The 21st century X-ray observatories XMM-Newton, Chandra, and Swift gave us completely new insights into the X-ray behaviour of nova outbursts. These new-generation X-ray observatories provide particularly high spectral resolution and high density in monitoring campaigns, simultaneously in X-rays and UV/optical. The entire evolution of several nova outbursts has been observed with the Swift XRT and UVOT instruments, allowing studies of the gradual shift of the peak of the SED from UV to X-rays, time scales to the onset and duration of the X-ray brightest supersoft source (SSS) phase, and pre- and post-SSS X-ray emission. In addition, XMM-Newton and Chandra observations can efficiently be scheduled, allowing deeper studies of strategically chosen evolutionary stages. Before Swift joined in 2005, Chandra and XMM-Newton blind shots in search of SSS emission unavoidably led to some underexposed observations taken before and/or after the SSS phase. More systematic Swift studies reduced this number while increasing the number of novae. Pre- and post-SSS spectra at low and high spectral resolution were successfully modelled with collisional plasma models. Pre-SSS emission arises in shocks and post-SSS emission in radiatively cooling thin ejecta. In contrast, the grating spectra taken during the SSS phase are a lot more complex than expected and have not yet been successfully modeled. Available hot WD radiation transport models give only approximate reproduction of the observations, and make some critical assumptions that are only valid in isolated WDs. More grating spectra which would be important to search for systematic trends between SSS spectra and system parameters.
Classical novae produce radioactive nuclei which are emitters of gamma-rays in the MeV range. Some examples are the lines at 478 and 1275 keV (from 7Be and 22Na) and the positron-electron annihilation emission (511 keV line and a continuum below this energy, with a cut-off at 20-30 keV). The analysis of gamma-ray spectra and light curves is a potential unique and powerful tool both to trace the corresponding isotopes and to give insights on the properties of the expanding envelope determining its transparency. Another possible origin of gamma-rays is the acceleration of particles up to very hi…
Detection of X-rays from classical novae, both in outburst and post-outburst, provides unique and crucial information about the explosion mechanism. Soft X-rays reveal the hot white dwarf photosphere, whenever hydrogen (H) nuclear burning is still on and expanding envelope is transparent enough, whereas harder X-rays give information about the ejecta and/or the accretion flow in the reborn cataclysmic variable. The duration of the supersoft X-ray emission phase is related to the turn-off of the classical nova, i.e., of the H-burning on top of the white dwarf core. A review of X-ray observation…
The detection of GeV $γ$-ray emission from Galactic novae by $Fermi$-LAT has become routine since 2010, and is generally associated with shocks internal to the nova ejecta. These shocks are also expected to heat plasma to $\sim 10^7$ K, resulting in detectable X-ray emission. In this paper, we investigate 13 $γ$-ray emitting novae observed with the Neil Gehrels $Swift$ Observatory, searching for 1-10 keV X-ray emission concurrent with $γ$-ray detections. We also analyze $γ$-ray observations of novae V407 Lup (2016) and V357 Mus (2018). We find that most novae do eventually show X-ray evidence …
The Fermi LAT discovery that classical novae produce >100 MeV gamma-rays establishes that shocks and relativistic particle acceleration are key features of these events. These shocks are likely to be radiative due to the high densities of the nova ejecta at early times coincident with the gamma-ray emission. Thermal X-rays radiated behind the shock are absorbed by neutral gas and reprocessed into optical emission, similar to Type IIn (interacting) supernovae. Gamma-rays are produced by collisions between relativistic protons with the nova ejecta (hadronic scenario) or Inverse Compton/bremsstra…
Novae were discovered to emit transient gamma rays during the period of several days to a few weeks after initial explosion, indicating presence of acceleration processes of particles in their expanding shells. In the case of recurrent novae, electrons can be in principle accelerated in the nova shells for the whole recurrence period of nova producing delayed $γ$ ray emission as considered in Bednarek (2022). Here we extend the ideas presented in this article by considering the fate of electrons which diffuse out of the shells of novae supplying fresh relativistic electrons to the recurrent no…
[Abridged] Classical novae (CNe) represent the major class of supersoft X-ray sources (SSSs) in the central region of our neighbouring galaxy M31. We performed a dedicated monitoring of the M31 central region, aimed to detect SSS counterparts of CNe, with XMM-Newton and Chandra between Nov and Mar of the years 2009/10, 2010/11 and 2011/12. In total we detected 24 novae in X-rays. Seven of these sources were known from previous observations, including the M31 nova with the longest SSS phase, M31N~1996-08b, which was found to fade below our X-ray detection limit 13.8 yr after outburst. Of the ne…
