Arcsecond Accuracy Research Articles

The GMRT High Resolution Southern Sky Survey for Pulsars and Transients. V. Localization of Two Millisecond Pulsars

The timing follow-up of newly discovered millisecond pulsars (MSPs) is hindered by the larger positional uncertainty (a few tens of arcminutes) associated with the discovery. In this paper, we present the localization of two MSPs, discovered by the GMRT High Resolution Southern Sky survey, up to arcsecond accuracy using a 33 MHz offline coherently dedispersed gated correlator. This gated correlator is an upgraded version of the earlier 16 MHz design. This new development with a factor of 2 enhancement in the observing bandwidth offers better sensitivity in the image domain, leading to more precise localization. Aided by the precise position, we followed up these two MSPs with sensitive phased-array (PA) beams of upgraded GMRT from 300 to 1460 MHz. More sensitive observations in the PA mode for these two MSPs yield precise (∼sub-μs) time-of-arrivals, with dispersion measure uncertainties in the range of 10−4–10−5 pc cm−3. We also report the profile evolution of the two MSPs over 300–1460 MHz. Finally, we discuss the suitability of these MSPs for the pulsar timing array experiments aimed to detect low-frequency gravitational waves.

Gamma Scientific Sets High Standards for Light Measurement

Gamma Scientific Sets High Standards for Light Measurement

A Decoupling Three-Position Calibration Method Based on Observability Analysis for SINS/CNS Integrated Navigation

The integrated strap-down inertial/celestial navigation system (SINS/CNS) has been widely applied in autonomous navigation. For long-term high precision performance, initialization is a vital process including the calibration of misalignment angles and system-level parameters. This paper proposes a decoupling three-position calibration method based on a Kalman filter. By measuring the velocity error and attitude error, it is capable to estimate the attitude angle, gyro bias, accelerometer bias and installation error of star sensor. Firstly, the observability degree analysis provides a theoretical account of the coupling of states and the effect of different rotation maneuvers. Secondly, the limitation of gyro noise on the accuracy of accelerometer bias is clarified by comparative experiments. Simultaneously, results indicate that the proposed method can achieve arc-second accuracy in attitude angle and installation error angle, and limit the accelerometer bias error to less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${3}\%$ </tex-math></inline-formula> regardless of the IMU performance. It is an optimal calibration method with advantages of fast convergence, high accuracy, good stability and repeatability.

The host galaxy and persistent radio counterpart of FRB 20201124A

ABSTRACT The physical properties of fast radio burst (FRB) host galaxies provide important clues towards the nature of FRB sources. The 16 FRB hosts identified thus far span three orders of magnitude in mass and specific star formation rate, implicating a ubiquitously occurring progenitor object. FRBs localized with ∼arcsecond accuracy also enable effective searches for associated multiwavelength and multi-time-scale counterparts, such as the persistent radio source associated with FRB 20121102A. Here we present a localization of the repeating source FRB 20201124A, and its association with a host galaxy (SDSS J050803.48+260338.0, z = 0.098) and persistent radio source. The galaxy is massive (${\sim}3\times 10^{10}\, \text{M}_{\odot }$), star-forming (few solar masses per year), and dusty. Very Large Array and Very Long Baseline Array observations of the persistent radio source measure a luminosity of 1.2 × 1029 erg s−1 Hz−1, and show that is extended on scales ≳50 mas. We associate this radio emission with the ongoing star formation activity in SDSS J050803.48+260338.0. Deeper, high-resolution optical observations are required to better utilize the milliarcsecond-scale localization of FRB 20201124A and determine the origin of the large dispersion measure (150–220 pc cm−3) contributed by the host. SDSS J050803.48+260338.0 is an order of magnitude more massive than any galaxy or stellar system previously associated with a repeating FRB source, but is comparable to the hosts of so far non-repeating FRBs, further building the link between the two apparent populations.

