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Yamagata-shi, Japan

Drout M.R.,Harvard - Smithsonian Center for Astrophysics | Milisavljevic D.,Harvard - Smithsonian Center for Astrophysics | Parrent J.,Harvard - Smithsonian Center for Astrophysics | Margutti R.,Harvard - Smithsonian Center for Astrophysics | And 16 more authors.
Astrophysical Journal | Year: 2016

We present extensive multiwavelength (radio to X-ray) observations of the Type Ib/c supernova (SN Ib/c) SN 2013ge from -13 to +457 days relative to maximum light, including a series of optical spectra and Swift UV-optical photometry beginning 2-4 days post-explosion. This data set makes SN 2013ge one of the best-observed normal SNe Ib/c at early times - when the light curve is particularly sensitive to the progenitor configuration and mixing of radioactive elements - and reveals two distinct light curve components in the UV bands. The first component rises over 4-5 days and is visible for the first week post-explosion. Spectra of the first component have blue continua and show a plethora of moderately high velocity (∼15,000 km s-1) but narrow (∼3500 km s-1) spectroscopic features, indicating that the line-forming region is restricted. The explosion parameters estimated for the bulk explosion ( ∼ 2-3 ∼ (1-2) × 1051 erg) are standard for SNe Ib/c, and there is evidence for weak He features at early times - in an object that would have otherwise been classified as Type Ic. In addition, SN 2013ge exploded in a low-metallicity environment (∼0.5 ), and we have obtained some of the deepest radio and X-ray limits for an SN Ib/c to date, which constrain the progenitor mass-loss rate to be < 4 ×10-6 yr-1. We are left with two distinct progenitor scenarios for SN 2013ge, depending on our interpretation of the early emission. If the first component is cooling envelope emission, then the progenitor of SN 2013ge either possessed an extended (30 ) envelope or ejected a portion of its envelope in the final yr before core collapse. Alternatively, if the first component is due to outwardly mixed 56Ni, then our observations are consistent with the asymmetric ejection of a distinct clump of nickel-rich material at high velocities. Current models for the collision of an SN shock with a binary companion cannot reproduce both the timescale and luminosity of the early emission in SN 2013ge. Finally, the spectra of the first component of SN 2013ge are similar to those of the rapidly declining SN 2002bj. © 2016. The American Astronomical Society. All rights reserved. Source

Henze M.,Institute Of Ciencies Of Lespai Csic Ieec | Darnley M.J.,Liverpool John Moores University | Kabashima F.,Miyaki Argenteus Observatory | Nishiyama K.,Miyaki Argenteus Observatory | And 2 more authors.
Astronomy and Astrophysics | Year: 2015

The Andromeda Galaxy recurrent nova M31N 2008-12a has been caught in eruption nine times. Six observed eruptions in the seven years from 2008 to 2014 suggested a duty cycle of ~1 yr, which makes this the most rapidly recurring system known and the leading single-degenerate Type Ia Supernova progenitor candidate; but no 2010 eruption has been found so far. Here we present evidence supporting the recovery of the 2010 eruption, based on archival images taken at and around the time of eruption. We detect the 2010 eruption in a pair of images at 2010 Nov. 20.52 UT, with a magnitude of mR = 17.84 ± 0.19. The sequence of seven eruptions shows significant indications of a duty cycle slightly shorter than one year, which makes successive eruptions occur progressively earlier in the year. We compared three archival X-ray detections with the well-observed multi-wavelength light curve of the 2014 eruption to accurately constrain the time of their optical peaks. The results imply that M31N 2008-12a might actually have a recurrence period of ~6 months (175 ± 11 days), making it even more exceptional. If this is the case, then we predict that two eruptions per year will be observable soon. Furthermore, we predict that the next eruption will occur in late Sep. 2015. We encourage additional observations. © ESO, 2015. Source

Henze M.,Max Planck Institute for Extraterrestrial Physics | Pietsch W.,Max Planck Institute for Extraterrestrial Physics | Haberl F.,Max Planck Institute for Extraterrestrial Physics | Della Valle M.,National institute for astrophysics | And 21 more authors.
Astronomy and Astrophysics | Year: 2013

