Fiona Murphy-Glaysher
Gather.town id
TA07
Poster Title
V392 Persei: a Gamma-ray Bright Nova
Institution
ARI, Liverpool John Moores University
Abstract (short summary)
One day after the discovery of the 2018 classical nova (CN) eruption of V392 Persei, a gamma-ray signal was detected from the position of V392 Per by the Fermi Gamma-Ray Space Telescope’s Large Area Telescope, sparking a panchromatic campaign of photometric and spectroscopic observations. As one of sixteen novae to date with detected gamma-ray emission, V392 Per provided an opportunity to probe the mechanism of the emission. This emission is thought to be due to particle acceleration by shocks between two or more different nova ejecta components, produced in multiple ejection episodes early in the eruption.
V392 Per, a known dwarf nova (DN), is the only DN whose subsequent CN eruption was detected in gamma-rays. It is one of only two DNe to later exhibit a CN eruption, and one of only nine cataclysmic variables to show clear evidence of both DN outbursts and a CN eruption. Archival observations available from the American Association of Variable Star Observers database, spanning over a decade, provide further information about the accretion history of the system.
A crucial component of the observing strategy was the use of the Neil Gehrels Swift Observatory, utilising its UV photometry and X-ray spectroscopy. I will present these observations, along with coordinated optical photometry and spectroscopy from ground based telescopes – spearheaded by the Liverpool Telescope – and discuss their significance.
V392 Per, a known dwarf nova (DN), is the only DN whose subsequent CN eruption was detected in gamma-rays. It is one of only two DNe to later exhibit a CN eruption, and one of only nine cataclysmic variables to show clear evidence of both DN outbursts and a CN eruption. Archival observations available from the American Association of Variable Star Observers database, spanning over a decade, provide further information about the accretion history of the system.
A crucial component of the observing strategy was the use of the Neil Gehrels Swift Observatory, utilising its UV photometry and X-ray spectroscopy. I will present these observations, along with coordinated optical photometry and spectroscopy from ground based telescopes – spearheaded by the Liverpool Telescope – and discuss their significance.
Plain text (extended) Summary
A classical nova eruption (CN) is the result of a thermonuclear runaway on the surface of a white dwarf (WD). This occurs in the H-rich material accreted (via an accretion disk) from the WD’s binary companion.
V392 Persei CN eruption discovered on 29th April 2018 – unfiltered magnitude 6.2 mag.
Already known dwarf nova system. Quiescent magnitude is V~17 mag. Eruption amplitude ~ 10.8 mag
Fermi-LAT detected γ-rays from V392 Per the day after discovery of the eruption.
Figure shows light curves for V392 Per in optical and UV filters.
The light curves were fitted with straight lines to find the gradient of the decline.
The fits were used to calibrate the spectra and calculate the time to decline from peak by 2 or 3 magnitudes, t2 and t3.
Plateaux appepar in the light curves 4-6 days after eruption. The accretion disk is unveiled by the receding photosphere of the expanding ejecta. This indicates the nova has entered the supersoft source (SSS) phase. If V392 Per were observable by Swift at this time, we would detect supersoft X-rays.
The spectra initially show strong Balmer lines Hα, Hᵦ, Hɣ and Fe II(42) and (49) lines during its principal and diffuse ionised spectra.
The nova is an Fe II type nova.
P Cygni features in early spectra, including double absorption troughs in Balmer lines.
The nova entered the nebular phase before it exited the Sun constraint.
The Balmer lines remained strong, but emission of forbidden [O III] and He II lines was brighter.
Indicates plasma was hot and dense, but now cooler and less dense.
In the late time spectra, O III emission has gone, but the Balmer lines, HeII and HeI still remain in the post-nova spectrum.
Swift X-ray and UV observations began in July 2018.
The hardness ratio of the X-rays was 2-3, and increased with time, suggesting we caught the end of the SSS phase.
The SSS phase begins when the photosphere recedes to the surface of the WD, allowing the detection of X-rays from steady-state hydrogen burning on the surface of the WD. It ends when the supply of hydrogen is exhausted.
V392 Per continued to emit X-rays at a fairly constant hardness ratio and count rate. The count rate increased slightly from ~360 days after eruption.
The hard X-ray emission from V392 Per continued for over two years after eruption, with the final Swift observation taken on 24th August 2020.
