Browsing by Author "Patat, F."
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- ItemLinear spectropolarimetry of 35 Type Ia supernovae with VLT/FORS : an analysis of the Si II line polarization(2019) Cikota, A.; Patat, F.; Wang, L.F.; Wheeler, J.C.; Bulla, M.; Baade, D.; Hoflich, P.; Cikota, S.; Clocchiatti, Alejandro; Maund, J.R.; Stevance, H.F.; Yang, Y.
- ItemProperties of extragalactic dust inferred from linear polarimetry of Type Ia Supernovae(2015) Patat, F.; Taubenberger, S.; Cox, N.; Baade, D.; Clocchiatti, Alejandro; Hoflich, P.; Maund, J.; Reilly, E.; Spyromilio, J.; Wang, L.; Wheeler, J. C.; Zelaya, P.
- ItemSN 2004aw(2006) Taubenberger, S.; Pastorello, A.; Mazzali, P. A.; Valenti, S.; Pignata, G.; Sauer, D. N.; Arbey, A.; Baernbantner, O.; Benetti, S.; Della Valle, A.; Deng, J.; Elias-Rosa, N.; Filippenko, A. V.; Foley, R. J.; Goobar, A.; Kotak, R.; Li, W.; Meikle, P.; Mendez, J.; Patat, F.; Pian, E.; Ries, C.; Ruiz-Lapuente, P.; Salvo, M.; Stanishev, V.; Turatto, M.; Hillebrandt, W.Optical and near-infrared (near-IR) observations of the Type Ic supernova (SN Ic) 2004aw are presented, obtained from -3 to +413 d with respect to the B-band maximum. The photometric evolution is characterized by a comparatively slow post-maximum decline of the light curves. The peaks in redder bands are significantly delayed relative to the bluer bands, the I-band maximum occurring 8.4 d later than that in B. With an absolute peak magnitude of -18.02 in the V band the SN can be considered fairly bright, but not exceptional. This also holds for the U through I bolometric light curve, where SN 2004aw has a position intermediate between SNe 2002ap and 1998bw. Spectroscopically SN 2004aw provides a link between a normal SN Ic like SN 1994I and the group of broad-lined SNe Ic. The spectral evolution is rather slow, with a spectrum at day +64 being still predominantly photospheric. The shape of the nebular [O-I] lambda lambda 6300, 6364 line indicates a highly aspherical explosion. Helium cannot be unambiguously identified in the spectra, even in the near-IR. Using an analytical description of the light-curve peak we find that the total mass of the ejecta in SN 2004aw is 3.5-8.0 M-circle dot, significantly larger than that in SN 1994I, although not as large as in SN 1998bw. The same model suggests that about 0.3 M-circle dot of Ni-56 has been synthesized in the explosion. No connection to a GRB can be firmly established.
- ItemSN 2018bsz: A Type I superluminous supernova with aspherical circumstellar material(2022) Pursiainen, M.; Leloudas, G.; Paraskeva, E.; Cikota, A.; Anderson, J. P.; Angus, C. R.; Brennan, S.; Bulla, M.; Camacho-Iniguez, E.; Charalampopoulos, P.; Chen, T-W; Delgado Mancheno, M.; Fraser, M.; Frohmaier, C.; Galbany, L.; Gutierrez, C. P.; Gromadzki, M.; Inserra, C.; Maund, J.; Mueller-Bravo, T. E.; Munoz Torres, S.; Nicholl, M.; Onori, F.; Patat, F.; Pessi, P. J.; Roy, R.; Spyromilio, J.; Wiseman, P.; Young, D. R.We present a spectroscopic analysis of the most nearby Type I superluminous supernova (SLSN-I), SN 2018bsz. The photometric evolution of SN 2018bsz has several surprising features, including an unusual pre-peak plateau and evidence for rapid formation of dust greater than or similar to 200 d post-peak. We show here that the spectroscopic and polarimetric properties of SN 2018bsz are also unique. While its spectroscopic evolution closely resembles SLSNe-I, with early O II absorption and C II P Cygni profiles followed by Ca, Mg, Fe, and other O features, a multi-component H alpha profile appearing at similar to 30 d post-maximum is the most atypical. The H alpha is at first characterised by two emission components, one at similar to+3000 km s(-1) and a second at similar to - 7500 km s(-1), with a third, near-zero-velocity component appearing after a delay. The blue and central components can be described by Gaussian profiles of intermediate width (FWHM similar to 2000-6000 km s(-1)), but the red component is significantly