Search

We report the analysis of planetary microlensing event OGLE-2018-BLG-1185, which was observed by a large number of ground-based telescopes and by the $Spitzer$ Space Telescope. The ground-based light curve indicates a low planet-host star mass ratio of $q = (6.9 \pm 0.2) \times 10^{-5}$, which is near the peak of the wide-orbit exoplanet mass-ratio distribution. We estimate the host star and planet masses with a Bayesian analysis using the measured angular Einstein radius under the assumption that stars of all masses have an equal probability to host this planet. The flux variation observed by $Spitzer$ was marginal, but still places a constraint on the microlens parallax. Imposing a conservative constraint that this flux variation should be $\Delta f_{\rm Spz} < 4$ instrumental flux units indicates a host mass of $M_{\rm host} = 0.37^{+0.35}_{-0.21}\ M_\odot$ and a planet mass of $m_{\rm p} = 8.4^{+7.9}_{-4.7}\ M_\oplus$. A Bayesian analysis including the full parallax constraint from $Spitzer$ suggests smaller host star and planet masses of $M_{\rm host} = 0.091^{+0.064}_{-0.018}\ M_\odot$ and $m_{\rm p} = 2.1^{+1.5}_{-0.4}\ M_\oplus$, respectively. Future high-resolution imaging observations with $HST$ or ELTs could distinguish between these two scenarios and help to reveal the planetary system properties in more detail., Comment: 30 pages, 11 figures, 5 tables, Accepted for publication in Astronomical Journal (AJ)

We reexamine high-magnification microlensing events in the previous data collected by the KMTNet survey with the aim of finding planetary signals that were not noticed before. In this work, we report the planetary system KMT-2018-BLG-1988L that was found from this investigation. The planetary signal appears as a deviation with $\lesssim 0.2$~mag from a single-lens light curve and lasted for about 6 hours. The deviation exhibits a pattern of a dip surrounded by weak bumps on both sides of the dip. The analysis of the lensing light curve indicates that the signal is produced by a low mass-ratio ($q\sim 4\times 10^{-5}$) planetary companion located near the Einstein ring of the host star. The mass of the planet, $M_{\rm planet}=6.8^{+4.7}_{-3.5}~M_\oplus$ and $5.6^{+3.8}_{-2.8}~M_\oplus$ for the two possible solutions, estimated from the Bayesian analysis indicates that the planet is in the regime of a super-Earth. The host of the planet is a disk star with a mass of $M_{\rm host} = 0.47^{+0.33}_{-0.25}~M_\odot$ and a distance of $D_{\rm L}= 4.2^{+1.8}_{-.14}$~kpc. KMT-2018-BLG-1988Lb is the seventeenth microlensing planet with a mass below the upper limit of a super-Earth. The fact that 14 out of 17 microlensing planets with masses $\lesssim 10~M_\oplus$ were detected during the last 5 years since the full operation of the KMTNet survey indicates that the KMTNet database is an important reservoir of very low-mass planets., Comment: 8 pages, 7 figures

We report the analysis of the microlensing event OGLE-2018-BLG-0677. A small feature in the light curve of the event leads to the discovery that the lens is a star-planet system. Although there are two degenerate solutions that could not be distinguished for this event, both lead to a similar planet-host mass ratio. We perform a Bayesian analysis based on a Galactic model to obtain the properties of the system and find that the planet corresponds to a super-Earth/sub-Neptune with a mass $M_{\mathrm{planet}} = {3.96}^{+5.88}_{-2.66}\mathrm{M_\oplus}$. The host star has a mass $ M_{\mathrm{host}} = {0.12}^{+0.14}_{-0.08}\mathrm{M_\odot}$. The projected separation for the inner and outer solutions are ${0.63}^{+0.20}_{-0.17}$~AU and ${0.72}^{+0.23}_{-0.19}$~AU respectively. At $\Delta\chi^2=\chi^2({\rm 1L1S})-\chi^2({\rm 2L1S})=46$, this is by far the lowest $\Delta\chi^2$ for any securely-detected microlensing planet to date, a feature that is closely connected to the fact that it is detected primarily via a "dip" rather than a "bump"., Comment: 15 page, 12 figures, Published in AJ

We report the discovery of KMT-2020-BLG-0414Lb, with a planet-to-host mass ratio $q_2 = 0.9$--$1.2 \times 10^{-5} = 3$--$4~q_{\oplus}$ at $1\sigma$, which is the lowest mass-ratio microlensing planet to date. Together with two other recent discoveries ($4 \lesssim q/q_\oplus \lesssim 6$), it fills out the previous empty sector at the bottom of the triangular $(\log s, \log q)$ diagram, where $s$ is the planet-host separation in units of the angular Einstein radius $\theta_{\rm E}$. Hence, these discoveries call into question the existence, or at least the strength, of the break in the mass-ratio function that was previously suggested to account for the paucity of very low-$q$ planets. Due to the extreme magnification of the event, $A_{\rm max}\sim 1450$ for the underlying single-lens event, its light curve revealed a second companion with $q_3 \sim 0.05$ and $|\log s_3| \sim 1$, i.e., a factor $\sim 10$ closer to or farther from the host in projection. The measurements of the microlens parallax $\pi_{\rm E}$ and the angular Einstein radius $\theta_{\rm E}$ allow estimates of the host, planet, and second companion masses, $(M_1, M_2, M_3) \sim (0.3M_{\odot}, 1.0M_{\oplus}, 17M_{J})$, the planet and second companion projected separations, $(a_{\perp,2}, a_{\perp,3}) \sim (1.5, 0.15~{\rm or}~15)$~au, and system distance $D_{\rm L} \sim 1$ kpc. The lens could account for most or all of the blended light ($I \sim 19.3$) and so can be studied immediately with high-resolution photometric and spectroscopic observations that can further clarify the nature of the system. The planet was found as part of a new program of high-cadence follow-up observations of high-magnification events. The detection of this planet, despite the considerable difficulties imposed by Covid-19 (two KMT sites and OGLE were shut down), illustrates the potential utility of this program., Comment: 23 pages, 5 figures; to be submitted to RAA