Novae are now firmly established as a high-energy (>100 MeV) gamma-ray source class by the Fermi Large Area Telescope (LAT). In symbiotic binary systems such as V407 Cyg 2010, there is a firm theoretical framework for the production of shock-accelerated particles in the nova ejecta from interactions with the dense wind of the red giant companion. Yet, the high-energy gamma-ray emission detected in classical novae involving less evolved stellar companions cannot be explained in the same way and could instead be produced in internal shocks in the ejecta. We summarize the Fermi-LAT gamma-ray obse…
In a dwarf nova, the accretion disk around the white dwarf is a source of ultraviolet, optical, and infrared photons, but is never hot enough to emit X-rays. Observed X-rays instead originate from the boundary layer between the disk and the white dwarf. As the disk switches between quiescence and outburst states, the 2-10 keV X-ray flux is usually seen to be anti-correlated with the optical brightness. Here we present RXTE monitoring observations of two dwarf novae, VW Hyi and WW Cet, confirming the optical/X-ray anti-correlation in these two systems. However, we do not detect any episodes of …
Classical Novae were revealed as a surprise source of gamma-rays in Fermi LAT observations. During the first 8 years since the LAT was launched, 6 novae in total have been detected to > 5 sigma in gamma-rays, in contrast to the 69 discovered optically in the same period. We attempt to resolve this discrepancy by assuming all novae are gamma-ray emitters, and assigning peak one-day fluxes based on a flat distribution of the known emitters to a simulated population. To determine optical parameters, the spatial distribution and magnitudes of bulge and disc novae in M31 are scaled to the Milky Way…
Novae have been reported as transients for more than two thousand years. Their bright optical outbursts are the result of explosive nuclear burning of gas accreted from a binary companion onto a white dwarf. Novae containing a white dwarf close to the Chandrasekhar mass limit and accreting at a high rate are potentially the unknown progenitors of the type Ia supernovae used to measure the acceleration of the Universe. Swift X-ray observations have radically transformed our view of novae by providing dense monitoring throughout the outburst, revealing new phenomena in the super-soft X-rays from…
The first supersoft source (SSS) identification with an optical nova in M 31 was based on ROSAT observations. Twenty additional X-ray counterparts (mostly identified as SSS by their hardness ratios) were detected using archival ROSAT, XMM-Newton and Chandra observations obtained before July 2002. Based on these results optical novae seem to constitute the major class of SSS in M 31. An analysis of archival Chandra HRC-I and ACIS-I observations obtained from July 2004 to February 2005 demonstrated that M 31 nova SSS states lasted from months to about 10 years. Several novae showed short X-ray o…
We discuss a scenario in which TeV neutrinos are produced during explosions of Novae. It is argued that hadrons are accelerated to very high energies in the inner part of a Nova wind, as a result of reconnection of the strong magnetic field of a White Dwarf. Hadrons are expected to interact efficiently with a dense matter of the wind, either already during the acceleration process or during their advection with the equatorial wind. We calculate the neutrino spectra, and estimate the muon neutrino event rates in the IceCube telescope, in the case of a few Novae. In general, those event rates ar…
[Abridged] Classical novae (CNe) represent the major class of supersoft X-ray sources (SSSs) in the central region of our neighbouring galaxy M 31. We performed a dedicated monitoring of the M 31 central region with XMM-Newton and Chandra between Nov 2007 and Feb 2008 and between Nov 2008 and Feb 2009 respectively, in order to find SSS counterparts of CNe, determine the duration of their SSS phase and derive physical outburst parameters. We systematically searched our data for X-ray counterparts of CNe and determined their X-ray light curves and spectral properties. We detected in total 17 X-r…
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, inclu…
Peaking at 3.7 mag on 2020 July 11, YZ Ret was the second-brightest nova of the decade. The nova's moderate proximity (2.7 kpc from Gaia) provided an opportunity to explore its multi-wavelength properties in great detail. Here we report on YZ Ret as part of a long-term project to identify the physical mechanisms responsible for high-energy emission in classical novae. We use simultaneous Fermi/LAT and NuSTAR observations complemented by XMM-Newton X-ray grating spectroscopy to probe the physical parameters of the shocked ejecta and the nova-hosting white dwarf. The XMM-Newton observations reve…
