High-cadence ultraviolet, optical, and near-infrared photometric and low-resolution spectroscopic observations of the peculiar Type II supernova (SN) 2018hna are presented. The early-phase multiband ...light curves (LCs) exhibit the adiabatic cooling envelope emission following the shock breakout up to ∼ 14 days from the explosion. SN 2018hna has a rise time of ∼ 88 days in the V band, similar to SN 1987A. A 56Ni mass of ∼0.087 0.004 M is inferred for SN 2018hna from its bolometric LC. Hydrodynamical modeling of the cooling phase suggests a progenitor with a radius ∼50 R , a mass of ∼14-20 M , and an explosion energy of ∼1.7-2.9 × 1051 erg. The smaller inferred radius of the progenitor than a standard red supergiant is indicative of a blue supergiant progenitor of SN 2018hna. A subsolar metallicity (∼0.3 Z ) is inferred for the host galaxy UGC 07534, concurrent with the low-metallicity environments of 1987A-like events.
Abstract
We report photometric and spectroscopic observations of the eclipsing SU UMa-type dwarf nova ASASSN-18aan. We observed the 2018 superoutburst with 2.3 mag brightening and found the orbital ...period (Porb) to be 0.149454(3) d, or 3.59 hr. This is longward of the period gap, establishing ASASSN-18aan as one of a small number of long-Porb SU UMa-type dwarf novae. The estimated mass ratio, q = M2/M1 = 0.278(1), is almost identical to the upper limit of tidal instability by the 3 : 1 resonance. From eclipses, we found that the accretion disk at the onset of the superoutburst may reach the 3 : 1 resonance radius, suggesting that the superoutburst of ASASSN-18aan results from the tidal instability. Considering the case of long-Porb WZ Sge-type dwarf novae, we suggest that the tidal dissipation at the tidal truncation radius is enough to induce SU UMa-like behavior in relatively high-q systems such as SU UMa-type dwarf novae, but that this is no longer effective in low-q systems such as WZ Sge-type dwarf novae. The unusual nature of the system extends to the secondary star, for which we find a spectral type of G9, much earlier than typical for the orbital period, and a secondary mass M2 of around 0.18 M⊙, smaller than expected for the orbital period and the secondary’s spectral type. We also see indications of enhanced sodium abundance in the secondary’s spectrum. Anomalously hot secondaries are seen in a modest number of other CVs and related objects. These systems evidently underwent significant nuclear evolution before the onset of mass transfer. In the case of ASASSN-18aan, this apparently resulted in a mass ratio lower than typically found at the system’s Porb, which may account for the occurrence of a superoutburst at this relatively long period.
We performed photo-polarimetry observations for the blazar BL Lacertae (BL Lac) in 2020 to 2021, in which BL Lac showed historical outburst. As a result, we obtained microvariability with a timescale ...about five minutes and wavelength dependence of polarization degree and angle. These results indicate multiple emission regions and turbulent magnetic field structure.
We present the early-phase spectra and the light curves of the broad-lined (BL) supernova (SN) 2016coi from t = 7 to 67 days after the estimated explosion date. This SN was initially reported as a BL ...Type SN Ic (SN Ic-BL). However, we found that spectra up to t = 12 days exhibited the He i λ5876, λ6678, and λ7065 absorption lines. We show that the smoothed and blueshifted spectra of normal SNe Ib are remarkably similar to the observed spectrum of SN 2016coi. The line velocities of SN 2016coi were similar to those of SNe Ic-BL and significantly faster than those of SNe Ib. Analyses of the line velocity and light curve suggest that the kinetic energy and the total ejecta mass of SN 2016coi are similar to those of SNe Ic-BL. Together with BL SNe 2009bb and 2012ap, for which the detection of He i was also reported, these SNe could be transitional objects between SNe Ic-BL and SNe Ib, and be classified as BL Type "Ib" SNe (SNe "Ib"-BL). Our work demonstrates the diversity of the outermost layer in BL SNe, which should be related to the variety of the evolutionary paths.
ABSTRACT We report on multiwavelength measurements of the accreting black hole Swift J1753.5-0127 in the hard state at low luminosity (L ∼ 2.7 × 1036 erg s−1 assuming a distance of d = 3 kpc) in 2014 ...April. The radio emission is optically thick synchrotron, presumably from a compact jet. We take advantage of the low extinction ( from earlier work) and model the near-IR to UV emission with a multitemperature disk model. Assuming a black hole mass of MBH = 5 M and a system inclination of i = 40°, the fits imply an inner radius for the disk of Rin/Rg > 212d3(MBH/5 M )−1, where Rg is the gravitational radius of the black hole and d3 is the distance to the source in units of 3 kpc. The outer radius is Rout/Rg=90,000 d3(MBH/5 M )−1, which corresponds to 6.6 × 1010 d3 cm, consistent with the expected size of the disk given previous measurements of the size of the companion's Roche lobe. The 0.5-240 keV energy spectrum measured by Swift/X-ray Telescope (XRT), Suzaku (XIS, PIN, and GSO), and Nuclear Spectroscopic Telescope Array is relatively well characterized by an absorbed power law with a photon index of Γ = 1.722 0.003 (90% confidence error), but a significant improvement is seen when a second continuum component is added. Reflection is a possibility, but no iron line is detected, implying a low iron abundance. We are able to fit the entire (radio to 240 keV) spectral energy distribution (SED) with a multitemperature disk component, a Comptonization component, and a broken power law, representing the emission from the compact jet. The broken power law cannot significantly contribute to the soft X-ray emission, and this may be related to why Swift J1753.5-0127 is an outlier in the radio/X-ray correlation. The broken power law (i.e., the jet) might dominate above 20 keV, which would constrain the break frequency to be between 2.4 × 1010 and 3.6 × 1012 Hz. Although the fits to the full SED do not include significant thermal emission in the X-ray band, previous observations have consistently seen such a component, and we find that there is evidence at the 3.1 level for a disk-blackbody component with a temperature of eV and an inner radius of 5Rg-14Rg. If this component is real, it might imply the presence of an inner optically thick accretion disk in addition to the strongly truncated (Rin> 212Rg) disk. We also perform X-ray timing analysis, and the power spectrum is dominated by a Lorentzian component with max = 0.110 0.003 Hz and max = 0.16 0.04 Hz as measured by XIS and XRT, respectively.
