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Papers by Yusufjon Tillayev

The astrophysical journal, May 1, 2023

Object GRB 221009A is the brightest gamma-ray burst (GRB) detected in more than 50 yr of study. I... more Object GRB 221009A is the brightest gamma-ray burst (GRB) detected in more than 50 yr of study. In this paper, we present observations in the X-ray and optical domains obtained by the GRANDMA Collaboration and the Insight Collaboration. We study the optical afterglow with empirical fitting using the GRANDMA+HXMT-LE data sets augmented with data from the literature up to 60 days. We then model numerically using a Bayesian approach, and we find that the GRB afterglow, extinguished by a large dust column, is most likely behind a combination of a large Milky Way dust column and moderate low-metallicity dust in the host galaxy. Using the GRANDMA+HXMT-LE+XRT data set, we find that the simplest model, where the observed afterglow is produced by synchrotron radiation at the forward external shock during the deceleration of a top-hat relativistic jet by a uniform medium, fits the multiwavelength observations only moderately well, with a tension between the observed temporal and spectral evolution. This tension is confirmed when using the augmented data set. We find that the consideration of a jet structure (Gaussian or power law), the inclusion of synchrotron self-Compton emission, or the presence of an underlying supernova do not improve the predictions. Placed in the global context of GRB optical afterglows, we find that the afterglow of GRB 221009A is luminous but not extraordinarily so, highlighting that some aspects of this GRB do not deviate from the global known sample despite its extreme energetics and the peculiar afterglow evolution.

The Astrophysical Journal, Sep 30, 2022

In this paper, we study the pulsation properties of KIC 3440495 using Kepler and TESS data. A Fou... more In this paper, we study the pulsation properties of KIC 3440495 using Kepler and TESS data. A Fourier analysis of the light curve reveals 24 pulsation modes as well as 29 frequencies associated with rotation. The rotation frequency is derived to be f rot = 2.322909(2) day −1 , and the rotational modulation is determined to be caused by starspots. A large frequency separation of Δν = 54.5 μHz is found by using a Fourier transform, the autocorrelation function, a histogram of frequency differences, and an échelle diagram. We use the large separation to estimate the refined stellar parameters of the star to be v = [239, 279] km s −1 , M = [1.5, 1.65] M e , R equator = [2.03, 2.30] R e , R polar = [1.72, 1.78] R e , and ω = [0.61, 0.77]. The phase modulations of the pulsating frequencies show a long-term trend which may be attributed to an orbital effect of a binary system; hence, the star may be a fast rotating pulsator in a binary system. KIC 3440495 has an amplitude spectrum similar to Altair, and is identified as a potential sister of Altair. Based on studies of Altair, KIC 3330495 is presumably a young star at a similar evolutionary stage.

Monthly Notices of the Royal Astronomical Society, Nov 11, 2019

We present the Global Rapid Advanced Network Devoted to the Multi-messenger Addicts (GRANDMA). Th... more We present the Global Rapid Advanced Network Devoted to the Multi-messenger Addicts (GRANDMA). The network consists of 21 telescopes with both photometric and spectroscopic facilities. They are connected together thanks to a dedicated infrastructure. The network aims at coordinating the observations of large sky position estimates of transient events to enhance their follow-up and reduce the delay between the initial detection and optical confirmation. The GRANDMA programme mainly focuses on follow-up of gravitational-wave alerts to find and characterize the electromagnetic counterpart during the third observational campaign of the Advanced LIGO and Advanced Virgo detectors. But it allows for follow-up of any transient alerts involving neutrinos or gamma-ray bursts, even those with poor spatial localization. We present the different facilities, tools, and methods we developed for this network and show its efficiency using observations of LIGO/Virgo S190425z, a binary neutron star merger candidate. We furthermore report on all GRANDMA follow-up observations performed during the first six months of the LIGO-Virgo observational campaign, and we derive constraints on the kilonova properties assuming that the events' locations were imaged by our telescopes.

