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Register a new userA hot and fast ultra-stripped supernova that likely formed a compact neutron star binary
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Compact neutron star binary systems are produced from binary massive stars through stellar evolution involving up to two supernova explosions. The final stages in the formation of these systems have not been directly observed. We report the discovery of iPTF 14gqr (SN 2014ft), a Type Ic supernova with a fast evolving light curve indicating an extremely low ejecta mass ($approx 0.2$ solar masses) and low kinetic energy ($approx 2 times 10^{50}$ ergs). Early photometry and spectroscopy reveal evidence of shock cooling of an extended He-rich envelope, likely ejected in an intense pre-explosion mass loss episode of the progenitor. Taken together, we interpret iPTF 14gqr as evidence for ultra-stripped supernovae that form neutron stars in compact binary systems.
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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.
We study explosion characteristics of ultra-stripped supernovae (SNe), which are candidates of SNe generating binary neutron stars (NSs). As a first step, we perform stellar evolutionary simulations of bare carbon-oxygen cores of mass from 1.45 to 2.0 $M_odot$ until the iron cores become unstable and start collapsing. We then perform axisymmetric hydrodynamics simulations with spectral neutrino transport using these stellar evolution outcomes as initial conditions. All models exhibit successful explosions driven by neutrino heating. The diagnostic explosion energy, ejecta mass, Ni mass, and NS mass are typically $sim 10^{50}$ erg, $sim 0.1 M_odot$, $sim 0.01M_odot$, and $approx 1.3 M_odot$, which are compatible with observations of rapidly-evolving and luminous transient such as SN 2005ek. We also find that the ultra-stripped SN is a candidate for producing the secondary low-mass NS in the observed compact binary NSs like PSR J0737-3039.
We propose a compact binary model with an eccentric orbit to explain periodically active fast radio burst (FRB) sources, where the system consists of a neutron star (NS) with strong dipolar magnetic fields and a magnetic white dwarf (WD). In our model, the WD fills its Roche lobe at periastron, and mass transfer occurs from the WD to the NS around this point. The accreted material may be fragmented into a number of parts, which arrive at the NS at different times. The fragmented magnetized material may trigger magnetic reconnection near the NS surface. The electrons can be accelerated to an ultra-relativistic speed, and therefore the curvature radiation of the electrons can account for the burst activity. In this scenario, the duty cycle of burst activity is related to the orbital period of the binary. We show that such a model may work for duty cycles roughly from ten minutes to two days. For the recently reported 16.35-day periodicity of FRB 180916.J0158+65, our model does not naturally explain such a long duty cycle, since an extremely high eccentricity ($e>0.95$) is required.
We present observations of ZTF18abfcmjw (SN2019dge), a helium-rich supernova with a fast-evolving light curve indicating an extremely low ejecta mass ($approx 0.3,M_odot$) and low kinetic energy ($approx 1.2times 10^{50},{rm erg}$). Early-time (<4 d after explosion) photometry reveal evidence of shock cooling from an extended helium-rich envelope of $sim0.1,M_odot$ located at $sim 3times 10^{12},{rm cm}$ from the progenitor. Early-time He II line emission and subsequent spectra show signatures of interaction with helium-rich circumstellar material, which extends from $gtrsim 5times 10^{13},{rm cm}$ to $gtrsim 2times 10^{16},{rm cm}$. We interpret SN2019dge as a helium-rich supernova from an ultra-stripped progenitor, which originates from a close binary system consisting of a mass-losing helium star and a low-mass main sequence star or a compact object (i.e., a white dwarf, a neutron star, or a black hole). We infer that the local volumetric birth rate of 19dge-like ultra-stripped SNe is in the range of 1400--8200$,{rm Gpc^{-3}, yr^{-1}}$ (i.e., 2--12% of core-collapse supernova rate). This can be compared to the observed coalescence rate of compact neutron star binaries that are not formed by dynamical capture.
We report the discovery and initial follow-up of a double neutron star (DNS) system, PSR J1946$+$2052, with the Arecibo L-Band Feed Array pulsar (PALFA) survey. PSR J1946$+$2052 is a 17-ms pulsar in a 1.88-hour, eccentric ($e , =, 0.06$) orbit with a $gtrsim 1.2 , M_odot$ companion. We have used the Jansky Very Large Array to localize PSR J1946$+$2052 to a precision of 0.09 arcseconds using a new phase binning mode. We have searched multiwavelength catalogs for coincident sources but did not find any counterparts. The improved position enabled a measurement of the spin period derivative of the pulsar ($dot{P} , = , 9,pm , 2 ,times 10^{-19}$); the small inferred magnetic field strength at the surface ($B_S , = , 4 , times , 10^9 , rm G$) indicates that this pulsar has been recycled. This and the orbital eccentricity lead to the conclusion that PSR J1946$+$2052 is in a DNS system. Among all known radio pulsars in DNS systems, PSR J1946$+$2052 has the shortest orbital period and the shortest estimated merger timescale, 46 Myr; at that time it will display the largest spin effects on gravitational wave waveforms of any such system discovered to date. We have measured the advance of periastron passage for this system, $dot{omega} , = , 25.6 , pm , 0.3, deg rm yr^{-1}$, implying a total system mass of only 2.50 $pm$ 0.04 $M_odot$, so it is among the lowest mass DNS systems. This total mass measurement combined with the minimum companion mass constrains the pulsar mass to $lesssim 1.3 , M_odot$.
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