Inter-calibration of atmospheric Cherenkov telescopes with UAV-based airborne calibration system

The recent advances in the flight capability of remotely piloted aerial vehicles (here after referred to as UAVs) have afforded the astronomical community the possibility of a new telescope calibration technique: UAV-based calibration. Building upon a feasibility study which characterised the potential that a UAV-based calibration system has for the future Cherenkov Telescope Array, we created a first-generation UAV-calibration prototype and undertook a field-campaign of inter-calibrating the sensitivity of the H.E.S.S. telescope array with two successful calibration flights. In this paper we report the key results of our first test campaign: firstly, by comparing the intensity of the UAV-calibration events, as recorded by the individual HESS-I cameras, we find that a UAV-based inter-calibration is consistent with the standard muon inter-calibration technique at the level of 5.4% and 5.8% for the two individual UAV-calibration runs. Secondly, by comparing the position of the UAV-calibration signal on the camera focal plane, for a variety of telescope pointing models, we were able to constrain the pointing accuracy of the HESS-I telescopes at the tens of arc-second accuracy level. This is consistent with the pointing accuracy derived from other pointing calibration methods. Importantly both the inter-calibration and pointing accuracy results were achieved with a first-generation UAV-calibration prototype, which eludes to the potential of the technique and highlights that a UAV-based system is a viable calibration technique for current and future ground-based γ-ray telescope arrays.

Control System Design Technique and Validation for A High-Resolution Mapping Satellite

With the rapid development of the national economy, the digital city and smart city have become the development trends of China’s urbanization, proposing higher and higher requirements for earth mapping. The emergence of high-resolution mapping satellites has satisfied the demand for national economic development. Since China’s first satellite measuring scale of 1:10,000 was launched in 2019, thus GF-7 satellite has realized the arc-second attitude measurement accuracy, where the degree of stability reached 10- 5°/s. Based on the author’s multi-year research on the design of high-resolution satellite control system, the key technologies and design methods for the high-precision attitude measurement and control system were expounded, the validation results were explained, and the future direction for improving the control precision of the high-resolution mapping satellite was proposed in the end.

DSA-10: a prototype array for localizing fast radio bursts

ABSTRACT The Deep Synoptic Array 10-dish prototype (DSA-10) is an instrument designed to detect and localize fast radio bursts with arcsecond accuracy in real time. Deployed at Owens Valley Radio Observatory, it consists of ten 4.5-m diameter dishes, equipped with a 250-MHz bandwidth dual polarization receiver, centred at 1.4 GHz. The 20 input signals are digitized and field programmable gate arrays are used to transform the data to the frequency domain and transmit it over ethernet. A series of computer servers buffer both raw data samples and perform a real time search for fast radio bursts on the incoherent sum of all inputs. If a pulse is detected, the raw data surrounding the pulse are written to disc for coherent processing and imaging. The prototype system was operational from 2017 June to 2018 February conducting a drift scan search. Giant pulses from the Crab Pulsar were used to test the detection and imaging pipelines. The 10-dish prototype system was brought online again in 2019 March, and will gradually be replaced with the new DSA-110, a 110-dish system, over the next 2 yr to improve sensitivity and localization accuracy.

The Optical Reference Error Analysis and Control Method in Ground Validation System of Stellar-Inertial Integration

The authenticity of the Stellar-Inertial integration ground validation system will eventually determine the navigation performance in flight. The optical reference error characteristics remain a crucial but unsolved issue due to the arc-second level accuracy in the ground validation system. The characteristic of the star simulator celestial angle error and the north reference error are discussed and analyzed in detail. A new error control method of the star simulators intersection angle is proposed with the help of the high precision three-axis turntable. The north reference error can be isolated as a certain azimuth bias error in ground validation. The synthesis of all the error sources is performed to give the criterion value of the evaluation accuracy for the ground validation system. Experimental tests confirm that the error analysis and control method are effective. The evaluation accuracy is improved from 10.99 to 4.88 arc-seconds under the condition of remaining the unchanged ground validation system. Meanwhile, such an in ground test system is close to the flight conditions and it can satisfy the stringent requirement for high-accuracy star sensors.

