arXiv subjects

Michael Prouza

Publications and source records attributed to Michael Prouza.

At least 19 recordsLinked to original sources

arXiv2023

Deep imaging with Milankovi\'c telescope: Linking merger history to kinematics of elliptical galaxies

Kinematical and morphological features observed in early-type galaxies provide valuable insights into the evolution of their hosts. We studied the origin of prolate rotation (i.e., rotation around the long axis) in Illustris large-scale cosmological hydrodynamical simulations. We found that basically all the simulated massive prolate rotators were created in relatively recent major mergers of galaxies. Such mergers are expected to produce tidal features such as tails, shells, asymmetric stellar halos. We investigated deep optical images of prolate rotators, including newly obtained Milankovi\'c data, revealing signs of galaxy interaction in all of them. This correlation proves to be statistically very significant when compared with a general sample of early-type galaxies from the MATLAS deep imaging survey. In an ongoing project, we use Milankovi\'c to assemble deep images of the complete sample of all known nearby massive prolate rotators. Additionally, we searched these data for asteroids to improve the accuracy of trajectories and even discover one previously unknown main-belt asteroid. The most frequent tidal features among the prolate rotators happen to be shells. We developed methods to calculate the probable time of the merger from optical images. This will allow us to compare the merger history of the sample with predictions from Illustris. Our plan is to expand these methods to even larger samples of shell galaxies supplied by upcoming large surveys like LSST at Rubin Observatory. This will provide an unprecedented amount of statistically significant data on the recent merger history of our Universe and allow extensive investigation of the impact of mergers to a wide range of other astrophysical phenomena.

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arXiv2022

GRB 190919B: Rapid optical rise explained as a flaring activity

Following the detection of a long GRB 190919B by INTEGRAL (INTErnational Gamma-Ray Astrophysics Laboratory), we obtained an optical photometric sequence of its optical counterpart. The light curve of the optical emission exhibits an unusually steep rise ~100 s after the initial trigger. This behaviour is not expected from a 'canonical' GRB optical afterglow. As an explanation, we propose a scenario consisting of two superimposed flares: an optical flare originating from the inner engine activity followed by the hydrodynamic peak of an external shock. The inner-engine nature of the first pulse is supported by a marginal detection of flux in hard X-rays. The second pulse eventually concludes in a slow constant decay, which, as we show, follows the closure relations for a slow cooling plasma expanding into the constant interstellar medium and can be seen as an optical afterglow sensu stricto.

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arXiv2021

Exceptionally bright optical emission from a rare and distant $\gamma-$ray burst

Long $\rm \gamma$-ray bursts (GRBs) are produced by the dissipation of ultra-relativistic jets launched by newly-born black holes after the collapse of massive stars. Right after the luminous and highly variable $\gamma$-ray emission, the multi-wavelength afterglow is released by the external dissipation of the jet in circumburst medium. We report the discovery of a very bright ($\rm \sim 10$ mag) optical emission $\rm \sim 28$ s after the explosion of the extremely luminous and energetic GRB 210619B located at redshift 1.937. Early multi-filter observations allowed us to witness the end of the shock wave propagation into the GRB ejecta. We observed the spectral transition from a bright reverse to the forward shock emission, demonstrating that the early and late GRB multi-wavelength emission is originated from a very narrow jet propagating into an unusually rarefied interstellar medium. We also find evidence of an additional component of radiation, coming from the jet wings which is able explain the uncorrelated optical/X-ray emission.

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arXiv2021

A New Method for Aerosol Measurement using Wide-field Photometry

We present a new method to measure the vertical aerosol optical depth (VAOD) during clear nights using a wide-field imager - a CCD camera with a photographic lens on an equatorial mount. A series of 30-second exposures taken at different altitudes above the horizon can be used to measure the VAOD with a precision better than 0.008 optical depths within a few minutes. Such a measurement does not produce any light and is thus suitable for use at sites where other astronomical instruments are located. The precision of the VAOD measurement depends on laboratory calibration of spectral properties of the system and of the response of the camera electronics to varying illumination levels, as well as careful considerations of details of stellar photometry and modelling of the dependence of measured stellar fluxes star color and position within the field of view. The results obtained with robotic setups at the future sites of the Cherenkov Telescope Array show good internal consistency and agreement with the simultaneous measurements from a Sun/Moon Photometer located at the same site.