GRANDMA es un proyecto internacional que coordina las observaciones de telescopio de fuentes tran... more GRANDMA es un proyecto internacional que coordina las observaciones de telescopio de fuentes transitorias con grandes incertidumbres de localización. Dichas fuentes incluyen eventos de ondas gravitacionales, explosiones de rayos gamma y neutrinos. GRANDMA actualmente coordina 25 telescopios (70 científicos), con el objetivo de optimizar las imágenes. La estrategia es maximizar la probabilidad de identificar una contraparteóptica de una fuente transitoria. Este artículo describe la motivación del proyecto, la estructura organizacional, la metodología y los resultados iniciales. ABSTRACT GRANDMA is an international project that coordinates telescope observations of transient sources with large localization uncertainties. Such sources include gravitational wave events, gamma-ray bursts and neutrino events. GRANDMA currently coordinates 25 telescopes (70 scientists), with the aim of optimizing the imaging strategy to maximize the probability of identifying an optical counterpart of a transient source. This paper describes the motivation for the project, organizational structure, methodology and initial results.

Proceedings of SPIE, Dec 11, 2009

The site testing studies at the Maidanak Observatory in Uzbekistan for the period 1996-2007 are p... more The site testing studies at the Maidanak Observatory in Uzbekistan for the period 1996-2007 are presented. Nightime seeing was measured with the ESO Differential Image Motion Monitor. The median zenith seeing (FWHM) value at 500 nm for the entire period of observations is 0.71 arcsec. A maximum clear sky season for Maidanak is July-September, with about 90% of possible clear time and a median seeing of 0.69 arcsec. The best monthly median seeing 0.62 arcsec observes in November. Negligible correlation between seeing and the wind velocity at ground level have been found. During an additional site testing campaign organized in July 1998, the median wavefront outer scale being 25.9 m and median isoplanatic angle being 2.48 arcsec were measured with the Generalized Seeing Monitor. This corresponds to a remarkably large atmospheric time constant. Simultaneous measurements of total seeing and microthermal measurements of surface layer optical turbulence were carried out in July-August 2002 which allowed us to estimate the surface layer contribution to the total seeing and which has been found to be about 8%.

Earth System Science Data, Mar 26, 2021

The regional research network Water in Central Asia (CAWa) funded by the German Federal Foreign O... more The regional research network Water in Central Asia (CAWa) funded by the German Federal Foreign Office consists of 18 remotely operated multi-parameter stations (ROMPSs) in Central Asia. These stations were installed by the German Research Centre for Geosciences (GFZ) in Potsdam, Germany, in close cooperation with the Central-Asian Institute for Applied Geosciences (CAIAG) in Bishkek, Kyrgyzstan; the national hydrometeorological services in Tajikistan and Uzbekistan; the Ulugh Beg Astronomical Institute in Tashkent, Uzbekistan; and the Kabul Polytechnic University, Afghanistan. The primary objective of these stations is to support the establishment of a reliable data basis of meteorological and hydrological data especially in remote areas with extreme climate conditions for applications in climate and water monitoring in Central Asia. Up to now, 10 years of data have been provided for an area of scarce station distribution and with limited open-access data which can be used for a wide range of scientific or engineering applications. The data described in this paper are made publicly available with the digital object identifier (DOI)

Proceedings of SPIE, Dec 29, 2000

The statistics of high altitude wind speed data at the tropopause (200mB) above Mt. Maidanak in U... more The statistics of high altitude wind speed data at the tropopause (200mB) above Mt. Maidanak in Uzbekistan are presented. These data were obtained in 1991 at three meteorological stations Kokand, Tashkent and Termez, located around Mt. Maidanak. The data processing show that the high altitude wind speed above Mt. Maidanak is slowly changed with predominant direction from the west. The average value of wind speed at 200 mB for the entire period of observations is 27.0 m/c. The comparison of results with data, obtained at Paranal observatory in Chile shows, that this parameter of atmosphere at Mt. Maidanak is comparably small than above Paranal.

InterConf, Oct 23, 2021

In this study we investigated the effects of ionosphere on variations of Total Electron Content (... more In this study we investigated the effects of ionosphere on variations of Total Electron Content (TEC), and consequently deviations on regional models of Vertical TEC (VTEC), as well as variations in ionospheric GPS stations was analyzed using PRN 1 and PRN 32 codes. The estimation algorithm is applied to the computed VTEC data for Maidanak GPS station on 24 September 2021.

We observed 43 young family asteroids (Karin, Iannini, Veritas) and 7 old family asteroids (Koron... more We observed 43 young family asteroids (Karin, Iannini, Veritas) and 7 old family asteroids (Koronis, Themis) at Maidanak Observatory, then determined their rotation period, lightcurve amplitude, B-V, V-R, V-I colors.