著者人数: 49名 (所属. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS): 鈴木, 大介), Number of authors: 49 (Affiliation. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS): Suzuki, Daisuke), Accepted: 2019-09-20, 資料番号: SA1190158000

Microlensing is a powerful and unique technique to probe isolated objects in the Galaxy. To study the characteristics of these interesting objects based on the microlensing method, measurement of the microlens parallax is required to determine the properties of the lens. Of the various methods to measure microlens parallax, the most robust way is to make simultaneous ground- and space-based observations, i.e., by measuring the space-based microlens parallax. However, space-based campaigns usually require "expensive" resources. Gould & Yee (2012) proposed an idea called the "cheap space-based microlens parallax" that can measure the lens-parallax using only $2$ or $3$ space-based observations of high-magnification events. This cost-effective observation strategy to measure microlens parallaxes could be used by space-borne telescopes to build a complete sample for studying isolated objects. This would enable a direct measurement of the mass function including both extremely low-mass objects and high-mass stellar remnants. However, to adopt this idea requires a test to check how it would work in actual situations. Thus, we present the first practical test of the idea using the high-magnification microlensing event OGLE-2016-BLG-1045, for which a subset of Spitzer observations fortuitously duplicate the prescription of Gould & Yee (2012). From the test, we confirm that the measurement of the lens-parallax adopting this idea has sufficient accuracy to determine the physical properties of the isolated lens., 7 Figures and 2 Tables, Accepted for publication in the ApJ

We present the analysis of the binary-lens microlensing event OGLE-2017-BLG-0537. The light curve of the event exhibits two strong caustic-crossing spikes among which the second caustic crossing was resolved by high-cadence surveys. It is found that the lens components with a mass ratio $\sim 0.5$ are separated in projection by $\sim 1.3\thetae$, where $\thetae$ is the angular Einstein radius. Analysis of the caustic-crossing part yields $\thetae=1.77\pm 0.16$~mas and a lens-source relative proper motion of $\mu =12.4\pm 1.1~{\rm mas}~{\rm yr}^{-1}$. The measured $\mu$ is the third highest value among the events with measured proper motions and $\sim 3$ times higher than the value of typical Galactic bulge events, making the event a strong candidate for follow-up observations to directly image the lens by separating it from the source. From the angular Einstein radius combined with the microlens parallax, it is estimated that the lens is composed of two main-sequence stars with masses $M_1\sim 0.4~M_\odot$ and $M_2\sim 0.2~M_\odot$ located at a distance of $D_{\rm L}\sim 1.2$~kpc. However, the physical lens parameters are not very secure due to the weak microlens-parallax signal, and thus we cross check the parameters by conducting a Bayesian analysis based on the measured Einstein radius and event timescale combined with the blending constraint. From this, we find that the physical parameters estimated from the Bayesian analysis are consistent with those based on the measured microlens parallax. Resolving the lens from the source can be done in about 5 years from high-resolution follow-up observations and this will provide a rare opportunity to test and refine the microlensing model., Comment: 9 pages, 6 figure, 2 tables

Mass measurements of gravitational microlenses require one to determine the microlens parallax $\pie$, but precise $\pie$ measurement, in many cases, is hampered due to the subtlety of the microlens-parallax signal combined with the difficulty of distinguishing the signal from those induced by other higher-order effects. In this work, we present the analysis of the binary-lens event OGLE-2017-BLG-0329, for which $\pie$ is measured with a dramatically improved precision using additional data from space-based $Spitzer$ observations. We find that while the parallax model based on the ground-based data cannot be distinguished from a zero-$\pie$ model at 2$\sigma$ level, the addition of the $Spitzer$ data enables us to identify 2 classes of solutions, each composed of a pair of solutions according to the well-known ecliptic degeneracy. It is found that the space-based data reduce the measurement uncertainties of the north and east components of the microlens-parallax vector $\pivec_{\rm E}$ by factors $\sim 18$ and $\sim 4$, respectively. With the measured microlens parallax combined with the angular Einstein radius measured from the resolved caustic crossings, we find that the lens is composed of a binary with components masses of either $(M_1,M_2)\sim (1.1,0.8)\ M_\odot$ or $\sim (0.4,0.3)\ M_\odot$ according to the two solution classes. The first solution is significantly favored but the second cannot be securely ruled out based on the microlensing data alone. However, the degeneracy can be resolved from adaptive optics observations taken $\sim 10$ years after the event., Comment: 9 pages, 4 tables, 6 figures