Available data for novae show that the X-ray and visible spectral regions correlate with each other as they evolve. Large differences in ionization exist simultaneously in the two wavelength regimes, and a straightforward model is proposed that explains the characteristics observed in both spectral regimes. Its key features are (1) ejected blobs of very high density gas from the white dwarf that expand to create within each clump a wide range of emitting density, ionization, and velocity, and (2) a more homogeneous circumbinary envelope of gas that is produced by secondary star mass loss. The …
We present X-ray observations of novae V2491 Cyg and KT Eri about 9 years post-outburst, of the dwarf nova and post-nova candidate EY Cyg, and of a VY Scl variable. The first three objects were observed with XMM-Newton, KT Eri also with the Chandra ACIS-S camera, V794 Aql with the Chandra ACIS-S camera and High Energy Transmission Gratings. The two recent novae, similar in outburst amplitude and light curve, appear very different at quiescence. Assuming half of the gravitational energy is irradiated in X-rays, V2491 Cyg is accreting at $\dot{m}=1.4\times10^{-9}-10^{-8}M_\odot/yr$, while for KT…
Classical novae produce radioactive nuclei which are emitters of gamma-rays in the MeV range. Some examples are the lines at 478 and 1275 keV (from 7Be and 22Na) and the positron-electron annihilation emission, with the 511 keV line and a continuum. Gamma-ray spectra and light curves are potential unique tools to trace the corresponding isotopes and to give insights on the properties of the expanding envelope. Another possible origin of gamma-rays is the acceleration of particles up to very high energies, so that either neutral pions or inverse Compton processes produce gamma-rays of energies …
(Abridged) Classical novae (CNe) have recently been reported to represent the major class of supersoft X-ray sources (SSSs) in the central region of our neighbour galaxy M 31. We carried out a dedicated monitoring of the M 31 central region with XMM-Newton and Chandra in order to find SSS counterparts of CNe, determine the duration of their SSS phase and derive physical outburst parameters. We systematically searched our data for X-ray counterparts of CNe and determined their X-ray light curves and spectral properties. Additionally, we determined luminosity upper limits for all novae from prev…
Detection of high-energy (~> 100 MeV) gamma rays by the Fermi Large Area Telescope (LAT) from a nova in the symbiotic binary system V407 Cygni has opened possibility of high-energy neutrino detection from this type of sources. Thermonuclear explosion on the white dwarf surface sets off a nova shell in motion that expands and slows down in a dense surrounding medium provided by the red giant companion. Particles are accelerated in the shocks of the shell, and interact with surrounding medium to produce observed gamma rays. We show that proton-proton interaction, which is most likely responsible…
Galactic Novae is at present well established class of gamma-ray sources. We wonder for how long the mechanism of acceleration of electrons operates in shells of Novae. In order to put constraints on the time scale of the electron acceleration, we consider a specific model for the injection and propagation of electrons within the shell of the recurrent Nova RS Ophiuchi. We calculate the equilibrium spectra of electrons within the Nova shell and the gamma-ray fluxes produced by these electrons in the comptonization of the soft radiation from the Red Giant within the Nova binary system and also …
The discovery of GeV gamma-rays from classical novae has led to a reassessment of these garden-variety explosions, and highlighted their importance for understanding radiative shocks, particle acceleration, and dust formation in more exotic, distant transients. Recent collaboration between observers and theorists has revealed that shocks in novae are energetically important, and can even dominate their bolometric luminosity. Shocks may also explain long-standing mysteries in novae such as dust production, super-Eddington luminosities, and `flares' in optical light curves. Here, we highlight th…
With rapid response capabilities, and a daily planning of its observing schedule, the Neil Gehrels Swift Observatory is ideal for monitoring transient and variable sources. Here we present a sample of the 12 novae with the most detailed ultraviolet (UV) follow-up by Swift -- the first uniform analysis of such UV light-curves. The fading of these specific light-curves can be modelled as power-law decays (plotting magnitude against log time), showing that the same physical processes dominate the UV emission for extended time intervals in individual objects. After the end of the nuclear burning i…
