* Astronomy

Blobrana · L

RE: Supernova 2009ip

Blobrana · L

Title: Spectropolarimetry of the 2012 outburst of SN 2009ip: a bi-polar explosion in a dense, disk-like CSM
Author: Emma Reilly, Justyn R. Maund, Dietrich Baade, J. Craig Wheeler, Peter Höflich, Jason Spyromilio, Ferdinando Patat, Lifan Wang

We present a sequence of eight spectropolarimetric observations monitoring the geometric evolution of the late phase of the major 2012 outburst of SN 2009ip. These were acquired with the FORS2 polarimeter mounted on ESO VLT. The continuum was polarised at 0.3-0.8 per cent throughout the observations, showing that the photosphere deviated substantially from spherical symmetry by 10-15 per cent. Significant line polarisation is detected for both hydrogen and helium at high velocities. The similarity in the polarised signal between these elements indicates that they form in the same location in the ejecta. The line polarisation (p~1-1.5 per cent) at low velocities revealed the presence of a highly-aspherical hydrogen and helium rich circumstellar medium (CSM). Monte Carlo simulations of the observed polarimetry were performed in an effort to constrain the shape of the CSM. The simulations imply that the polarimetry can be understood within the framework of a disk-like CSM inclined by 14±2 degrees out of the line of sight, obscuring the photosphere only at certain epochs. The varying temporal evolution of polarisation at high and low velocities indicated that the fast-moving ejecta expanded with a preferred direction orthogonal to that of the CSM.

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Title: SN 2009ip: Constraining the latest explosion properties by its late-phase light curve
Author: Takashi J. Moriya

We constrain the explosion and circumstellar properties at the 2012b event of SN 2009ip based on its late-phase bolometric light curve recently reported. The explosion energy and ejected mass at the 2012b event are estimated as 0.02 Msun and 2e49 erg, respectively. The circumstellar medium is assumed to have two components: an inner shell and an outer wind. The inner shell which is likely created at the 2012a event has 0.2 Msun. The outer wind is created by the wind mass loss before the 2012a mass ejection, and the progenitor is estimated to have had the mass-loss rate about 0.1 Msun/yr with the wind velocity 550 km/s before the 2012a event. The estimated explosion energy and ejected mass indicate that the 2012b event is not caused by a regular supernova.

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Title: SN 2009ip at late times - an interacting transient at +2 years
Author: Morgan Fraser, Rubina Kotak, Andrea Pastorello, Anders Jerkstrand, Stephen J. Smartt, Ting-Wan Chen, Michael Childress, Gerard Gilmore, Cosimo Inserra, Erkki Kankare, Steve Margheim, Seppo Mattila, Stefano Valenti, Christopher Ashall, Stefano Benetti, Maria Teresa Botticella, Franz Erik Bauer, Heather Campbell, Nancy Elias-Rosa, Mathilde Fleury, Avishay Gal-Yam, Stephan Hachinger, D. Andrew Howell, Laurent Le Guillou, Pierre-François Léget, Antonia Morales-Garoffolo, Joe Polshaw, Susanna Spiro, Mark Sullivan, Stefan Taubenberger, Massimo Turatto, Emma S. Walker, David R. Young, Bonnie Zhang

We present photometric and spectroscopic observations of the interacting transient SN 2009ip taken during the 2013 and 2014 observing seasons. We characterise the photometric evolution as a steady and smooth decline in all bands, with a decline rate that is slower than expected for a solely ⁵⁶Co-powered supernova at late phases. No further outbursts or eruptions were seen over a two year period from 2012 December until 2014 December. SN 2009ip remains brighter than its historic minimum from pre-discovery images. Spectroscopically, SN 2009ip continues to be dominated by strong, narrow (\lesssim2000 km~s^-1) emission lines of H, He, Ca, and Fe. While we make tenuous detections of [Fe ii] \lambda\7155 and [O i] \lambda\lambda6300,6364 lines at the end of 2013 June and the start of 2013 October respectively, we see no strong broad nebular emission lines that could point to a core-collapse origin. In general, the lines appear relatively symmetric, with the exception of our final spectrum in 2014 May, when we observe the appearance of a redshifted shoulder of emission at +550 km~s^-1. The lines are not blue-shifted, and we see no significant near- or mid-infrared excess. From the spectroscopic and photometric evolution of SN 2009ip until 820 days after the start of the 2012a event, we still see no conclusive evidence for core-collapse, although whether any such signs could be masked by ongoing interaction is unclear.

