SN 2008D Research Articles

SUPERNOVAE AND GAMMA-RAY BURSTS: A DECADE OF OBSERVATIONS

In this paper I shall shortly review the observational status of the Supernova and Gamma-ray Bursts connection including the most recent observations: the discovery of a new case of association at z = 0.53 (SN 2008 hw/GRB 081007) and the case of SN 2008D associated with the XRF 080109, a borderline object which may link GRBs with "standard" core-collapse events.

Recent Observations of GRB-Supernovae

AbstractThe GRB-SNe connection has been strengthened since 2008 by the detection of 6 additional GRB-SNe at both local and cosmological redshifts. This review summarizes the recent observations of SNe associated with GRBs 081007, 090618, 091127, 100316D, 101219B and 111211A, as well as the observations of SN 2008D, which was associated with a bright X-ray flash (XRF 080109) and may represent a link between “plain” SN and GRB-SNe. It is now clear that most – if not all – long-duration GRBs are produced by the core collapse of massive stars.

Optical studies of SN 2009jf: a Type Ib supernova with an extremely slow decline and aspherical signature

Optical UBVRI photometry and medium-resolution spectroscopy of the Type Ib supernova SN 2009jf, during the period from ∼ −15 to +250 d, with respect to the B maximum are reported. The light curves are broad, with an extremely slow decline. The early post-maximum decline rate in the V band is similar to SN 2008D; however, the late-phase decline rate is slower than other Type Ib supernovae studied. With an absolute magnitude of MV=−17.96 ± 0.19 at peak, SN 2009jf is a normally bright supernova. The peak bolometric luminosity and the energy deposition rate via the 56Ni →56Co chain indicate that ∼0.17+0.03−0.03 M⊙ of 56Ni was ejected during the explosion. The He i 5876 Å line is clearly identified in the first spectrum of day ∼ −15, at a velocity of ∼16 000 km s−1. The [O i] 6300–6364 Å line seen in the nebular spectrum has a multipeaked and asymmetric emission profile, with the blue peak being stronger. The estimated flux in this line implies that ≳1.34 M⊙ oxygen was ejected. The slow evolution of the light curves of SN 2009jf indicates the presence of a massive ejecta. The high expansion velocity in the early phase and broader emission lines during the nebular phase suggest it to be an explosion with a large kinetic energy. A simple qualitative estimate leads to the ejecta mass of Mej= 4–9 M⊙ and kinetic energy EK= 3–8 × 1051 erg. The ejected mass estimate is indicative of an initial main-sequence mass of ≳20–25 M⊙.

Constraints on high-energy neutrino emission from SN 2008D

SN 2008D, a core collapse supernova at a distance of 27 Mpc, was serendipitously discovered by the Swift satellite through an associated X-ray flash. Core collapse supernovae have been observed in association with long gamma-ray bursts and X-ray flashes and a physical connection is widely assumed. This connection could imply that some core collapse supernovae possess mildly relativistic jets in which high-energy neutrinos are produced through proton-proton collisions. The predicted neutrino spectra would be detectable by Cherenkov neutrino detectors like IceCube. A search for a neutrino signal in temporal and spatial correlation with the observed X-ray flash of SN 2008D was conducted using data taken in 2007-2008 with 22 strings of the IceCube detector. Events were selected based on a boosted decision tree classifier trained with simulated signal and experimental background data. The classifier was optimized to the position and a "soft jet" neutrino spectrum assumed for SN 2008D. Using three search windows placed around the X-ray peak, emission time scales from 100 - 10000 s were probed. No events passing the cuts were observed in agreement with the signal expectation of 0.13 events. Upper limits on the muon neutrino flux from core collapse supernovae were derived for different emission time scales and the principal model parameters were constrained.

THE EARLY UV/OPTICAL EMISSION FROM CORE-COLLAPSE SUPERNOVAE

We derive a simple approximate model describing the early, hours to days, UV/optical (UV/O) supernova emission, which is produced by the expansion of the outer ≲10−2 M☉ part of the shock-heated envelope, and precedes optical emission driven by radioactive decay. Our model includes an approximate description of the time dependence of the opacity (mainly due to recombination), and of the deviation of the emitted spectrum from a blackbody spectrum. We show that the characteristics of the early UV/O emission constrain the radius of the progenitor star, R*, its envelope composition, and the ratio of the ejecta energy to its mass, E/M. For He envelopes, neglecting the effect of recombination may lead to an overestimate of R* by more than an order of magnitude. We also show that the relative extinction at different wavelengths (Aλ − AV) may be inferred from the light curves at these wavelengths, removing the uncertainty in the estimate of R* due to reddening (but not the uncertainty in E/M due to uncertainty in absolute extinction). The early UV/O observations of the types Ib SN 2008D and IIp SNLS−04D2dc are consistent with our model predictions. For SN 2008D, we find R* ≈ 1011 cm, and an indication that the He envelope contains a significant C/O fraction.

