We report on the X-ray spectral evolution of the nearby Type IIn supernova (SN) 2005ip based on Chandra and Swift observations covering ~1-6 yr after explosion. X-ray spectra in all epochs are well ...fitted by a thermal emission model with kT gap 7 keV. The somewhat high temperature suggests that the X-ray emission mainly arises from the circumstellar medium (CSM) heated by the forward shock. We find that the spectra taken two to three years after the explosion are heavily absorbed (N sub(H) ~ 5 x 10 super(22) cm super(-2)), but the absorption gradually decreases to the level of the Galactic absorption (N sub(H) ~ 4 x 10 super(20) cm super(-2)) at the final epoch. This indicates that the SN went off in a dense CSM and that the forward shock has overtaken it. The intrinsic X-ray luminosity stays constant until the final epoch, when it drops by a factor of ~2. The intrinsic 0.2-10 keV luminosity during the plateau phase is measured to be ~1.5 x 10 super(41) erg s super(-1), ranking SN 2005ip as one of the brightest X-ray SNe. Based on the column density, we derive a lower limit of a mass-loss rate to be M ~ 1.5 x 10 super(-2) (V sub(w)/100 km s super(-1)) M sub(middot in circle) yr super(-1), which roughly agrees with that inferred from the X-ray luminosity, M ~ 2 x 10 super(-2) (V sub(w)/100 km s super(-1)) M sub(middot in circle) yr super(-1), where V sub(w) is the circumstellar wind speed. Such a high mass-loss rate suggests that the progenitor star had eruptive mass ejections similar to a luminous blue variable star. The total mass ejected in the eruptive period is estimated to be ~15 M sub(middot in circle), indicating that the progenitor mass is gap25 M sub(middot in circle).
ABSTRACT We present multi-epoch X-ray spectral observations of three Type IIn supernovae (SNe), SN 2005kd, SN 2006jd, and SN 2010jl, acquired with Chandra, XMM-Newton, Suzaku, and Swift. Previous ...extensive X-ray studies of SN 2010jl have revealed that X-ray spectra are dominated by thermal emission, which likely arises from a hot plasma heated by a forward shock propagating into a massive circumstellar medium (CSM). Interestingly, an additional soft X-ray component was required to reproduce the spectra at a period of ∼1-2 years after the SN explosion. Although this component is likely associated with the SN, its origin remained an open question. We find a similar, additional soft X-ray component from the other two SNe IIn as well. Given this finding, we present a new interpretation for the origin of this component; it is thermal emission from a forward shock essentially identical to the hard X-ray component, but directly reaches us from a void of the dense CSM. Namely, the hard and soft components are responsible for the heavily and moderately absorbed components, respectively. The co-existence of the two components with distinct absorptions as well as the delayed emergence of the moderately absorbed X-ray component could be evidence for asphericity of the CSM. We show that the X-ray spectral evolution can be qualitatively explained by considering a torus-like geometry for the dense CSM. Based on our X-ray spectral analyses, we estimate the radius of the torus-like CSM to be on the order of ∼5 × 1016 cm.
ABSTRACT
The Type IIb supernova (SN) 2011dh exploded in the nearby galaxy M51 (the Whirlpool galaxy) and provides us with one of the best laboratories to study early high‐energy emission from SNe. We ...give here a comprehensive view of the X‐ray properties of SN 2011dh from the analyses of two pointed XMM–Newton early observations as well as the full Swift X‐ray Telescope (XRT) data set (163 ks). Due to the high XMM–Newton throughput, we were able to satisfactorily fit the X‐ray spectrum with two hot diffuse gas components including an additional absorption component to our Galaxy. A power‐law model provided a worse description of the data. In addition, the early Swift XRT light curve hints of a flux excess at early times (≲3 d), consistent with the adiabatic cooling of stellar’s photosphere a few days after the shock breakout.