Context. Classical novae (CNe) represent the main class of supersoft X-ray sources (SSSs) in the central region of our neighbouring galaxy M 31. Only three confirmed novae and three SSSs have been discovered in globular clusters (GCs) of any galaxy so far, of which one nova and two SSSs (including the nova) were found in M 31 GCs. Aims. To study the SSS state of CNe we carried out a high-cadence X-ray monitoring of the M 31 central area with XMM-Newton and Chandra. This project is supplemented by regular optical monitoring programmes at various observatories. Methods. We analysed X-ray and optical monitoring data of a new transient X-ray source in the M 31 GC Bol 126, discovered serendipitously in Swift observations. Our optical data set was based on regular M 31 monitoring programmes from five different small telescopes and was reduced using a homogeneous method. Additionally, we made use of Pan-STARRS 1 data obtained during the PAndromeda survey. We extracted light curves of the source in the optical and X-rays, as well as X-ray spectra. Results. Our observations reveal that the X-ray source in Bol 126 is the third SSS in an M 31 GC and can be confirmed as the second CN in the M 31 GC system. This nova is named M31N 2010-10f. Its properties in the X-ray (high black-body temperature, short SSS phase) and optical (relatively high maximum magnitude, fast decline) regimes agree with a massive white dwarf (MWD ≳ 1.3 M⊙) in the binary system. Incorporating the data on previously found (suspected) novae in M 31 GCs we used our high-cadence X-ray monitoring observations to estimate a tentative nova rate in the M 31 GC system of 0.05 yr-1 GC-1. An optical estimate, based on the recent 10.5-year WeCAPP survey, gives a lower nova rate, which is compatible with the X-ray rate on the 95% confidence level. Conclusions. Although still based on small-number statistics, there is growing evidence that the nova rate in GCs is higher than expected from primordial binary formation and under conditions as in the field. Dynamical binary formation and/or additional accretion from the intracluster medium are possible scenarios for an increased nova rate, but observational confirmation for this enhancement has been absent, so far. Regular X-ray monitoring observations of M 31 provide a promising strategy to find these novae. © 2013 ESO. All Rights Reserved. Source

Kato T.,Kyoto University | Hambsch F.-J.,Groupe Europeen dObservations Stellaires GEOS | Maehara H.,Kyoto University | Masi G.,Virtual Telescope Project | And 84 more authors.
Publications of the Astronomical Society of Japan | Year: 2013

Continuing the project described by Kato et al. (2009, PASJ, 61, S395), we collected times of superhump maxima for 86 SU UMa-type dwarf novae, mainly observed during the 2011-2012 season. We confirmed general trends recorded in our previous studies, such as the relation between period derivatives and orbital periods. There are some systems showing positive period derivatives despite the long orbital period. We observed the 2011 outburst of the WZ Sge-type dwarf nova BW Scl, and recorded an O - C diagram similar to those of previously known WZSge-type dwarf novae. The WZ Sge-type dwarf nova OT J184228.1+483742 showed an unusual pattern of double outbursts composed of an outburst with early superhumps and one with ordinary superhumps. We propose an interpretation that a very small growth rate of the 3:1 resonance due to an extremely low mass-ratio led to quenching the superoutburst before the ordinary superhump appeared. We systematically studied ER UMa-type dwarf novae, and found that V1159 Ori showed positive superhumps similar to ER UMa in the 1990s. The recently recognized ER UMa-type object BK Lyn dominantly showed negative superhumps, and its behavior was very similar to the present-day state of ER UMa. The pattern of period variations in AM CVn-type objects was very similar to that of short-period hydrogen-rich SU UMa-type dwarf novae, making them a helium analogue of hydrogenrich SU UMa-type dwarf novae. SBS 1108+574, a peculiar hydrogen-rich dwarf nova below the period minimum, showed a very similar pattern of period variations to those of short-period SU UMa-type dwarf novae. The massratio derived from the detected orbital period suggests that this secondary is a somewhat evolved star whose hydrogen envelope was mostly stripped during the mass-exchange. CC Scl, MASTER OT J072948.66+593824.4, and OT J173516.9+154708 showed only low-amplitude superhumps with complex profiles. These superhumps are likely to be a combination of two closely separated periods. © 2013. Astronomical Society of Japan. Source

Kato T.,Kyoto University | Maehara H.,Kyoto University | Miller I.,Furzehill House | Ohshima T.,Kyoto University | And 76 more authors.
Publications of the Astronomical Society of Japan | Year: 2012

Continuing the project described by Kato et al. (2009, PASJ, 61, S395), we collected the times of superhump maxima for 51 SU UMa-type dwarf novae, mainly observed during the 2010-2011 season. Although most of the new data for systems with short superhump periods basically confirmed the findings by Kato et al. (ibid.) and Kato et al. (2010, PASJ, 62, 1525), the long-period system GX Cas showed an exceptionally large positive-period derivative. An analysis of public Kepler data of V344 Lyr and V1504 Cyg yielded less-striking stage transitions. In V344 Lyr, there was a prominent secondary component growing during the late stage of superoutbursts, and this component persisted for at least two more cycles of successive normal outbursts. We also investigated the superoutburst of two conspicuous eclipsing objects: HT Cas and the WZ Sge-type object SDSS J080434.20+510349.2. Strong beat phenomena were detected in both objects, and late-stage superhumps in the latter object had an almost constant luminosity during repeated rebrightenings. The WZ Sge-type object SDSS J133941.11+484727.5 showed a phase reversal around the rapid fading from the superoutburst. The object showed a prominent beat phenomenon, even after the end of the superoutburst. A pilot study of superhump amplitudes indicated that the amplitude of superhumps is strongly correlated with the orbital period, and the dependence on the inclination is weak in systems with inclinations smaller than 80°. © 2012. Astronomical Society of Japan. Source

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