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Korea Astronomy & Space Science Institute (KASI) has installed a 1-m robotic telescope at Mt. Lemmon, AZ, in collaboration
with a company, Astronomical Consultants & Equipment, Inc (ACE). The telescope system is totally designed to make fully robotic
observations, and can be operated in both interactive and unattended robotic modes. The telescope i...
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... (i) The first run of time-series observations of NGC 2126 was carried out during eight nights using the 1.0-m robotic telescope (Han et al. 2005) at the Mount Lemmon Optical Astronomy Observatory (LOAO) in Arizona which is operated by the Korea Astronomy and Space Science Institute (KASI) using remote control from Korea via a network connection. The detector was 2k × 2k CCD camera. ...
We present the results of an analysis of photometric time-series observations for NGC 2126 acquired during the years 2004, 2013 and 2015. NGC 2126 is an intermediate-age open cluster which has a population of stars inside the δ Scuti instability strip. The main purpose is to search for new variable stars, to study their light curves and pulsation spectra. Eleven variables are reported, two of which are new discoveries, eight are pulsating and three eclipsing binary stars, one of which has a pulsating component (V551 Aur). Our ten times of light minimum along with others compiled from the literature were used to revise the orbital period of V551 Aur: Porb = 1.1731752(8) d. The Wilson-Devinney technique was used to analyse its light curves and to determine a new set of the system’s parameters. We found a single pulsation period Ppul = 0.12964977(3) d in the residuals which lies near the 9th harmonic of the orbital period. We determined the accurate value of high proper motion star LHS 1809 as μαcos δ=115.7±0.1 mas/yr and μδ = −823.7 ± 0.1 mas/yr. From the construction of the colour-magnitude diagram, we estimated the physical parameters of the cluster. We found that the shape of the colour-magnitude diagram at the turn-off point is well reproduced with an isochrone with log(t) of 9.1±0.1 yr, metallicity of 0.019, E(B − V) = 0.27±0.01 mag and (m − M)0 =10.80±0.05 mag.
The discovery of a kilonova associated with the GW170817 binary neutron star merger had far-reaching implications for our understanding of several open questions in physics and astrophysics. Unfortunately, since then, only one robust binary neutron star merger was detected through gravitational waves, GW190425, and no electromagnetic counterpart was identified for it. We analyze all reported electromagnetic followup observations of GW190425 and find that while the gravitational-wave localization uncertainty was large, most of the 90% probability region could have been covered within hours had the search been coordinated. Instead, more than 5 days after the merger, the uncoordinated search covered only 50% of the probability, with some areas observed over 100 times, and some never observed. We further show that, according to some models, it would have been possible to detect the GW190425 kilonova, despite the larger distance and higher component masses compared to GW170817. These results emphasize the importance of coordinating followup of gravitational-wave events, not only to avoid missing future kilonovae, but also to discover them early. Such coordination, which is especially important given the rarity of these events, can be achieved with the Treasure Map, a tool developed specifically for this purpose.
Context . Gamma-ray bursts (GRBs) are ideal probes of the Universe at high redshift (ɀ), pinpointing the locations of the earliest star-forming galaxies and providing bright backlights with simple featureless power-law spectra that can be used to spectrally fingerprint the intergalactic medium and host galaxy during the period of reionization. Future missions such as Gamow Explorer (hereafter Gamow) are being proposed to unlock this potential by increasing the rate of identification of high-ɀ (ɀ > 5) GRBs in order to rapidly trigger observations from 6 to 10 m ground telescopes, the James Webb Space Telescope (JWST), and the upcoming Extremely Large Telescopes (ELTs).
Aims . Gamow was proposed to the NASA 2021 Medium-Class Explorer (MIDEX) program as a fast-slewing satellite featuring a wide-field lobster-eye X-ray telescope (LEXT) to detect and localize GRBs with arcminute accuracy, and a narrow-field multi-channel photo-ɀ infrared telescope (PIRT) to measure their photometric redshifts for > 80% of the LEXT detections using the Lyman- α dropout technique. We use a large sample of observed GRB afterglows to derive the PIRT sensitivity requirement.
Methods . We compiled a complete sample of GRB optical–near-infrared (optical-NIR) afterglows from 2008 to 2021, adding a total of 66 new afterglows to our earlier sample, including all known high-ɀ GRB afterglows. This sample is expanded with over 2837 unpublished data points for 40 of these GRBs. We performed full light-curve and spectral-energy-distribution analyses of these after-glows to derive their true luminosity at very early times. We compared the high-ɀ sample to the comparison sample at lower redshifts. For all the light curves, where possible, we determined the brightness at the time of the initial finding chart of Gamow, at different high redshifts and in different NIR bands. This was validated using a theoretical approach to predicting the afterglow brightness. We then followed the evolution of the luminosity to predict requirements for ground- and space-based follow-up. Finally, we discuss the potential biases between known GRB afterglow samples and those to be detected by Gamow.