Observatory Operations: Strategies, Processes, and Systems IX

GRANDMA is a worldwide collaboration with the primary scientific goal of studying gravitational-w... more GRANDMA is a worldwide collaboration with the primary scientific goal of studying gravitational-wave sources, discovering their electromagnetic counterparts and characterizing their emission. GRANDMA involves astronomers, astrophysicists, gravitational-wave physicists, and theorists. GRANDMA is now a truly global network of telescopes, with (so far) 30 telescopes in both hemispheres. It incorporates a citizen science programme (Kilonova-Catcher) which constitutes an opportunity to spread the interest in time-domain astronomy. The telescope network is an heterogeneous set of already-existing observing facilities that operate coordinated as a single observatory. Within the network there are wide-field imagers that can observe large areas of the sky to search for optical counterparts, narrow-field instruments that do targeted searches within a predefined list of host-galaxy candidates, and larger telescopes that are devoted to characterization and follow-up of the identified counterparts. Here we present an overview of GRANDMA after the third observing run of the LIGO/VIRGO gravitational-wave observatories in 2019 − 2020 and its ongoing preparation for the forthcoming fourth observational campaign (O4). Additionally, we review the potential of GRANDMA for the discovery and follow-up of other types of astronomical transients.

Monthly Notices of the Royal Astronomical Society

We present our follow-up observations with GRANDMA of transient sources revealed by the Zwicky Tr... more We present our follow-up observations with GRANDMA of transient sources revealed by the Zwicky Transient Facility (ZTF). Over a period of six months, all ZTF alerts were examined in real time by a dedicated science module implemented in the Fink broker, which will be used in filtering of transients discovered by the Vera C. Rubin Observatory. In this article, we present three selection methods to identify kilonova candidates. Out of more than 35 million alerts, a hundred sources have passed our selection criteria. Six were then followed-up by GRANDMA (by both professional and amateur astronomers). The majority were finally classified either as asteroids or as supernovae events. We mobilized 37 telescopes, bringing together a large sample of images, taken under various conditions and quality. To complement the orphan kilonova candidates, we included three additional supernovae alerts to conduct further observations during summer 2021. We demonstrate the importance of the amateur astr...

Atmosphere

In this article, we present the results of astronomical seeing measurements conducted at the Maid... more In this article, we present the results of astronomical seeing measurements conducted at the Maidanak observatory and the influence of meteorological parameters on astronomical seeing. A differential image motion monitor (DIMM) was used to measure astronomical seeing. Astronomical seeing observations were made between 2018–2022, mainly in the summer and autumn months. A total of 266 night observations were conducted between 2018 and 2022. For the whole time frame, the median seeing value was 0.69 arc seconds. With a median value of 0.65″, 2019 is the year with the best seeing, and 2021 has the worst seeing (0.71″). Analysis of long-term variations of the amount of clear time revealed a small trend of decrease in the amount. The correlation between the meteorological parameters and seeing was analyzed. It was determined that the meteorological parameters with the greatest impact on the seeing are wind speed and nighttime temperature variation. The correlation coefficient was equal to...

Journal of Astronomical Telescopes, Instruments, and Systems

Astronomy and Astrophysics Supplement Series, 2000

The atmospheric turbulence and meteorology of the Maidanak Observatory in Uzbekistan are reviewed... more The atmospheric turbulence and meteorology of the Maidanak Observatory in Uzbekistan are reviewed. Night time seeing was measured during the period August 1996-November 1999 with the ESO Differential Image Motion Monitor. The median zenith seeing (FWHM) for the entire period of observations is 0.69 at 0.5 µm. A maximum clear sky season for Maidanak is July-September, with about 90% of possible clear time and a median seeing of 0.69. The best monthly median seeing, 0.62 , is observed in November. The winter maximum of clear time is usually observed in February (up to 50%) with a FWHM of 0.77. During an additional site testing campaign (9 nights) organized in July 1998, the median wavefront outer scale L 0 of 25.9 m and a median isoplanatic angle θ 0 of 2.48 were measured with the Generalized Seeing Monitor developed at the University of Nice. The temporal evolution of the wavefront can be described by several layers moving at slow velocities with predominant direction from the West. This corresponds to a remarkably large atmospheric time constant. No correlation between wavefront velocity and the wind velocity at ground level was found. The good seeing, large isoplanatic angle and, especially, slow wind, place Maidanak Observatory among the best international astronomical sites for high angular resolution observations by interferometry and adaptive optics.

