Abstract
We report comprehensive multi-wavelength observations of a peculiar Type Ia-like supernova (“SN Ia-pec”) ASASSN-15pz. ASASSN-15pz is a spectroscopic “twin” of SN 2009dc, a so-called ...“Super-Chandrasekhar-mass” SN, throughout its evolution, but it has a peak luminosity
that is
dimmer and comparable to the SN 1991T sub-class of SNe Ia at the luminous end of the normal width-luminosity relation. The synthesized
56
Ni mass of
is also substantially less than that found for several 2009dc-like SNe. Previous well-studied 2009dc-like SNe have generally suffered from large and uncertain amounts of host-galaxy extinction, which is negligible for ASASSN-15pz. Based on the color of ASASSN-15pz, we estimate a host extinction for SN 2009dc of
and confirm its high luminosity (
). The 2009dc-like SN population, which represents ∼1% of SNe Ia, exhibits a range of peak luminosities, and do not fit onto the tight width-luminosity relation. Their optical light curves also show significant diversity of late-time (≳50 days) decline rates. The nebular-phase spectra provide powerful diagnostics to identify the 2009dc-like events as a distinct class of SNe Ia. We suggest referring to these sources using the phenomenology-based “2009dc-like SN Ia-pec” instead of “Super-Chandrasekhar SN Ia,” which is based on an uncertain theoretical interpretation.
The Changing-look Blazar B2 1420+32 Mishra, Hora D.; Dai, Xinyu; Chen, Ping ...
The Astrophysical journal,
06/2021, Letnik:
913, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract
Blazars are active galactic nuclei with their relativistic jets pointing toward the observer, comprising two major subclasses, flat-spectrum radio quasars (FSRQs) and BL Lac objects. We ...present multiwavelength photometric and spectroscopic monitoring observations of the blazar B2 1420+32, focusing on its outbursts in 2018–2020. Multiepoch spectra show that the blazar exhibited large-scale spectral variability in both its continuum and line emission, accompanied by dramatic gamma-ray and optical variability by factors of up to 40 and 15, respectively, on week to month timescales. Over the last decade, the gamma-ray and optical fluxes increased by factors of 1500 and 100, respectively. B2 1420+32 was an FSRQ with broad emission lines in 1995. Following a series of flares starting in 2018, it transitioned between BL Lac and FSRQ states multiple times, with the emergence of a strong Fe pseudocontinuum. Two spectra also contain components that can be modeled as single-temperature blackbodies of 12,000 and 5200 K. Such a collection of “changing-look” features has never been observed previously in a blazar. We measure gamma-ray–optical and interband optical lags implying emission-region separations of less than 800 and 130 gravitational radii, respectively. Since most emission-line flux variations, except the Fe continuum, are within a factor of 2–3, the transitions between FSRQ and BL Lac classifications are mainly caused by the continuum variability. The large Fe continuum flux increase suggests the occurrence of dust sublimation releasing more Fe ions in the central engine and an energy transfer from the relativistic jet to subrelativistic emission components.
ABSTRACT We present Multi Unit Spectroscopic Explorer (MUSE) integral field spectroscopic observations of the host galaxy (PGC 043234) of one of the closest (z = 0.0206, D 90 Mpc) and best-studied ...tidal disruption events (TDEs), ASASSN-14li. The MUSE integral field data reveal asymmetric and filamentary structures that extend up to 10 kpc from the post-starburst host galaxy of ASASSN-14li. The structures are traced only through the strong nebular O iii λ5007, N ii λ6584, and H emission lines. The total off-nuclear O iii λ5007 luminosity is 4.7 × 1039 erg s−1, and the ionized H mass is . Based on the Baldwin-Phillips-Terlevich diagram, the nebular emission can be driven by either AGN photoionization or shock excitation, with AGN photoionization favored given the narrow intrinsic line widths. The emission line ratios and spatial distribution strongly resemble ionization nebulae around fading AGNs such as IC 2497 (Hanny's Voorwerp) and ionization "cones" around Seyfert 2 nuclei. The morphology of the emission line filaments strongly suggest that PGC 043234 is a recent merger, which likely triggered a strong starburst and AGN activity leading to the post-starburst spectral signatures and the extended nebular emission line features we see today. We briefly discuss the implications of these observations in the context of the strongly enhanced TDE rates observed in post-starburst galaxies and their connection to enhanced theoretical TDE rates produced by supermassive black hole binaries.
