skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: X-ray evolution of the nova V959 Mon suggests a delayed ejection and a non-radiative shock
ABSTRACT X-ray observations of shocked gas in novae can provide a useful probe of the dynamics of the ejecta. Here we report on X-ray observations of the nova V959 Mon, which was also detected in GeV gamma-rays with the Fermi satellite. We find that the X-ray spectra are consistent with a two-temperature plasma model with non-solar abundances. We interpret the X-rays as due to shock interaction between the slow equatorial torus and the fast polar outflow that were inferred from radio observations of V959 Mon. We further propose that the hotter component, responsible for most of the flux, is from the reverse shock driven into the fast outflow. We find a systematic drop in the column density of the absorber between days 60 and 140, consistent with the expectations for such a picture. We present intriguing evidence for a delay of around 40 d in the expulsion of the ejecta from the central binary. Moreover, we infer a relatively small (a few times 10−6 M⊙) ejecta mass ahead of the shock, considerably lower than the mass of 104 K gas inferred from radio observations. Finally, we infer that the dominant X-ray shock was likely not radiative at the time of our observations, and that the shock power was considerably higher than the observed X-ray luminosity. It is unclear why high X-ray luminosity, closer to the inferred shock power, is never seen in novae at early times, when the shock is expected to have high enough density to be radiative.  more » « less
Award ID(s):
1751874
PAR ID:
10225216
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ;
Date Published:
Journal Name:
Monthly Notices of the Royal Astronomical Society
Volume:
500
Issue:
3
ISSN:
0035-8711
Page Range / eLocation ID:
2798 to 2812
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; ; (, The Astrophysical journal)
    We report the first detection of hard (>10 keV) X-ray emission simultaneous with gamma-rays in a nova eruption. Observations of the nova V5855 Sgr carried out with the NuSTAR satellite on Day 12 of the eruption revealed faint, highly absorbed thermal X-rays. The extreme equivalent hydrogen column density toward the X-ray emitting region (˜3 × 10^24 cm^-2) indicates that the shock producing the X-rays was deeply embedded within the nova ejecta. The slope of the X-ray spectrum favors a thermal origin for the bulk of the emission, and the constraints of the temperature in the shocked region suggest a shock velocity compatible with the ejecta velocities inferred from optical spectroscopy. While we do not claim the detection of nonthermal X-rays, the data do not allow us to rule out an additional, fainter component dominating at energies above 20 keV, for which we obtained upper limits. The inferred luminosity of the thermal X-rays is too low to be consistent with the gamma-ray luminosities if both are powered by the same shock under standard assumptions regarding the efficiency of nonthermal particle acceleration and the temperature distribution of the shocked gas. 
    more » « less
  2. ; ; ; ; ; ; ; ; ; ; et al (, Monthly Notices of the Royal Astronomical Society)
    null (Ed.)
    ABSTRACT Shocks in γ-ray emitting classical novae are expected to produce bright thermal and non-thermal X-rays. We test this prediction with simultaneous NuSTAR and Fermi/LAT observations of nova V906 Car, which exhibited the brightest GeV γ-ray emission to date. The nova is detected in hard X-rays while it is still γ-ray bright, but contrary to simple theoretical expectations, the detected 3.5–78 keV emission of V906 Car is much weaker than the simultaneously observed >100 MeV emission. No non-thermal X-ray emission is detected, and our deep limits imply that the γ-rays are likely hadronic. After correcting for substantial absorption (NH ≈ 2 × 1023 cm−2), the thermal X-ray luminosity (from a 9 keV optically thin plasma) is just ∼2 per cent of the γ-ray luminosity. We consider possible explanations for the low thermal X-ray luminosity, including the X-rays being suppressed by corrugated, radiative shock fronts or the X-rays from the γ-ray producing shock are hidden behind an even larger absorbing column (NH > 1025 cm−2). Adding XMM–Newton and Swift/XRT observations to our analysis, we find that the evolution of the intrinsic X-ray absorption requires the nova shell to be expelled 24 d after the outburst onset. The X-ray spectra show that the ejecta are enhanced in nitrogen and oxygen, and the nova occurred on the surface of a CO-type white dwarf. We see no indication of a distinct supersoft phase in the X-ray light curve, which, after considering the absorption effects, may point to a low mass of the white dwarf hosting the nova. 