We report the discovery, via the microlensing method, of a new very-low-mass binary system. By combining measurements from Earth and from the Spitzer telescope in Earth-trailing orbit, we are able to measure the microlensing parallax of the event, and find that the lens likely consists of an $(12.0 \pm 0.6) M_{\rm J}$ + $(15.7 \pm 1.5) M_{\rm J}$ super-Jupiter / brown-dwarf pair. The binary is located at a distance of $(3.08 \pm 0.18)$ kpc in the Galactic Plane, and the components have a projected separation of $(0.43 \pm 0.03)$ AU. Two alternative solutions with much lower likelihoods are also discussed, an 8- and 6-$M_{\rm J}$ model and a 90- and 70-$M_{\rm J}$ model. Although disfavored at the 3-$\sigma$ and 5-$\sigma$ levels, these alternatives cannot be rejected entirely. We show how the more-massive of these models could be tested with future direct imaging., Comment: 23 pages, 7 figures, submitted to AAS Journals

We report the discovery of a giant planet in the OGLE-2017-BLG-1522 microlensing event. The planetary perturbations were clearly identified by high-cadence survey experiments despite the relatively short event timescale of $t_{\rm E} \sim 7.5$ days. The Einstein radius is unusually small, $\theta_{\rm E} = 0.065\,$mas, implying that the lens system either has very low mass or lies much closer to the microlensed source than the Sun, or both. A Bayesian analysis yields component masses $(M_{\rm host}, M_{\rm planet})=(46_{-25}^{+79}, 0.75_{-0.40}^{+1.26})~M_{\rm J}$ and source-lens distance $D_{\rm LS} = 0.99_{-0.54}^{+0.91}~{\rm kpc}$, implying that this is a brown-dwarf/Jupiter system that probably lies in the Galactic bulge, a location that is also consistent with the relatively low lens-source relative proper motion $\mu = 3.2 \pm 0.5~{\rm mas}~{\rm yr^{-1}}$. The projected companion-host separation is $0.59_{-0.11}^{+0.12}~{\rm AU}$, indicating that the planet is placed beyond the snow line of the host, i.e., $a_{sl} \sim 0.12~{\rm AU}$. Planet formation scenarios combined with the small companion-host mass ratio $q \sim 0.016$ and separation suggest that the companion could be the first discovery of a giant planet that formed in a protoplanetary disk around a brown dwarf host., Comment: 20 pages, 6 figures

著者人数: 110名(JAXA職員: 鈴木, 大介), Accepted: 2017-11-17, 資料番号: SA1170210000

We report two microlensing events, KMT-2017-BLG-1038 and KMT-2017-BLG-1146 that are caused by planetary systems. These events were discovered by KMTNet survey observations from the $2017$ bulge season. The discovered systems consist of a planet and host star with mass ratios, $5.3_{-0.4}^{+0.2} \times 10^{-3}$ and $2.0_{-0.1}^{+0.6} \times 10^{-3}$, respectively. Based on a Bayesian analysis assuming a Galactic model without stellar remnant hosts, we find that the planet, KMT-2017-BLG-1038Lb, is a super Jupiter-mass planet ($M_{\rm p}= 2.04_{-1.15}^{+2.02}\,M_{\rm J}$) orbiting a mid-M dwarf host ($M_{\rm h}= 0.37_{-0.20}^{+0.36}\, M_{\odot}$) that is located at $6.01_{-1.72}^{+1.27}$ kpc toward the Galactic bulge. The other planet, KMT-2017-BLG-1146Lb, is a sub Jupiter-mass planet ($M_{\rm p}= 0.71_{-0.42}^{+0.80}\,M_{\rm J}$) orbiting a mid-M dwarf host ($M_{\rm h}= 0.33_{-0.20}^{+0.36}\,M_{\odot}$) at a distance toward the Galactic bulge of $6.50_{-2.00}^{+1.38}$ kpc. Both are potentially gaseous planets that are beyond their hosts' snow lines. These typical microlensing planets will be routinely discovered by second-generation microlensing surveys, rapidly increasing the number of detections., Comment: 8 pages, 10 figures, 2 tables, accepted for publication in AJ

We analyze the binary gravitational microlensing event OGLE-2017-BLG-1130 (mass ratio q~0.45), the first published case in which the binary anomaly was only detected by the Spitzer Space Telescope. This event provides strong evidence that some binary signals can be missed by observations from the ground alone but detected by Spitzer. We therefore invert the normal procedure, first finding the lens parameters by fitting the space-based data and then measuring the microlensing parallax using ground-based observations. We also show that the normal four-fold space-based degeneracy in the single-lens case can become a weak eight-fold degeneracy in binary-lens events. Although this degeneracy is resolved in event OGLE-2017-BLG-1130, it might persist in other events., Comment: 14 pages, 5 figures

著者人数: 65名ほか (所属. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS): 鈴木, 大介), Accepted: 2018-03-27, 資料番号: SA1180046000

著者人数: 61名ほか (所属. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS): 鈴木, 大介), Accepted: 2018-05-02, 資料番号: SA1180047000

We present the analysis of OGLE-2016-BLG-0613, for which the lensing light curve appears to be that of a typical binary-lens event with two caustic spikes but with a discontinuous feature on the trough between the spikes. We find that the discontinuous feature was produced by a planetary companion to the binary lens. We find 4 degenerate triple-lens solution classes, each composed of a pair of solutions according to the well-known wide/close planetary degeneracy. One of these solution classes is excluded due to its relatively poor fit. For the remaining three pairs of solutions, the most-likely primary mass is about $M_1\sim 0.7\,M_\odot$ while the planet is a super-Jupiter. In all cases the system lies in the Galactic disk, about half-way toward the Galactic bulge. However, in one of these three solution classes, the secondary of the binary system is a low-mass brown dwarf, with relative mass ratios (1 : 0.03 : 0.003), while in the two others the masses of the binary components are comparable. These two possibilities can be distinguished in about 2024 when the measured lens-source relative proper motion will permit separate resolution of the lens and source., 14 pages, 9 figures