Recent observations found that electrons are accelerated to $\sim$10 GeV and emit synchrotron hard X-rays in two magnetic white dwarfs (WDs), also known as cataclysmic variables (CVs). In nova outbursts of WDs, multi-GeV gamma-rays were detected inferring that protons are accelerated to 100 GeV or higher. In recent optical surveys, the WD density is found to be higher near the Sun than in the Galactic disk by a factor $\sim$2.5. The cosmic rays (CR) produced by local CVs and novae will accumulate in the local bubble for $10^6$ - $10^7$ yrs. On these findings, we search for CRs from historic CV…
For several novae, a bright X-ray source with a spectrum resembling the class of Super Soft X-ray Sources (SSS) has been observed a few weeks to months after outburst. Novae are powered by explosive nuclear burning on the surface of a white dwarf, and enough energy is produced to power a radiatively driven wind. Owing to the evolution of the opacity of the ejecta, the observable spectrum gradually shifts from optical to soft X-rays (SSS phase). It has sometimes been assumed that at the beginning of the SSS phase no more mass loss occurs. However, high-resolution X-ray spectra of some novae hav…
We report the Fermi Large Area Telescope (LAT) detections of high-energy (>100 MeV) gamma-ray emission from two recent optically bright classical novae, V1369 Centauri 2013 and V5668 Sagittarii 2015. At early times, Fermi target-of-opportunity observations prompted by their optical discoveries provided enhanced LAT exposure that enabled the detections of gamma-ray onsets beginning ~2 days after their first optical peaks. Significant gamma-ray emission was found extending to 39-55 days after their initial LAT detections, with systematically fainter and longer duration emission compared to previ…
A classical nova results from runaway thermonuclear explosions on the surface of a white dwarf that accretes matter from a low-mass main-sequence stellar companion. In 2012 and 2013, three novae were detected in gamma rays and stood in contrast to the first gamma-ray detected nova V407 Cygni 2010, which belongs to a rare class of symbiotic binary systems. Despite likely differences in the compositions and masses of their white dwarf progenitors, the three classical novae are similarly characterized as soft spectrum transient gamma-ray sources detected over 2-3 week durations. The gamma-ray det…
We measure the duty cycles for an existing sample of well observed, nearby dwarf novae using data from AAVSO, and present a quantitative empirical relation between the duty cycle of dwarf novae outbursts and the X-ray luminosity of the system in quiescence. We have found that $\log DC=0.63(\pm0.21)\times(\log L_{X}({\rm erg\,s^{-1}})-31.3)-0.95(\pm0.1)$, where DC stands for duty cycle. We note that there is intrinsic scatter in this relation greater than what is expected from purely statistical errors. Using the dwarf nova X-ray luminosity functions from \citet{Pretorius12} and \citet{Byckling…
In the last few years the Fermi-LAT instrument has detected GeV gamma-ray emission from several novae. Such GeV emission can be interpreted in terms of inverse Compton emission from electrons accelerated in the shock or in terms of emission from hadrons accelerated in the same conditions. The latter might reach much higher energies and could produce a second component in the gamma-ray spectrum at TeV energies. We perform follow-up observations of selected novae and dwarf novae in search of the second component in TeV energy gamma rays. This can shed light on the acceleration process of leptons…
The discovery of novae as sources of ~GeV gamma-rays highlights the key role of shocks and relativistic particle acceleration in these transient systems. Although there is evidence for a spectral cut-off above energies ~1-100 GeV at particular epochs in some novae, the maximum particle energy achieved in these accelerators has remained an open question. The high densities of the nova ejecta (~10 orders of magnitude larger than in supernova remnants) render the gas far upstream of the shock neutral and shielded from ionizing radiation. The amplification of the magnetic field needed for diffusiv…
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$_\odot$ of freely expanding, photoionized ejecta. Absorption features in the optical spectrum and the peak optical brightness suggest that V5589 Sgr lies 4 kpc a…
Context. A number of novae have been found to emit high-energy gamma rays (>100 MeV). However, the origin of this emission is not yet understood. We report on the search for gamma-ray emission from 75 optically-detected Galactic novae in the first 7.4 years of operation of the Fermi Large Area Telescope using the Pass 8 data set. Aims. We compile an optical nova catalog including light curves from various resources and estimate the optical peak time and optical peak magnitude in order to search for gamma-ray emission to test if all novae are gamma-ray emitters. Methods. We repeat the analysis …
Probing Physical Conditions in Classical and Symbiotic Novae with the Square Kilometre Array Observatory
