Astrometric positions of radio-emitting active galactic nuclei (AGNs) can be determined with sub-milliarcsec accuracy using very long baseline interferometry (VLBI). The usually small apparent proper ...motion of distant extragalactic targets allow us to realize the fundamental celestial reference frame with VLBI observations. However, long-term astrometric monitoring may reveal extreme changes in some AGN positions. Using new VLBI observations in 2018-2021, we show here that four extragalactic radio sources (3C48, CTA21, 1144+352, 1328+254) have a dramatic shift in their positions by 20-130 milliarcsec over two decades. For all four sources, the apparent positional shift is caused by their radio structure change.
We present the first results from the Southern Hemisphere Parallax Interferometric Radio Astrometry Legacy Survey (\spirals): \(10\mu\)as-accurate parallaxes and proper motions for two southern ...hemisphere 6.7 GHz methanol masers obtained using the inverse MultiView calibration method. Using an array of radio telescopes in Australia and New Zealand, we measured the trigonometric parallax and proper motions for the masers associated with the star formation region G232.62+00.99 of \(\pi = 0.610\pm0.011\)~mas, \(\mu_x=-2.266\pm0.021\)~mas~y\(^{-1}\) and \(\mu_y=2.249\pm0.049\)~mas~y\(^{-1}\), which implies its distance to be \(d=1.637\pm0.029\)~kpc. These measurements represent an improvement in accuracy by more than a factor of 3 over the previous measurements obtained through Very Long Baseline Array observations of the 12~GHz methanol masers associated with this region. We also measure the trigonometric parallax and proper motion for G323.74--00.26 as \(\pi = 0.364\pm0.009\)~mas, \(\mu_x=-3.239\pm0.025\)~mas~y\(^{-1}\) and \(\mu_y=-3.976\pm0.039\)~mas~y\(^{-1}\), which implies a distance of \(d=2.747\pm0.068\)~kpc. These are the most accurate measurements of trigonometric parallax obtained for 6.7~GHz class II methanol masers to date. We confirm that G232.62+00.99 is in the Local arm and find that G323.74--00.26 is in the Scutum-Centaurus arm. We also investigate the structure and internal dynamics of both masers.
We report discovering an exoplanet from following up a microlensing event alerted by Gaia. The event Gaia22dkv is toward a nearby disk source at ~2.5 kpc rather than the traditional bulge ...microlensing fields. Our primary analysis yields a Jovian planet with M_p = 0.50 +/- 0.05 M_J at a projected orbital separation r_perp = 1.63 +/- 0.17 AU. The host is a turnoff star with mass 1.24 +/- 0.06 M_sun and distance of 1.35 +/- 0.09 kpc, and at r'~14, it is far brighter than any previously discovered microlensing planet host, opening up the opportunity of testing the microlensing model with radial velocity (RV) observations. RV data can be used to measure the planet's orbital period and eccentricity, and they also enable searching for inner planets of the microlensing cold Jupiter, as expected from the "inner-outer correlation" inferred from Kepler and RV discoveries. Furthermore, we show that Gaia astrometric microlensing will not only allow precise measurements of its angular Einstein radius theta_E, but also directly measure the microlens parallax vector and unambiguously break a geometric light-curve degeneracy, leading to definitive characterization of the lens system.
We inspect 4 microlensing events KMT-2021-BLG-1968, KMT-2021-BLG-2010, KMT-2022-BLG-0371, and KMT-2022-BLG-1013, for which the light curves exhibit partially covered short-term central anomalies. We ...conduct detailed analyses of the events with the aim of revealing the nature of the anomalies. We test various models that can give rise to the anomalies of the individual events including the binary-lens (2L1S) and binary-source (1L2S) interpretations. Under the 2L1S interpretation, we thoroughly inspect the parameter space to check the existence of degenerate solutions, and if they exist, we test the feasibility of resolving the degeneracy. We find that the anomalies in KMT-2021-BLG-2010 and KMT-2022-BLG-1013 are uniquely defined by planetary-lens interpretations with the planet-to-host mass ratios of \(q\sim 2.8\times 10^{-3}\) and \(\sim 1.6\times 10^{-3}\), respectively. For KMT-2022-BLG-0371, a planetary solution with a mass ratio \(q\sim 4\times 10^{-4}\) is strongly favored over the other three degenerate 2L1S solutions with different mass ratios based on the \(\chi^2\) and relative proper motion arguments, and a 1L2S solution is clearly ruled out. For KMT-2021-BLG-1968, on the other hand, we find that the anomaly can be explained either by a planetary or a binary-source interpretation, making it difficult to firmly identify the nature of the anomaly. From the Bayesian analyses of the identified planetary events, we estimate that the masses of the planet and host are \((M_{\rm p}/M_{\rm J}, M_{\rm h}/M_\odot) = (1.07^{+1.15}_{-0.68}, 0.37^{+0.40}_{-0.23})\), \((0.26^{+0.13}_{-0.11}, 0.63^{+0.32}_{-0.28})\), and \((0.31^{+0.46}_{-0.16}, 0.18^{+0.28}_{-0.10})\) for KMT-2021-BLG-2010L, KMT-2022-BLG-0371L, and KMT-2022-BLG-1013L, respectively.