Observatory Operations: Strategies, Processes, and Systems IX

Monthly Notices of the Royal Astronomical Society, 2020

GRANDMA (Global Rapid Advanced Network Devoted to the Multi-messenger Addicts) is a network of 25... more GRANDMA (Global Rapid Advanced Network Devoted to the Multi-messenger Addicts) is a network of 25 telescopes of different sizes, including both photometric and spectroscopic facilities. The network aims to coordinate follow-up observations of gravitational-wave (GW) candidate alerts, especially those with large localization uncertainties, to reduce the delay between the initial detection and the optical confirmation. In this paper, we detail GRANDMA’s observational performance during Advanced LIGO/Advanced Virgo Observing Run 3 (O3), focusing on the second part of O3; this includes summary statistics pertaining to coverage and possible astrophysical origin of the candidates. To do so, we quantify our observation efficiency in terms of delay between GW candidate trigger time, observations, and the total coverage. Using an optimized and robust coordination system, GRANDMA followed-up about 90 per cent of the GW candidate alerts, that is 49 out of 56 candidates. This led to coverage of...

Advances in Space Research, 2013

Abstract This paper reports the ionospheric anomalies observed during strong local earthquakes ( ... more Abstract This paper reports the ionospheric anomalies observed during strong local earthquakes ( M ⩾5.0) which occurred mostly in and around Uzbekistan in seismically active zones, during years 2006 to 2009 within approximately 1000 km distance from the observing GPS stations located in Tashkent and Kitab, Uzbekistan. The solar and geomagnetic conditions were quiet during occurrence of the selected strong earthquakes. We produce Total Electron Content (TEC) time series over both sites and apply them to detect anomalous TEC signals preceding or accompanying the local earthquakes. The results show anomalous increase or decrease of TEC before or during the earthquakes. In general the anomalies occurred 1–7 days before the earthquakes as ionospheric electromagnetic precursors. To identify the anomalous values of TEC we calculated differential TEC (dTEC). dTEC is obtained by subtracting monthly averaged diurnal vTEC from the values of observed vTEC at each epoch. This procedure removes normal diurnal variations of vTEC. The present results are in good agreement with the previous observations on ionospheric earthquake precursors reported by various researchers.

The astrophysical journal, May 1, 2023

Object GRB 221009A is the brightest gamma-ray burst (GRB) detected in more than 50 yr of study. I... more Object GRB 221009A is the brightest gamma-ray burst (GRB) detected in more than 50 yr of study. In this paper, we present observations in the X-ray and optical domains obtained by the GRANDMA Collaboration and the Insight Collaboration. We study the optical afterglow with empirical fitting using the GRANDMA+HXMT-LE data sets augmented with data from the literature up to 60 days. We then model numerically using a Bayesian approach, and we find that the GRB afterglow, extinguished by a large dust column, is most likely behind a combination of a large Milky Way dust column and moderate low-metallicity dust in the host galaxy. Using the GRANDMA+HXMT-LE+XRT data set, we find that the simplest model, where the observed afterglow is produced by synchrotron radiation at the forward external shock during the deceleration of a top-hat relativistic jet by a uniform medium, fits the multiwavelength observations only moderately well, with a tension between the observed temporal and spectral evolution. This tension is confirmed when using the augmented data set. We find that the consideration of a jet structure (Gaussian or power law), the inclusion of synchrotron self-Compton emission, or the presence of an underlying supernova do not improve the predictions. Placed in the global context of GRB optical afterglows, we find that the afterglow of GRB 221009A is luminous but not extraordinarily so, highlighting that some aspects of this GRB do not deviate from the global known sample despite its extreme energetics and the peculiar afterglow evolution.

The Astrophysical Journal, Sep 30, 2022

In this paper, we study the pulsation properties of KIC 3440495 using Kepler and TESS data. A Fou... more In this paper, we study the pulsation properties of KIC 3440495 using Kepler and TESS data. A Fourier analysis of the light curve reveals 24 pulsation modes as well as 29 frequencies associated with rotation. The rotation frequency is derived to be f rot = 2.322909(2) day −1 , and the rotational modulation is determined to be caused by starspots. A large frequency separation of Δν = 54.5 μHz is found by using a Fourier transform, the autocorrelation function, a histogram of frequency differences, and an échelle diagram. We use the large separation to estimate the refined stellar parameters of the star to be v = [239, 279] km s −1 , M = [1.5, 1.65] M e , R equator = [2.03, 2.30] R e , R polar = [1.72, 1.78] R e , and ω = [0.61, 0.77]. The phase modulations of the pulsating frequencies show a long-term trend which may be attributed to an orbital effect of a binary system; hence, the star may be a fast rotating pulsator in a binary system. KIC 3440495 has an amplitude spectrum similar to Altair, and is identified as a potential sister of Altair. Based on studies of Altair, KIC 3330495 is presumably a young star at a similar evolutionary stage.

