from a Wolf-Rayet SN exploding through a thick wind and show that it naturally explains all the observed features of SN 2008D X-ray emission, including the energetics, the spectrum and the detailed luminosity evolution. We find that the inferred progenitor and SN parameters are typical for an exploding Wolf-Rayet. A comparison of the wind density found at the breakout radius to the density at much larger radii, as inferred by late radio observations, suggests an enhanced mass loss rate taking effect about ten days or less prior to the SN explosion. This finding joins accumulating evidence for a possible late phase in the stellar evolution of massive stars, involving vigorous mass loss a short time before the SN explosion.

Read more (131kb, PDF)



__________________


L

Posts: 131433
Date:
RE: Supernova 2008D
Permalink  
 


Title: Early UV/Optical Emission of The Type Ib SN 2008D
Authors: Melina C. Bersten, Masaomi Tanaka, Nozomu Tominaga, Omar G. Benvenuto, Ken'ichi Nomoto

We propose an alternative explanation for the post-breakout emission of SN 2008D associated with the X-ray transient 080109. Observations of this object show a very small contrast of 0.35 dex between the light-curve minimum occurring soon after the breakout, and the main luminosity peak that is due to radioactive heating of the ejecta. Hydrodynamical models show that the cooling of a shocked Wolf-Rayet star leads to a much greater difference (> 0.9 dex). Our proposed scenario is that of a jet produced during the explosion which deposits 56Ni-rich material in the outer layers of the ejecta. The presence of high-velocity radioactive material allows us to reproduce the complete luminosity evolution of the object. Without outer 56Ni it could be possible to reproduce the early emission purely from cooling of the shocked envelope by assuming a larger progenitor than a Wolf-Rayet star, but that would require an initial density structure significantly different from what is predicted by stellar evolution models. Analytic models of the cooling phase have been proposed reproduce the early emission of SN 2008D with an extended progenitor. However, we found that the models are valid only until 1.5 days after the explosion where only two data of SN 2008D are available. We also discuss the possibility of the interaction of the ejecta with a binary companion, based on published analytic expressions. However, the binary separation required to fit the early emission should be < 3 solar radii which is too small for a system containing two massive stars.

Read more (134kb, PDF)



__________________


L

Posts: 131433
Date:
Permalink  
 

Title: From Shock Breakout to Peak and Beyond: Extensive Panchromatic Observations of the Type Ib Supernova 2008D associated with Swift X-ray Transient 080109
Authors: Maryam Modjaz, W. Li, N. Butler, R. Chornock, D. Perley, S. Blondin, J. S. Bloom, A. V. Filippenko, R. P. Kirshner, D. Kocevski, D. Poznanski, M. Hicken, R. J. Foley, G. S. Stringfellow, P. Berlind, D. Barrado y Navascues, C. H. Blake, H. Bouy, W. R. Brown, P. Challis, H. Chen, W. H. de Vries, P. Dufour, E. Falco, A. Friedman, M. Ganeshalingam, P. Garnavich, B. Holden, G. Illingworth, J. Liebert, G. H. Marion, N. Lee, S. S. Olivier, J. X. Prochaska, J. M. Silverman, N. Smith, D. Starr, T. N. Steele, A. Stockton, G. G. Williams, W. M. Wood-Vasey
(Version v3)

We present extensive early photometric (ultraviolet through near-infrared) and spectroscopic (optical and near-infrared) data on supernova (SN) 2008D as well as X-ray data analysis on the associated Swift/X-ray transient (XRT) 080109. Our data span a time range of 5 hours before the detection of the X-ray transient to 150 days after its detection, and detailed analysis allowed us to derive constraints on the nature of the SN and its progenitor; throughout we draw comparisons with results presented in the literature and find several key aspects that differ. We show that the X-ray spectrum of XRT 080109 can be fit equally well by an absorbed power law or a superposition of about equal parts of both power law and blackbody. Our data first established that SN 2008D is a spectroscopically normal SN Ib (i.e., showing conspicuous He lines), and show that SN 2008D had a relatively long rise time of 18 days and a modest optical peak luminosity. The early-time light curves of the SN are dominated by a cooling stellar envelope (for \Delta t~0.1- 4 day, most pronounced in the blue bands) followed by 56^Ni decay. We construct a reliable measurement of the bolometric output for this stripped-envelope SN, and, combined with estimates of E_K and M_ej from the literature, estimate the stellar radius R_star of its probable Wolf-Rayet progenitor. According to the model of Waxman et al. and of Chevalier & Fransson, we derive R_star^{W07}= 1.20.7 R_sun and R_star^{CF08}= 127 R_sun, respectively; the latter being more in line with typical WN stars. Spectra obtained at 3 and 4 months after maximum light show double-peaked oxygen lines that we associate with departures from spherical symmetry, as has been suggested for the inner ejecta of a number of SN Ib cores.