We present a set of photometric and spectroscopic observations of a bright Type Ib supernova SN 2012au from ?6 days until ~+150 days after maximum. The shape of its early R-band light curve is ...similar to that of an average Type Ib/c supernova. The peak absolute magnitude is M sub(R) = -18.7 + or - 0.2 mag, which suggests that this supernova belongs to a very luminous group among Type Ib supernovae. The line velocity of He I lambda5876 is about 15,000 km s super(?1) around maximum, which is much faster than that in a typical Type Ib supernova. From the quasi-bolometric peak luminosity of (6.7 + or - 1.3) x 10 super(42) erg s super(?1), we estimate the super(56)Ni mass produced during the explosion as ~0.30 M sub(middot in circle). We also give a rough constraint to the ejecta mass 5-7 M sub(middot in circle) and the kinetic energy (7-18) x 10 super(51) erg. We find a weak correlation between the peak absolute magnitude and He I velocity among Type Ib SNe. The similarities to SN 1998bw in the density structure inferred from the light-curve model as well as the large peak bolometric luminosity suggest that SN 2012au had properties similar to energetic Type Ic supernovae.
Abstract
We report on the multi-wavelength photometry of the 2018 superoutburst in EG Cnc. We have detected stage A superhumps and long-lasting late-stage superhumps via the optical photometry and ...have constrained the binary mass ratio and its possible range. The median value of the mass ratio is 0.048 and the upper limit is 0.057, which still implies that EG Cnc is one of the possible candidates for period bouncers. This object also showed multiple rebrightenings in this superoutburst which are the same as those in its previous superoutburst in 1996–1997, despite the difference in the main superoutburst. This would represent that the rebrightening type is inherent to each object and is independent of the initial disk mass at the beginning of superoutbursts. We also found that B − I and J − Ks colors were unusually red just before the rebrightening phase and became bluer during the quiescence between rebrightenings, which would mean that the low-temperature mass reservoir at the outermost disk accreted with time after the main superoutburst. Also, the ultraviolet flux was sensitive to rebrightenings as well as the optical flux, and the U − B color became redder during the rebrightening phase, which would indicate that the inner disk became cooler when this object repeated rebrightenings. Our results thus basically support the idea that the cool mass reservoir in the outermost disk is responsible for rebrightenings.
We report on multiwavelength measurements of the accreting black hole Swift J1753.5-0127 in the hard state at low luminosity (L ~ 2.7 x 10 super(36) erg s super(-1) assuming a distance of d = 3 kpc) ...in 2014 April. The radio emission is optically thick synchrotron, presumably from a compact jet. The 0.5-240 keV energy spectrum measured by Swift/X-ray Telescope (XRT), Suzaku (XIS, PIN, and GSO), and Nuclear Spectroscopic Telescope Array is relatively well characterized by an absorbed power law with a photon index of Gamma = 1.722 + or - 0.003 (90% confidence error), but a significant improvement is seen when a second continuum component is added. Reflection is a possibility, but no iron line is detected, implying a low iron abundance. We also perform X-ray timing analysis, and the power spectrum is dominated by a Lorentzian component with v sub(max) = 0.110 + or - 0.003 Hz and = 0.16 + or - 0.04 Hz as measured by XIS and XRT, respectively.
ABSTRACT Multi-wavelength observations of the black widow binary system 2FGL J2339.6-0532 are reported. The Fermi gamma-ray source 2FGL J2339.6-0532 was recently categorized as a black widow in which ...a recycled millisecond pulsar (MSP) is evaporating the companion star with its powerful pulsar wind. Our optical observations show clear sinusoidal light curves due to the asymmetric temperature distribution of the companion star. Assuming a simple geometry, we constrained the range of the inclination angle of the binary system to , which enables us to discuss the interaction between the pulsar wind and the companion in detail. The X-ray spectrum consists of two components: a soft, steady component that seems to originate from the surface of the MSP, and a hard, variable component from the wind-termination shock near the companion star. The measured X-ray luminosity is comparable to the bolometric luminosity of the companion, meaning that the heating efficiency is less than 0.5. In the companion orbit, 1011 cm from the pulsar, the pulsar wind is already in the particle-dominant stage with a magnetization parameter of . In addition, we precisely investigated the time variations of the X-ray periodograms and detected a weakening of the orbital modulation. The observed phenomenon may be related to unstable pulsar wind activity or weak mass accretion, both of which can result in the temporal extinction of the radio pulse.
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