broader (FWHM greater than or similar to 10000 km s(-1)) and Lorentzian. The blue H alpha component evolves towards a lower-velocity offset before abruptly fading at similar to + 100 d post-maximum brightness, concurrently with a light curve break. Multi-component profiles are observed in other hydrogen lines, including Pa beta, and in lines of Ca II and He I. Spectropolarimetry obtained before (10.2 d) and after (38.4 d) the appearance of the H lines shows a large shift on the Stokes Q - U plane consistent with SN 2018bsz undergoing radical changes in its projected geometry. Assuming the supernova is almost unpolarised at 10.2 d, the continuum polarisation at 38.4 d reaches P similar to 1.8%, implying an aspherical configuration. We propose that the observed evolution of SN 2018bsz can be explained by highly aspherical, possibly disk-like, circumstellar material (CSM) with several emitting regions. After the supernova explosion, the CSM is quickly overtaken by the ejecta, but as the photosphere starts to recede, the different CSM regions re-emerge, producing the peculiar line profiles. Based on the first appearance of H alpha, we can constrain the distance of the CSM to be less than similar to 6.5 x 10(15) cm (430 AU), or even lower (less than or similar to 87 AU) if the pre-peak plateau is related to an eruption that created the CSM. The presence of CSM has been inferred previously for other SLSNe-I, both directly and indirectly. However, it is not clear whether the rare properties of SN 2018bsz can be generalised for SLSNe-I, for example in the context of pulsational pair instability, or whether they are the result of an uncommon evolutionary path, possibly involving a binary companion.
- ItemSpectropolarimetry of Galactic stars with anomalous extinction sightlines(2018) Cikota, A.; Hoang, T.; Taubenberger, S.; Patat, F.; Mazzei, P.; Cox, N.; Zelaya García, Paula Andrea; Cikota, S.; Tomasella, L.; Benetti, S.; Rodeghiero, G.
- ItemSpectropolarimetry of the Type IIb SN 2008aq(2016) Stevance, H. F.; Maund, J. R.; Baade, D.; Hoflich, P.; Patat, F.; Spyromilio, J.; Wheeler, J. C.; Clocchiatti, Alejandro; Wang, L.; Yang, Y.; Zelaya, P.
- ItemThe 3D shape of Type IIb SN 2011hs(2019) Stevance, H. F.; Maund, J. R.; Baade, D.; Bruten, J.; Cikota, A.; Hoflich, P.; Wang, L.; Wheeler, J. C.; Clocchiatti, A.; Spyromilio, J.; Patat, F.; Yang, Y.; Crowther, P.We observed seven epochs of spectropolarimetry in optical wavelengths for the Type IIb SN 2011hs, ranging from -3 to + 40 d with respect to V-band maximum. A high degree of interstellar polarization was detected (up to similar to 3 per cent), with a peak lying blueward of 4500 angstrom. Similar behaviours have been seen in some Type Ia supernovae (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 d (p = 0.55 +/- 0.12 per cent and 0.75 +/- 0.11 per cent, 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 degrees in the continuum polarization angle between -2 and + 18 d 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.
- ItemThe shape of SN 1993J re-analysed(OUP, 2020) Stevance, H. F.; Baade, D.; Bruten, J. R.; Cikota, A.; Clocchiatti, Alejandro; Hines, D. C.; Höflich, P.; Maund, J. R.; Patat, F.; Vallely, P. J.; Wheeler, J. C.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 H β, He i λ5876, H α, He i λ6678, He i λ7065, and high velocity (HV) components of He i λ5876 and H α. 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 H α 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.
- ItemThe young and nearby normal type Ia supernova 2018gv : UV-optical observations and the earliest spectropolarimetry(2020) Yang, Y.; Hoeflich, P.; Baade, D.; Maund J. R.; Wang, L.; Brown, P. J.; Stevance, H. F.; Arcavi, I.; Burke, J.; Clocchiatti, Alejandro; Cikota, A.; Gal-Yam, A.; Graham, M. L.; Hiramatsu, D.; Hosseinzadeh, G.; Howell, D. A.; Jha, S. W.; McCully, C.; Patat, F.; Sand, D. J.; Schulze, S.; Spyromilio, J.; Valenti, S.; Vinkó, J.; Wang, X.; Wheeler, J. C.; Yaron, O.; Zhang, J.