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Register a new userPTF11kx: A Type Ia Supernova with Hydrogen Emission Persisting After 3.5 Years
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The optical transient PTF11kx exhibited both the characteristic spectral features of Type Ia supernovae (SNe Ia) and the signature of ejecta interacting with circumstellar material (CSM) containing hydrogen, indicating the presence of a nondegenerate companion. We present an optical spectrum at $1342$ days after peak from Keck Observatory, in which the broad component of H$alpha$ emission persists with a similar profile as in early-time observations. We also present $Spitzer$ IRAC detections obtained $1237$ and $1818$ days after peak, and an upper limit from $HST$ ultraviolet imaging at $2133$ days. We interpret our late-time observations in context with published results - and reinterpret the early-time observations - in order to constrain the CSMs physical parameters and compare to theoretical predictions for recurrent nova systems. We find that the CSMs radial extent may be several times the distance between the star and the CSMs inner edge, and that the CSM column density may be two orders of magnitude lower than previous estimates. We show that the H$alpha$ luminosity decline is similar to other SNe with CSM interaction, and demonstrate how our infrared photometry is evidence for newly formed, collisionally heated dust. We create a model for PTF11kxs late-time CSM interaction and find that X-ray reprocessing by photoionization and recombination cannot reproduce the observed H$alpha$ luminosity, suggesting that the X-rays are thermalized and that H$alpha$ radiates from collisional excitation. Finally, we discuss the implications of our results regarding the progenitor scenario and the geometric properties of the CSM for the PTF11kx system.
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There is a consensus that Type-Ia supernovae (SNe Ia) arise from the thermonuclear explosion of white dwarf stars that accrete matter from a binary companion. However, direct observation of SN Ia progenitors is lacking, and the precise nature of the binary companion remains uncertain. A temporal series of high-resolution optical spectra of the SN Ia PTF 11kx reveals a complex circumstellar environment that provides an unprecedentedly detailed view of the progenitor system. Multiple shells of circumsteller are detected and the SN ejecta are seen to interact with circumstellar material (CSM) starting 59 days after the explosion. These features are best described by a symbiotic nova progenitor, similar to RS Ophiuchi.
PTF11kx was a Type Ia supernova (SN Ia) that showed time-variable absorption features, including saturated Ca II H&K lines that weakened and eventually went into emission. The strength of the emission component of H{alpha} increased, implying that the SN was undergoing significant interaction with its circumstellar medium (CSM). These features were blueshifted slightly and showed a P-Cygni profile, likely indicating that the CSM was directly related to, and probably previously ejected by, the progenitor system itself. These and other observations led Dilday et al. (2012) to conclude that PTF11kx came from a symbiotic nova progenitor like RS Oph. In this work we extend the spectral coverage of PTF11kx to 124-680 rest-frame days past maximum brightness. These spectra of PTF11kx are dominated by H{alpha} emission (with widths of ~2000 km/s), strong Ca II emission features (~10,000 km/s wide), and a blue quasi-continuum due to many overlapping narrow lines of Fe II. Emission from oxygen, He I, and Balmer lines higher than H{alpha} is weak or completely absent at all epochs, leading to large observed H{alpha}/H{beta} intensity ratios. The broader (~2000 km/s) H{alpha} emission appears to increase in strength with time for ~1 yr, but it subsequently decreases significantly along with the Ca II emission. Our latest spectrum also indicates the possibility of newly formed dust in the system as evidenced by a slight decrease in the red wing of H{alpha}. During the same epochs, multiple narrow emission features from the CSM temporally vary in strength. The weakening of the H{alpha} and Ca II emission at late times is possible evidence that the SN ejecta have overtaken the majority of the CSM and agrees with models of other strongly interacting SNe Ia. The varying narrow emission features, on the other hand, may indicate that the CSM is clumpy or consists of multiple thin shells.
Models for the spectra and the light curve, in the photospheric as well as in the late nebular phase, are used to infer the properties of the very radio-bright, broad-lined type IIb Supernova 2003bg. Consistent fits to the light curve and the spectral evolution are obtained with an explosion that ejected ~ 4 M_sun of material with a kinetic energy of ~ 5 10^51 erg. A thin layer of hydrogen, comprising ~ 0.05 M_sun, is inferred to be present in the ejecta at the highest velocities (v >~ 9000 km/s), while a thicker helium layer, comprising ~ 1.25 M_sun, was ejected at velocities between 6500 and 9000 km/s. At lower velocities, heavier elements are present, including ~ 0.2 M_sun of 56Ni that shape the light curve and the late-time nebular spectra. These values suggest that the progenitor star had a mass of ~ 20-25 M_sun (comparable to, but maybe somewhat smaller than that of the progenitor of the XRF/SN 2008D). The rather broad-lined early spectra are the result of the presence of a small amount of material (~ 0.03 M_sun) at velocities > 0.1 c, which carries ~ 10 % of the explosion kinetic energy. No clear signatures of a highly aspherical explosion are detected.
The mode of explosive burning in Type Ia SNe remains an outstanding problem. It is generally thought to begin as a subsonic deflagration, but this may transition into a supersonic detonation (the DDT). We argue that this transition leads to a breakout shock, which would provide the first unambiguous evidence that DDTs occur. Its main features are a hard X-ray flash (~20 keV) lasting ~0.01 s with a total radiated energy of ~10^{40} ergs, followed by a cooling tail. This creates a distinct feature in the visual light curve, which is separate from the nickel decay. This cooling tail has a maximum absolute visual magnitude of M_V = -9 to -10 at approximately 1 day, which depends most sensitively on the white dwarf radius at the time of the DDT. As the thermal diffusion wave moves in, the composition of these surface layers may be imprinted as spectral features, which would help to discern between SN Ia progenitor models. Since this feature should accompany every SNe Ia, future deep surveys (e.g., m=24) will see it out to a distance of approximately 80 Mpc, giving a maximum rate of ~60/yr. Archival data sets can also be used to study the early rise dictated by the shock heating (at about 20 days before maximum B-band light). A similar and slightly brighter event may also accompany core bounce during the accretion induced collapse to a neutron star, but with a lower occurrence rate.
X-ray emission is one of the signposts of circumstellar interaction in supernovae (SNe), but until now, it has been observed only in core-collapse SNe. The level of thermal X-ray emission is a direct measure of the density of the circumstellar medium (CSM), and the absence of X-ray emission from Type Ia SNe has been interpreted as a sign of a very low density CSM. In this paper, we report late-time (500--800 days after discovery) X-ray detections of SN 2012ca in {it Chandra} data. The presence of hydrogen in the initial spectrum led to a classification of Type Ia-CSM, ostensibly making it the first SN~Ia detected with X-rays. Our analysis of the X-ray data favors an asymmetric medium, with a high-density component which supplies the X-ray emission. The data suggest a number density $> 10^8$ cm$^{-3}$ in the higher-density medium, which is consistent with the large observed Balmer decrement if it arises from collisional excitation. This is high compared to most core-collapse SNe, but it may be consistent with densities suggested for some Type IIn or superluminous SNe. If SN 2012ca is a thermonuclear SN, the large CSM density could imply clumps in the wind, or a dense torus or disk, consistent with the single-degenerate channel. A remote possibility for a core-degenerate channel involves a white dwarf merging with the degenerate core of an asymptotic giant branch star shortly before the explosion, leading to a common envelope around the SN.
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