Monthly Notices of the Royal Astronomical Society, Nov 11, 2019

We present the Global Rapid Advanced Network Devoted to the Multi-messenger Addicts (GRANDMA). Th... more We present the Global Rapid Advanced Network Devoted to the Multi-messenger Addicts (GRANDMA). The network consists of 21 telescopes with both photometric and spectroscopic facilities. They are connected together thanks to a dedicated infrastructure. The network aims at coordinating the observations of large sky position estimates of transient events to enhance their follow-up and reduce the delay between the initial detection and optical confirmation. The GRANDMA programme mainly focuses on follow-up of gravitational-wave alerts to find and characterize the electromagnetic counterpart during the third observational campaign of the Advanced LIGO and Advanced Virgo detectors. But it allows for follow-up of any transient alerts involving neutrinos or gamma-ray bursts, even those with poor spatial localization. We present the different facilities, tools, and methods we developed for this network and show its efficiency using observations of LIGO/Virgo S190425z, a binary neutron star merger candidate. We furthermore report on all GRANDMA follow-up observations performed during the first six months of the LIGO-Virgo observational campaign, and we derive constraints on the kilonova properties assuming that the events' locations were imaged by our telescopes.

GRANDMA es un proyecto internacional que coordina las observaciones de telescopio de fuentes tran... more GRANDMA es un proyecto internacional que coordina las observaciones de telescopio de fuentes transitorias con grandes incertidumbres de localización. Dichas fuentes incluyen eventos de ondas gravitacionales, explosiones de rayos gamma y neutrinos. GRANDMA actualmente coordina 25 telescopios (70 científicos), con el objetivo de optimizar las imágenes. La estrategia es maximizar la probabilidad de identificar una contraparteóptica de una fuente transitoria. Este artículo describe la motivación del proyecto, la estructura organizacional, la metodología y los resultados iniciales. ABSTRACT GRANDMA is an international project that coordinates telescope observations of transient sources with large localization uncertainties. Such sources include gravitational wave events, gamma-ray bursts and neutrino events. GRANDMA currently coordinates 25 telescopes (70 scientists), with the aim of optimizing the imaging strategy to maximize the probability of identifying an optical counterpart of a transient source. This paper describes the motivation for the project, organizational structure, methodology and initial results.

Proceedings of SPIE, Dec 11, 2009

The site testing studies at the Maidanak Observatory in Uzbekistan for the period 1996-2007 are p... more The site testing studies at the Maidanak Observatory in Uzbekistan for the period 1996-2007 are presented. Nightime seeing was measured with the ESO Differential Image Motion Monitor. The median zenith seeing (FWHM) value at 500 nm for the entire period of observations is 0.71 arcsec. A maximum clear sky season for Maidanak is July-September, with about 90% of possible clear time and a median seeing of 0.69 arcsec. The best monthly median seeing 0.62 arcsec observes in November. Negligible correlation between seeing and the wind velocity at ground level have been found. During an additional site testing campaign organized in July 1998, the median wavefront outer scale being 25.9 m and median isoplanatic angle being 2.48 arcsec were measured with the Generalized Seeing Monitor. This corresponds to a remarkably large atmospheric time constant. Simultaneous measurements of total seeing and microthermal measurements of surface layer optical turbulence were carried out in July-August 2002 which allowed us to estimate the surface layer contribution to the total seeing and which has been found to be about 8%.

