20 research outputs found
A Detailed Observational Analysis of V1324 Sco, the Most Gamma-Ray Luminous Classical Nova to Date
It has recently been discovered that some, if not all, classical novae emit
GeV gamma rays during outburst, but the mechanisms involved in the production
of the gamma rays are still not well understood. We present here a
comprehensive multi-wavelength dataset---from radio to X-rays---for the most
gamma-ray luminous classical nova to-date, V1324 Sco. Using this dataset, we
show that V1324 Sco is a canonical dusty Fe-II type nova, with a maximum ejecta
velocity of 2600 km s and an ejecta mass of few
M. There is also evidence for complex shock interactions, including a
double-peaked radio light curve which shows high brightness temperatures at
early times. To explore why V1324~Sco was so gamma-ray luminous, we present a
model of the nova ejecta featuring strong internal shocks, and find that higher
gamma-ray luminosities result from higher ejecta velocities and/or mass-loss
rates. Comparison of V1324~Sco with other gamma-ray detected novae does not
show clear signatures of either, and we conclude that a larger sample of
similarly well-observed novae is needed to understand the origin and variation
of gamma rays in novae.Comment: 26 pages, 13 figure
Early evolution of the extraordinary Nova Del 2013 (V339 Del)
We determine the temporal evolution of the luminosity L(WD), radius R(WD) and
effective temperature Teff of the white dwarf (WD) pseudophotosphere of V339
Del from its discovery to around day 40. Another main objective was studying
the ionization structure of the ejecta. These aims were achieved by modelling
the optical/near-IR spectral energy distribution (SED) using low-resolution
spectroscopy (3500 - 9200 A), UBVRcIc and JHKLM photometry. During the fireball
stage (Aug. 14.8 - 19.9, 2013), Teff was in the range of 6000 - 12000 K, R(WD)
was expanding non-uniformly in time from around 66 to around 300 (d/3 kpc)
R(Sun), and L(WD) was super-Eddington, but not constant. After the fireball
stage, a large emission measure of 1.0-2.0E+62 (d/3 kpc)**2 cm**(-3)
constrained the lower limit of L(WD) to be well above the super-Eddington
value. The evolution of the H-alpha line and mainly the transient emergence of
the Raman-scattered O VI 1032 A line suggested a biconical ionization structure
of the ejecta with a disk-like H I region persisting around the WD until its
total ionization, around day 40. It is evident that the nova was not evolving
according to the current theoretical prediction. The unusual non-spherically
symmetric ejecta of nova V339 Del and its extreme physical conditions and
evolution during and after the fireball stage represent interesting new
challenges for the theoretical modelling of the nova phenomenon.Comment: 14 pages, 9 figures, 3 tables, accepted for Astronomy and
Astrophysic
The ambiguous transient ASASSN-17hx
Aims. Some transients, although classified as novae based on their maximum and early decline optical spectra, cast doubts on their true nature, and raise the question of whether nova impostors might exist.
Methods. We monitored a candidate nova that displayed a distinctly unusual light curve at maximum and early decline through optical spectroscopy (3000â10 000 â«, 500 < R < 100 000) complemented with Swift UV and AAVSO optical photometry. We use the spectral line series to characterize the ejecta dynamics, structure, and mass.
Results. We find that the ejecta are in free ballistic expansion and have a typical classical nova structure. However, their derived mass is at least an order of magnitude higher than the typical ejecta masses obtained for classical novae. Specifically, we find Mej â9 Ă 10â3 Mâ independent of the distance for a filling factor Δ = 1. By constraining the distance we derived Δ in the range 0.08â0.10, giving a mass 7 Ă 10â4 âČ Mej âČ 9 Ă 10â4 Mâ. The nebular spectrum, characterized by unusually strong coronal emission lines, confines the ionizing source energy to the range 20â250 eV, possibly peaking in the range 75â100 or 75â150 eV.
Conclusions. We link this source to other slow novae that show similar behavior, and we suggest that they might form a distinct physical subgroup. The sources may result from a classical nova explosion occurring on a very low-mass white dwarf or they may be impostors for an entirely different type of transient
An ATCA radio-continuum study of the Small Magellanic Cloud - I. Source catalogues at 1.42, 2.37, 4.80 and 8.64 GHz
We have analysed radio-continuum mosaics of the Small Magellanic Cloud (SMC) obtained using both the Australia Telescope Compact Array (ATCA) and the Parkes telescope and present a new catalogue of sources in the SMC at 1.42, 2.37, 4.80 and 8.64 GHz (λ=20, 13, 6 and 3 cm). We find a total of 717 radio-continuum sources at these frequencies in the field of the SMC, which is three times more than previous Parkes surveys. From these 717 radio-continuum sources, some 534 were detected at 1.42 GHz, 697 at 2.37 GHz, 75 at 4.80 GHz and 54 at 8.64 GHz. The integrated flux density was measured for each of these sources. We have assessed the accuracy of the position and flux measurements of our catalogue and found no significant discrepancy with previous catalogues. Our new data show a significant improvement in sensitivity (over 10 times) and positional accuracy (<1 arcsec) over previous catalogues