We present an analysis of microlensing event OGLE-2016-BLG-0693, based on the survey-only microlensing observations by the OGLE and KMTNet groups. In order to analyze the light curve, we consider the effects of parallax, orbital motion, and baseline slope, and also refine the result using a Galactic model prior. From the microlensing analysis, we find that the event is a binary composed of a low-mass brown dwarf 49+-20 M_J companion and a K- or G-dwarf host, which lies at a distance 5.0+-0.6 kpc toward the Galactic bulge. The projected separation between the brown dwarf and its host star is less than 5 AU, and thus it is likely that the brown dwarf companion is located in the brown dwarf desert., 27 pages, 7 figures, 4 tables, Accepted for publication in AJ

We report the analysis of the first resolved caustic-crossing binary-source microlensing event OGLE-2016-BLG-1003. The event is densely covered by the round-the-clock observations of three surveys. The light curve is characterized by two nested caustic-crossing features, which is unusual for typical caustic-crossing perturbations. From the modeling of the light curve, we find that the anomaly is produced by a binary source passing over a caustic formed by a binary lens. The result proves the importance of high-cadence and continuous observations, and the capability of second-generation microlensing experiments to identify such complex perturbations that are previously unknown. However, the result also raises the issues of the limitations of current analysis techniques for understanding lens systems beyond two masses and of determining the appropriate multiband observing strategy of survey experiments., 7 pages, 6 figures, Accepted for the publication in ApJ

We combine $Spitzer$ and ground-based KMTNet microlensing observations to identify and precisely measure an Earth-mass ($1.43^{+0.45}_{-0.32} M_\oplus$) planet OGLE-2016-BLG-1195Lb at $1.16^{+0.16}_{-0.13}$ AU orbiting a $0.078^{+0.016}_{-0.012} M_\odot$ ultracool dwarf. This is the lowest-mass microlensing planet to date. At $3.91^{+0.42}_{-0.46}$ kpc, it is the third consecutive case among the $Spitzer$ "Galactic distribution" planets toward the Galactic bulge that lies in the Galactic disk as opposed to the bulge itself, hinting at a skewed distribution of planets. Together with previous microlensing discoveries, the seven Earth-size planets orbiting the ultracool dwarf TRAPPIST-1, and the detection of disks around young brown dwarfs, OGLE-2016-BLG-1195Lb suggests that such planets might be common around ultracool dwarfs. It therefore sheds light on the formation of both ultracool dwarfs and planetary systems at the limit of low-mass protoplanetary disks., Comment: 19 pages, 4 figures, 2 tables. Main difference from previous version is new CMD, since previous patch was too small to locate clump properly. Accepted for publication in ApJL

We detect a cold, terrestrial planet in a binary-star system using gravitational microlensing. The planet has low mass (2 Earth masses) and lies projected at $a_{\perp,ph}$ ~ 0.8 astronomical units (AU) from its host star, similar to the Earth-Sun distance. However, the planet temperature is much lower, T, Published in Science, Main and supplementary material combined

We report the discovery of a binary composed of two brown dwarfs, based on the analysis of the microlensing event OGLE-2016-BLG-1469. Thanks to detection of both finite-source and microlens-parallax effects, we are able to measure both the masses $M_1\sim 0.05\ M_\odot$, $M_2\sim 0.01\ M_\odot$, and distance $D_{\rm L} \sim 4.5$ kpc, as well as the projected separation $a_\perp \sim 0.33$ au. This is the third brown-dwarf binary detected using the microlensing method, demonstrating the usefulness of microlensing in detecting field brown-dwarf binaries with separations less than 1 au., Comment: 8 pages, 8 figures

A long-standing paradigm in astrophysics is that collisions- or mergers- of two neutron stars (NSs) form highly relativistic and collimated outflows (jets) powering gamma-ray bursts (GRBs) of short (< 2 s) duration. However, the observational support for this model is only indirect. A hitherto outstanding prediction is that gravitational wave (GW) events from such mergers should be associated with GRBs, and that a majority of these GRBs should be off-axis, that is, they should point away from the Earth. Here we report the discovery of the X-ray counterpart associated with the GW event GW170817. While the electromagnetic counterpart at optical and infrared frequencies is dominated by the radioactive glow from freshly synthesized r-process material in the merger ejecta, known as kilonova, observations at X-ray and, later, radio frequencies exhibit the behavior of a short GRB viewed off-axis. Our detection of X-ray emission at a location coincident with the kilonova transient provides the missing observational link between short GRBs and GWs from NS mergers, and gives independent confirmation of the collimated nature of the GRB emission., 38 pages, 10 figures, Nature, in press

