ABSTRACT
We present 3D hydrodynamic models of the interaction between the outflows of evolved, pulsating, Asymptotic Giant Branch (AGB) stars and nearby (<3 stellar radii) substellar companions ...(Mcomp ≲ 40 MJ). Our models show that due to resonances between the orbital period of the companion and the pulsation period of the AGB star, multiple spiral structures can form; the shocks driven by the pulsations are enhanced periodically in different regions as they encounter the denser material created by the substellar companion’s wake. We discuss the properties of these spiral structures and the effect of the companion parameters on them. We also demonstrate that the gravitational potential of the nearby companion enhances the mass-loss from the AGB star. For more massive (Mcomp > 40 MJ) and more distant companions (>4 stellar radii), a single spiral arm forms. We discuss the possibility of observing these structures with the new generations of high-resolution, high-sensitivity instruments, and using them to ‘find’ substellar companions around bright, evolved stars. Our results also highlight possible structures that could form in our Solar system when the Sun turns into an AGB star.
Abstract
Shock interaction has been argued to play a role in powering a range of optical transients, including supernovae, 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 of ion acceleration, including its efficiency and energy spectrum, under similar physical conditions to shocks in extragalactic transients. Here we introduce a model for connecting the radiated optical fluence of nonrelativistic transients to their maximal neutrino and gamma-ray fluence. We apply this technique to a wide range of extragalactic transient classes in order to place limits on their contributions to the cosmological high-energy gamma-ray and neutrino backgrounds. Based on a simple model for diffusive shock acceleration at radiative shocks, calibrated to novae, we demonstrate that several of the most luminous transients can accelerate protons up to 10
16
eV, sufficient to contribute to the IceCube astrophysical background. Furthermore, several of the considered sources—particularly hydrogen-poor supernovae—may serve as “gamma-ray-hidden” neutrino sources owing to the high gamma-ray opacity of their ejecta, evading constraints imposed by the nonblazar Fermi Large Area Telescope background. However, adopting an ion acceleration efficiency of ∼0.3%–1% motivated by nova observations, we find that currently known classes of nonrelativistic, potentially shock-powered transients contribute at most a few percent of the total IceCube background.
Abstract
In 2021 August, the Fermi Large Area Telescope, H.E.S.S., and MAGIC detected GeV and TeV
γ
-ray emission from an outburst of recurrent nova RS Ophiuchi. This detection represents the first ...very high-energy
γ
-rays observed from a nova, and it opens a new window to study particle acceleration. Both H.E.S.S. and MAGIC described the observed
γ
-rays as arising from a single, external shock. In this paper, we perform detailed, multi-zone modeling of RS Ophiuchi’s 2021 outburst, including a self-consistent prescription for particle acceleration and magnetic field amplification. We demonstrate that, contrary to previous work, a single shock cannot simultaneously explain RS Ophiuchi’s GeV and TeV emission, in particular the spectral shape and distinct light-curve peaks. Instead, we put forward a model involving multiple shocks that reproduces the observed
γ
-ray spectrum and temporal evolution. The simultaneous appearance of multiple distinct velocity components in the nova optical spectrum over the first several days of the outburst supports the presence of distinct shocks, which may arise either from the strong latitudinal dependence of the density of the external circumbinary medium (e.g., in the binary equatorial plane versus the poles) or due to internal collisions within the white dwarf ejecta (which power the
γ
-ray emission in classical novae).
Discovery of carbon-rich Miras in the Galactic bulge Matsunaga, Noriyuki; Menzies, John W; Feast, Michael W ...