Conclusions
V392 Per is a very fast nova, with decline times:
In B, t2=2.3 d, t3=4.5 d
In V, t2=1.8 d, t3=4.3 d
Hard X-rays detected for more than two years after CN eruption, indicating ongoing shocks.
Suggests collimation of accretion flow onto WD
Hints at strong magnetic field, channelling accreted material towards poles.
Either Intermediate Polar or Polar system.
P Cygni profiles on the Balmer lines in the early spectra indicates multiple ejection events. The earlier ejecta components travel slower than the later components. The timing of shocks from ejecta components colliding is consistent with the detection of γ-rays.
Balmer and He I emission lines in early spectra had a triple-peaked structure. The narrow central peak was present throughout and continued into the post-nova spectrum.
O III and He II emission lines appeared in the nebular spectra. O III had a double-peaked structure and faded away before the post-nova spectrum was reached. He II had a triple-peaked structure and the central peak persisted into the post-nova spectrum.
The time different species reached their flux plateau and the line profile shapes provide information about the ionization conditions in the ejecta.
Look out for our paper – coming soon!
V392 Persei CN eruption discovered on 29th April 2018 – unfiltered magnitude 6.2 mag.
Already known dwarf nova system. Quiescent magnitude is V~17 mag. Eruption amplitude ~ 10.8 mag
Fermi-LAT detected γ-rays from V392 Per the day after discovery of the eruption.
Figure shows light curves for V392 Per in optical and UV filters.
The light curves were fitted with straight lines to find the gradient of the decline.
The fits were used to calibrate the spectra and calculate the time to decline from peak by 2 or 3 magnitudes, t2 and t3.
Plateaux appepar in the light curves 4-6 days after eruption. The accretion disk is unveiled by the receding photosphere of the expanding ejecta. This indicates the nova has entered the supersoft source (SSS) phase. If V392 Per were observable by Swift at this time, we would detect supersoft X-rays.
The spectra initially show strong Balmer lines Hα, Hᵦ, Hɣ and Fe II(42) and (49) lines during its principal and diffuse ionised spectra.
The nova is an Fe II type nova.
P Cygni features in early spectra, including double absorption troughs in Balmer lines.
The nova entered the nebular phase before it exited the Sun constraint.
The Balmer lines remained strong, but emission of forbidden [O III] and He II lines was brighter.
Indicates plasma was hot and dense, but now cooler and less dense.
In the late time spectra, O III emission has gone, but the Balmer lines, HeII and HeI still remain in the post-nova spectrum.
Swift X-ray and UV observations began in July 2018.
The hardness ratio of the X-rays was 2-3, and increased with time, suggesting we caught the end of the SSS phase.
The SSS phase begins when the photosphere recedes to the surface of the WD, allowing the detection of X-rays from steady-state hydrogen burning on the surface of the WD. It ends when the supply of hydrogen is exhausted.
V392 Per continued to emit X-rays at a fairly constant hardness ratio and count rate. The count rate increased slightly from ~360 days after eruption.
The hard X-ray emission from V392 Per continued for over two years after eruption, with the final Swift observation taken on 24th August 2020.
Conclusions
V392 Per is a very fast nova, with decline times:
In B, t2=2.3 d, t3=4.5 d
In V, t2=1.8 d, t3=4.3 d
Hard X-rays detected for more than two years after CN eruption, indicating ongoing shocks.
Suggests collimation of accretion flow onto WD
Hints at strong magnetic field, channelling accreted material towards poles.
Either Intermediate Polar or Polar system.
P Cygni profiles on the Balmer lines in the early spectra indicates multiple ejection events. The earlier ejecta components travel slower than the later components. The timing of shocks from ejecta components colliding is consistent with the detection of γ-rays.
Balmer and He I emission lines in early spectra had a triple-peaked structure. The narrow central peak was present throughout and continued into the post-nova spectrum.
O III and He II emission lines appeared in the nebular spectra. O III had a double-peaked structure and faded away before the post-nova spectrum was reached. He II had a triple-peaked structure and the central peak persisted into the post-nova spectrum.
The time different species reached their flux plateau and the line profile shapes provide information about the ionization conditions in the ejecta.
Look out for our paper – coming soon!
URL
F.J.MurphyGlaysher@2018.ljmu.ac.uk
Poster file