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Title: SN2009ip: Constraints on the progenitor mass-loss rate
Authors: E. O. Ofek, L. Lin, C. Kouveliotou, G. Younes, E. Gogus, M. M. Kasliwal, Y. Cao

Some supernovae (SNe) show evidence for mass-loss events taking place prior to their explosions. Measuring their pre-outburst mass-loss rates provide essential information regarding the mechanisms that are responsible for these events. Here we present XMM-Newton and Swift X-ray observations taken after the latest, and presumably the final, outburst of SN 2009ip. We use these observations as well as new near infra-red and visible light spectra, and published radio and visible light observations to put six independent order-of-magnitude constrains on the mass-loss rate of the SN progenitor prior to the explosion. Our methods utilise: the X-ray luminosity, the bound-free absorption, the H alpha luminosity, the SN rise-time, free-free absorption, and the bolometric luminosity of the outburst detected prior to the explosion. Assuming spherical mass-loss with a wind density profile, we estimate that the effective mass-loss rate from the progenitor was between 10^-3 to 10^-2 solar masses per year, over a few years prior to the explosion, with a velocity of ~1000 km/s. This mass-loss rate corresponds to a total circum stellar matter mass of ~0.04 solar masses, within 6x10^15 cm of the SN. We note that the mass-loss rate estimate based on the H alpha luminosity is higher by an order of magnitude. This can be explained if the narrow line H alpha component is generated at radii larger than the shock radius, or if the CSM has an aspherical geometry. We discuss simple geometries which are consistent with our results.

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Title: SN 2009ip á la PESSTO: No evidence for core-collapse yet
Authors: Morgan Fraser, Cosimo Inserra, Anders Jerkstrand, Rubina Kotak, Giuliano Pignata, Stefano Benetti, Maria-Teresa Botticella, Filomena Bufano, Michael Childress, Seppo Mattila, Andrea Pastorello, Stephen J. Smartt, Massimo Turatto, Fang Yuan, Joe P. Anderson, Daniel D.R. Bayliss, Franz Erik Bauer, Ting-Wan Chen, Francisco Förster Burón, Avishay Gal-Yam, Joshua B. Haislip, Cristina Knapic, Laurent Le Guillou, Sebastián Marchi, Paolo Mazzali, Marco Molinaro, Justin P. Moore, Daniel Reichart, Riccardo Smareglia, Ken W. Smith, Assaf Sternberg, Mark Sullivan, Katalin Takáts, Brad E. Tucker, Stefano Valenti, Ofer Yaron, David R. Young, George Zhou

We present observations of the interacting transient SN 2009ip, from the start of the outburst in October 2012 until the end of the 2012 observing season. The transient reached a peak of M_V=-17.7 mag before fading rapidly, with a total integrated luminosity of 1.9 x 10^{49} erg over the period of August-December 2012. The optical and near infrared spectra are dominated by narrow emission lines, signalling a dense circumstellar environment, together with multiple components of broad emission and absorption in H and He at velocities between 0.5-1.2 x 10^4 km s^{-1}. We see no evidence for nucleosynthesised material in SN 2009ip, even in late-time pseudo-nebular spectra. We set a limit of <0.02 solar masses on the mass of any synthesized ^{56}Ni from the late time lightcurve. A simple model for the narrow Balmer lines is presented, and used to derive number densities for the circumstellar medium of between ~ 10^{9}-10^{10} cm^{-3}. Our near-infrared data does not show any excess at longer wavelengths. Our last data, taken in December 2012, shows that SN 2009ip has spectroscopically evolved to something quite similar to its appearance in late 2009, albeit with higher velocities. It is possible that neither of the eruptive and high luminosity events of SN 2009ip were induced by a core-collapse. We show that the peak and total integrated luminosity can be due to the efficient conversion of kinetic energy from colliding ejecta, and that around 0.05-0.1 solar masses of material moving at 0.5-1 x 10^4 km s^{-1} could comfortably produce the observed luminosity. The ejection of multiple shells, lack of evidence for nucleosynthesied elements and broad nebular lines, are all consistent with the pulsational-pair instability scenario. In this case the progenitor star may still exist, and will be observed after the current outburst fades.

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Title: Near-Infrared Spectroscopy of SN2009ip's 2012 Brightening Reveals a Dusty Pre-Supernova Environment
Authors: Nathan Smith, Jon C. Mauerhan, Mansi M. Kasliwal, Adam J. Burgasser