Results . We find that the luminosity distribution of high-ɀ GRB afterglows is comparable to those at lower redshift, and we therefore are able to use the afterglows of lower-ɀ GRBs as proxies for those at high ɀ. We find that a PIRT sensitivity of 15 µJy (21 mag AB) in a 500 s exposure simultaneously in five NIR bands within 1000 s of the GRB trigger will meet the Gamow mission requirements. Depending on the ɀ and NIR band, we find that between 75% and 85% of all afterglows at ɀ > 5 will be recovered by Gamow at 5 σ detection significance, allowing the determination of a robust photo-ɀ. As a check for possible observational biases and selection effects, we compared the results with those obtained through population-synthesis models, and find them to be consistent.
Conclusions . Gamow and other high-ɀ GRB missions will be capable of using a relatively modest 0.3 m onboard NIR photo-ɀ telescope to rapidly identify and report high-ɀ GRBs for further follow-up by larger facilities, opening a new window onto the era of reionization and the high-redshift Universe.
We report on the first open-use based Atacama Large Millimeter/submm Array (ALMA) 345-GHz observation for the late afterglow phase of GRB131030A. The ALMA observation constrained a deep limit at 17.1 d for the afterglow and host galaxy. We also identified a faint submillimeter source (ALMAJ2300-0522) near the GRB131030A position. The deep limit at 345 GHz and multifrequency observations obtained using {\it Swift} and RATIR yielded forward shock modeling with a two-dimensional relativistic hydrodynamic jet simulation and described X-ray excess in the afterglow. The excess was inconsistent with the synchrotron self-inverse Compton radiation from the forward shock. The host galaxy of GRB131030A and optical counterpart of ALMAJ2300-0522 were also identified in the SUBARU image. Based on the deep ALMA limit for the host galaxy, the 3-$\sigma$ upper limits of IR luminosity and the star formation rate (SFR) is estimated as $L_{IR}<1.11\times10^{11} L_{\odot}$ and SFR$<18.7$ ($M_{\odot}$~yr$^{-1}$), respectively. Although the separation angle from the burst location (3.5 arcsec) was rather large, ALMAJ2300-0522 may be one component of the GRB131030A host galaxy, according to previous host galaxy cases.
We present multi-wavelength observations of a typical long duration GRB 120326A at z = 1.798, including rapid observations using a Submillimeter Array (SMA) and a comprehensive monitoring in the X-ray and optical. The SMA observation provided the fastest detection to date among seven submillimeter afterglows at 230 GHz. The prompt spectral analysis, using Swift and Suzaku, yielded a spectral peak energy of keV and an equivalent isotropic energy of E
iso as erg. The temporal evolution and spectral properties in the optical were consistent with the standard forward shock synchrotron with jet collimation (669 ± 016). The forward shock modeling, using a two-dimensional relativistic hydrodynamic jet simulation, was also determined by the reasonable burst explosion and the synchrotron radiation parameters for the optical afterglow. The X-ray light curve showed no apparent jet break and the temporal decay index relation between the X-ray and optical (αo – αX
= –1.45 ± 0.10) indicated different radiation processes in each of them. Introducing synchrotron self-inverse Compton radiation from reverse shock is a possible solution, and the detection and slow decay of the afterglow in submillimeter supports that this is a plausible idea. The observed temporal evolution and spectral properties, as well as forward shock modeling parameters, enabled us to determine reasonable functions to describe the afterglow properties. Because half of the events share similar properties in the X-ray and optical as the current event, GRB 120326A will be a benchmark with further rapid follow-ups, using submillimeter instruments such as an SMA and the Atacama Large Millimeter/submillimeter Array.
We present multi-band results for GRB071010B based on Swift, Suzaku, and ground-based optical observations. This burst is an ideal target to evaluate the robustness of the E srcpeak – E iso and E srcpeak – E γ relations, whose studies have been in stagnation due to the lack of the combined estimation of E srcpeak and long-term optical monitoring. The joint prompt spectral fitting using Swift/Burst Alert Telescope and Suzaku/Wide-band All-sky Monitor data yielded the spectral peak energy as E srcpeak of 86.5+6.4–6.3 keV and E iso of 2.25+0.19–0.16× 1052 erg with z = 0.947. The optical afterglow light curve is well fitted by a simple power law with temporal index α = –0.60 ± 0.02. The lower limit of temporal break in the optical light curve is 9.8 days. Our multi-wavelength analysis reveals that GRB071010B follows E srcpeak – E iso but violates the E srcpeak – E γ and E iso – E srcpeak – t srcjet at more than the 3σ level.