Monthly notices of the Royal Astronomical Society,
08/2017, Volume:
469, Issue:
4
Journal Article
Peer reviewed
Open access
Abstract
Only one carbon-rich (C-rich, hereinafter) Mira variable has so far been suggested as a member of the Galactic bulge and this is in a symbiotic system. Here we describe a method for ...selecting C-rich candidates from an infrared colour–colour diagram, (J − K
s) versus (9 − 18). Follow-up low-resolution spectroscopy resulted in the detection of eight C-rich Mira variables from a sample of 36 candidates towards the Galactic bulge. Our near-infrared photometry indicates that two of these, including the known symbiotic, are closer than the main body of the bulge while a third is a known foreground object. Of the five bulge members, one shows He i and O ii emission and is possibly another symbiotic star. Our method is useful for identifying rare C-rich stars in the Galactic bulge and elsewhere. The age of these C-rich stars and the evolutionary process which produced them remain uncertain. They could be old and the products of either binary mass transfer or mergers, i.e. the descendants of blue stragglers, but we cannot rule out the possibility that they belong to a small in situ population of metal-poor intermediate age (<5 Gyr) stars in the bulge or that they have been accreted from a dwarf galaxy.
Abstract
We present the study of multiwavelength observations of an unidentified Fermi Large Area Telescope (LAT) source, 4FGL J1910.7−5320, a new candidate redback millisecond pulsar binary. In the ...4FGL 95% error region of 4FGL J1910.7−5320, we find a possible binary with a 8.36 hr orbital period from the Catalina Real-Time Transient Survey, confirmed by optical spectroscopy using the SOAR telescope. This optical source was recently independently discovered as a redback pulsar by the TRAPUM project, confirming our prediction. We fit the optical spectral energy distributions of 4FGL J1910.7−5320 with a blackbody model, inferring a maximum distance of 4.1 kpc by assuming that the companion fills its Roche lobe with a radius of
R
= 0.7
R
☉
. Using a 12.6 ks Chandra X-ray observation, we identified an X-ray counterpart for 4FGL J1910.7−5320, with a spectrum that can be described by an absorbed power law with a photon index of 1.0 ± 0.4. The spectrally hard X-ray emission shows tentative evidence for orbital variability. Using more than 12 yr of Fermi-LAT data, we refined the position of the
γ
-ray source, and the optical candidate still lies within the 68% positional error circle. In addition to 4FGL J1910.7−5320, we find a variable optical source with a periodic signal of 4.28 hr inside the 4FGL catalog 95% error region of another unidentified Fermi source, 4FGL J2029.5−4237. However, the
γ
-ray source does not have a significant X-ray counterpart in an 11.7 ks Chandra observation, with a 3
σ
flux upper limit of 2.4 × 10
−14
erg cm
−2
s
−1
(0.3–7 keV). Moreover, the optical source is outside our updated Fermi-LAT 95% error circle. These observational facts all suggest that this new redback millisecond pulsar powers the gamma-ray source 4FGL J1910.7−5320 while 4FGL J2029.5−4237 is unlikely the
γ
-ray counterpart to the 4.28 hr variable.
We report observations of the hydrogen-deficient supernova (SN) 2019bkc/ATLAS19dqr. With B- and r-band decline between peak and 10 days post peak of mag and mag, respectively, SN 2019bkc is the most ...rapidly declining SN I discovered so far. While its closest matches are the rapidly declining SN 2005ek and SN 2010X, the light curves and spectra of SN 2019bkc show some unprecedented characteristics. SN 2019bkc appears "hostless," with no identifiable host galaxy near its location, although it may be associated with the galaxy cluster MKW1 at z = 0.02. We evaluate a number of existing models of fast-evolving SNe, and we find that none of them can satisfactorily explain all aspects of SN 2019bkc observations.