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arXiv2021

Evaluation of scientific CMOS sensors for sky survey applications

Scientific CMOS image sensors are a modern alternative for a typical CCD detectors, as they offer both low read-out noise, large sensitive area, and high frame rates. All these makes them promising devices for a modern wide-field sky surveys. However, the peculiarities of CMOS technology have to be properly taken into account when analyzing the data. In order to characterize these, we performed an extensive laboratory testing of two Andor cameras based on sCMOS chips -- Andor Neo and Andor Marana. Here we report its results, especially on the temporal stability, linearity and image persistence. We also present the results of an on-sky testing of these sensors connected to a wide-field lenses, and discuss its applications for an astronomical sky surveys.

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arXiv2019

Prototype operations of atmospheric calibration devices for the Cherenkov Telescope Array

The atmospheric monitoring devices for the planned calibration system of the Cherenkov Telescope Array (CTA) are undergoing intensive development, prototyping and testing. The All-Sky Cameras, the Sun/Moon Photometers and the FRAM telescopes have been gradually deployed at the future CTA sites with the primary goal of site characterization, simultaneously allowing the assessment of their operational reliability in realistic environmental conditions. All three devices have shown the ability to work smoothly in both the extreme dryness and the large temperature variations of the southern site as well as in the occasional adverse weather during winter months at the northern site. The target availability of 95\% of time has not yet been reached mostly due to minor hardware failures that have proven difficult to fix due to the remoteness of the installation in the absence of the future CTA infrastructure. The experience gathered during the prototype operations will contribute to the improved reliability of the final instruments. The Raman LIDARs, described in separate proceedings of this conference, and the infrared Ceilometer, ready for testing in Prague, will complement the set of atmospheric calibration devices in near future. The final operational procedures for the atmospheric calibration of the CTA during its operation are being finalized foreseeing the use of the All-sky Cameras and the Ceilometer for the monitoring of clouds over the whole sky and the LIDARs and FRAMs for precision measurements of the atmospheric transmission as a function of altitude and position within the field-of-view of the CTA array.

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arXiv2019

Characterization of atmospheric properties at the future sites of the Cherenkov Telescope Array

Advanced knowledge of the detailed atmospheric properties of both the future sites of the Cherenkov Telescope Array is essential in preparation of the arrival of the first scientific data. Meteorological variables are studied using a dedicated characterization station installed at the southern site in Chile and a wealth of data from existing observatories around the northern site on the La Palma island. Campaigns using radiosondes launched on balloons are foreseen to complement these data in the near future. Cloudiness during the night has been continuously monitored at both sites for several years using All-sky Cameras which assess the presence of clouds based on detection of stars. The integrated aerosol optical depth over the southern site has been measured using a Sun/Moon Photometer since 2016 and the small robotic FRAM telescope since 2017; identical instruments have been deployed at the northern site in autumn 2018. Also in October 2018, the ARCADE Raman lidar (RL) has started to take measurements on routine basis at the northern site, providing data on the vertical profile of the aerosol optical properties (i.e., extinction and scattering) and of the water vapour mixing ratio. We present the data currently available from these instruments from both sites with emphasis on characteristics important for the (future) operation of Imaging Atmospheric Cherenkov Telescopes.