Earth System Science Data, Mar 26, 2021

The regional research network Water in Central Asia (CAWa) funded by the German Federal Foreign O... more The regional research network Water in Central Asia (CAWa) funded by the German Federal Foreign Office consists of 18 remotely operated multi-parameter stations (ROMPSs) in Central Asia. These stations were installed by the German Research Centre for Geosciences (GFZ) in Potsdam, Germany, in close cooperation with the Central-Asian Institute for Applied Geosciences (CAIAG) in Bishkek, Kyrgyzstan; the national hydrometeorological services in Tajikistan and Uzbekistan; the Ulugh Beg Astronomical Institute in Tashkent, Uzbekistan; and the Kabul Polytechnic University, Afghanistan. The primary objective of these stations is to support the establishment of a reliable data basis of meteorological and hydrological data especially in remote areas with extreme climate conditions for applications in climate and water monitoring in Central Asia. Up to now, 10 years of data have been provided for an area of scarce station distribution and with limited open-access data which can be used for a wide range of scientific or engineering applications. The data described in this paper are made publicly available with the digital object identifier (DOI)

Proceedings of SPIE, Dec 29, 2000

The statistics of high altitude wind speed data at the tropopause (200mB) above Mt. Maidanak in U... more The statistics of high altitude wind speed data at the tropopause (200mB) above Mt. Maidanak in Uzbekistan are presented. These data were obtained in 1991 at three meteorological stations Kokand, Tashkent and Termez, located around Mt. Maidanak. The data processing show that the high altitude wind speed above Mt. Maidanak is slowly changed with predominant direction from the west. The average value of wind speed at 200 mB for the entire period of observations is 27.0 m/c. The comparison of results with data, obtained at Paranal observatory in Chile shows, that this parameter of atmosphere at Mt. Maidanak is comparably small than above Paranal.

InterConf, Oct 23, 2021

In this study we investigated the effects of ionosphere on variations of Total Electron Content (... more In this study we investigated the effects of ionosphere on variations of Total Electron Content (TEC), and consequently deviations on regional models of Vertical TEC (VTEC), as well as variations in ionospheric GPS stations was analyzed using PRN 1 and PRN 32 codes. The estimation algorithm is applied to the computed VTEC data for Maidanak GPS station on 24 September 2021.

We observed 43 young family asteroids (Karin, Iannini, Veritas) and 7 old family asteroids (Koron... more We observed 43 young family asteroids (Karin, Iannini, Veritas) and 7 old family asteroids (Koronis, Themis) at Maidanak Observatory, then determined their rotation period, lightcurve amplitude, B-V, V-R, V-I colors.

Observatory Operations: Strategies, Processes, and Systems IX

GRANDMA is a worldwide collaboration with the primary scientific goal of studying gravitational-w... more GRANDMA is a worldwide collaboration with the primary scientific goal of studying gravitational-wave sources, discovering their electromagnetic counterparts and characterizing their emission. GRANDMA involves astronomers, astrophysicists, gravitational-wave physicists, and theorists. GRANDMA is now a truly global network of telescopes, with (so far) 30 telescopes in both hemispheres. It incorporates a citizen science programme (Kilonova-Catcher) which constitutes an opportunity to spread the interest in time-domain astronomy. The telescope network is an heterogeneous set of already-existing observing facilities that operate coordinated as a single observatory. Within the network there are wide-field imagers that can observe large areas of the sky to search for optical counterparts, narrow-field instruments that do targeted searches within a predefined list of host-galaxy candidates, and larger telescopes that are devoted to characterization and follow-up of the identified counterparts. Here we present an overview of GRANDMA after the third observing run of the LIGO/VIRGO gravitational-wave observatories in 2019 − 2020 and its ongoing preparation for the forthcoming fourth observational campaign (O4). Additionally, we review the potential of GRANDMA for the discovery and follow-up of other types of astronomical transients.

Monthly Notices of the Royal Astronomical Society

We present our follow-up observations with GRANDMA of transient sources revealed by the Zwicky Tr... more We present our follow-up observations with GRANDMA of transient sources revealed by the Zwicky Transient Facility (ZTF). Over a period of six months, all ZTF alerts were examined in real time by a dedicated science module implemented in the Fink broker, which will be used in filtering of transients discovered by the Vera C. Rubin Observatory. In this article, we present three selection methods to identify kilonova candidates. Out of more than 35 million alerts, a hundred sources have passed our selection criteria. Six were then followed-up by GRANDMA (by both professional and amateur astronomers). The majority were finally classified either as asteroids or as supernovae events. We mobilized 37 telescopes, bringing together a large sample of images, taken under various conditions and quality. To complement the orphan kilonova candidates, we included three additional supernovae alerts to conduct further observations during summer 2021. We demonstrate the importance of the amateur astr...

