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Register a new userThe shape of SN 1993J re-analyzed
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SN 1993J is one of the best studied Type IIb supernovae. Spectropolarimetric data analyses were published over two decades ago at a time when the field of supernova spectropolarimetry was in its infancy. Here we present a new analysis of the spectropolarimetric data of SN 1993J and an improved estimate of its interstellar polarization (ISP) as well as a critical review of ISP removal techniques employed in the field. The polarization of SN 1993J is found to show significant alignment on the $q-u$ plane, suggesting the presence of a dominant axis and therefore of continuum polarization. We also see strong line polarization features, including $mathrm{Hbeta}$, He,{sc i} $lambda 5876$, $mathrm{Halpha}$, He,{sc i} $lambda 6678$, He,{sc i} $lambda 7065$, and high velocity (HV) components of He,{sc i} $lambda 5876$ and $mathrm{Halpha}$. SN 1993J is therefore the second example of a stripped envelope supernova, alongside iPTF13bvn, with prominent HV helium polarization features, and the first to show a likely HV halpha contribution. Overall, we determine that the observed features can be interpreted as the superposition of anisotropically distributed line forming regions over ellipsoidal ejecta. We cannot exclude the possibility of an off-axis energy source within the ejecta. These data demonstrate the rich structures that are inaccessible if solely considering the flux spectra but can be probed by spectropolarimetric observations. In future studies, the new ISP corrected data can be used in conjunction with 3D radiative transfer models to better map the geometry of the ejecta of SN 1993J.
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We report on updated radio imaging observations of the radio remnant of Supernova 1987A (SN 1987A) at 9 GHz, taken with the Australia Telescope Compact Array (ATCA), covering a 25-year period (1992-2017). We use Fourier modeling of the supernova remnant to model its morphology, using both a torus model and a ring model, and find both models show an increasing flux density, and have shown a continuing expansion of the remnant. As found in previous studies, we find the torus model most accurately fits our data, and has shown a change in the remnant expansion at Day 9,300 $pm$210 from 2,300 $pm$200 km/s to 3,610 $pm$240 km/s. We have also seen an increase in brightness in the western lobe of the remnant, although the eastern lobe is still the dominant source of emission, unlike what has been observed at contemporary optical and X-ray wavelengths. We expect to observe a reversal in this asymmetry by the year $sim$2020, and note the south-eastern side of the remnant is now beginning to fade, as has also been seen in optical and X-ray data. Our data indicate that high-latitude emission has been present in the remnant from the earliest stages of the shockwave interacting with the equatorial ring around Day 5,000. However, we find the emission has become increasingly dominated by the low-lying regions by Day 9,300, overlapping with the regions of X-ray emission. We conclude that the shockwave is now leaving the equatorial ring, exiting first from the south-east region of the remnant, and is re-accelerating as it begins to interact with the circumstellar medium beyond the dense inner ring.
The Type IIb supernova (SN) 1993J is one of only a few stripped-envelope supernovae with a progenitor star identified in pre-explosion images. SN IIb models typically invoke H envelope stripping by mass transfer in a binary system. For the case of SN 1993J, the models suggest that the companion grew to 22 M_solar and became a source of ultraviolet (UV) excess. Located in M81, at a distance of only 3.6 Mpc, SN 1993J offers one of the best opportunities to detect the putative companion and test the progenitor model. Previously published near-UV spectra in 2004 showed evidence for absorption lines consistent with a hot (B2 Ia) star, but the field was crowded and dominated by flux from the SN. Here we present Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) and Wide-Field Camera 3 (WFC3) observations of SN 1993J from 2012, at which point the flux from the SN had faded sufficiently to potentially measure the UV continuum properties from the putative companion. The resulting UV spectrum is consistent with contributions from both a hot B star and the SN, although we cannot rule out line-of-sight coincidences.