ASPHERICAL SUPERNOVA SHOCK BREAKOUT AND THE OBSERVATIONS OF SUPERNOVA 2008D

Shock breakout is the earliest, readily-observable emission from a core-collapse supernova explosion. Observing supernova shock breakout may yield information about the nature of the supernova shock prior to exiting the progenitor and, in turn, about the core-collapse supernova mechanism itself. X-ray Outburst 080109, later associated with SN 2008D, is a very well-observed example of shock breakout from a core-collapse supernova. Despite excellent observational coverage and detailed modeling, fundamental information about the shock breakout, such as the radius of breakout and driver of the light curve time scale, is still uncertain. The models constructed for explaining the shock breakout emission from SN 2008D all assume spherical symmetry. We present a study of the observational characteristics of {\it aspherical} shock breakout from stripped-envelope core-collapse supernovae. We conduct two-dimensional, jet-driven supernova simulations from stripped-envelope progenitors and calculate the resulting shock breakout X-ray spectra and light curves. The X-ray spectra evolve significantly in time as the shocks expand outward and are not well-fit by single-temperature and radius black bodies. The time scale of the X-ray burst light curve of the shock breakout is related to the shock crossing time of the progenitor, not the much shorter light crossing time that sets the light curve time scale in spherical breakouts. This could explain the long shock breakout light curve time scale observed for XRO 080109/SN 2008D.

Study of the NGC 2770 interstellar medium through H α, millimetric and optical polarimetric data of SN 2008D and SN 2007uy

We present the preliminary results of the recent H α narrow-band imaging carried out for NGC 2770 with the Gran Telescopio Canarias (GTC) equipped with OSIRIS. We put the polarization measurements reported in Gorosabel et al. (2010) for SN 2007uy and SN 2008D in the context of the morphological information inferred from the H α imaging. We estimated the orientation of the interstellar polarization (ISP) at the position of SN 2007uy and, most interestingly, at the site of SN 2008D which has been subject of an intensive debate due to its possible connection with Gamma-Ray Bursts (GRBs). The H α imaging reveals a clumpy interstellar medium (ISM) composed of hundreds of compact emitting regions, for which we determined their sizes. The derived size for the H α emitting region coincident with SN 2008D is consistent with the ISM cell size limits imposed by Gorosabel et al. (2010) based on millimetric data. A deeper data analysis is under way and will be published elsewhere. This article represents the first attempt to study the site of a possible GRB-like event combining millimetric, polarimetric and narrow-band data.

Study of envelope velocity evolution of core-collapse type Ib-c supernovae from observations of XRF 080109 / SN 2008D and GRB 060218 / SN 2006aj with BTA

Results of modeling the spectra of two supernovae SN 2008D and SN 2006aj related to the X-ray flash XRF 080109 and gamma-ray burst GRB / XRF 060218, respectively, are studied. The spectra were obtained with the 6-meter BTA telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences in 6.48 and 27.61 days after the explosion of SN 2008D, and in 2.55 and 3.55 days after the explosion of SN 2006aj. The spectra were interpreted in the Sobolev approximation with the SYNOW code. An assumption about the presence of envelopes around the progenitor stars is confirmed by an agreement between the velocities of lines interpreted as hydrogen and helium, and the empiric power-law velocity drop with time for the envelopes of classic core-collapse supernovae. Detection of a P Cyg profile of the H-beta line in the spectra of optical afterglows of GRBs can be a determinative argument in favor of this hypothesis.

THE EARLY ASYMMETRIES OF SUPERNOVA 2008D/XRF 080109

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 polarized, although the largest contribution is due to the interstellar polarization component of Q_ISP=0+/-0.1% and U_ISP=-1.2+/-0.1%. 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 polarization 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 polarized high-velocity Ca II features in Type Ibc SNe. The polarization 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. (abridged)

NGC 2770: A SUPERNOVA Ib FACTORY?