We complete the publication of all microlensing planets (and ``possible planets'') identified by the uniform approach of the KMT AnomalyFinder system in the 21 KMT subprime fields during the 2019 ...observing season, namely KMT-2019-BLG-0298, KMT-2019-BLG-1216, KMT-2019-BLG-2783, OGLE-2019-BLG-0249, and OGLE-2019-BLG-0679 (planets), as well as OGLE-2019-BLG-0344, and KMT-2019-BLG-0304 (possible planets). The five planets have mean log mass-ratio measurements of \((-2.6,-3.6,-2.5,-2.2,-2.3)\), median mass estimates of \((1.81,0.094,1.16,7.12,3.34)\, M_{\rm Jup}\), and median distance estimates of \((6.7,2.7,5.9,6.4,5.6)\, {\rm kpc}\), respectively. The main scientific interest of these planets is that they complete the AnomalyFinder sample for 2019, which has a total of 25 planets that are likely to enter the statistical sample. We find statistical consistency with the previously published 33 planets from the 2018 AnomalyFinder analysis according to an ensemble of five tests. Of the 58 planets from 2018-2019, 23 were newly discovered by AnomalyFinder. Within statistical precision, half of all the planets have caustic crossings while half do not (as predicted by Zhu et al. 2014), an equal number of detected planets result from major-image and minor-image light-curve perturbations, and an equal number come from KMT prime fields versus subprime fields.
The CNIa0.02 project aims to collect a complete, nearby sample of Type Ia supernovae (SNe Ia) light curves, and the SNe are volume-limited with host-galaxy redshifts z_host < 0.02. The main ...scientific goal is to infer the distributions of key properties (e.g., the luminosity function) of local SNe Ia in a complete and unbiased fashion in order to study SN explosion physics. We spectroscopically classify any SN candidate detected by the All-Sky Automated Survey for Supernovae (ASAS-SN) that reaches peak brightness < 16.5 mag. Since ASAS-SN scans the full sky and does not target specific galaxies, our target selection is effectively unbiased by host-galaxy properties. We perform multi-band photometric observations starting from the time of discovery. In the first data release (DR1), we present the optical light curves obtained for 247 SNe from our project (including 148 SNe in the complete sample), and we derive parameters such as the peak fluxes, dm15 and s_BV.
We report the first unambiguous detection and mass measurement of an isolated stellar-mass black hole (BH). We used the Hubble Space Telescope (HST) to carry out precise astrometry of the source star ...of the long-duration (t_E~270 days), high-magnification microlensing event MOA-2011-BLG-191/OGLE-2011-BLG-0462 (hereafter designated as MOA-11-191/OGLE-11-462), in the direction of the Galactic bulge. HST imaging, conducted at eight epochs over an interval of six years, reveals a clear relativistic astrometric deflection of the background star's apparent position. Ground-based photometry of MOA-11-191/OGLE-11-462 shows a parallactic signature of the effect of the Earth's motion on the microlensing light curve. Combining the HST astrometry with the ground-based light curve and the derived parallax, we obtain a lens mass of 7.1 +/- 1.3 Msun and a distance of 1.58 +/- 0.18 kpc. We show that the lens emits no detectable light, which, along with having a mass higher than is possible for a white dwarf or neutron star, confirms its BH nature. Our analysis also provides an absolute proper motion for the BH. The proper motion is offset from the mean motion of Galactic-disk stars at similar distances by an amount corresponding to a transverse space velocity of ~45 km/s, suggesting that the BH received a 'natal kick' from its supernova explosion. Previous mass determinations for stellar-mass BHs have come from radial-velocity measurements of Galactic X-ray binaries, and from gravitational radiation emitted by merging BHs in binary systems in external galaxies. Our mass measurement is the first for an isolated stellar-mass BH using any technique.
Using data from the Complete Nearby ($z_{host}<0.02$) sample of Type Ia
Supernovae (CNIa0.02), we discover a linear relation between two parameters
derived from the $B-V$ color curves of Type Ia ...supernovae: the "color stretch"
$s_{BV}$ and the rising color slope $s_0^*(B-V)$ after the peak, and this
relation applies to the full range of $s_{BV}$. The $s_{BV}$ parameter is known
to be tightly correlated with the peak luminosity, and especially for "fast
decliners" (dim Type Ia supernovae), and the luminosity correlation with
$s_{BV}$ is markedly better than with the classic light-curve width parameters
such as $\Delta{m_{15}(B)}$. Thus our new linear relation can be used to infer
peak luminosity from $s_0^*$. Unlike $s_{BV}$ (or $\Delta{m_{15}}$), the
measurement of $s_0^*(B-V)$ does not rely on the well-determined time of
light-curve peak or color maximum, making it less demanding on the light-curve
coverage than past approaches.
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