We present our observations of the radio emission from supernova (SN) 1993J, in M 81 (NGC 3031), made with the VLA, from 90 to 0.7 cm, as well as numerous measurements from other telescopes. The combined data set constitutes probably the most detailed set of measurements ever established for any SN outside of the Local Group in any wavelength range. Only SN 1987A in the LMC has been the subject of such an intensive observational program. The radio emission evolves regularly in both time and frequency, and the usual interpretation in terms of shock interaction with a circumstellar medium (CSM) formed by a pre-SN stellar wind describes the observations rather well considering the complexity of the phenomenon. However: 1) The 85 - 110 GHz measurements at early times are not well fitted by the parameterization, unlike the cm wavelength measurements. 2) At mid-cm wavelengths there is some deviation from the fitted radio light curves. 3) At a time ~3100 days after shock breakout, the decline rate of the radio emission steepens without change in the spectral index. This decline is best described as an exponential decay starting at day 3100 with an e-folding time of ~1100 days. 4) The best overall fit to all of the data is a model including both non-thermal synchrotron self-absorption (SSA) and a thermal free-free absorbing (FFA) components at early times, evolving to a constant spectral index, optically thin decline rate, until the break in that decline rate. Moreover, neither a purely SSA nor a purely FFA absorbing models can provide a fit that simultaneously reproduces the light curves, the spectral index evolution, and the brightness temperature evolution. 5) The radio and X-ray light curves exhibit similar behavior and suggest a sudden drop in the SN progenitor mass-loss rate at ~8000 years prior to shock breakout.
We observed seven epochs of spectropolarimetry in optical wavelengths for the Type IIb SN 2011hs, ranging from -3 to +40 days with respect to V -band maximum. A high degree of interstellar polarization was detected (up to ~3 percent), with a peak lying blueward of 4500A. Similar behaviours have been seen in some Type Ia SNe, but had never been observed in a Type IIb. We find that it is most likely the result of a relative enhancement of small silicate grains in the vicinity of the SN. Significant intrinsic continuum polarization was recovered at -3 and +2 days (p = 0.55 +- 0.12 percent and p = 0.75 +- 0.11 percent, respectively). We discuss the change of the polarization angle across spectral lines and in the continuum as diagnostics for the 3D structure of the ejecta. We see a gradual rotation by about -50 degree in the continuum polarization angle between -2 and +18 days after V - band maximum. A similar rotation in He I {lambda}5876, H{alpha} and the Ca II infrared triplet seems to indicate a strong influence of the global geometry on the line polarization features. The differences in the evolution of their respective loops on the Stokes q - u plane suggest that line specific geometries are also being probed. Possible interpretations are discussed and placed in the context of literature. We find that the spectropolarimetry of SN 2011hs is most similar to that of SN 2011dh, albeit with notable differences.
We present multi-epoch mid-infrared (IR) photometry and the optical discovery observations of the impostor supernova (SN) 2010da in NGC 300 using new and archival Spitzer Space Telescope images and ground-based observatories. The mid-IR counterpart of SN 2010da was detected as SPIRITS 14bme in the SPitzer InfraRed Intensive Transient Survey (SPIRITS), an ongoing systematic search for IR transients. A sharp increase in the 3.6 $mu$m flux followed by a rapid decrease measured ~150 d before and ~80 d after the initial outburst, respectively, reveal a mid-IR counterpart to the coincident optical and high luminosity X-ray outbursts. At late times after the outburst (~2000 d), the 3.6 and 4.5 $mu$m emission increased to over a factor of 2 times the progenitor flux. We attribute the re-brightening mid-IR emission to continued dust production and increasing luminosity of the surviving system associated with SN 2010da. We analyze the evolution of the dust temperature, mass, luminosity, and equilibrium temperature radius in order to resolve the nature of SN 2010da. We address the leading interpretation of SN 2010da as an eruption from a luminous blue variable (LBV) high-mass X-ray binary (HMXB) system. We propose that SN 2010da is instead a supergiant (sg)B[e]-HMXB based on similar luminosities and dust masses exhibited by two other known sgB[e]-HMXB systems. Additionally, the SN 2010da progenitor occupies a similar region on a mid-IR color-magnitude diagram (CMD) with known sgB[e] stars in the Large Magellanic Cloud. The lower limit estimated for the orbital eccentricity of the sgB[e]-HMXB (e>0.82) from X-ray luminosity measurements is high compared to known sgHMXBs and supports the claim that SN 2010da may be associated with a newly formed HMXB system.
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