Radboud University（拉博德大学）；Joint Institute for VLBI ERIC（甚长基线干涉测量欧洲研究联盟联合研究所）；ASTRON（荷兰射电天文研究所）；University of Manchester（曼彻斯特大学）；The University of Sydney（悉尼大学）；ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav)（引力波发现卓越研究中心）；Texas Tech University（德克萨斯理工大学）
More than a dozen binary systems are now established as sources of variable, high energy (HE, 0.1-100 GeV) gamma rays. Five are also established sources of very high energy (VHE, >100 GeV) gamma rays. The mechanisms behind gamma-ray emission in binaries are very diverse. My current understanding is that they divide up into four types of systems: gamma-ray binaries, powered by pulsar rotation; microquasars, powered by accretion onto a black hole or neutron star; novae, powered by thermonuclear runaway on a white dwarf; colliding wind binaries, powered by stellar winds from massive stars. Some o…
Symbiotic stars often contain white dwarfs with quasi-steady shell burning on their surfaces. However, in most symbiotics, the origin of this burning is unclear. In symbiotic slow novae, however, it is linked to a past thermonuclear runaway. In June 2015, the symbiotic slow nova AG Peg was seen in only its second optical outburst since 1850. This recent outburst was of much shorter duration and lower amplitude than the earlier eruption, and it contained multiple peaks -- like outbursts in classical symbiotic stars such as Z And. We report Swift X-ray and UV observations of AG Peg made between …
Shock interaction has been argued to play a role in powering a range of optical transients, including supernovae (particularly the superluminous class), classical novae, stellar mergers, tidal disruption events, and fast blue optical transients. These same shocks can accelerate relativistic ions, generating high-energy neutrino and gamma-ray emission via hadronic pion production. The recent discovery of time-correlated optical and gamma-ray emission in classical novae has revealed the important role of radiative shocks in powering these events, enabling an unprecedented view of the properties …
Classical novae are among the most frequent transient events in the Milky Way, and key agents of ongoing nucleosynthesis. Despite their large numbers, they have never been observed in soft $γ$-ray emission. Measurements of their $γ$-ray signatures would provide both, insights on explosion mechanism as well as nucleosynthesis products. Our goal is to constrain the ejecta masses of $\mathrm{^7Be}$ and $\mathrm{^{22}Na}$ from classical novae through their $γ$-ray line emissions at 478 and 1275 keV. We extract posterior distributions on the line fluxes from archival data of the INTEGRAL/SPI spectr…
The nucleosynthesis in classical novae, in particular that of radioactive isotopes, is directly measurable by its $γ$-ray signature. Despite decades of observations, MeV $γ$-rays from novae have never been detected -- neither individually at the time of the explosion, nor as a result of radioactive decay, nor the diffuse Galactic emission from the nova population. Thanks to recent developments in modeling of instrumental background for MeV telescopes such as INTEGRAL/SPI and Fermi/GBM, the prospects to finally detect these elusive transients are greatly enhanced. This demands for updated and r…
[Abridged] Classical novae (CNe) represent the main class of supersoft X-ray sources (SSSs) in the central region of our neighbouring galaxy M 31. Only three confirmed novae and three SSSs have been discovered in globular clusters (GCs) of any galaxy so far, of which one nova and two SSSs (including the nova) were found in M 31 GCs. To study the SSS state of CNe we carried out a high-cadence X-ray monitoring of the M 31 central area with XMM-Newton and Chandra. We analysed X-ray and optical data of a new transient X-ray source in the M 31 GC Bol 126, discovered serendipitously in Swift observa…
The flux of cosmic rays in the heliosphere is subjected to variations that are related to the Sun's magnetic activity. To study this effect, updated time series of multichannel observations are needed. Here we present a web application that collects real-time data on solar activity proxies, interplanetary plasma parameters, and charged cosmic-ray data. The data are automatically retrieved on daily basis from several space missions or observatories. With this application, the data can be visualized and download into a common format. Along with observational data, the application aims to provide…
Supernovae (SNe) are the most fascinating objects in astronomy and are intensely investigated. However, many mysteries such as nucleosynthesis and the origin of SNe Ia remain unsolved. Although the thermonuclear explosion of a single-degenerate white dwarf has been considered to be the origin of SNe Ia, a merger of two white dwarfs (double-degenerate scenario) has been frequently denoted to be more promising than a single-degenerate white dwarf. Recently the importance of observing the MeV gamma-ray band to conclusively determine the origin has been remarked. MeV gamma-rays are unique probes d…