Read more (680kb, PDF)

__________________


L

Posts: 131433
Date:
Permalink  
 

Title: The Early Asymmetries of Supernova 2008D / XRF 080109
Authors: J.R. Maund, J.C. Wheeler, D.Baade, F. Patat, P.A. Hoflich, L. Wang, A. Clocchiatti

Spectropolarimetry of the Type Ib SN 2008D, associated with the XRF 080109, at two separate epochs, are presented. The epochs of these observations correspond to V-band light curve maximum and 15 days after light curve maximum (or 21 and 36 days after the XRF). We find SN 2008D to be significantly polarised, although the largest contribution is due to the interstellar polarisation component of Q_ISP=00.1% and U_ISP=-1.20.1%. At the two epochs, the spectropolarimetry of SN 2008D is classified as being D1+L(HeI)+L(Ca II). The intrinsic polarization of continuum wavelength regions is <0.4%, at both epochs, implying an asymmetry of the photosphere of <10%. Similar to other Type Ibc SNe, such as 2005bf, 2006aj and 2007gr, we observed significant polarisation corresponding to the spectral features of Ca II, He I, Mg I, Fe II and, possibly, O I 7774, about a close-to-spherically-symmetric photosphere. We introduce a new plot showing the chemically distinct line forming regions in the ejecta and comment on the apparent ubiquity of highly polarised high-velocity Ca II features in Type Ibc SNe. The polarisation angle of Ca II IR triplet was significantly different, at both epochs, to those of the other species, suggesting high-velocity Ca II forms in a separate part of the ejecta. The apparent structure in the outer layers of SN 2008D has implications for the interpretation of the early-time X-ray emission associated with shock break-out.

Read more (1011kb, PDF)

__________________


L

Posts: 131433
Date:
Type Ib Supernova 2008D
Permalink  
 


Title: Nebular Phase Observations of the Type Ib Supernova 2008D/X-ray Transient 080109: Side-Viewed Bipolar Explosion
Authors: Masaomi Tanaka, Masayuki Yamanaka, Keiichi Maeda, Koji S. Kawabata, Takashi Hattori, Takeo Minezaki, Stefano Valenti, Massimo Della Valle, D. K. Sahu, G. C. Anupama, Nozomu Tominaga, Ken'ichi Nomoto, Paolo A. Mazzali, Elena Pian

We present optical spectroscopic and photometric observations of supernova (SN) 2008D, associated with the luminous X-ray transient 080109, at >300 days after the explosion (nebular phases). We also give flux measurements of emission lines from the H II region at the site of the SN, and estimates of the local metallicity. The brightness of the SN at nebular phases is consistent with the prediction of the explosion models with an ejected 56Ni mass of 0.07 Msun, which explains the light curve at early phases. The [O I] line in the nebular spectrum shows a double-peaked profile while the [Ca II] line does not. The double-peaked [O I] profile strongly indicates that SN 2008D is an aspherical explosion. The profile can be explained by a torus-like distribution of oxygen viewed from near the plane of the torus. We suggest that SN 2008D is a side-viewed, bipolar explosion with a viewing angle of > 50 from the polar direction.

Read more (361kb, PDF)

__________________


L

Posts: 131433
Date:
RE: Supernova 2008D
Permalink  
 




__________________


L

Posts: 131433
Date:
Permalink  
 

Title: Type Ib Supernova 2008D associated with the Luminous X-ray Transient 080109: An Energetic Explosion of a Massive Helium Star
Authors: Masaomi Tanaka, Nozomu Tominaga, Ken'ichi Nomoto, S. Valenti, D.K. Sahu, T. Minezaki, Y. Yoshii, M. Yoshida, G.C. Anupama, S. Benetti, G. Chincarini, M. Della Valle, P. A. Mazzali, E. Pian
(Version v3)