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arXiv2018

FRAM telescopes and their measurements of aerosol content at the Pierre Auger Observatory and at future sites of the Cherenkov Telescope Array

A FRAM (F/(Ph)otometric Robotic Atmospheric Monitor) telescope is a system of a robotic mount, a large-format CCD camera and a fast telephoto lens that can be used for atmospheric monitoring at any site when information about the atmospheric transparency is required with high spatial or temporal resolution and where continuous use of laser-based methods for this purpose would interfere with other observations. The original FRAM has been operated at the Pierre Auger Observatory in Argentina for more than a decade, while three more FRAMs are foreseen to be used by the Cherenkov Telescope Array (CTA). The CTA FRAMs are being deployed ahead of time to characterize the properties of the sites prior to the operation of the CTA telescopes; one FRAM has been running on the planned future CTA site in Chile for a year while two others are expected to become operational before the end of 2018. We report on the hardware and current status of operation and/or deployment of all the FRAM instruments in question as well as on some of the preliminary results of integral aerosol measurements by the FRAMs in Argentina and Chile

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arXiv2018

New developments in aerosol measurements using stellar photometry

The idea of using stellar photometry for atmospheric monitoring for optical experiments in high-energy astrophysics is seemingly straightforward, but reaching high precision of the order of 0.01 in the determination of the vertical aerosol optical depth (VAOD) has proven difficult. Wide-field photometry over a large span of altitudes allows a fast determination of VAOD independently of the absolute calibration of the system, while providing this calibration as a useful by-product. Using several years of data taken by the FRAM (F/(Ph)otometric Robotic Atmospheric Monitor) telescope at the Pierre Auger Observatory in Argentina and about a year of data taken by a similar instrument deployed at the planned future Southern site of the Cherenkov Telescope Array in Chile, we have developed methods to improve the precision of this measurement technique towards and possibly beyond the 0.01 mark. Detailed laboratory measurements of the response of the whole system to both the spectrum and intensity of incoming light have proven indispensable in this analysis as the usual assumption of linearity of the CCD detectors is not valid anymore for the conditions of the observations.

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arXiv2017

Sun/Moon photometer for the Cherenkov Telescope Array - first results

Determination of the energy and flux of the gamma photons by Imaging Atmospheric Cherenkov Technique is strongly dependent on optical properties of the atmosphere. Therefore, atmospheric monitoring during the future observations of the Cherenkov Telescope Array (CTA) as well as anticipated long-term monitoring in order to characterize overal properties and annual variation of atmospheric conditions are very important. Several instruments are already installed at the CTA sites in order to monitor atmospheric conditions on long-term. One of them is a Sun/Moon photometer CE318-T, installed at the Southern CTA site. Since the photometer is installed at a place with very stable atmospheric conditions, it can be also used for characterization of its performance and testing of new methods of aerosol optical depth (AOD) retrieval, cloud-screening and calibration. In this work, we describe our calibration method for nocturnal measurements and the modification of cloud-screening for purposes of nocturnal AOD retrieval. We applied these methods on two months of observations and present the distribution of AODs in four photometric passbands together with their uncertainties.

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arXiv2015

Real-time atmospheric monitoring for the Cherenkov Telescope Array using a wide-field optical telescope

The Cherenkov Telescope Array (CTA) is the next generation of ground-based very high energy gamma-ray instruments and is planned to be built on two sites (one in each hemisphere) in the coming years, with full array operation foreseen to begin 2020. The goal of performing high precision gamma-ray energy measurements while maximizing the use of observation time demands detailed and fast information about atmospheric conditions. Besides LIDARs designed to monitor clouds and aerosol content of the atmosphere in the pointing direction of the CTA telescopes, we propose to use the "FRAM" (F(/Ph)otometric Robotic Atmospheric Monitor) device, which is a small robotic astronomical telescope with a large field of view and a sensitive CCD camera that together ensure precise atmospheric characterization over the complete field-of-view of the CTA. FRAM will use stellar photometry to measure atmospheric extinction across the field of view of the CTA without interfering with the observation (unlike laser-based methods). This allows FRAM to operate with high temporal resolution and provide both real-time data for on-the-fly scheduling decisions and an offline database for calibration and selection of scientific data. The fast robotic mount of the telescope supports quick observation of multiple fields when the array is split and even a check of the conditions in the directions of the upcoming observations is possible. The FRAM concept is built upon experience gained with a similar device operated at the Pierre Auger Observatory. A working prototype of FRAM proposed for CTA is being built in Prague for extensive testing before deployment on site; first results and experiences with this prototype are presented.