We present low-resolution near-IR spectra of SN2009ip, taken immediately before, during, and just after its rapid brightening in late September/October 2012. The first epoch shows the same general spectral characteristics as the later epochs (smooth continuum, narrow H and HeI emission lines), but the continuum shape is substantially redder than the later epochs. The continuum can be matched by reddening the peak-luminosity (epoch 3) spectrum by E(B-V)=1.0 mag, but the blue colour seen in visual-wavelength spectra at the same time indicates that strong wavelength-dependent extinction by circumstellar dust is not the correct explanation. Instead, we favour the hypothesis that the redder colour before the brightening arises from excess emission from hot 2000K CSM dust, heated in an infrared echo by radiation from the pre-SN outburst. The radius (120 AU) deduced from the dust temperature and observed luminosity of the transient, combined with the observed expansion speed in the precursor outbursts of SN2009ip, suggest an ejection 1.1 yr earlier. Thus, the observed pre-SN outbursts of this object were able to efficiently form dust into which the SN ejecta and radiation now propagate. This is consistent with the notion that the same pre-SN eruptions that generally give rise to SNe IIn also give rise to the dust needed for their commonly observed IR echoes. We also discuss some aspects of the IR line profiles, including HeI 10830.

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Title: Direct Distance Measurements to SN2009ip
Authors: M. Potashov, S. Blinnikov, P. Baklanov, A. Dolgov

We show applicability of our new method, Dense Shell Method (DSM), for measuring astronomical distances using an example of supernova SN2009ip, which had several outbursts. The method is based on the original Baade idea. Distance to this supernova is well measured via Cosmic Distance Ladder and generally assumed to be 20.4 Mpc. Our method directly gives a very close result, namely we find that the median distance is 20.1±0.8 (68% CL) Mpc to SN2009ip assuming the most reasonable values for its parameters.

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Title: Explaining the supernova impostor sn 2009ip as mergerburst
Authors: Noam Soker (Technion, Israel), Amit Kashi (Univ. of Nevada)

We propose that the energetic major outburst of the supernovae (SN) impostor SN 2009ip in September 2012 (outburst 2012b) was a mergerburst event, where two massive stars merged. The previous outbursts of 2009 and 2011 occurred during near periastron passages of the binary system prior to the merger, in a similar manner to the luminosity peaks in the ninetieth century Great Eruption of the massive binary system Eta Carinae. The major 2012b outburst and the 2012a pre-outburst, resemble the light curve of the mergerburst event V838 Mon. A merger of stars with masses of M_1~100Mo and M_2~0.2-0.4M_1 can account for the energy of SN 2009ip. The ejected nebula is expected to have a bipolar structure. The observed fast blue-shifted absorption suggests that we observe the system along the polar direction.

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Blobrana · L

Title: Interacting Supernovae and Supernova Impostors. I. SN 2009ip, is this the end?
Authors: A. Pastorello, E. Cappellaro, C. Inserra, S. J. Smartt, G. Pignata, S. Benetti, S. Valenti, M. Fraser, K. Takats, I. Arcavi, S. Benitez, M. T. Botticella, J. Brimacombe, F. Bufano, F. Cellier-Holzem, M. T. Costado, G. Cupani, N. Elias-Rosa, M. Ergon, J. P. U. Fynbo, M. Hamuy, A. Harutyunyan, K. M. Ivarson, E. Kankare, R. Kotak, A. P. LaCluyze, K. Maguire, S. Mattila, J. Maza, M. McCrum, M. Miluzio, H. U. Norgaard-Nielsen, M. C. Nysewander, P. Ochner, Y.-C. Pan, M. L. Pumo, D. E. Reichart, S. Taubenberger, L. Tomasella, M. Turatto, D. Wright

We report the results of a 3 year-long dedicated monitoring campaign of a restless Luminous Blue Variable (LBV) in NGC 7259. The object, named SN 2009ip, was observed photometrically and spectroscopically in the optical and near-infrared domains. We monitored a number of erupting episodes in the past few years, and increased the density of our observations during eruptive episodes. In this paper we present the full historical data set from 2009-2012 with multi-wavelength dense coverage of the two high luminosity events between August - September 2012. We construct bolometric light curves and measure the total luminosities of these eruptive or explosive events. We label them the 2012a event (lasting ~50 days) with a peak of 3X10^41 erg/s, and the 2012b event (14 day rise time, still ongoing) with a peak of 8X10^42 erg/s. The latter event has reached an absolute R-band magnitude of about -18, comparable in brightness and luminosity to that of a core-collapse supernova (SN). Our historical monitoring has detected high-velocity spectral features (~13000 km/s) in September 2011, one year before the current SN-like event. This suggests that the detection of such high velocity outflows cannot, conclusively, point to a core-collapse SN origin. We suggest that the initial peak in the 2012a event was unlikely to be due to a faint core-collapse SN. We propose that the high intrinsic luminosity of the latest peak, the variability history of SN 2009ip, and the detection of broad spectral lines indicative of high-velocity ejecta are consistent with a pulsational pair-instability event, in which the star may have survived the last outburst. The question of the survival of the LBV progenitor star and its future fate remain open issues, only to be answered with future monitoring of this historically unique explosion.

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