著者人数: 86名 (JAXA職員: 鈴木, 大介), Accepted: 2017-07-14, 資料番号: SA1170116000

著者人数: 55名 (JAXA職員: 鈴木, 大介), Accepted: 2017-08-08, 資料番号: SA1170115000

We analyze the single microlensing event OGLE-2015-BLG-1482 simultaneously observed from two ground-based surveys and from \textit{Spitzer}. The \textit{Spitzer} data exhibit finite-source effects due to the passage of the lens close to or directly over the surface of the source star as seen from \textit{Spitzer}. Such finite-source effects generally yield measurements of the angular Einstein radius, which when combined with the microlens parallax derived from a comparison between the ground-based and the \textit{Spitzer} light curves, yields the lens mass and lens-source relative parallax. From this analysis, we find that the lens of OGLE-2015-BLG-1482 is a very low-mass star with the mass $0.10 \pm 0.02 \ M_\odot$ or a brown dwarf with the mass $55\pm 9 \ M_{J}$, which are respectively located at $D_{\rm LS} = 0.80 \pm 0.19\ \textrm{kpc}$ and $ D_{\rm LS} = 0.54 \pm 0.08\ \textrm{kpc}$, and thus it is the first isolated low-mass microlens that has been decisively located in the Galactic bulge. The fundamental reason for the degeneracy is that the finite-source effect is seen only in a single data point from \textit{Spitzer} and this single data point gives rise to two solutions for $\rho$. Because the $\rho$ degeneracy can be resolved only by relatively high cadence observations around the peak, while the \textit{Spitzer} cadence is typically $\sim 1\,{\rm day}^{-1}$, we expect that events for which the finite-source effect is seen only in the \textit{Spitzer} data may frequently exhibit this $\rho$ degeneracy. For OGLE-2015-BLG-1482, the relative proper motion of the lens and source for the low-mass star is $\mu_{\rm rel} = 9.0 \pm 1.9\ \textrm{mas yr$^{-1}$}$, while for the brown dwarf it is $5.5 \pm 0.5\ \textrm{mas yr$^{-1}$}$. Hence, the degeneracy can be resolved within $\sim 10\ \rm yrs$ from direct lens imaging by using next-generation instruments with high spatial resolution., Comment: 18 pages, 4 figures, accepted for publication in ApJ

We report the discovery of an extrasolar planet detected from the combined data of a microlensing event OGLE-2015-BLG-0051/KMT-2015-BLG-0048 acquired by two microlensing surveys. Despite that the short planetary signal occurred in the very early Bulge season during which the lensing event could be seen for just about an hour, the signal was continuously and densely covered. From the Bayesian analysis using models of the mass function, matter and velocity distributions combined with the information of the angular Einstein radius, it is found that the host of the planet is located in the Galactic bulge. The planet has a mass $0.72_{-0.07}^{+0.65}\ M_{\rm J}$ and it is orbiting a low-mass M-dwarf host with a projected separation $d_\perp=0.73 \pm 0.08$ AU. The discovery of the planet demonstrates the capability of the current high-cadence microlensing lensing surveys in detecting and characterizing planets., 7 pages, 6 figures

Spitzer microlensing parallax observations of OGLE-2015-BLG-1212 decisively breaks a degeneracy between planetary and binary solutions that is somewhat ambiguous when only ground-based data are considered. Only eight viable models survive out of an initial set of 32 local minima in the parameter space. These models clearly indicate that the lens is a stellar binary system possibly located within the bulge of our Galaxy, ruling out the planetary alternative. We argue that several types of discrete degeneracies can be broken via such space-based parallax observations., Comment: 27 pages, 6 figures, accepted by ApJ

We report results from a 1 week multi-wavelength campaign to monitor the BL Lac object S5 0716+714 (on December 9-16, 2009). In the radio bands the source shows rapid (~ (0.5-1.5) day) intra-day variability with peak amplitudes of up to ~ 10 %. The variability at 2.8 cm leads by about 1 day the variability at 6 cm and 11 cm. This time lag and more rapid variations suggests an intrinsic contribution to the source's intraday variability at 2.8 cm, while at 6 cm and 11 cm interstellar scintillation (ISS) seems to predominate. Large and quasi-sinusoidal variations of ~ 0.8 mag were detected in the V, R and I-bands. The X-ray data (0.2-10 keV) do not reveal significant variability on a 4 day time scale, favoring reprocessed inverse-Compton over synchrotron radiation in this band. The characteristic variability time scales in radio and optical bands are similar. A quasi-periodic variation (QPO) of 0.9 - 1.1 days in the optical data may be present, but if so it is marginal and limited to 2.2 cycles. Cross-correlations between radio and optical are discussed. The lack of a strong radio-optical correlation indicates different physical causes of variability (ISS at long radio wavelengths, source intrinsic origin in the optical), and is consistent with a high jet opacity and a compact synchrotron component peaking at ~= 100 GHz in an ongoing very prominent flux density outburst. For the campaign period, we construct a quasi-simultaneous spectral energy distribution (SED), including gamma-ray data from the FERMI satellite. We obtain lower limits for the relativistic Doppler-boosting of delta >= 12-26, which for a BL\,Lac type object, is remarkably high.

The microlensing event OGLE-2008-BLG-510 is characterised by an evident asymmetric shape of the peak, promptly detected by the ARTEMiS system in real time. The skewness of the light curve appears to be compatible both with binary-lens and binary-source models, including the possibility that the lens system consists of an M dwarf orbited by a brown dwarf. The detection of this microlensing anomaly and our analysis demonstrates that: 1) automated real-time detection of weak microlensing anomalies with immediate feedback is feasible, efficient, and sensitive, 2) rather common weak features intrinsically come with ambiguities that are not easily resolved from photometric light curves, 3) a modelling approach that finds all features of parameter space rather than just the `favourite model' is required, and 4) the data quality is most crucial, where systematics can be confused with real features, in particular small higher-order effects such as orbital motion signatures. It moreover becomes apparent that events with weak signatures are a silver mine for statistical studies, although not easy to exploit. Clues about the apparent paucity of both brown-dwarf companions and binary-source microlensing events might hide here.

