47 research outputs found
A dynamic model of filament eruptions and two ribbon flares
Two basically different models for the filament equilibrium by Kippenhahn and Schluter (1957) and Kuperus and Raadu (1974) have appeared in the literature. A further analyses by van Tend and Kuperus (1978) added the force due to the horizontal component of the background field to the Kuperus and Raadu model. In order to obtain a better model which actually describes these phenomena, the evolution of the filament has to be considered in detail. A first attempt was recently presented by Kaastra. Kaastra did not formulate the precise energy balance equations for the problem, as is done in the present work. In the present model not only the force balance, but also the energy balance of the filament is taken into account. Thus a fully closed system of equations is obtained, that describes the evolution of the filament, first in force equilibrium during the current build-up phase, then in the non-equilibrium phase before the eruption, and the eruption itself. A neutral point appears above the photospheric surface in the non-equilibrium phase, but long before the eruption. It was found that although the filament itself may be in non-equilibrium, the evolution may still be slow up to the height where the eruption takes place. The eruption of the filament itself causes a large induced electric field at the neutral point which leads to the observed flare phenomena
Spectroscopic diagnostics of dust formation and evolution in classical nova ejecta
A fraction of classical novae form dust during the early stages of their
outbursts. The classical CO nova V5668 Sgr (Nova Sgr. 2015b) underwent a deep
photometric minimum about 100 days after outburst that was covered across the
spectrum. A similar event was observed for an earlier CO nova, V705 Cas (Nova
Cas 1993) and a less optically significant event for the more recent CO nova
V339 Del (Nova Del 2013). This study provides a "compare and contrast" of these
events to better understand the very dynamical event of dust formation. We show
the effect of dust formation on multiwavelength high resolution line profiles
in the interval 1200\AA\ - 9200\AA\ using a biconical ballistic structure that
has been applied in our previous studies of the ejecta. We find that both V5668
Sgr and V339 Del can be modeled using a grey opacity for the dust, indicating
fairly large grains (at least 0.1 micron) and that the persistent asymmetries
of the line profiles in late time spectra, up to 650 days after the event for
V5668 Sgr and 866 days for V339 Del, point to the survival of the dust well
into the transparent, nebular stage of the ejecta evolution. This is a general
method for assessing the properties of dust forming novae well after the
infrared is completely transparent in the ejecta.Comment: 15 pages 14 figures, accepted for publication in A&A, 2018 June 2
SOUSA: the Swift Optical/Ultraviolet Supernova Archive
The Ultra-Violet Optical Telescope on the Swift spacecraft has observed
hundreds of supernovae, covering all major types and most subtypes. Here we
introduce the Swift Optical/Ultraviolet Supernova Archive (SOUSA), which will
contain all of the supernova images and photometry. We describe the observation
and reduction procedures and how they impact the final data. We show photometry
from well-observed examples of most supernova classes, whose absolute
magnitudes and colors may be used to infer supernova types in the absence of a
spectrum. A full understanding of the variety within classes and a robust
photometric separation of the groups requires a larger sample, which will be
provided by the final archive. The data from the existing Swift supernovae are
also useful for planning future observations with Swift as well as future UV
observatories.Comment: Accepted for publication in the UV issue of Astrophysics and Space
Science 10 pages, 6 figures SOUSA is an archive in progress with data being
posted to the Swift SN website:
http://swift.gsfc.nasa.gov/docs/swift/sne/swift_sn.htm
Multiwavelength spectroscopic study of shock driven phenomena in explosive outbursts in symbiotic-like recurrent novae with emphasis on RS Ophiuchi
To detail the development of RS Ophiuchi and the other Galactic
Symbiotic-like Recurrent Novae throughout their outburst and quiescence, with a
particular emphasis on the propagation of the shock wave during the outburst of
the binaries. The spectral analysis has been performed using archival data
according to the features of the individual datasets. Swift grism spectra were
reduced and extracted using a combination of the pre-existing UVOTPY Python
routine and newly written pipelines in Matlab. Other datasets were directly
available in reduced form, already corrected for instrumental or background
contamination, calibrated in wavelength and flux or intensity. The work on
these was done through pipelines suited for reading the data and elaborating
them to extract quantities of interest for the analysis. We find striking
similarities in different outbursts of the same object and for different novae.
