Showing papers by "A. Goobar published in 2016"

An Intermediate Type Ia Supernova Between Normal And Super-Chandrasekhar

Abstract: In this paper, we report observations of a peculiar Type Ia supernova iPTF13asv (a.k.a., SN2013cv) from the onset of the explosion to months after its peak. The early-phase spectra of iPTF13asv show absence of iron absorption, indicating that synthesized iron elements are confined to low-velocity regions of the ejecta, which, in turn, implies a stratified ejecta structure along the line of sight. Our analysis of iPTF13asv's light curves and spectra shows that it is an intermediate case between normal and super-Chandrasekhar events. On the one hand, its light curve shape (B-band $\Delta m_{15}=1.03\pm0.01$) and overall spectral features resemble those of normal Type Ia supernovae. On the other hand, similar to super-Chandrasekhar events, it shows large peak optical and UV luminosity ($M_B=-19.84\,\rm{mag}$, $M_{uvm2}=-15.5\,\rm{mag}$) a relatively low but almost constant \ion{Si}{2} velocities of about $10,000\,\rm{km}\,\rm{s}^{-1}$, and persistent carbon absorption in the spectra. We estimate a $^{56}$Ni mass of $0.81^{+0.10}_{-0.18}M_\odot$ and a total ejecta mass of $1.59^{+0.45}_{-0.12}M_\odot$. The large ejecta mass of iPTF13asv and its stratified ejecta structure together seemingly favor a double-degenerate origin.

The discovery of the multiply-imaged lensed Type Ia supernova iPTF16geu

Abstract: We report the discovery of a gravitationally lensed Type Ia supernova (SN Ia) by the intermediate Palomar Transient Factor (iPTF). The light originating from SNIa iPTF16geu, at redshift $z_{SN}=0.409$, is magnified by an intervening galaxy at $z_{l}=0.216$, acting as a gravitational lens. Using Laser Guide Star Adaptive Optics (LGSAO) OSIRIS and NIRC2 observations at the Keck telescope, as well as measurements with the Hubble Space Telescope, we were able to detect the strong bending of the light path, both for iPTF16geu and its host galaxy. We detect four images of the supernova, approximately 0.3" from the center of the lensing galaxy. iPTF16geu is the first \snia for which multiple images have been observed. From the fits of the multi-color lightcurve we derive a lensing magnification, $\Delta m = 4.37 \pm 0.15$ mag, corresponding to a total amplification of the supernova flux by a factor $\mu \sim 56$. The discovery of iPTF16geu suggests that lensing by sub-kpc structures may have been greatly underestimated. In that scenario, many discoveries of gravitationally magnified objects can be expected in forthcoming surveys of transient phenomena, opening up a new window to precision cosmology with supernovae.