We present spatially and spectrally resolved Atacama Large Millimeter/submillimeter Array (ALMA) observations of gas and dust orbiting the pre-main-sequence hierarchical triple-star system GW Ori. A ...forward modeling of the 13CO and C18O J = 2-1 transitions permits a measurement of the total stellar mass in this system, , and the circumtriple disk inclination, . Optical spectra spanning a 35 yr period were used to derive new radial velocities and, coupled with a spectroscopic disentangling technique, revealed that the A and B components of GW Ori form a double-lined spectroscopic binary with a period of 241.50 0.05 days; a tertiary companion orbits that inner pair with a period of 4218 50 days. Combining the results from the ALMA data and the optical spectra with three epochs of astrometry in the literature, we constrain the individual stellar masses in the system ( , , ) and find strong evidence that at least one of the stellar orbital planes (and likely both) is misaligned with the disk plane by as much as 45°. A V-band light curve spanning 30 yr reveals several new ∼30-day eclipse events 0.1-0.7 mag in depth and a 0.2 mag sinusoidal oscillation that is clearly phased with the AB-C orbital period. Taken together, these features suggest that the A-B pair may be partially obscured by material in the inner disk as the pair approaches apoastron in the hierarchical orbit. Lastly, we conclude that stellar evolutionary models are consistent with our measurements of the masses and basic photospheric properties if the GW Ori system is ∼1 Myr old.
The Long Term Evolution of ASASSN-14li Brown, J. S.; Holoien, T. W.-S.; Auchettl, K. ...
Monthly notices of the Royal Astronomical Society,
05/2017, Letnik:
466, Številka:
4
Journal Article
Recenzirano
Odprti dostop
We present late-time optical spectroscopy taken with the Large Binocular Telescope's Multi-Object Double Spectrograph, late-time Swift UVOT and X-ray Telescope observations, as well as improved ...All-Sky Automated Survey for SuperNovae (ASAS-SN) pre-discovery limits on the nearby (d = 90.3 Mpc, z = 0.0206) tidal disruption event (TDE) ASASSN-14li. The late-time optical spectra show Hα emission well in excess of that seen in the SDSS host galaxy spectrum, indicating that the processes powering the luminous flares associated with TDEs can operate for several hundreds of days. The Swift observations reveal the presence of lingering apparently thermal UV (TUV ~ 3.5 × 104 K) and X-ray (TX ~ 7 × 105 K) emission. The characteristic temperatures evolve by, at most, a factor of ~2 over the 600 d follow-up campaign. The X-ray, UV and Hα luminosities evolve roughly in tandem and at a rate that is consistent with a power-law decay at late times. This behaviour is in stark contrast with the majority of optically discovered TDEs, which are X-ray faint and evolve on shorter time-scales. Finally, we address how the unique properties of ASASSN-14li can be used to probe the relationship between the TDE rate and host galaxy properties.
Abstract
ASASSN-14ko is a recently discovered periodically flaring transient at the center of the active galactic nucleus (AGN) ESO 253−G003 with a slowly decreasing period. Here, we show that the ...flares originate from the northern, brighter nucleus in this dual-AGN, post-merger system. The light curves for the two flares that occurred in 2020 May and September are nearly identical over all wavelengths. For both events, Swift observations showed that the UV and optical wavelengths brightened in unison. The effective temperature of the UV/optical emission rises and falls with the increase and subsequent decline in the luminosity. The X-ray flux, by contrast, first rapidly drops over ∼2.6 days, rises for ∼5.8 days, drops again over ∼4.3 days, and then recovers. The X-ray spectral evolution of the two flares differ, however. During the 2020 May peak the spectrum softened with increases in the X-ray luminosity, while we observed the reverse for the 2020 September peak. We found a small change in the period derivative, which seems to indicate that the system does not have a static period derivative and there is some stochasticity in its evolution.
