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تسجيل مستخدم جديدA remarkable recurrent nova in M31: Discovery and optical/UV observations of the predicted 2014 eruption
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The Andromeda Galaxy recurrent nova M31N 2008-12a had been caught in eruption eight times. The inter-eruption period of M31N 2008-12a is ~1 year, making it the most rapidly recurring system known, and a strong single-degenerate Type Ia Supernova progenitor candidate. Following the 2013 eruption, a campaign was initiated to detect the predicted 2014 eruption and to then perform high cadence optical photometric and spectroscopic monitoring using ground-based telescopes, along with rapid UV and X-ray follow-up with the Swift satellite. Here we report the results of a high cadence multicolour optical monitoring campaign, the spectroscopic evolution, and the UV photometry. We also discuss tantalising evidence of a potentially related, vastly-extended, nebulosity. The 2014 eruption was discovered, before optical maximum, on October 2, 2014. We find that the optical properties of M31N 2008-12a evolve faster than all Galactic recurrent novae known, and all its eruptions show remarkable similarity both photometrically and spectroscopically. Optical spectra were obtained as early as 0.26 days post maximum, and again confirm the nova nature of the eruption. A significant deceleration of the inferred ejecta expansion velocity is observed which may be caused by interaction of the ejecta with surrounding material, possibly a red giant wind. We find a low ejected mass and low ejection velocity, which are consistent with high mass-accretion rate, high mass white dwarf, and short recurrence time models of novae. We encourage additional observations, especially around the predicted time of the next eruption, towards the end of 2015.
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Context: In late November 2013 a fifth eruption in five years of the M31 recurrent nova M31N 2008-12a was announced. Aims: In this Letter we address the optical lightcurve and progenitor system of M31N 2008-12a. Methods: Optical imaging data of t
he 2013 eruption from the Liverpool Telescope, La Palma, and Danish 1.54m Telescope, La Silla, and archival Hubble Space Telescope near-IR, optical and near-UV data are astrometrically and photometrically analysed. Results: Photometry of the 2013 eruption, combined with three previous eruptions, enabled construction of a template light curve of a very fast nova, t2(V)~4 days. The archival data allowed recovery of the progenitor system in optical and near-UV data, indicating a red-giant secondary with bright accretion disk, or alternatively a system with a sub-giant secondary but dominated by a disk. Conclusions: The eruptions of M31N 2008-12a, and a number of historic X-ray detections, indicate a unique system with a recurrence timescale of ~1 year. This implies the presence of a very high mass white dwarf and a high accretion rate. The recovered progenitor system is consistent with such an elevated rate of accretion.We encourage additional observations, especially towards the end of 2014.
The Andromeda Galaxy recurrent nova M31N 2008-12a had been observed in eruption ten times, including yearly eruptions from 2008-2014. With a measured recurrence period of $P_mathrm{rec}=351pm13$ days (we believe the true value to be half of this) and
a white dwarf very close to the Chandrasekhar limit, M31N 2008-12a has become the leading pre-explosion supernova type Ia progenitor candidate. Following multi-wavelength follow-up observations of the 2013 and 2014 eruptions, we initiated a campaign to ensure early detection of the predicted 2015 eruption, which triggered ambitious ground and space-based follow-up programs. In this paper we present the 2015 detection; visible to near-infrared photometry and visible spectroscopy; and ultraviolet and X-ray observations from the Swift observatory. The LCOGT 2m (Hawaii) discovered the 2015 eruption, estimated to have commenced at Aug. $28.28pm0.12$ UT. The 2013-2015 eruptions are remarkably similar at all wavelengths. New early spectroscopic observations reveal short-lived emission from material with velocities $sim13000$ km s$^{-1}$, possibly collimated outflows. Photometric and spectroscopic observations of the eruption provide strong evidence supporting a red giant donor. An apparently stochastic variability during the early super-soft X-ray phase was comparable in amplitude and duration to past eruptions, but the 2013 and 2015 eruptions show evidence of a brief flux dip during this phase. The multi-eruption Swift/XRT spectra show tentative evidence of high-ionization emission lines above a high-temperature continuum. Following Henze et al. (2015a), the updated recurrence period based on all known eruptions is $P_mathrm{rec}=174pm10$ d, and we expect the next eruption of M31N 2008-12a to occur around mid-Sep. 2016.
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 year, 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. We detect the 2010 eruption in a pair of images at 2010 Nov 20.52 UT, with a magnitude of m_R = 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 have in fact a recurrence period of ~6 months (175 +/- 11 days), making it even more exceptional. If this is the case, then we predict that soon two eruptions per year will be observable. Furthermore, we predict the next eruption will occur around late Sep 2015. We encourage additional observations.
We report the discovery by B. G. Harris and S. Dvorak on JD 2455224.9385 (2010 Jan 28.4385 UT) of the predicted eruption of the recurrent nova U Scorpii (U Sco). We also report on 815 magnitudes (and 16 useful limits) on the pre-eruption light curve
in the UBVRI and Sloan r and i bands from 2000.4 up to 9 hours before the peak of the January 2010 eruption. We found no significant long-term variations, though we did find frequent fast variations (flickering) with amplitudes up to 0.4 mag. We show that U Sco did not have any rises or dips with amplitude greater than 0.2 mag on timescales from one day to one year before the eruption. We find that the peak of this eruption occurred at JD 2455224.69+-0.07 and the start of the rise was at JD 2455224.32+-0.12. From our analysis of the average B-band flux between eruptions, we find that the total mass accreted between eruptions is consistent with being a constant, in agreement with a strong prediction of nova trigger theory. The date of the next eruption can be anticipated with an accuracy of +-5 months by following the average B-band magnitudes for the next ~10 years, although at this time we can only predict that the next eruption will be in the year 2020+-2.
The 2008 discovery of an eruption of M31N 2008-12a began a journey on which the true nature of this remarkable recurrent nova continues to be revealed. M31N 2008-12a contains a white dwarf close to the Chandrasekhar limit, accreting at a high rate fr
om its companion, and undergoes thermonuclear eruptions which are observed yearly and may even be twice as frequent. In this paper, we report on Hubble Space Telescope Space Telescope Imaging Spectrograph ultraviolet spectroscopy taken within days of the predicted 2015 eruption, coupled with Keck spectroscopy of the 2013 eruption. Together, this spectroscopy permits the reddening to be constrained to E(B-V) = 0.10 +/- 0.03. The UV spectroscopy reveals evidence for highly ionized, structured, and high velocity ejecta at early times. No evidence for neon is seen in these spectra however, but it may be that little insight can be gained regarding the composition of the white dwarf (CO vs ONe).
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