We outline our GRB afterglow observation program using the 1-m telescope
at Mt. Lemmon Optical Astronomy Observatory (LOAO), and report the first
observations of the GRB afterglows. During the 2007B semester, we
performed follow-up imaging obsrevations of 6 GRBs, and succeeded in
detecting four GRB afterglows (GRB 071010B, GRB 071018, GRB 071020, and
GRB 071025) while placing useful upper limits on the light curves of the
other GRBs. Among the observed events, we find that three events are
special and interesting. GRB 071010B has a light curve which has an
unusually long jet break time of 11.8 days. For GRB 071025, its red
R-I~(˜ 2) color suggests that it is likely to be at z˜5.
GRB 071020 has a light curve which shows a clear brightening at 0.3-1
days after the burst, where our LOAO data play a crucial role by
providing an unambiguous evidence for the brightening. These are the
first successful detections of GRB afterglows by a facility owned and
operated by a Korean institution, demonstrating the usefulness of the
1-m telescope for transient phenomena such as GRBs up to very high
redshift.
New CCD photometric observations of the eclipsing system AR Boo were obtained from 2006 February to 2008 April. The star's photometric properties are derived from detailed studies of the period variability and of all available light curves. We find that over about 56 yr the orbital period of the system has varied due to a combination of an upward parabola and a sinusoid rather than in a monotonic fashion. Mass transfer from the less massive primary to the more massive secondary component is likely responsible for at least a significant part of the secular period change. The cyclical variation with a period of 7.57 yr and a semi-amplitude of 0.0015 d can be produced either by a light-travel-time effect due to an unseen companion with a scaled mass of M
3sin i
3 = 0.081 M
☉ or by a magnetic period modulation in the secondary star. Historical light curves of AR Boo, as well as our own, display season-to-season light variability, which are best modeled by including both a cool spot and a hot one on the secondary star. We think that the spots express magnetic dynamo-related activity and offer limited support for preferring the magnetic interpretation of the 7.57 yr cycle over the third-body interpretation. Our solutions confirm that AR Boo belongs to the W-subtype contact binary class, consisting of a hotter, less massive primary star with a spectral type of G9 and a companion of spectral type K1.
Massive black holes are believed to reside at the centres of most galaxies.
They can be- come detectable by accretion of matter, either continuously from a
large gas reservoir or impulsively from the tidal disruption of a passing star,
and conversion of the gravitational energy of the infalling matter to light.
Continuous accretion drives Active Galactic Nuclei (AGN), which are known to be
variable but have never been observed to turn on or off. Tidal disruption of
stars by dormant massive black holes has been inferred indirectly but the on-
set of a tidal disruption event has never been observed. Here we report the
first discovery of the onset of a relativistic accretion-powered jet in the new
extragalactic transient, Swift J164449.3+573451. The behaviour of this new
source differs from both theoretical models of tidal disruption events and
observations of the jet-dominated AGN known as blazars. These differences may
stem from transient effects associated with the onset of a powerful jet. Such
an event in the massive black hole at the centre of our Milky Way galaxy could
strongly ionize the upper atmosphere of the Earth, if beamed towards us.
GRB 090426 is a short-duration burst detected by Swift ( s in the observer frame and s in the burst frame at z= 2.609). Its host galaxy properties and some gamma-ray-related correlations are analogous to those seen in long-duration
gamma-ray bursts (GRBs), which are believed to be of a massive star origin (so-called Type II GRBs). We present the results
of its early optical observations with the 0.8-m Tsinghua University–National Astronomical Observatory of China Telescope
(TNT) at Xinglong Observatory and the 1-m LOAO telescope at Mt Lemmon Optical Astronomy Observatory in Arizona. Our well-sampled
optical afterglow light curve covers from to 104 s after the GRB trigger. It shows two shallow decay episodes that are likely due to energy injection, which end at and 7100 s, respectively. The decay slopes after the injection phases are consistent with each other (). The X-ray afterglow light curve appears to trace the optical, although the second energy-injection phase was missed due
to visibility constraints introduced by the Swift orbit. The X-ray spectral index is without temporal evolution. Its decay slope is consistent with the prediction of the forward shock model. Both X-ray and
optical emission are consistent with being in the same spectral regime above the cooling frequency (). The fact that is below the optical band from the very early epoch of the observation provides a constraint on the burst environment, which
is similar to that seen in classical long-duration GRBs. We therefore suggest that death of a massive star is the possible
progenitor of this short burst.