POLOCALC: A Novel Method to Measure the Absolute Polarization Orientation of the Cosmic Microwave Background

We describe a novel method to measure the absolute orientation of the polarization plane of the Cosmic Microwave Background (CMB) photons with arcsecond accuracy, enabling unprecedented measurements for cosmology and fundamental physics. Existing and planned CMB polarization instruments looking for primordial B-mode signals need an independent, experimental method for systematics control on the absolute polarization orientation. The lack of such a method limits the accuracy of the detection of inflationary gravitational waves, the constraining power on the neutrino sector through measurements of gravitational lensing of the CMB, the possibility of detecting Cosmic Birefringence (CB), and the ability to measure primordial magnetic fields. Sky signals used for calibration and direct measurements of the detector orientation cannot provide an accuracy better than 1[Formula: see text]. Self-calibration methods provide better accuracy, but may be affected by foreground signals and rely heavily on model assumptions, losing constraining power on fundamental processes, like CB, Faraday Rotation and chiral gravity models. The POLarization Orientation CALibrator for Cosmology, POLOCALC, will dramatically improve instrumental accuracy by means of an artificial calibration source flying on high-altitude balloons and aerial drones. Polarization angle calibration requires observation of a well-characterized distant source at high elevation angles. A balloon-borne calibrator will provide a source in the far field of larger telescopes, while an aerial drone can be used for tests and smaller polarimeters. POLOCALC will also allow a unique method to measure the telescopes’ polarized beam. Even a two-hour balloon flight will allow enough time to perform polarization angle calibration and polarized beam function measurements. The source will make use of both narrow and broadband microwave emitters between 40[Formula: see text]GHz and 150[Formula: see text]GHz coupled to precise polarizing filters. The orientation of the source polarization plane will be registered to absolute celestial coordinates by star cameras and gyroscopes with arcsecond accuracy. This project can become a rung in the calibration ladder for the field: any existing or future CMB polarization experiment observing our novel polarization calibrator will enable measurements of the polarization angle for each detector with respect to absolute sky coordinates.

Searching for giga-Jansky fast radio bursts from the Milky Way with a global array of low-cost radio receivers

If fast radio bursts (FRBs) originate from galaxies at cosmological distances, then their all-sky rate implies that the Milky Way may host an FRB on average once every 30-1500 years. If FRBs repeat for decades or centuies, a local FRB could be active now. A typical Galactic FRB would produce a millisecond radio pulse with ~1 GHz flux density of ~3E10 Jy, comparable to the radio flux levels and frequencies of cellular communication devices (cell phones, Wi-Fi, GPS). We propose to search for Galactic FRBs using a global array of low-cost radio receivers. One possibility is to use the ~1GHz communication channel in cellular phones through a Citizens-Science downloadable application. Participating phones would continuously listen for and record candidate FRBs and would periodically upload information to a central data processing website, which correlates the incoming data from all participants, to identify the signature of a real, globe-encompassing, FRB from an astronomical distance. Triangulation of the GPS-based pulse arrival times reported from different locations will provide the FRB sky position, potentially to arc-second accuracy. Pulse arrival times from phones operating at diverse frequencies, or from an on-device de-dispersion search, will yield the dispersion measure (DM) which will indicate the FRB source distance within the Galaxy. A variant of this approach would be to use the built-in ~100 MHz FM-radio receivers present in cell phones for an FRB search at lower frequencies. Alternatively, numerous "software-defined radio" (SDR) devices, costing ~$10 US each, could be plugged into USB ports of personal computers around the world (particularly in radio quiet regions) to establish the global network of receivers.