NGC 2770 has been the host of three supernovae of Type Ib during the last 10 years, SN 1999eh, SN 2007uy and SN 2008D. SN 2008D attracted special attention due to the serendipitous discovery of an associated X-ray transient. In this paper, we study the properties of NGC 2770 and specifically the three SN sites to investigate whether this galaxy is in any way peculiar to cause a high frequency of SNe Ib. We model the global SED of the galaxy from broadband data and derive a star-formation and SN rate comparable to the values of the Milky Way. We further study the galaxy using longslit spectroscopy covering the major axis and the three SN sites. From the spectroscopic study we find subsolar metallicities for the SN sites, a high extinction and a moderate star-formation rate. In a high resolution spectrum, we also detect diffuse interstellar bands in the line-of-sight towards SN 2008. A comparison of NGC 2770 to the global properties of a galaxy sample with high SN occurance (at least 3 SN in the last 100 years) suggests that NGC 2770 is not particularly destined to produce such an enhancement of observed SNe observed. Its properties are also very different from gamma-ray burst host galaxies. Statistical considerations on SN Ib detection rates give a probability of ~1.5% to find a galaxy with three Ib SNe detected in 10 years. The high number of rare Ib SNe in this galaxy is therefore likely to be a coincidence rather than special properties of the galaxy itself. NGC 2770 has a small irregular companion, NGC 2770B, which is highly starforming, has a very low mass and one of the lowest metallicities detected in the nearby universe as derived from longslit spectroscopy. In the most metal poor part, we even detect Wolf-Rayet features, against the current models of WR stars which require high metallicities.

VERY-LONG-BASELINE INTERFEROMETRY OBSERVATIONS OF SN 2008D

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 3σ upper limit of ~ 0.75 c on the expansion velocity of a circular source. For an elongated source, our measurements are compatible with mildly relativistic expansion. However, our 3σ upper limit on the proper motion is 4 μas day–1, corresponding to an apparent velocity of less than 0.6 c, and is consistent with a stationary flux centroid. This limit rules out a relativistic jet such as a gamma-ray burst jet away from the line of sight, which would be expected to show apparent proper motion of greater than 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 less than 30,000 km s–1 and small proper motions (< 500 km s–1) seen in typical supernovae.

EARLY SPECTROSCOPIC IDENTIFICATION OF SN 2008D

SN 2008D was discovered while following up an unusually bright X-ray transient in the nearby spiral galaxy NGC 2770. We present early optical spectra (obtained 1.75 days after the X-ray transient) which allowed the first identification of the object as a supernova at redshift z = 0.007. These spectra were acquired during the initial declining phase of the light curve, likely produced in the stellar envelope cooling after shock breakout, and rarely observed. They exhibit a rather flat spectral energy distribution with broad undulations, and a strong, W-shaped feature with minima at 3980 and 4190 AA (rest frame). We also present extensive spectroscopy and photometry of the supernova during the subsequent photospheric phase. Unlike supernovae associated with gamma-ray bursts, SN 2008D displayed prominent He features and is therefore of Type Ib.