We analyze the combined Spitzer and ground-based data for OGLE-2017-BLG-1140 and show that the event was generated by a Jupiter-class $(m_p\simeq 1.6\,M_{\rm jup})$ planet orbiting a mid-late M dwarf $(M\simeq 0.2\,M_\odot)$ that lies $D_{LS}\simeq 1.0\,\mathrm{kpc}$ in the foreground of the microlensed, Galactic-bar, source star. The planet-host projected separation is $a_\perp \simeq 1.0\,\mathrm{au}$, i.e., well-beyond the snow line. By measuring the source proper motion ${\mathbf{\mu}}_s$ from ongoing, long-term OGLE imaging, and combining this with the lens-source relative proper motion ${\mathbf{\mu}}_\mathrm{rel}$ derived from the microlensing solution, we show that the lens proper motion ${\mathbf{\mu}}_l={\mathbf{\mu}}_\mathrm{rel} + {\mathbf{\mu}}_s$ is consistent with the lens lying in the Galactic disk, although a bulge lens is not ruled out. We show that while the Spitzer and ground-based data are comparably well fitted by planetary (i.e., binary-lens, 2L1S) models and by binary-source (1L2S) models, the combination of Spitzer and ground-based data decisively favor the planetary model. This is a new channel to resolve the 2L1S/1L2S degeneracy, which can be difficult to break in some cases., Comment: Revised version accepted for publication in The Astronomical Journal

The blazar AO 0235+164 was claimed to show a quasi-periodic behaviour in the radio and optical bands. Moreover, an extra emission component contributing to the UV and soft X-ray flux was detected, whose nature is not yet clear. A predicted optical outburst was observed in late 2006/early 2007. We here present the radio-to-optical WEBT light curves during the outburst, together with UV data acquired by Swift in the same period. We found the optical outburst to be as strong as the big outbursts of the past: starting from late September 2006, a brightness increase of 5 mag led to the outburst peak in February 19-21, 2007. We also observed an outburst at mm and then at cm wavelengths, with an increasing time delay going toward lower frequencies during the rising phase. Cross-correlation analysis indicates that the 1 mm and 37 GHz flux variations lagged behind the R-band ones by about 3 weeks and 2 months, respectively. These short time delays suggest that the corresponding jet emitting regions are only slightly separated and/or misaligned. In contrast, during the outburst decreasing phase the flux faded contemporaneously at all cm wavelengths. This abrupt change in the emission behaviour may suggest the presence of some shutdown mechanism of intrinsic or geometric nature. The behaviour of the UV flux closely follows the optical and near-IR one. By separating the synchrotron and extra component contributions to the UV flux, we found that they correlate, which suggests that the two emissions have a common origin., Comment: 9 pages, 7 figures, in press for Astronomy and Astrophysics

We report the discovery of a high mass-ratio planet $q=0.012$, i.e., 13 times higher than the Jupiter/Sun ratio. The host mass is not presently measured but can be determined or strongly constrained from adaptive optics imaging. The planet was discovered in a small archival study of high-magnification events in pure-survey microlensing data, which was unbiased by the presence of anomalies. The fact that it was previously unnoticed may indicate that more such planets lie in archival data and could be discovered by similar systematic study. In order to understand the transition from predominantly survey+followup to predominately survey-only planet detections, we conduct the first analysis of these detections in the observational $(s,q)$ plane. Here $s$ is projected separation in units of the Einstein radius. We find some evidence that survey+followup is relatively more sensitive to planets near the Einstein ring, but that there is no statistical difference in sensitivity by mass ratio., Comment: 10 pages, 1 table, 10 figures

Aims. Most hot Jupiters are expected to spiral in toward their host stars because the angular momentum of the orbital motion is transferred to the stellar spin. Their orbits can also precess as a result of planet-star interactions. Calculations show that both effects might be detected for the very-hot exoplanet WASP-12 b using the method of precise transit-timing over a time span of about 10 yr. Methods. We acquired new precise light curves for 29 transits of WASP-12 b, spannning four observing seasons from November 2012 to February 2016. New mid-transit times, together with those from the literature, were used to refine the transit ephemeris and analyze the timing residuals. Results. We find that the transit times of WASP-12 b do not follow a linear ephemeris with a 5σ confidence level. They may be approximated with a quadratic ephemeris that gives a change rate in the orbital period of (-2.56 ± 0.40) × 10 s yr. The tidal quality parameter of the host star was found to be equal to 2.5 × 10, which is similar to theoretical predictions for Sun-like stars. We also considered a model in which the observed timing residuals are interpreted as a result of the apsidal precession. We find, however, that this model is statistically less probable than the orbital decay., G.M. acknowledges funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement number RG226604 (OPTICON). G.M. and G.N. acknowledge the financial support from the Polish Ministry of Science and Higher Education through the Iuventus Plus grant and IP2011 031971. MF was supported by the Spanish grant AYA2014-54348-C3-1-R. T.C.H., J.W.L. & C.U.L. acknowledge travel support from KASI grant number 2013-9-400-00 and astronomical observations were carried out during a KRCF Young Scientist Research Fellowship Program. D.K. acknowledges the financial support from Shumen University, project RD 08-81. A part of this paper is the result of the exchange and joint research project Spectral and photometric studies of variable stars between the Polish and Bulgarian Academies of Sciences. The data presented here were obtained in part with ALFOSC, which is provided by the Instituto de Astrofisica de Andalucia (IAA) under a joint agreement with the University of Copenhagen and NOTSA.