Thermal control of spacecraft star sensor attitude control system based on the solution of a coupled thermoelasticity problem

The paper is devoted to the study of thermal control of the platform of star sensors designed for spacecraft attitude control under operating conditions. An optimal platform design with an arrangement of sensing elements is presented. The temperature field and the stress-strain state of the platform under the influence of heat sources is considered taking into account the operation of an air-conditioning system based on a numerical solution of a coupled thermoelasticity problem. The temperature field and the strain fields are calculated using the finite-element method with the help of the ANSYS software package. A finite-element model of the platform is developed on the basis of a geometric 3D model. The steady-state velocity field of the coolant in the platform channels is calculated at first. Then the temperature field of the platform is calculated with account for the coolant dynamics. The strained state of the platform under the influence of heat is calculated on the basis of the calculated temperature field. Angular deviations of the mounting seats of star sensors (2 degrees on the average) are determined as compared with the undeformed state. It is shown that angular deviations of the seats of star sensors do not exceed admissible limit values (5 arc seconds). Proposals for creating a high-precision star sensor position control system with a 1 arc second-accuracy are developed.

SEARCHES FOR MILLISECOND PULSAR CANDIDATES AMONG THE UNIDENTIFIEDFERMIOBJECTS

Here we report the results of searching millisecond pulsar (MSP) candidates from the Fermi LAT second source catalog (2FGL). Seven unassociated $\gamma-$ray sources in this catalog are identified as promising MSP candidates based on their $\gamma$-ray properties. Through the X-ray analysis, we have detected possible X-ray counterparts, localized to an arcsecond accuracy. We have systematically estimated their X-ray fluxes and compared with the corresponding $\gamma$-ray fluxes. The X-ray to $\gamma$-ray flux ratios for 2FGL J1653.6-0159 and 2FGL J1946.4-5402 are comparable with the typical value for pulsars. For 2FGL J1625.2-0020, 2FGL J1653.6-0159 and 2FGL J1946.4-5402, their candidate X-ray counterparts are bright enough for performing a detailed spectral and temporal analysis to discriminate their thermal/non thermal nature and search for the periodic signal. We have also searched for possible optical/IR counterparts at the X-ray positions. For the optical/IR source coincident with the brightest X-ray object that associated with 2FGL J1120.0-2204, its spectral energy distribution is comparable with a late-type star. Evidence for the variability has also been found by examining its optical light curve. All the aforementioned 2FGL sources resemble a pulsar in one or more aspects, which make them as the promising targets for follow-up investigations.

Measuring System with Dual Magnetic Sensors for Outer-Rotor Type Torque Motor

As there is no round optical grating and magnetic grating with large diameter that is over 0.5m in the market, a measuring system adopting dual magnetic sensors based on FPGA is proposed in this paper to measure the position/displacement and velocity of the rotating outer-rotor motor. Through using strip-type magnetic grating to stick around the outer rotor over half circumstance, the proposed system is able to produce continuous position pulse signals by switching the signals of dual magnetic sensors. The system core chip distinguishes, subdivides and filters the signals from two sensors, judging the operational state of the sensor and generating the dual magnetic sensor switching signals. It can switches the sensor signals in real time during motor operation and measures the position/displacement and velocity of motor in a precise manner. Moreover, the position/displacement, operating time and positive/negative rotation can be displayed through man-machine interactive unit. The experimental results show that arc-second control accuracy of the outer-rotor torque motor can be achieved by using the proposed system to measure the speed and position/ displacement of the outer-rotor torque motor as the feedback signal through the motion control system of motor.