Abstract
We have discovered a new candidate redback millisecond pulsar binary near the center of the error ellipse of the bright unassociated Fermi-LAT
γ
-ray source 4FGL J0940.3–7610. The candidate ...counterpart is a variable optical source that also shows faint X-ray emission. Optical photometric and spectroscopic monitoring with the SOAR telescope indicates that the companion is a low-mass star in a 6.5 hr orbit around an invisible primary, showing both ellipsoidal variations and irradiation and consistent with the properties of known redback millisecond pulsar binaries. Given the orbital parameters, preliminary modeling of the optical light curves suggests an edge-on inclination and a low-mass (∼1.2–1.4
M
⊙
) neutron star, along with a secondary mass somewhat more massive than the typical ≳0.4
M
⊙
. This combination of inclination and secondary properties could make radio eclipses more likely for this system, explaining its previous nondiscovery in radio pulsation searches. Hence, 4FGL J0940.3–7610 may be a strong candidate for a focused search for
γ
-ray pulsations to enable the future detection of a millisecond pulsar.
Abstract
We report the discovery of a new low-mass X-ray binary near the center of the unassociated Fermi GeV
γ
-ray source 4FGL J0540.0–7552. The source shows the persistent presence of an optical ...accretion disk and exhibits extreme X-ray and optical variability. It also has an X-ray spectrum well-fit by a hard power law with Γ = 1.8 and a high ratio of X-ray to
γ
-ray flux. Together, these properties are consistent with the classification of the binary as a transitional millisecond pulsar (tMSP) in the subluminous disk state. Uniquely among the candidate tMSPs, 4FGL J0540.0–7552 shows consistent optical, X-ray, and
γ
-ray evidence for having undergone a state change, becoming substantially brighter in the optical and X-rays and fainter in GeV
γ
-rays sometime in mid-2013. In its current subluminous disk state, and like one other candidate tMSP in the Galactic field, 4FGL J0540.0–7552 appears to always be in an X-ray “flare mode,” indicating that this could be common phenomenology for tMSPs.
Abstract
We present the discovery of a new optical/X-ray source likely associated with the Fermi
γ
-ray source 4FGL J1408.6–2917. Its high-amplitude periodic optical variability, large spectroscopic ...radial-velocity semiamplitude, evidence for optical emission lines and flaring, and X-ray properties together imply the source is probably a new black widow millisecond pulsar binary. We compile the properties of the 41 confirmed and suspected field black widows, finding a median secondary mass of 0.027 ± 0.003
M
⊙
. Considered jointly with the more massive redback millisecond pulsar binaries, we find that the “spider” companion mass distribution remains strongly bimodal, with essentially zero systems having companion masses of between ∼0.07 and 0.1
M
⊙
. X-ray emission from black widows is typically softer and less luminous than in redbacks, consistent with less efficient particle acceleration in the intrabinary shock in black widows, excepting a few systems that appear to have more efficient “redback-like” shocks. Together black widows and redbacks dominate the census of the fastest spinning field millisecond pulsars in binaries with known companion types, making up ≳80% of systems with
P
spin
< 2 ms. Similar to redbacks, the neutron star masses in black widows appear on average significantly larger than the canonical 1.4
M
⊙
, and many of the highest-mass neutron stars claimed to date are black widows with
M
NS
≳ 2.1
M
⊙
. Both of these observations are consistent with an evolutionary picture where spider millisecond pulsars emerge from short orbital period progenitors that had a lengthy period of mass transfer initiated while the companion was on the main sequence, leading to fast spins and high masses.
We present the discovery of a likely new redback millisecond pulsar (MSP) binary associated with the Fermi γ-ray source 4FGL J2333.1-5527. Using optical photometric and spectroscopic observations ...from the Southern Astrophysical Research telescope, we identify a low-mass, main-sequence-like companion in a 6.9 hr, highly inclined orbit around a suspected massive neutron star primary. Archival XMM-Newton X-ray observations show this system has a hard power-law spectrum Γ = 1.6 0.3 and LX ∼ 5 × 1031 erg s−1, consistent with redback MSP binaries. Our data suggest that for secondary masses typical of redbacks, the mass of the neutron star is likely well in excess of ∼1.4 M , but future timing of the radio pulsar is necessary to bolster this tentative conclusion. This work shows that a bevy of nearby compact binaries still await discovery, and that unusually massive neutron stars continue to be common in redbacks.
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