Atmosphere

In this article, we present the results of astronomical seeing measurements conducted at the Maid... more In this article, we present the results of astronomical seeing measurements conducted at the Maidanak observatory and the influence of meteorological parameters on astronomical seeing. A differential image motion monitor (DIMM) was used to measure astronomical seeing. Astronomical seeing observations were made between 2018–2022, mainly in the summer and autumn months. A total of 266 night observations were conducted between 2018 and 2022. For the whole time frame, the median seeing value was 0.69 arc seconds. With a median value of 0.65″, 2019 is the year with the best seeing, and 2021 has the worst seeing (0.71″). Analysis of long-term variations of the amount of clear time revealed a small trend of decrease in the amount. The correlation between the meteorological parameters and seeing was analyzed. It was determined that the meteorological parameters with the greatest impact on the seeing are wind speed and nighttime temperature variation. The correlation coefficient was equal to...

Journal of Astronomical Telescopes, Instruments, and Systems

Astronomy and Astrophysics Supplement Series, 2000

The atmospheric turbulence and meteorology of the Maidanak Observatory in Uzbekistan are reviewed... more The atmospheric turbulence and meteorology of the Maidanak Observatory in Uzbekistan are reviewed. Night time seeing was measured during the period August 1996-November 1999 with the ESO Differential Image Motion Monitor. The median zenith seeing (FWHM) for the entire period of observations is 0.69 at 0.5 µm. A maximum clear sky season for Maidanak is July-September, with about 90% of possible clear time and a median seeing of 0.69. The best monthly median seeing, 0.62 , is observed in November. The winter maximum of clear time is usually observed in February (up to 50%) with a FWHM of 0.77. During an additional site testing campaign (9 nights) organized in July 1998, the median wavefront outer scale L 0 of 25.9 m and a median isoplanatic angle θ 0 of 2.48 were measured with the Generalized Seeing Monitor developed at the University of Nice. The temporal evolution of the wavefront can be described by several layers moving at slow velocities with predominant direction from the West. This corresponds to a remarkably large atmospheric time constant. No correlation between wavefront velocity and the wind velocity at ground level was found. The good seeing, large isoplanatic angle and, especially, slow wind, place Maidanak Observatory among the best international astronomical sites for high angular resolution observations by interferometry and adaptive optics.

Observatory Operations: Strategies, Processes, and Systems IX

Monthly Notices of the Royal Astronomical Society, 2020

GRANDMA (Global Rapid Advanced Network Devoted to the Multi-messenger Addicts) is a network of 25... more GRANDMA (Global Rapid Advanced Network Devoted to the Multi-messenger Addicts) is a network of 25 telescopes of different sizes, including both photometric and spectroscopic facilities. The network aims to coordinate follow-up observations of gravitational-wave (GW) candidate alerts, especially those with large localization uncertainties, to reduce the delay between the initial detection and the optical confirmation. In this paper, we detail GRANDMA’s observational performance during Advanced LIGO/Advanced Virgo Observing Run 3 (O3), focusing on the second part of O3; this includes summary statistics pertaining to coverage and possible astrophysical origin of the candidates. To do so, we quantify our observation efficiency in terms of delay between GW candidate trigger time, observations, and the total coverage. Using an optimized and robust coordination system, GRANDMA followed-up about 90 per cent of the GW candidate alerts, that is 49 out of 56 candidates. This led to coverage of...

Advances in Space Research, 2013

Abstract This paper reports the ionospheric anomalies observed during strong local earthquakes ( ... more Abstract This paper reports the ionospheric anomalies observed during strong local earthquakes ( M ⩾5.0) which occurred mostly in and around Uzbekistan in seismically active zones, during years 2006 to 2009 within approximately 1000 km distance from the observing GPS stations located in Tashkent and Kitab, Uzbekistan. The solar and geomagnetic conditions were quiet during occurrence of the selected strong earthquakes. We produce Total Electron Content (TEC) time series over both sites and apply them to detect anomalous TEC signals preceding or accompanying the local earthquakes. The results show anomalous increase or decrease of TEC before or during the earthquakes. In general the anomalies occurred 1–7 days before the earthquakes as ionospheric electromagnetic precursors. To identify the anomalous values of TEC we calculated differential TEC (dTEC). dTEC is obtained by subtracting monthly averaged diurnal vTEC from the values of observed vTEC at each epoch. This procedure removes normal diurnal variations of vTEC. The present results are in good agreement with the previous observations on ionospheric earthquake precursors reported by various researchers.