Calculating stellar magnitude to enhance guide star catalogs

When compiling guide star catalogs formodern star trackers, the use of instrument stellar magnitudes, rather than standard photometric star catalogs, can help avoid ‘blind spots’ in the sky, where the instrument’s field of view has an insufficient number of stars to enable satellite orientation. The calculation of instrument stellar magnitude is a necessary step in developing guide star catalogs for star trackers that use silicon photosensors, such as star tracker 348K (see Figures 1 and 2). Using standard photometric star catalogs—as used in older trackers—may lead either to the tracking of too many stars that a guide star catalog lacks and that will be regarded by the instrument as pseudo-stars, or to stars emerging in the catalog that will never be tracked by the instrument. Working out a guide star catalog requires that one transfer stellar magnitudes to the star tracker’s passband. This allows optimization of a tracker’s characteristics, namely, weight dimension characteristics of the optical system, the amount of memory used by the instrument calculating unit, and the time of calculations required for orientation purposes. Star tracker 348K, developed by JSC NPP Geofizika-Cosmos, is an autonomous multiple-head star tracker with a 19 degree field of view. Each optical head comprises an active pixel sensor (APS)-based camera with a Peltier cooler. Using advanced field and spectral correction and radiation-hard glass, each optical head has three variants of baffles: 40, 30, and 25 degrees. A unique feature of 348K is an internal optical reference mechanism in the optical head. This provides in-orbit self-calibration of bias shift and estimation of object defocus. Using its tracker hardware and software, 348K can reach 11 arcseconds (three sigma) accuracy of attitude determination during its 150,000 hour lifetime. Figure 1. Star tracker 348K.

Water maser follow-up of the Methanol Multi-Beam Survey.

AbstractThe Australia Telescope Compact Array has been used to observe all the 603 6.7 GHz methanol masers detected in the Methanol Multi-Beam survey between l = 310° - 20°. To date we have measured positions with arcsecond accuracy for all the observations in the l = 6° - 20°.

An unbiased pilot survey for Galactic water masers

The Australia Telescope Compact Array has been used in a fast surveying mode to study the 22-GHz transition of water in two small sample regions of the southern Galactic plane. The observations allow an unbiased search for water masers, including any that may have no association with masers from other molecules (or indeed, no association with any other detectable celestial object). Positions with arcsecond accuracy were obtained from the original survey data for detected sources, and these were re-observed at an epoch more than two years later. Variability of the spectra between the epochs was considerable: our total of 32 masers comprises 24 detected at both epochs, two detected at only the first epoch and six detected at only the follow-up epoch. The success of our surveying mode shows it to be a practical strategy for the difficult task of extending unbiased water maser surveys to a large portion of the Galactic plane. Our results show quantitatively the effect of variability on the completeness of surveys conducted at a single epoch. Most of our maser detections are new discoveries. Only four had previously been detected (in searches towards interesting targets in the survey area). The high density of water masers from our unbiased survey supports earlier suggestions that they are the most populous maser species, and one of the most sensitive and reliable tracers of massive young stellar objects – newly forming massive young stars. The spectra of nine masers show high-velocity emission, and they show a striking preponderance of blueshifted high-velocity features. This is compatible with such blueshifts being a characteristic of populations dominated by masers at the earliest evolutionary stage of star formation, in some cases prior to the onset of methanol masers. Amongst the high-velocity emission sources there are two new examples where blueshifted high-velocity outflows dominate the total emission; these substantially increase the previously known meagre population of five such objects and suggest that they may be surprisingly abundant.

Water masers accompanying OH and methanol masers in star formation regions

The ATCA has been used to measure positions with arcsecond accuracy for 379 masers at the 22-GHz transition of water. The principal observation targets were 202 OH masers of the variety associated with star formation regions (SFR)s in the Southern Galactic plane. At a second epoch, most of these targets were observed again, and new targets of methanol masers were added. Many of the water masers reported here are new discoveries. Variability in the masers is often acute, with very few features directly corresponding to those discovered two decades ago. Within our current observations, less than a year apart, spectra are often dissimilar, but positions at the later epoch, even when measured for slightly different features, mostly correspond to the detected maser site measured earlier, to within the typical extent of the whole site, of a few arcseconds. The precise water positions show that approximately 79% (160 of 202) of the OH maser sites show coincident water maser emission, the best estimate yet obtained for this statistic; however, there are many instances where additional water sites are present offset from the OH target, and consequently less than half of the water masers coincide with a 1665-MHz ground-state OH maser counterpart. We explore the differences between the velocities of peak emission from the three species (OH, methanol and water), and quantify the typically larger deviations shown by water maser peaks from systemic velocities. Clusters of two or three distinct but nearby sites, each showing one or several of the principal molecular masing transitions, are found to be common. In combination with an investigation of correlations with IR sources from the GLIMPSE catalogue, these comparative studies allow further progress in the use of the maser properties to assign relative evolutionary stages in star formation to individual sites.