We present optical photometric and low-resolution spectroscopic observations of the Type II plateau supernova (SN) 2008in, which occurred in the outskirts of the nearly face-on spiral galaxy M61. ...Photometric data in the X-ray, ultraviolet, and near-infrared bands have been used to characterize this event. The SN field was imaged with the ROTSE-IIIb optical telescope about seven days before the explosion. This allowed us to constrain the epoch of the shock breakout to JD = 2454825.6. The duration of the plateau phase, as derived from the photometric monitoring, was ~98 days. The spectra of SN 2008in show a striking resemblance to those of the archetypal low-luminosity IIP SNe 1997D and 1999br. A comparison of ejecta kinematics of SN 2008in with the hydrodynamical simulations of Type IIP SNe by Dessart et al. indicates that it is a less energetic event (~5 X 1050 erg). However, the light curve indicates that the production of radioactive 56Ni is significantly higher than that in the low-luminosity SNe. Adopting an interstellar absorption along the SN direction of AV ~ 0.3 mag and a distance of 13.2 Mpc, we estimated a synthesized 56Ni mass of ~0.015 M . Employing semi-analytical formulae derived by Litvinova and Nadezhin, we derived a pre-SN radius of ~126 R , an explosion energy of ~5.4 X 1050 erg, and a total ejected mass of ~16.7 M . The latter indicates that the zero-age main-sequence mass of the progenitor did not exceed 20 M . Considering the above properties of SN 2008in and its occurrence in a region of sub-solar metallicity (O/H ~ 8.44 dex), it is unlikely that fall-back of the ejecta onto a newly formed black hole occurred in SN 2008in. We therefore favor a low-energy explosion scenario of a relatively compact, moderate-mass progenitor star that generates a neutron star.
We examine the absolute magnitudes and light-curve shapes of 14 nearby (redshift z = 0.004-0.027) Type Ia supernovae (SNe Ia) observed in the ultraviolet (UV) with the Swift Ultraviolet/Optical ...Telescope. Colors and absolute magnitudes are calculated using both a standard Milky Way extinction law and one for the Large Magellanic Cloud that has been modified by circumstellar scattering. We find very different behavior in the near-UV filters (uvw1{sub rc} covering {approx}2600-3300 A after removing optical light, and u {approx} 3000-4000 A) compared to a mid-UV filter (uvm2 {approx}2000-2400 A). The uvw1{sub rc} - b colors show a scatter of {approx}0.3 mag while uvm2-b scatters by nearly 0.9 mag. Similarly, while the scatter in colors between neighboring filters is small in the optical and somewhat larger in the near-UV, the large scatter in the uvm2 - uvw1 colors implies significantly larger spectral variability below 2600 A. We find that in the near-UV the absolute magnitudes at peak brightness of normal SNe Ia in our sample are correlated with the optical decay rate with a scatter of 0.4 mag, comparable to that found for the optical in our sample. However, in the mid-UV the scatter is larger, {approx}1 mag, possibly indicating differences in metallicity. We find no strong correlation between either the UV light-curve shapes or the UV colors and the UV absolute magnitudes. With larger samples, the UV luminosity might be useful as an additional constraint to help determine distance, extinction, and metallicity in order to improve the utility of SNe Ia as standardized candles.
We analyze the Type II plateau supernovae (SNe IIP) SN 2005cs and SN 2006bp with the non-LTE model atmosphere code CMFGEN. We fit 13 spectra in the first month for SN 2005cs and 18 for SN 2006bp. ...Swift ultraviolet photometry and ground-based optical photometry calibrate each spectrum. Our analysis shows that both objects were discovered less than 3 days after they exploded, making these the earliest SN IIP spectra ever studied. They reveal broad and very weak lines from highly ionized fast ejecta with an extremely steep density profile. We identify He ii lambda4686 emission in the SN 2006bp ejecta. Days later, the spectra resemble the prototypical Type IIP SN 1999em, which had a supergiant-like photospheric composition. Despite the association of SN 2005cs with possible X-ray emission, the emergent UV and optical light comes from the photosphere, not from circumstellar emission. We surmise that the very steep density falloff we infer at early times may be a fossil of the combined actions of the shock wave passage and radiation driving at shock breakout. Based on tailored CMFGEN models, the direct fitting technique and the expanding photosphere method both yield distances and explosion times that agree within a few percent. We derive a distance to NGC 5194, the host of SN 2005cs, of image Mpc and image Mpc for SN 2006bp in NGC 3953. The luminosity of SN 2006bp is 1.5 times that of SN 1999em and 6 times that of SN 2005cs. Reliable distances to SNe IIP that do not depend on a small range in luminosity provide an independent route to the Hubble constant and improved constraints on other cosmological parameters.
The merger of two white dwarfs (aka double-degenerate merger) has often been cited as a potential progenitor of Type Ia supernovae. Here we combine population synthesis, merger, and explosion models ...with radiation-hydrodynamics light-curve models to study the implications of such a progenitor scenario on the observed Type Ia supernova population. Our standard model, assuming double-degenerate mergers do produce thermonuclear explosions, produces supernova light curves that are broader than the observed type Ia sample. In addition, we discuss how the shock breakout and spectral features of these double-degenerate progenitors will differ from the canonical bare Chandrasekhar-massed explosion models. We conclude with a discussion of how one might reconcile these differences with current observations.
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