In the process of analyzing an observed light curve, one often confronts various scenarios that can mimic the planetary signals causing difficulties in the accurate interpretation of the lens system. In this paper, we present the analysis of the microlensing event OGLE-2016-BLG-0733. The light curve of the event shows a long-term asymmetric perturbation that would appear to be due to a planet. From the detailed modeling of the lensing light curve, however, we find that the perturbation originates from the binarity of the source rather than the lens. This result demonstrates that binary sources with roughly equal-luminosity components can mimic long-term perturbations induced by planets with projected separations near the Einstein ring. The result also represents the importance of the consideration of various interpretations in planet-like perturbations and of high-cadence observations for ensuring the unambiguous detection of the planet., Comment: 7 pages, 1 tables, 7 figures, Accepted to AJ

The Angstrom Project is using a distributed network of two-meter class telescopes to conduct a high cadence pixel-lensing survey of the bulge of the Andromeda Galaxy (M31). With the expansion of global telescope network, the detection efficiency of pixel-lensing surveys is rapidly improving. In this paper, we estimate the detection rate of binary lens events expected from high-cadence pixel-lensing surveys toward M31 such as the Angstrom Project based on detailed simulation of events and application of realistic observational conditions. Under the conservative detection criteria that only high signal-to-noise caustic-crossing events with long enough durations between caustic crossings can be firmly identified as binary lens events, we estimate that the rate would be $\Gamma_{\rm b}\sim (7-15)f_{\rm b}(N/50)$ per season, where $f_{\rm b}$ is the fraction of binaries with projected separations of $10^{-3} {\rm AU}, Comment: 6 pages, 4 figures

We present photometric results for four new variable stars discovered in the vicinity of the ZZ Ceti-type pulsating white dwarf BR Cam. Observations were performed on 5 nights in November 2003 using the 1.8m telescope at Bohyunsan Optical Astronomy Observatory with no filter, on 3 nights in December 2003 using the 0.61m telescope at Sobaeksan Optical Astronomy Observatory with V, I filters, and on 3 nights in October 2004 using the 1.0m telescope at Mt. Lemmon Optical Astronomy Observatory with V, I filters. We estimated their periods from the phase-match technique for one eclipsing binary and the multiple frequency analysis for three pulsating stars. By considering the light curve shape, period and amplitude difference between two passbands, we classified the objects by their variability types as follows: V1 (USNO-A2.0 1425-05691757) is a W UMa-type eclipsing binary with an orbital period of ; V2 (USNO-A2.0 1425-05703335) is a multi-periodic Set-type pulsating star with a dominant period of ; V3 (USNO-A2.0 1425-05699659) is also a Set-type pulsating star with a period of ; and V 4 (USNO-A2.0 1425-05707705) is a RR Lyr-type pulsating star with a period of .

We present new multiband photometric results for 29 ROTSE-I δ Scuti stars and a Fourier decomposition light-curve analysis in order to reclassify their variability types. For the classification between eclipsing and pulsating stars, we use the criterion that pulsating stars have larger amplitude differences between passbands than eclipsing binaries, because the brightness changes in pulsating stars are mainly due to variations in temperature. From this investigation, we find that 24 of our 29 observation targets are W Ursae Majoris type eclipsing binaries. Fourier analysis of the data for all 91 ROTSE-I δ Scuti stars shows that the phase parameters 21 of the high-amplitude δ Scuti variables identified in this study are concentrated around 4.0. This high-probability area characterized by 21 is in good agreement with the finding from OGLE data. Our results suggest that most of the ROTSE-I δ Scuti stars located outside the high-probability area are in fact W UMa type eclipsing binaries.

We present new photometric results of the Algol-type semidetached eclipsing binary AB Per which was recently discovered to have a Delta Scuti pulsating component.

We present multi-passband CCD photometry of 20 ROTSE-I Scuti type pulsating stars and 1 RR Lyrae star to re- classify their variable types using the comparison of amplitudes between V and I passbands. For the re-classification, we used a criterion that pulsating stars have larger amplitude dierences between passbands than eclipsing binaries because brightness changes of pulsating stars are mainly due to the temperature variations. As a result, only six stars were re-confirmed as Scuti variables and thirteen stars turned out to be W UMa type eclipsing binaries. The other two stars were identified as one cataclysmic variable and one non-variable, respectively. Our results suggest that a number of ROTSE-I Scuti type stars, which do not show typical pulsating light curves of high amplitude Scuti stars, are W UMa type eclipsing binaries.

We present the analysis of the gravitational microlensing event OGLE-2013-BLG-0102. The light curve of the event is characterized by a strong short-term anomaly superposed on a smoothly varying lensing curve with a moderate magnification $A_{\rm max}\sim 1.5$. It is found that the event was produced by a binary lens with a mass ratio between the components of $q = 0.13$ and the anomaly was caused by the passage of the source trajectory over a caustic located away from the barycenter of the binary. From the analysis of the effects on the light curve due to the finite size of the source and the parallactic motion of the Earth, the physical parameters of the lens system are determined. The measured masses of the lens components are $M_{1} = 0.096 \pm 0.013~M_{\odot}$ and $M_{2} = 0.012 \pm 0.002~M_{\odot}$, which correspond to near the hydrogen-burning and deuterium-burning mass limits, respectively. The distance to the lens is $3.04 \pm 0.31~{\rm kpc}$ and the projected separation between the lens components is $0.80 \pm 0.08~{\rm AU}$., 6 figures, 2 tables, ApJ submitted