Early x-ray burst sighting

We were intrigued by the story “X-ray Outburst Reveals a Supernova Before It Explodes” ( Physics Today 0031-9228 61 8 2008 21 https://doi.org/10.1063/1.2970204. http://dx.doi.org/10.1063/1.2970204 ), which describes the likely discovery of a core-collapse supernova by Alicia Soderberg and colleagues. 1 1. A. M. Soderberg, et al. , Nature 453, 469 (2008). https://doi.org/10.1038/nature06997 The story’s figure 2 resembles a similar x-ray light curve, reported by collaborators at Los Alamos National Laboratory, 2 2. R. D. Belian, J. P. Conner, W. D. Evans, Astrophys. J. Lett. 171, L87 (1972). https://doi.org/10.1086/180874 from an x-ray outburst that occurred on 7 July 1969 and preceded by two days the x-ray nova Centaurus XR-4. 3 3. W. D. Evans, R. D. Belian, J. P. Conner, Astrophys. J. Lett. 159, L57 (1970). https://doi.org/10.1086/180477 The spin periods of the Vela satellites that recorded the 1969 event were roughly 1 minute, and any location within the instruments’ field of view would be sampled for 2 or 3 seconds out of that period, followed by subsequent samplings every 60 seconds or so. When first observed, the precursor to the Cen XR-4 nova was already at its highest level, but the subsequent decline is almost identical to that of SN 2008D.The outburst was discernable above background for seven minutes; 2 2. R. D. Belian, J. P. Conner, W. D. Evans, Astrophys. J. Lett. 171, L87 (1972). https://doi.org/10.1086/180874 the Physics Today item indicates a similar duration for the outburst of SN 2008D. The x-ray nova part of the transient Cen XR-4 was observed two days later on 9 July 1969, the next time the satellites’ detector scanned that part of the sky.An article about the original discovery of Cen XR-4 was published right around the time the nova phase was rapidly declining. By 24 September 1969, the source was no longer visible above background. In a second article covering the known life of the Cen XR-4 x-ray nova, 3 3. W. D. Evans, R. D. Belian, J. P. Conner, Astrophys. J. Lett. 159, L57 (1970). https://doi.org/10.1086/180477 we stated that there was no definite optical identification of Cen XR-4; a nova outburst had not been reported at the location of the source. It is not clear whether Cen XR-4 was a core-collapse supernova as the similarities between it and SN 2008D suggest. But it is certainly clear that the occurrence of x-ray precursors to energetic cosmic processes was documented in the 1972 event and again in 2008.REFERENCESSection:ChooseTop of pageREFERENCES <<1. A. M. Soderberg, et al. , Nature 453, 469 (2008). https://doi.org/10.1038/nature06997 , Google ScholarCrossref, ISI2. R. D. Belian, J. P. Conner, W. D. Evans, Astrophys. J. Lett. 171, L87 (1972). https://doi.org/10.1086/180874 , Google ScholarCrossref, ISI3. W. D. Evans, R. D. Belian, J. P. Conner, Astrophys. J. Lett. 159, L57 (1970). https://doi.org/10.1086/180477 , Google ScholarCrossref, ISI© 2008 American Institute of Physics.

Shock Breakout Emission from a Type Ib/c Supernova: XRT 080109/SN 2008D

The X-ray flash 080109, associated with SN 2008D, can be attributed to the shock breakout emission from a normal Type Ib/c supernova. If the observed emission is interpreted as blackbody emission, the temperature and radiated energy are close to expectations, considering that scattering dominates absorption processes so that spectrum formation occurs deep within the photosphere. The X-ray emission observed at ~10 days is attributed to inverse Compton scattering of photospheric photons with relativistic electrons produced in the interaction of the supernova with the progenitor wind. A simple model for the optical/ultraviolet emission from shock breakout is developed and applied to SN 1987A, SN 1999ex, SN 2008D, and SN 2006aj, all of which have optical emission observed at t~1 day. The emission from the first three can plausibly be attributed to shock breakout emission. The photospheric temperature is most sensitive to the radius of the progenitor star core and the radii in these cases are in line with expectations from stellar evolution. The early optical/ultraviolet observations of SN 2006aj cannot be accommodated by a shock breakout model in a straightforward way.

The Metamorphosis of Supernova SN 2008D/XRF 080109: A Link Between Supernovae and GRBs/Hypernovae

The only supernovae (SNe) to show gamma-ray bursts (GRBs) or early x-ray emission thus far are overenergetic, broad-lined type Ic SNe (hypernovae, HNe). Recently, SN 2008D has shown several unusual features: (i) weak x-ray flash (XRF), (ii) an early, narrow optical peak, (iii) disappearance of the broad lines typical of SN Ic HNe, and (iv) development of helium lines as in SNe Ib. Detailed analysis shows that SN 2008D was not a normal supernova: Its explosion energy (E approximately 6x10(51) erg) and ejected mass [ approximately 7 times the mass of the Sun (M(middle dot in circle))] are intermediate between normal SNe Ibc and HNe. We conclude that SN 2008D was originally a approximately 30 M(middle dot in circle) star. When it collapsed, a black hole formed and a weak, mildly relativistic jet was produced, which caused the XRF. SN 2008D is probably among the weakest explosions that produce relativistic jets. Inner engine activity appears to be present whenever massive stars collapse to black holes.

