J/A+A/638/A130 VLBI images of gamma-ray nova V407 Cygni (Giroletti+, 2020)
Very long baseline interferometry imaging of the advancing ejecta in the first
gamma-ray nova V407 Cygni.
Giroletti M., Munari U., Koerding E., Mioduszewski A., Sokoloski J.,
Cheung C.C., Corbel S., Schinzel F., Sokolovsky K., O'Brien T.J.
<Astron. Astrophys. 638, A130 (2020)>
=2020A&A...638A.130G 2020A&A...638A.130G (SIMBAD/NED BibCode)
ADC_Keywords: Binaries, cataclysmic ; Novae ; Gamma rays ; VLBI
Keywords: binaries: symbiotic - novae - cataclysmic variables -
radio continuum: stars - gamma rays: stars -
stars: individual: V407 Cyg
Abstract:
In 2010 March, the Large Area Telescope on board Fermi revealed a
transient gamma-ray source that is positionally coincident with the
optical nova in the symbiotic binary, V407 Cyg. This event marked the
first discovery of gamma-ray emission from a nova.
We aim to obtain resolved radio imaging of the material involved in
the nova event, to determine the ejecta geometry and advance velocity
directly in the image plane, and to constrain the physical conditions
of the system.
We observed the source with the European VLBI (Very Long Baseline
Interferometry) Network in real time mode, at 1.6 and 5GHz, and the
Very Long Baseline Array at 1.6, 5, and 8.4GHz. In total, we observed
the source over 16 epochs, starting 20 days after the optical
discovery and continuing for over six months.
Milliarcsecond-scale radio emission is detected in 10/16 epochs of
observations. The source is initially very dim but it later shows a
substantial increase in brightness and a resolved shell-like structure
40-90 days after the optical event. The shell has a projected
elliptical shape and is asymmetric in brightness and spectral index,
being brighter and characterised by a rising spectrum at the
south-eastern edge. We determine a projected expansion velocity of
∼3500km/s in the initial phase (for an adopted 2.7kpc distance), and
∼2100km/s between day 20 and 91. We also found an emitting feature
about 350 mas (940AU) to the north-west, advancing at a projected
velocity of ∼700km/s along the polar axis of the binary. The total
flux density in the VLBI images is significantly lower than that
previously reported at similar epochs and over much wider angular
scales with the VLA.
Optical spectra convincingly demonstrated that in 2010 we were viewing
V407 Cyg along the equatorial plane and from behind the Mira. Our
radio observations image the bipolar flow of the ejecta perpendicular
to the orbital plane, where deceleration is much lower than through
the equatorial plane probed by the truncated profile of optical
emission lines. The separated polar knot at 350 mas and the bipolar
flow strictly resemble a similar arrangement seen in Hen 2-104,
another symbiotic Mira seen equator-on that went through a large
outburst ∼5700yrs ago. The observed ∼700km/s expansion constrains the
launch date of the polar knot around 2004, during the accretion-fed
active phase preceding the 2010 nova outburst.
Description:
We observed V407 Cyg six times with the EVN between 2010 March 30 and
September 29, that is between 20 days and 6.7 months after the optical
event.
We observed the source with the VLBA ten times, starting as soon as
2010 March 28 (t=18d) and ending on 2010 May 21 (t=72d).
Objects:
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RA (2000) DE Designation(s)
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21 02 09.82 +45 46 32.7 V407 Cygni = NOVA Cyg 1936
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 121 11 List of fits images
fits/* . 11 Individual fits images
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See also:
J/A+A/600/A96 : V407 Cyg spectral variations (Iijima+, 2017)
Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 23 I4 --- Nx Number of pixels along X-axis
25- 28 I4 --- Ny Number of pixels along Y-axis
30- 39 A10 "date" Obs.date Observaiton date
41- 47 F7.5 GHz Freq Observed frequency
49- 52 I4 Kibyte size Size of FITS file
54- 67 A14 --- FileName Name of FITS file, in subdirectory fits
69-121 A53 --- Title Title of the FITS file
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Acknowledgements:
Marcello Giroletti, marcello.giroletti(at)inaf.it
(End) Patricia Vannier [CDS] 13-May-2020