ABSTRACT We present multi-epoch mid-infrared (IR) photometry and the optical discovery observations of the "impostor" supernova (SN) 2010da in NGC 300 using new and archival Spitzer Space Telescope ...images and ground-based observatories. The mid-infrared counterpart of SN 2010da was detected as Spitzer Infrared Intensive Transient Survey (SPIRITS) 14bme in the SPIRITS, an ongoing systematic search for IR transients. Before erupting on 2010 May 24, the SN 2010da progenitor exhibited a constant mid-IR flux at 3.6 and only a slight ∼10% decrease at 4.5 m between 2003 November and 2007 December. A sharp increase in the 3.6 m flux followed by a rapid decrease measured ∼150 days before and ∼80 days after the initial outburst, respectively, reveal a mid-IR counterpart to the coincident optical and high luminosity X-ray outbursts. At late times, after the outburst (∼2000 days), the 3.6 and 4.5 m emission increased to over a factor of two times the progenitor flux and is currently observed (as of 2016 Feb) to be fading, but still above the progenitor flux. We attribute the re-brightening mid-IR emission to continued dust production and increasing luminosity of the surviving system associated with SN 2010da. We analyze the evolution of the dust temperature (Td ∼ 700-1000 K), mass (Md ∼ 0.5-3.8 × 10−7 M ), luminosity (LIR ∼ 1.3-3.5 × 104 L ), and the equilibrium temperature radius (Req ∼ 6.4-12.2 au) in order to resolve the nature of SN 2010da. We address the leading interpretation of SN 2010da as an eruption from a luminous blue variable high-mass X-ray binary (HMXB) system. We propose that SN 2010da is instead a supergiant (sg)Be-HMXB based on similar luminosities and dust masses exhibited by two other known sgBe-HMXB systems. Additionally, the SN 2010da progenitor occupies a similar region on a mid-IR color-magnitude diagram (CMD) with known sgBe stars in the Large Magellanic Cloud. The lower limit estimated for the orbital eccentricity of the sgBe-HMXB (e > 0.82) from X-ray luminosity measurements is high compared to known sgHMXBs and supports the claim that SN 2010da may be associated with a newly formed HMXB system.
ABSTRACT The main progenitor candidates of Type Ia supernovae (SNe Ia) are white dwarfs in binary systems where the companion star is another white dwarf (double degenerate (DD) system) or a ...less-evolved, non-degenerate star with R* 0.1 R (single degenerate system). However, no direct observational evidence exists to tell us which progenitor system is more common. Recent studies suggest that the light curve of a supernova shortly after its explosion can be used to set a limit on the progenitor size, R*. Here, we report high-cadence monitoring observations of SN 2015F, a normal SN Ia in the galaxy NGC 2442, starting about 84 days before the first light time. Using our daily cadence data, we capture the emergence of the radioactively powered light curve; more importantly, with >97.4% confidence, we detect possible dim precursor emission that appears roughly 1.5 days before the rise of the radioactively powered emission. The signal is consistent with theoretical expectations for a progenitor system involving a companion star with R* 0.1-1 R or a prompt explosion of a DD system, but is inconsistent with the typically invoked size of a white dwarf progenitor of R* ∼ 0.01 R . Upper limits on the precursor emission also constrain the progenitor size to be R* 0.1 R with a companion star size of R* 1.0 R , excluding a very large companion star in the progenitor system. Additionally, we find that the distance to SN 2015F is 23.9 0.4 Mpc.
It is well known that massive stars (M > 8 M☉) evolve up to the collapse of the stellar core, resulting in most cases in a supernova (SN) explosion. Their heterogeneity is related mainly to different ...configurations of the progenitor star at the moment of the explosion and to their immediate environments. We present photometry and spectroscopy of SN 2010bt, which was classified as a Type IIn SN from a spectrum obtained soon after discovery and was observed extensively for about 2 months. After the seasonal interruption owing to its proximity to the Sun, the SN was below the detection threshold, indicative of a rapid luminosity decline. We can identify the likely progenitor with a very luminous star (log L/L☉ 7) through comparison of Hubble Space Telescope images of the host galaxy prior to explosion with those of the SN obtained after maximum light. Such a luminosity is not expected for a quiescent star, but rather for a massive star in an active phase. This progenitor candidate was later confirmed via images taken in 2015 (∼5 yr post-discovery), in which no bright point source was detected at the SN position. Given these results and the SN behavior, we conclude that SN 2010bt was likely a Type IIn SN and that its progenitor was a massive star that experienced an outburst shortly before the final explosion, leading to a dense H-rich circumstellar environment around the SN progenitor.
We present high-speed ULTRACAM photometry of the eclipsing post-common-envelope binaries DE CVn, GK Vir, NN Ser, QS Vir, RR Cae, RX J2130.6+4710, SDSS 0110+1326 and SDSS 0303+0054 and use these data ...to measure precise mid-eclipse times in order to detect any period variations. We detect a large (∼250 s) departure from linearity in the eclipse times of QS Vir which Applegate's mechanism fails to reproduce by an order of magnitude. The only mechanism able to drive this period change is a third body in a highly elliptical orbit. However, the planetary/sub-stellar companion previously suggested to exist in this system is ruled out by our data. Our eclipse times show that the period decrease detected in NN Ser is continuing, with magnetic braking or a third body the only mechanisms able to explain this change. The planetary/sub-stellar companion previously suggested to exist in NN Ser is also ruled out by our data. Our precise eclipse times also lead to improved ephemerides for DE CVn and GK Vir. The width of a primary eclipse is directly related to the size of the secondary star and variations in the size of this star could be an indication of Applegate's mechanism or Wilson (starspot) depressions which can cause jitter in the O−C curves. We measure the width of primary eclipses for the systems NN Ser and GK Vir over several years but find no definitive variations in the radii of the secondary stars. However, our data are precise enough (ΔRsec/Rsec < 10−5) to show the effects of Applegate's mechanism in the future. We find no evidence of Wilson depressions in either system. We also find tentative indications that flaring rates of the secondary stars depend on their mass rather than rotation rates.