The X-ray transient 080109 in NGC 2770: an X-ray flash associated with a normal core-collapse supernova

Although it is generally thought that long-duration gamma-ray bursts (LGRBs) are associated with core-collapse supernovae (SNe), so far only four pairs of GRBs and SNe with firmly established connection have been found. All the four GRB-SNe belong to special class of Type Ic – called the broad-lined SNe indicative of a large explosion energy, suggesting that only a small fraction of SNe Ibc have GRBs associated with them. This scheme has been refreshed by the discovery of a bright X-ray transient in NGC 2770 on 2008 January 9, which was followed by a rather normal Type Ib SN 2008D. In this paper, I argue that the transient 080109 is an X-ray flash (XRF, the soft version of a GRB) because of the following evidence. (1) The transient cannot be interpreted as a SN shock breakout event. (2) The GRB X-ray flare interpretation is not supported by the high-energy observation. I then show that XRF 080109 satisfies the well-known relation between the isotropic-equivalent energy and the peak spectral energy for LGRBs, which highly strengthens the XRF interpretation. Finally, I point out that the peak spectral energy of XRF 080109 and the maximum bolometric luminosity of SN 2008D agree with the Eγ,peak–LSN,max relationship of Li, strengthening the validity of the relationship. I speculate that events like XRF 080109 may occur at a rate comparable to SNe Ibc, and a soft X-ray telescope devoted to surveying for nearby X-ray flares will be very fruitful in discovering them.

ESC observations of SN 2005cf

The ESC-RTN optical spectroscopy data set for SN 2005cf is presented and analyzed. The observations range from -11.6 and +77.3 days with respect to B-band maximum light. The evolution of the spectral energy distribution of SN 2005cf is characterized by the presence of high velocity and features. SYNOW synthetic spectra are used to investigate the ejecta geometry of silicon. Based on the synthetic spectra, the high-velocity feature appears detached at 19 500 km s-1. We also securely establish the presence of such a feature in SN 1990N, SN 1994D, SN 2002er, and SN 2003du. In a morphological study both the IR triplet and H&K absorption lines of SN 2005cf show high-velocity features centered around 24 000 km s-1. When compared with other type Ia SNe based on the scheme presented in [CITE][ApJ, 623, 1011]2005ApJ...623.1011B, SN 2005cf definitely belongs to the LVG group.

A Radio and X-Ray Study of Historical Supernovae in M83

We report the results of 15 years of radio observations of the six historical supernovae (SNe) in M83 using the Very Large Array. We note the near linear decline in radio emission from SN 1957D, a type II SN, which remains a non-thermal radio emitter. The measured flux densities from SNe 1923A and 1950B have flattened as they begin to fade below detectable limits, also type II SNe. The luminosities for these three SNe are comparable with the radio luminosities of other decades-old SNe at similar epochs. SNe 1945B, 1968L, and 1983N were not detected in the most recent observations and these non-detections are consistent with previous studies. We report the X-ray non-detections of all six historical SNe using the Chandra X-ray Observatory, consistent with previous X-ray searches of other decades-old SNe, and low inferred mass loss rates of the progenitors.

Comparative Direct Analysis of Type Ia Supernova Spectra. I. SN 1994D

ABSTRACTAs the first step in a comprehensive, comparative, direct analysis of the spectra of Type Ia supernovae (SNe Ia), we use the parameterized supernova synthetic‐spectrum code SYNOW to interpret 26 spectra of the well‐observed SN 1994D. Our results are consistent with the traditional view that the composition structure (element abundance fractions versus ejection velocity) is radially stratified. We find that resonance‐scattering features due to permitted lines of Ca ii, Na i, and Fe ii persist to more than 100 days after explosion. The fitting parameters for SN 1994D, together with those to be determined for other SNe Ia, will provide an internally consistent quantification of the spectroscopic diversity among SNe Ia and shed light on how the various manifestations of observational diversity are related to their physical causes.

Very Large Telescope FORS1 Imaging Polarimetry of M83 (NGC 5236). I. Search for Light Echoes from Historical Supernovae

We have used FORS1 at the ESO Very Large Telescope to search for light echoes in imaging polarimetry from four historical supernovae in the face-on nearby spiral galaxy M83 (NGC 5236). No echoes were detected around our targets (SN 1923A, SN 1945B, SN 1950B, and SN 1957D). This implies that the interstellar medium in their environs is rather tenuous (a few particles per cm3), possibly as a result of previous supernova explosions that could have cleared the immediate vicinities of our targets. The merits and limitations of searching for light echoes in imaging polarimetry are discussed. From the photometry of the sources detected at the supernova locations, we estimate star cluster masses of 720, 400, and 300 M☉ for the cluster progenitors of SN 1957D, SN 1923A, and SN 1950B, respectively, and an upper limit of a few tens of solar masses for SN 1945B.