For example, RS Oph 2021 was almost identical to the 2006 outburst, despite
having occurred at a different orbital phase with the observations made from a
different line of sight through the red giant wind. Despite the intrinsically
different properties of the binaries, striking similarities are found for
different systems of the same class, for instance, that the trend of the
electron density over time during outburst appears to follow a general temporal
development.Comment: 20 pages, 40 figure
Ultraviolet Observations of Super-Chandrasekhar Mass Type Ia Supernova Candidates with Swift UVOT
Among Type Ia supernovae (SNe~Ia) exist a class of overluminous objects whose
ejecta mass is inferred to be larger than the canonical Chandrasekhar mass. We
present and discuss the UV/optical photometric light curves, colors, absolute
magnitudes, and spectra of three candidate Super-Chandrasekhar mass
SNe--2009dc, 2011aa, and 2012dn--observed with the Swift Ultraviolet/Optical
Telescope. The light curves are at the broad end for SNe Ia, with the light
curves of SN~2011aa being amongst the broadest ever observed. We find all three
to have very blue colors which may provide a means of excluding these
overluminous SNe from cosmological analysis, though there is some overlap with
the bluest of "normal" SNe Ia. All three are overluminous in their UV absolute
magnitudes compared to normal and broad SNe Ia, but SNe 2011aa and 2012dn are
not optically overluminous compared to normal SNe Ia. The integrated luminosity
curves of SNe 2011aa and 2012dn in the UVOT range (1600-6000 Angstroms) are
only half as bright as SN~2009dc, implying a smaller 56Ni yield. While not
enough to strongly affect the bolometric flux, the early time mid-UV flux makes
a significant contribution at early times. The strong spectral features in the
mid-UV spectra of SNe 2009dc and 2012dn suggest a higher temperature and lower
opacity to be the cause of the UV excess rather than a hot, smooth blackbody
from shock interaction. Further work is needed to determine the ejecta and 56Ni
masses of SNe 2011aa and 2012dn and fully explain their high UV luminosities.Comment: 12 pages, 8 figures Accepted for publication in the Astrophysical
Journal Data available on the Swift supernova website
http://swift.gsfc.nasa.gov/docs/swift/sne/swift_sn.htm
Discovery of an optical counterpart to the hyperluminous X-ray source in ESO 243-49
The existence of black holes of masses ~ 10^2-10^5 Msun has important
implications for the formation and evolution of star clusters and supermassive
black holes. One of the strongest candidates to date is the hyperluminous X-ray
source HLX1, possibly located in the S0-a galaxy ESO243-49, but the lack of an
identifiable optical counterpart had hampered its interpretation. Using the
Magellan telescope, we have discovered an unresolved optical source with R =
(23.80 +/- 0.25) mag and V = (24.5 +/- 0.3) mag within HLX1's positional error
circle. This implies an average X-ray/optical flux ratio ~ 500. Taking the same
distance as ESO243-49, we obtain an intrinsic brightness M_R = (-11.0 +/- 0.3)
mag, comparable to that of a massive globular cluster. Alternatively, the
optical source is consistent with a main-sequence M star in the Galactic halo
(for example an M4.4 star at ~ 2.5 kpc). We also examined the properties of
ESO243-49 by combining Swift/UVOT observations with stellar population
modelling. We found that the overall emission is dominated by a ~5 Gyr old
stellar population, but the UV emission at ~2000 Ang is mostly due to ongoing
star-formation at a rate of ~ 0.03 Msun/yr. The UV emission is more intense (at
least a 9-sigma enhancement above the mean) North East of the nucleus, in the
same quadrant as HLX1. With the combined optical and X-ray measurements, we put
constraints on the nature of HLX1. We rule out a foreground star and a
background AGN. Two alternative scenarios are still viable. HLX1 could be an
accreting intermediate-mass black hole in a star cluster, which may itself be
the stripped nucleus of a dwarf galaxy that passed through ESO243-49, an event
which might have caused the current episode of star formation. Or, it could be
a neutron star in the Galactic halo, accreting from an M4-M5 donor star.Comment: 7 pages, accepted by MNRAS. Several improvements from Oct 7 version:
stronger evidence of the optical counterpart; more accurate estimate of its
brightness (a factor of 2 brighter than previously estimated); use of a
larger set of Swift/UVOT data to measure the recent star formation rate in
ESO243-49; improved discussion and comparison of the competing scenario