The 2008 optical transient in NGC 300 is one of a growing class of intermediate-luminosity transients that brighten several orders of magnitude from a previously optically obscured state. The origin ...of their eruptions is not understood. Our multi-wavelength photometry and spectroscopy from maximum light to more than a year later provide a record of its post-eruption behavior. We describe its changing spectral energy distribution, the evolution of its absorption- and emission-line spectrum, the development of a bipolar outflow, and the rapid transition from a dense wind to an optically thin ionized wind. In addition to strong, narrow hydrogen lines, the F-type absorption-line spectrum of the transient is characterized by strong Ca II and Ca II emission. The very broad wings of the Ca II triplet and the asymmetric Ca II emission lines are due to strong Thomson scattering in the expanding ejecta. Post-maximum, the hydrogen and Ca II lines developed double-peaked emission profiles that we attribute to a bipolar outflow. Between approximately 60 and 100 days after maximum, the F-type absorption spectrum, formed in its dense wind, weakened and the wind became transparent to ionizing radiation. We discuss the probable evolutionary state of the transient and similar objects such as SN 2008S and conclude that they were most likely post-red supergiants or post-asymptotic giant branch stars on a blue loop to warmer temperatures when the eruption occurred. These objects are not luminous blue variables.
Abstract
This catalogue summarizes information for all supernovae discovered by the All-Sky Automated Survey for SuperNovae (ASAS-SN) and all other bright (m
peak ≤ 17), spectroscopically confirmed ...supernovae discovered in 2016. We then gather the near-infrared through ultraviolet magnitudes of all host galaxies and the offsets of the supernovae from the centres of their hosts from public data bases. We illustrate the results using a sample that now totals 668 supernovae discovered since 2014 May 1, including the supernovae from our previous catalogues, with type distributions closely matching those of the ideal magnitude limited sample from Li et al. This is the third of a series of yearly papers on bright supernovae and their hosts from the ASAS-SN team.
Explosion of a massive, He-rich star at z = 0.16 Elias-Rosa, N; Pastorello, A; Nicholl, M ...
Monthly notices of the Royal Astronomical Society,
08/2015, Letnik:
451, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We present spectroscopic and photometric data of the peculiar SN 2001gh, discovered by the Southern inTermediate Redshift ESO Supernova Search at a redshift z = 0.16. SN 2001gh has relatively high ...luminosity at maximum (M
B
= −18.55 mag), while the light curve shows a broad peak. An early-time spectrum shows an almost featureless, blue continuum with a few weak and shallow P-Cygni lines that we attribute to He i. He i lines remain the only spectral features visible in a subsequent spectrum, obtained one month later. A remarkable property of SN 2001gh is the lack of significant spectral evolution over the temporal window of nearly one month separating the two spectra. In order to explain the properties of SN 2001gh, three powering mechanism are explored, including radioactive decays of a moderately large amount of 56Ni, magnetar spin-down, and interaction of SN ejecta with circumstellar medium. We favour the latter scenario, with a SN Ib wrapped in a dense, circumstellar shell. The fact that no models provide an excellent fit with observations, confirms the troublesome interpretation of the nature of SN 2001gh. A rate estimate for SN 2001gh-like event is also provided, confirming the intrinsic rarity of these objects.
A luminous optical transient (OT) that appeared in NGC 300 in early 2008 had a maximum brightness, MV -12 to -13, intermediate between classical novae and supernovae. We present ground-based ...photometric and spectroscopic monitoring and adaptive-optics imaging of the OT, as well as pre- and postoutburst space-based imaging with the Hubble Space Telescope (HST) and Spitzer. The optical spectrum at maximum showed an F-type supergiant photosphere with superposed emission lines of hydrogen, Ca II, and Ca II, similar to the spectra of low-luminosity Type IIn 'supernova impostors' like SN 2008S, as well as cool hypergiants like IRC +10420. The emission lines have a complex, double structure, indicating a bipolar outflow with velocities of ~75 km s-1. The luminous energy released in the eruption was ~1047 erg, most of it emitted in the first two months. By registering new HST images with deep archival frames, we have precisely located the OT site, and find no detectable optical progenitor brighter than broadband V magnitude 28.5. However, archival Spitzer images reveal a bright, nonvariable mid-infrared (mid-IR) preoutburst source. We conclude that the NGC 300 OT was a heavily dust-enshrouded luminous star, of ~10-15 M , which experienced an eruption that cleared the surrounding dust and initiated a bipolar wind. The progenitor was likely an OH/IR source which had begun to evolve on a blue loop toward higher temperatures, but the precise cause of the outburst remains uncertain.
Abstract
We present optical photometry of six intermediate polars that exhibit transitions to a low-flux state. For four of these systems, DW Cnc, V515 And, V1223 Sgr, and RX J2133.7+5107, we are ...able to perform timing analysis in and out of the low states. We find that, for DW Cnc and V515 And, the dominant periodicities in the light curves change as the flux decreases, indicating a change in the sources’ accretion properties as they transition to the low state. For V1223 Sgr, we find that the variability is almost completely quenched at the lowest flux, but we do not find evidence for a changing accretion geometry. For RX J2133.7+5107, the temporal properties do not change in the low state, but we do see a period of enhanced accretion that is coincident with increased variability on the beat frequency, which we do not associate with a change in the accretion mechanisms in the system.
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