Abstract
We identify a pre-explosion counterpart to the nearby Type IIP supernova ASASSN-16fq (SN 2016cok) in archival Hubble Space Telescope data. The source appears to be a blend of several stars ...that prevents obtaining accurate photometry. However, with reasonable assumptions about the stellar temperature and extinction, the progenitor almost certainly had an initial mass M
* ≲ 17 M⊙, and was most likely in the mass range of M
* = 8–12 M⊙. Observations once ASASSN-16fq has faded will have no difficulty accurately determining the properties of the progenitor. In 8 yr of Large Binocular Telescope (LBT) data, no significant progenitor variability is detected to rms limits of roughly 0.03 mag. Of the six nearby supernova (SN) with constraints on the low-level variability, SN 1987A, SN 1993J, SN 2008cn, SN 2011dh, SN 2013ej and ASASSN-16fq, only the slowly fading progenitor of SN 2011dh showed clear evidence of variability. Excluding SN 1987A, the 90 per cent confidence limit implied by these sources on the number of outbursts over the last decade before the SN that last longer than 0.1 yr (full width at half-maximum) and are brighter than M
R
< −8 mag is approximately N
out ≲ 3. Our continuing LBT monitoring programme will steadily improve constraints on pre-SN progenitor variability at amplitudes far lower than achievable by SN surveys.
We present basic statistics for all supernovae discovered by the All-Sky Automated Survey for SuperNovae (ASAS-SN) during its first year-and-a-half of operations, spanning 2013 and 2014. We also ...present the same information for all other bright (mV less than or equal to 17), spectroscopically confirmed supernovae discovered from 2014 May 1 through the end of 2014, providing a comparison to the ASAS-SN sample starting from the point where ASAS-SN became operational in both hemispheres. In addition, we present collected redshifts and near-UV through IR magnitudes, where available, for all host galaxies of the bright supernovae in both samples. This work represents a comprehensive catalogue of bright supernovae and their hosts from multiple professional and amateur sources, allowing for population studies that were not previously possible because the all-sky emphasis of ASAS-SN redresses many previously existing biases. In particular, ASAS-SN systematically finds bright supernovae closer to the centres of host galaxies than either other professional surveys or amateurs, a remarkable result given ASAS-SN's poorer angular resolution. This is the first of a series of yearly papers on bright supernovae and their hosts that will be released by the ASAS-SN team.
Abstract We report the discovery and characterization of TIC 350842552 (“Zvrk”), an apparently isolated, rapidly rotating ( P rot ∼ 99 days) red giant observed by TESS in its southern Continuous ...Viewing Zone. The star’s fast surface rotation is independently verified by the use of p -mode asteroseismology, strong periodicity in TESS and ASAS-SN photometry, and measurements of spectroscopic rotational broadening. A two-component fit to APOGEE spectra indicates a coverage fraction of its surface features consistent with the amplitude of the photometric rotational signal. Variations in the amplitude of its photometric modulations over time suggest the evolution of its surface morphology and therefore enhanced magnetic activity. We further develop and deploy new asteroseismic techniques to characterize radial differential rotation, but find at best only weak evidence for rotational shear within Zvrk’s convective envelope. This high surface rotation rate is incompatible with models of angular-momentum transport in single-star evolution. Spectroscopic abundance estimates also indicate a high lithium abundance, among other chemical anomalies. Taken together, all of these suggest a planet-ingestion scenario for the formation of this rotational configuration, various models for which we examine in detail.
We present the discovery of PS18kh, a tidal disruption event discovered at the center of SDSS J075654.53+341543.6 (d 322 Mpc) by the Pan-STARRS Survey for Transients. Our data set includes ...pre-discovery survey data from Pan-STARRS, the All-sky Automated Survey for Supernovae, and the Asteroid Terrestrial-impact Last Alert System as well as high-cadence, multiwavelength follow-up data from ground-based telescopes and Swift, spanning from 56 days before peak light until 75 days after. The optical/UV emission from PS18kh is well-fit as a blackbody with temperatures ranging from T 12,000 K to T 25,000 K and it peaked at a luminosity of L 8.8 × 1043 erg s−1. PS18kh radiated E = (3.45 0.22) × 1050 erg over the period of observation, with (1.42 0.20) × 1050 erg being released during the rise to peak. Spectra of PS18kh show a changing, boxy/double-peaked H emission feature, which becomes more prominent over time. We use models of non-axisymmetric accretion disks to describe the profile of the H line and its evolution. We find that at early times the high accretion rate leads the disk to emit a wind which modifies the shape of the line profile and makes it bell-shaped. At late times, the wind becomes optically thin, allowing the non-axisymmetric perturbations to show up in the line profile. The line-emitting portion of the disk extends from rin ∼ 60rg to an outer radius of rout ∼ 1400rg and the perturbations can be represented either as an eccentricity in the outer rings of the disk or as a spiral arm in the inner disk.
PDF