We present a theoretical model for supernova (SN) 2008D associated with the luminous X-ray transient 080109. The bolometric light curve and optical spectra of the SN are modelled based on the progenitor models and the explosion models obtained from hydrodynamic/nucleosynthetic calculations. We find that SN 2008D is a more energetic explosion than normal core-collapse supernovae, with an ejecta mass of Mej = 5.3 1.0 Msun and a kinetic energy of E = 6.0 2.5 x 10^{51} erg. The progenitor star of the SN has a 6-8 Msun He core with essentially no H envelope (< 5 x 10^{-4} Msun) prior to the explosion. The main-sequence mass of the progenitor is estimated to be Mms =20-25 Msun, with additional systematic uncertainties due to convection, mass loss, rotation, and binary effects. These properties are intermediate between those of normal SNe and hypernovae associated with gamma-ray bursts. The mass of the central remnant is estimated as 1.6 - 1.8 Msun, which is near the boundary between neutron star and black hole formation.

Read more (308kb, PDF)

__________________


L

Posts: 131433
Date:
Permalink  
 

Title: VLBI Observations of SN 2008D
Authors: M. F. Bietenholz, A. M. Soderberg, N. Bartel
(Version v2)

We report on two epochs of very-long-baseline interferometry (VLBI) observations of the Type Ib/c supernova SN 2008D, which was associated with the X-ray outburst XRF 080109. At our first epoch, at t = 30 days after the explosion, we observed at 22 and 8.4 GHz, and at our second, at t = 133 days, at 8.4 and 5.0 GHz. The VLBI observations allow us to accurately measure the source's size and position at each epoch, and thus constrain its expansion velocity and proper motion. We find the source at best marginally resolved at both epochs, allowing us to place a 3sigma upper limit of ~0.75c on the expansion velocity of a circular source. For an elongated source, our measurements are compatible with mildly relativistic expansion. However, our 3sigma upper limit on the proper motion is 4 micro-arcsec/day, corresponding to an apparent velocity of <0.6c, and is consistent with a stationary flux centroid. This limit rules out a relativistic jet such as an gamma-ray burst jet away from the line of sight, which would be expected to show apparent proper motion of >c. Taken together, our measurements argue against the presence of any long-lived relativistic outflow in SN 2008D. On the other hand, our measurements are consistent with the nonrelativistic expansion velocities of <30,000 km/s and small proper motions (<500 km/s) seen in typical supernovae.

Read more (31kb, PDF)

__________________


L

Posts: 131433
Date:
Permalink  
 

Title: Supernova 2008D: A Repetition of Supernova 1987A In a Binary
Authors: Gerald E. Brown, Chang-Hwan Lee

The Supernova 2008D is similar to that of SN 1987A without the H-envelope. Soderberg et al.(2008) reported the serendipitous discovery of the SN2008D at the time of the explosion, accompanied by an X-ray outburst XRF080109. The central remnant, which we believe to be the black-hole (BH) central engine in the Blandford-Znajek mechanism, is estimated, on the basis of the 7% 56Ni production, to have a mass of 1.6-1.8 M_sun. This is not much larger than the upper limit of 1.56 m_sun for the mass of the compact object in SN1987A found by Bethe & Brown (1995); also, on the basis of the 7.5% 56Ni production, they interpreted it as a low-mass BH. Redoing the light curve so as to take into account the absence of convective carbon burning from zero age main sequence 18-24 M_sun and replacing it by carbon shell burning, we see that the remnant in SN2008D must be less massive than in SN 1987A; there of 18 M_sun. Thus, the maximum neutron star mass is 1.5 M_sun. Note that the metallicity of the host galaxy of SN2008D is similar to that of our Galaxy.

Read more (15kb, PDF)

__________________


L

Posts: 131433
Date:
Permalink  
 

A European-led team of international astronomers have discovered clues that suggest that a star that recently went supernova may have exploded more violently than previously thought and collapsed into a black hole. This brutal explosion produced a series of gamma-ray bursts that were only just able to be registered by the astronomers. This discovery could mark an important milestone for astronomers everywhere, as it is providing them with more information of one of the galaxy's most violent events.

Read more

__________________
1 2 3  >  Last»  | Page of 3  sorted by
Quick Reply

Please log in to post quick replies.



Create your own FREE Forum
Report Abuse
Powered by ActiveBoard