    more » « less
  3. ; ; ; ; ; ; ; ; ; ; et al (, Monthly Notices of the Royal Astronomical Society)
    ABSTRACT Classical novae are shock-powered multiwavelength transients triggered by a thermonuclear runaway on an accreting white dwarf. V1674 Her is the fastest nova ever recorded (time to declined by two magnitudes is t2 = 1.1 d) that challenges our understanding of shock formation in novae. We investigate the physical mechanisms behind nova emission from GeV γ-rays to cm-band radio using coordinated Fermi-LAT, NuSTAR, Swift, and VLA observations supported by optical photometry. Fermi-LAT detected short-lived (18 h) 0.1–100 GeV emission from V1674 Her that appeared 6 h after the eruption began; this was at a level of (1.6 ± 0.4) × 10−6 photons cm−2 s−1. Eleven days later, simultaneous NuSTAR and Swift X-ray observations revealed optically thin thermal plasma shock-heated to kTshock = 4 keV. The lack of a detectable 6.7 keV Fe Kα emission suggests super-solar CNO abundances. The radio emission from V1674 Her was consistent with thermal emission at early times and synchrotron at late times. The radio spectrum steeply rising with frequency may be a result of either free-free absorption of synchrotron and thermal emission by unshocked outer regions of the nova shell or the Razin–Tsytovich effect attenuating synchrotron emission in dense plasma. The development of the shock inside the ejecta is unaffected by the extraordinarily rapid evolution and the intermediate polar host of this nova. 
    more » « less
  4. ; ; ; ; (, The Astrophysical Journal)
    Abstract When the ejecta of a supernova (SN) interact with the progenitor star's circumstellar environment, a strong shock is driven back into the ejecta, causing the material to become bright optically and in X-rays. Most notably, as the shock traverses the H-rich envelope, it begins to interact with metal-rich material. Thus, continued monitoring of bright and nearby SNe provides valuable clues about both the progenitor structure and its pre-SN evolution. Here we present late-time, multiepoch optical and Chandra X-ray spectra of the core-collapse SN, SN 1996cr. Magellan IMACS optical spectra taken in 2017 July and 2021 August show a very different spectrum from that seen in 2006 with broad, double-peaked optical emission lines of oxygen, argon, and sulfur with expansion velocities of ±4500 km s−1. Redshifted emission components are considerably fainter compared to the blueshifted components, presumably due to internal extinction from dust in the SN ejecta. Broad ±2400 km s−1Hαis also seen, which we infer is shocked progenitor pre-SN, mass-loss, H-rich material. Chandra data indicate a slow but steady decline in the overall X-ray luminosity, suggesting that the forward shock has broken through any circumstellar shell or torus, which is inferred from prior deep Chandra ACIS-S/HETG observations. The X-ray properties are consistent with what is expected from a shock breaking out into a lower-density environment. Though originally identified as a Type IIn SN, based upon late-time optical emission-line spectra, we argue that the SN 1996cr progenitor was partially or highly stripped, suggesting a Type IIb/Ib SN. 
    more » « less
  5. ; ; (, Annual Review of Astronomy and Astrophysics)
    We survey our understanding of classical novae—nonterminal, thermonuclear eruptions on the surfaces of white dwarfs in binary systems. The recent and unexpected discovery of GeV gamma rays from Galactic novae has highlighted the complexity of novae and their value as laboratories for studying shocks and particle acceleration. We review half a century of nova literature through this new lens, and conclude the following: ▪  The basics of the thermonuclear runaway theory of novae are confirmed by observations. The white dwarf sustains surface nuclear burning for some time after runaway, and until recently, it was commonly believed that radiation from this nuclear burning solely determines the nova's bolometric luminosity. ▪  The processes by which novae eject material from the binary system remain poorly understood. Mass loss from novae is complex (sometimes fluctuating in rate, velocity, and morphology) and often prolonged in time over weeks, months, or years. ▪  The complexity of the mass ejection leads to gamma-ray-producing shocks internal to the nova ejecta. When gamma rays are detected (around optical maximum), the shocks are deeply embedded and the surrounding gas is very dense. ▪  Observations of correlated optical and gamma-ray light curves confirm that the shocks are radiative and contribute significantly to the bolometric luminosity of novae. Novae are therefore the closest and most common interaction-powered transients. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email