Multiwavelength properties of a new Geminga-like pulsar: PSR J2021+4026

In this paper, we report a detailed investigation of the multiwavelength properties of a newly detected gamma-ray pulsar, PSR J2021+4026, in both observational and theoretical aspects. We firstly identify an X-ray source in the XMM-Newton serendipitous source catalogue, 2XMM J202131.0+402645, located within the 95% confidence circle of PSR J2021+4026. With an archival Chandra observation, this identification provides an X-ray position with arcsecond accuracy which is helpful in facilitating further investigations. Searching for the pulsed radio emission at the position of 2XMM J202131.0+402645 with a 25-m telescope at Urumqi Astronomical Observatory resulted in null detection and places an upper-limit of 0.1~mJy for any pulsed signal at 18~cm. Together with the emission properties in X-ray and gamma-ray, the radio quietness suggests PSR J2021+4026 to be another member of Geminga-like pulsars. In the radio sky survey data, extended emission features have been identified in the gamma-ray error circle of PSR J2021+4026. We have also re-analyzed the gamma-ray data collected by FERMI's Large Area Telescope. We found that the X-ray position of 2XMM J202131.0+402645 is consistent with that of the optimal gamma-ray timing solution. We have further modeled the results in the context of outer gap model which provides us with constraints for the pulsar emission geometry such as magnetic inclination angle and the viewing angle. We have also discussed the possibility of whether PSR J2021+4026 has any physical association with the supernova remnant G78.2+2.1 (gamma-Cygni).

Far-Infrared Interferometric Telescope Experiment : I. Interferometer Optics

We have developed a far-infrared interferometer (Far-Infrared Interferometric Telescope Experiment: FITE). It will be the first astronomical infrared interferometer working in space. FITE is a balloon-borne telescope, and operated in the stratosphere (the altitude of 35 km). The aim of the FITE project is to achieve a high spatial resolution of 1 arcsecond at the wavelength of 100 micrometers. FITE is a Michelson stellar interferometer, and is able to realize a long base line beyond the size of the collecting mirror by using four plane mirrors. The first flight is scheduled for November 2008 in Brazil, and the aim is to measure the interference fringes with a spatial resolution of 2.5 arcseconds. In order to achieve this, the two beams must be focused within 2.5 arcsecond accuracy in the imaging quality, within 10 arcsecond accuracy in the beam alignment and within 30 micrometers accuracy in the optical path length between the two beams. In order to archive these accuracies, the structural parts of the telescope were made of carbon-fiber reinforced plastics, which have very low thermal expansion coefficient and large Young's modulus. During observation of a target, the optical alignment is actively adjusted and the orientation of the telescope is stabilized by the three-axis control.

Phase referencing VLBI astrometry observation system: VERA

AbstractVERA aims at astrometric observations using phase referencing VLBI techniques, whose goal is a 10 micro arc-second accuracy for annual parallax measurements. VERA has four 20-m diameter VLBI radio telescopes in Japanese archipelago with the maximum baseline length of 2,300 km. They have the two-beam observing system, which makes simultaneous observations of two objects possible. This leads to very accurate phase referencing VLBI observations. An important science goal is to make a 3-dimensional map of the Galaxy and reveal its dynamics. In order to achieve this, VERA has the 22GHz and 43GHz bands for H2O and SiO maser objects, respectively. Maser objects are compact and suitable for astrometry observations. VERA's construction was started in 2000 and the array became operational in 2004. We have already measured annual parallaxes and proper motions of some galactic objects. In the future, VERA will collaborate with Korean and Chinese VLBI stations.