Algol ($\beta$ Persei) is the prototypical semi-detached eclipsing binary and a hierarchical triple system. From 2006 to 2010 we obtained 121 high-resolution and high-S/N \'{e}chelle spectra of this object. Spectral disentangling yields the individual spectra of all three stars, and greatly improved elements both the inner and outer orbits. We find masses of $M_{\rm A} = 3.39\pm0.06$ M$_\odot$, $M_{\rm B} = 0.770\pm0.009$ M$_\odot$ and $M_{\rm C} = 1.58\pm0.09$ M$_\odot$. The disentangled spectra also give the light ratios between the components in the $B$ and $V$ bands. Atmospheric parameters for the three stars are determined, including detailed elemental abundances for Algol A and Algol C. We find the following effective temperatures: $T_{\rm A} = 12\,550\pm120$ K, $T_{\rm B} = 4900\pm300$ K and $T_{\rm C} = 7550\pm250$ K. The projected rotational velocities are $v_{\rm A} \sin i_{\rm A} = 50.8\pm0.8$ km/s, $v_{\rm B} \sin i_{\rm B} = 62\pm2$ km/s and $v_{\rm C} \sin i_{\rm C} = 12.4\pm0.6$ km/s. This is the first measurement of the rotational velocity for Algol B, and confirms that it is synchronous with the orbital motion. The abundance patterns of components A and C are identical to within the measurement errors, and are basically solar. They can be summarised as mean metal abundances: [M/H]$_{\rm A} = -0.03\pm0.08$ and [M/H]$_{\rm C} = 0.04\pm0.09$. A carbon deficiency is confirmed for Algol A, with tentative indications for a slight overabundance of nitrogen. The ratio of their abundances is (C/N)$_{\rm A} = 2.0\pm0.4$, half of the solar value of (C/N)$_{\odot} = 4.0\pm0.7$. The new results derived in this study, including detailed abundances and metallicities, will enable tight constraints on theoretical evolutionary models for this complex system., Comment: Accepted for publication in MNRAS

We present the analysis of MOA-2007-BLG-197Lb, the first brown dwarf companion to a Sun-like star detected through gravitational microlensing. The event was alerted and followed-up photometrically by a network of telescopes from the PLANET, MOA, and uFUN collaborations, and observed at high angular resolution using the NaCo instrument at the VLT. From the modelling of the microlensing light curve, we derived the binary lens separation in Einstein radius units (s~1.13) and a mass ratio of (4.732+/-0.020)x10^{-2}. Annual parallax, lens orbital motion and finite source effects were included in the models. To recover the lens system's physical parameters, we combined the resulting light curve best-fit parameters with (J,H,Ks) magnitudes obtained with VLT NaCo and calibrated using IRSF and 2MASS data. We derived a lens total mass of 0.86+/-0.04 Msun and a lens distance of 4.2+/-0.3 kpc. We find that the companion of MOA-2007-BLG-197L is a brown dwarf of 41+/-2 Mjup observed at a projected separation of 4.3+/-0.1 AU, and orbits a 0.82+/-0.04 Msun G-K dwarf star. We study the statistical properties of this population of brown dwarfs detected by microlensing, transit, radial velocity, and direct imaging (most of these objects orbit solar-type stars), and we performed a two-dimensional, non-parametric probability density distribution fit to the data, which draws a structured brown dwarf landscape. We confirm the existence of a region that is strongly depleted in objects at short periods and intermediate masses (P500 d) and high masses (M>50 Mjup). While these data provide important clues on mechanisms of brown dwarfs formation, more data are needed to establish their relative importance, in particular as a function of host star mass., 16 pages, 12 figures

We present microlensing planet OGLE-2017-BLG-0173Lb, with planet-host mass ratio either $q\simeq 2.5\times 10^{-5}$ or $q\simeq 6.5\times 10^{-5}$, the lowest or among the lowest ever detected. The planetary perturbation is strongly detected, $\Delta\chi^2\sim 10,000$, because it arises from a bright (therefore, large) source passing over and enveloping the planetary caustic: a so-called "Hollywood" event. The factor $\sim 2.5$ offset in $q$ arises because of a previously unrecognized discrete degeneracy between Hollywood events in which the caustic is fully enveloped and those in which only one flank is enveloped, which we dub "Cannae" and "von Schlieffen", respectively. This degeneracy is "accidental" in that it arises from gaps in the data. Nevertheless, the fact that it appears in a $\Delta\chi^2=10,000$ planetary anomaly is striking. We present a simple formalism to estimate the sensitivity of other Hollywood events to planets and show that they can lead to detections close to, but perhaps not quite reaching, the Earth/Sun mass ratio of $3\times 10^{-6}$. This formalism also enables an analytic understanding of the factor $\sim 2.5$ offset in $q$ between the Cannae and von Schlieffen solutions. The Bayesian estimates for the host-mass, system distance, and planet-host projected separation are $M=0.39^{+0.40}_{-0.24}\,M_\odot$, $D_L=4.8^{+1.5}_{-1.8}\,\kpc$, and $a_\perp=3.8\pm 1.6\,\au$. The two estimates of the planet mass are $m_p=3.3^{+3.8}_{-2.1}\,M_\oplus$ and $m_p=8^{+11}_{-6}\,M_\oplus$. The measured lens-source relative proper motion $\mu=6\,\masyr$ will permit imaging of the lens in about 15 years or at first light on adaptive-optics imagers on next-generation telescopes. These will allow to measure the host mass but probably cannot resolve the planet-host mass-ratio degeneracy., Comment: 30 pages, 9 figures, AJ in press