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\(^{-1}\) and an ejecta mass of few \(\times 10^{-5}\) M\(_{\odot}\). 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.
We present multiwavelength observations of the persistent Fermi-LAT unidentified gamma-ray source 1FGL J1417.7-4407, showing it is likely to be associated with a newly discovered X-ray binary ...containing a massive neutron star (nearly 2 M_sun) and a ~ 0.35 M_sun giant secondary with a 5.4 day period. SOAR optical spectroscopy at a range of orbital phases reveals variable double-peaked H-alpha emission, consistent with the presence of an accretion disk. The lack of radio emission and evidence for a disk suggests the gamma-ray emission is unlikely to originate in a pulsar magnetosphere, but could instead be associated with a pulsar wind, relativistic jet, or could be due to synchrotron self-Compton at the disk--magnetosphere boundary. Assuming a wind or jet, the high ratio of gamma-ray to X-ray luminosity (~ 20) suggests efficient production of gamma-rays, perhaps due to the giant companion. The system appears to be a low-mass X-ray binary that has not yet completed the pulsar recycling process. This system is a good candidate to monitor for a future transition between accretion-powered and rotational-powered states, but in the context of a giant secondary.
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 ofgamma-rays are still not well understood. ...We present here a comprehensive multiwavelength data set-from radio to X-rays-for the most gamma-ray-luminous classical nova to date, V1324 Sco. Using this data set, we show that V1324 Sco is a canonical dusty Fe II-type nova, with a maximum ejecta velocity of 2600 km s(-1) and an ejecta mass of a few x 10(-5) M-circle dot. 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.
Since the Fermi discovery of γ-rays from novae, one of the biggest questions in the field has been how novae generate such high-energy emission. Shocks must be a fundamental ingredient. Six months of ...radio observations of the 2012 Nova V5589 Sgr with the VLA and 15 weeks of X-ray observations with Swift/XRT show that the radio emission consisted of: (1) a shock-powered, non-thermal flare; and (2) weak thermal emission from 10−5 M⊙ of freely expanding, photoionized ejecta. Absorption features in the optical spectrum and the peak optical brightness suggest that V5589 Sgr lies 4 kpc away (3.2–4.6 kpc). The shock-powered flare dominated the radio light curve at low frequencies before day 100. The spectral evolution of the radio flare, its high radio brightness temperature, the presence of unusually hard (kT
x
> 33 keV) X-rays, and the ratio of radio to X-ray flux near radio maximum all support the conclusions that the flare was shock-powered and non-thermal. Unlike most other novae with strong shock-powered radio emission, V5589 Sgr is not embedded in the wind of a red-giant companion. Based on the similar inclinations and optical line profiles of V5589 Sgr and V959 Mon, we propose that shocks in V5589 Sgr formed from collisions between a slow flow with an equatorial density enhancement and a subsequent faster flow. We speculate that the relatively high speed and low mass of the ejecta led to the unusual radio emission from V5589 Sgr, and perhaps also to the non-detection of γ-rays.
The importance of shocks in nova explosions has been highlighted by Fermi's discovery of γ-ray-producing novae. Over three years of multiband Very Large Array radio observations of the 2010 nova ...V1723 Aql show that shocks between fast and slow flows within the ejecta led to the acceleration of particles and the production of synchrotron radiation. Soon after the start of the eruption, shocks in the ejecta produced an unexpected radio flare, resulting in a multipeaked radio light curve. The emission eventually became consistent with an expanding thermal remnant with mass 2 × 10−4 M⊙ and temperature 104 K. However, during the first two months, the ≳106 K brightness temperature at low frequencies was too high to be due to thermal emission from the small amount of X-ray-producing shock-heated gas. Radio imaging showed structures with velocities of 400 km s−1 (d/6 kpc) in the plane of the sky, perpendicular to a more elongated 1500 km s−1 (d/6 kpc) flow. The morpho-kinematic structure of the ejecta from V1723 Aql appears similar to nova V959 Mon, where collisions between a slow torus and a faster flow collimated the fast flow and gave rise to γ-ray-producing shocks. Optical spectroscopy and X-ray observations of V1723 Aql during the radio flare are consistent with this picture. Our observations support the idea that shocks in novae occur when a fast flow collides with a slow collimating torus. Such shocks could be responsible for hard X-ray emission, γ-ray production, and double-peaked radio light curves from some classical novae.
Classical Novae at Radio Wavelengths Chomiuk, Laura; Linford, Justin D.; Aydi, Elias ...