Multiwavelength radiation from relativistic particles accelerated at shocks in novae and other astrophysical sources carries a wealth of information about the outflow properties and the microphysical processes at work near the shocks. The observation of GeV gamma-rays from novae by Fermi/LAT demonstrates that the shocks in these systems can accelerate particles to energies of at least $\sim 10$ GeV. The low-energy extension of the same non-thermal particle distribution inevitably gives rise to emission extending into the X-ray band. Above $\gtrsim 10$ keV this radiation can escape the system w…
Diversity of the X-ray observations of dwarf nova are still not fully understood. I review the X-ray spectral characteristics of dwarf novae during the quiescence in general explained by cooling flow models and the outburst spectra that show hard X-ray emission dominantly with few sources that reveal soft X-ray/EUV blackbody emission. The nature of aperiodic time variability of brightness of dwarf novae shows band limited noise, which can be adequately described in the framework of the model of propagating fluctuations. The frequency of the break (1-6 mHz) indicates inner disk truncation of th…
We have analyzed 16 years of observations dedicated to the Crab (pulsar + nebula) with the INTEGRAL SPI instrument to investigate its polarization properties. We find that the source presents a substantially polarized emission (PF = 24%) in the hard X-ray domain, with the electric vector aligned with the pulsar spin axis, in agreement with other results at various wavelengths. The stability of the polarization characteristics with energy and over the 16 years covered by the data is remarkable, completing the standard candle status of the source in the spectral domain. The polarization measurem…
The Fermi-LAT telescope has unexpectedly discovered GeV gamma-ray emission from the symbiotic Nova V407 Cygni. We investigate the radiation processes due to electrons and hadrons accelerated during the explosion of this Nova. We consider a scenario in which GeV gamma-ray emission observed by Fermi is produced by the electrons with energies of a few tens of GeV in the inverse Compton scattering of stellar radiation. On the other hand, the hadrons are expected to reach larger energies, due to the lack of radiation losses during acceleration process, producing TeV gamma-rays and neutrinos. We pre…
The diffuse hard X-ray emission that fills the Galactic center, bulge, and ridge is believed to arise from unresolved populations of X-ray binary systems. However, the identity of the dominant class of accreting objects in each region remains unclear. Recent studies of Fe line properties and the low-energy (<10 keV) X-ray continuum of the bulge indicate a major population fraction of non-magnetic cataclysmic variables (CVs), in particular quiescent dwarf novae. This is in contrast to previous high-energy (>10 keV) X-ray measurements of the bulge and ridge, which indicate a dominant population …
There are insufficient super soft (~ 0.1 keV) X-ray sources in either spiral or elliptical galaxies to account for the rate of explosion of Type Ia supernovae in either the single degenerate or the double degenerate scenarios. We quantify the amount of circumstellar matter that would be required to suppress the soft X-ray flux by yielding a column density in excess of 10^{23} cm^{-2}. We summarize evidence that appropriate quantities of matter are extant in SN Ia and in recurrent novae that may be supernova precursors. The obscuring matter is likely to have a large, but not complete, covering …
An Optically Motivated Gamma-ray Study of Fermi-LAT Novae
Department of Astrophysics, American Museum of Natural History（美国自然历史博物馆天体物理系）；Department of Earth & Physical Sciences, York College, City University of New York（纽约市立大学约克学院地球与物理科学系）；Department of Natural Sciences, LaGuardia Community College, City University of New York（纽约市立大学拉瓜迪亚社区学院自然科学系）
Recent observations of GeV gamma-rays from novae have led to a paradigm shift in the understanding of these objects. While it is now believed that shocks contribute significantly to the energy budget of novae, it is still unknown if the emission is hadronic or leptonic in origin. Neutrinos could hold the key to definitively differentiating between these two scenarios, though the energies of such particles would be much lower than are typically targeted with neutrino telescopes. IceCube's densely instrumented DeepCore sub-array provides the ability to reduce the threshold for observation from 1…
The discovery of GeV gamma-rays from classical novae indicates that shocks and relativistic particle acceleration are energetically key in these events. Further evidence for shocks comes from thermal keV X-ray emission and an early peak in the radio light curve on a timescale of months with a brightness temperature which is too high to result from freely expanding photo-ionized gas. Paper I developed a one dimensional model for the thermal emission from nova shocks. This work concluded that the shock-powered radio peak cannot be thermal if line cooling operates in the post-shock gas at the rat…