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arXiv2014

All Sky Camera instrument for night sky monitoring

The All Sky Camera (ASC) was developed as an universal device for a monitoring of the night sky quality and night sky background measurement. ASC system consists of an astronomical CCD camera, a fish eye lens, a control computer and associated electronics. The measurement is carried out during astronomical twilight. The analysis results are the cloud fraction (the percentage of the sky covered by clouds), night sky brightness (in mag/arcsec2) and light background in the field of view of the camera. The analysis of the cloud fraction is based on the astrometry (comparison to catalogue positions) of the observed stars.

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arXiv2013

All Sky Cameras for the characterization of the Cherenkov Telescope Array candidate sites

The All Sky Camera (ASC) was developed as a universal device for the monitoring of the night sky quality. Eight ASCs are already installed and measure night sky parameters at eight of the candidate sites of the Cherenkov Telescope Array (CTA) gamma-ray observatory. The ACS system consists of an astronomical CCD camera, a fish eye lens, a control computer and associated electronics. The measurement is carried out during astronomical night. The images are automatically taken every 5 minutes and automatically processed using the control computer of the device. The analysis results are the cloud fraction (the percentage of the sky covered by clouds) and night sky brightness (in mag/arcsec$^{2}$)

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arXiv2012

BOOTES Observation of GRB 080603B

We report on multicolor photometry of long GRB080603B afterglow from BOOTES-1B and BOOTES-2. The optical afterglow has already been reported to present a break in the optical lightcurve at 0.12+/-0.2 days after the trigger. We construct the lightcurve and the spectral energy distribution and discuss the nature of the afterglow.

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arXiv2007

New method for atmospheric calibration at the Pierre Auger Observatory using FRAM, a robotic astronomical telescope

FRAM - F/(Ph)otometric Robotic Atmospheric Monitor is the latest addition to the atmospheric monitoring instruments of the Pierre Auger Observatory. An optical telescope equipped with CCD camera and photometer, it automatically observes a set of selected standard stars and a calibrated terrestrial source. Primarily, the wavelength dependence of the attenuation is derived and the comparison between its vertical values (for stars) and horizontal values (for the terrestrial source) is made. Further, the integral vertical aerosol optical depth can be obtained. A secondary program of the instrument, the detection of optical counterparts of gamma-ray bursts, has already proven successful. The hardware setup, software system, data taking procedures, and first analysis results are described in this paper.

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arXiv2007

Systematic study of atmosphere-induced influences and uncertainties on shower reconstruction at the Pierre Auger Observatory

A wide range of atmospheric monitoring instruments is employed at the Pierre Auger Observatory: two laser facilities, elastic lidar stations, aerosol phase function monitors, a horizontal attenuation monitor, star monitors, weather stations, and balloon soundings. We describe the impact of analyzed atmospheric data on the accuracy of shower reconstructions, and in particular study the effect of the data on the shower energy and the depth of shower maximum (Xmax). These effects have been studied using the subset of golden hybrid events - events observed with high quality in the fluorescence and surface detector - used in the calibration of the surface detector energy spectrum.

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arXiv2007

GRB 060117: Reverse + forward shock solution

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arXiv2006

The bright optical flash from GRB 060117

We present a discovery and observation of an extraordinarily bright prompt optical emission of the GRB 060117 obtained by a wide-field camera atop the robotic telescope FRAM of the Pierre Auger Observatory from 2 to 10 minutes after the GRB. We found rapid average temporal flux decay of alpha = -1.7 +- 0.1 and a peak brightness R = 10.1 mag. Later observations by other instruments set a strong limit on the optical and radio transient fluxes, unveiling an unexpectedly rapid further decay. We present an interpretation featuring a relatively steep electron-distribution parameter p ~ 3.0 and providing a straightforward solution for the overall fast decay of this optical transient as a transition between reverse and forward shock.

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