The Astrophysical journal. Supplement series,
12/2021, Letnik:
257, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract
We present radio observations (1–40 GHz) for 36 classical novae, representing data from over five decades compiled from the literature, telescope archives, and our own programs. Our targets ...display a striking diversity in their optical parameters (e.g., spanning optical fading timescales,
t
2
= 1–263 days), and we find a similar diversity in the radio light curves. Using a brightness temperature analysis, we find that radio emission from novae is a mixture of thermal and synchrotron emission, with nonthermal emission observed at earlier times. We identify high brightness temperature emission (
T
B
> 5 × 10
4
K) as an indication of synchrotron emission in at least nine (25%) of the novae. We find a class of synchrotron-dominated novae with mildly evolved companions, exemplified by V5589 Sgr and V392 Per, that appear to be a bridge between classical novae with dwarf companions and symbiotic binaries with giant companions. Four of the novae in our sample have two distinct radio maxima (the first dominated by synchrotron and the later by thermal emission), and in four cases the early synchrotron peak is temporally coincident with a dramatic dip in the optical light curve, hinting at a common site for particle acceleration and dust formation. We publish the light curves in a machine-readable table and encourage the use of these data by the broader community in multiwavelength studies and modeling efforts.
We present radio observations (1--40 GHz) for 36 classical novae, representing data from over five decades compiled from the literature, telescope archives, and our own programs. Our targets display ...a striking diversity in their optical parameters (e.g., spanning optical fading timescales, t_2 = 1--263 days), and we find a similar diversity in the radio light curves. Using a brightness temperature analysis, we find that radio emission from novae is a mixture of thermal and synchrotron emission, with non-thermal emission observed at earlier times. We identify high brightness temperature emission (T_B > 5x10^4 K) as an indication of synchrotron emission in at least 9 (25%) of the novae. We find a class of synchrotron-dominated novae with mildly evolved companions, exemplified by V5589 Sgr and V392 Per, that appear to be a bridge between classical novae with dwarf companions and symbiotic binaries with giant companions. Four of the novae in our sample have two distinct radio maxima (the first dominated by synchrotron and the later by thermal emission), and in four cases the early synchrotron peak is temporally coincident with a dramatic dip in the optical light curve, hinting at a common site for particle acceleration and dust formation. We publish the light curves as tables and encourage use of these data by the broader community in multi-wavelength studies and modeling efforts.
Since the Fermi discovery of \(\gamma\)-rays from novae, one of the biggest questions in the field has been how novae generate such high-energy emission. Shocks must be a fundamental ingredient. Six ...months of radio observations of the 2012 nova V5589 Sgr with the VLA and 15 weeks of X-ray observations with Swift/XRT show that the radio emission consisted of: 1) a shock-powered, non-thermal flare; and 2) weak thermal emission from \(10^{-5}\) M\(_\odot\) of freely expanding, photoionized ejecta. Absorption features in the optical spectrum and the peak optical brightness suggest that V5589 Sgr lies 4 kpc away (3.2-4.6 kpc). The shock-powered flare dominated the radio light curve at low frequencies before day 100. The spectral evolution of the radio flare, its high radio brightness temperature, the presence of unusually hard (\(kT_x > 33\) keV) X-rays, and the ratio of radio to X-ray flux near radio maximum all support the conclusions that the flare was shock-powered and non-thermal. Unlike most other novae with strong shock-powered radio emission, V5589 Sgr is not embedded in the wind of a red-giant companion. Based on the similar inclinations and optical line profiles of V5589 Sgr and V959 Mon, we propose that shocks in V5589 Sgr formed from collisions between a slow flow with an equatorial density enhancement and a subsequent faster flow. We speculate that the relatively high speed and low mass of the ejecta led to the unusual radio emission from V5589 Sgr, and perhaps also to the non-detection of \(\gamma\)-rays.
The importance of shocks in nova explosions has been highlighted by Fermi's discovery of \gamma-ray producing novae. Over three years of multi-band VLA radio observations of the 2010 nova V1723 Aql ...show that shocks between fast and slow flows within the ejecta led to the acceleration of particles and the production of synchrotron radiation. Soon after the start of the eruption, shocks in the ejecta produced an unexpected radio flare, resulting in a multi-peaked radio light curve. The emission eventually became consistent with an expanding thermal remnant with mass \(2 \times 10^{-4} M_\odot\) and temperature \(10^4\) K. However, during the first two months, the \(\gtrsim 10^6\) K brightness temperature at low frequencies was too high to be due to thermal emission from the small amount of X-ray producing shock-heated gas. Radio imaging showed structures with velocities of 400 km s\(^{-1}\) (d/6 kpc) in the plane of the sky, perpendicular to a more elongated 1500 km s\(^{-1}\) (d/6 kpc) flow. The morpho-kinematic structure of the ejecta from V1723 Aql appears similar to nova V959 Mon, where collisions between a slow torus and a faster flow collimated the fast flow and gave rise to \gamma -ray producing shocks. Optical spectroscopy and X-ray observations of V1723 Aql during the radio flare are consistent with this picture. Our observations support the idea that shocks in novae occur when a fast flow collides with a slow collimating torus. Such shocks could be responsible for hard X-ray emission, \gamma -ray production, and double-peaked radio light curves from some classical novae.
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