Wide Field Monitor Research Articles

Front-end application-specific integrated circuits for the Spectroscopic Time-Resolving Observatory for Broadband Energy X-rays High Energy Modular Array and Wide Field Monitor detectors: concept and design

Front-end application-specific integrated circuits for the Spectroscopic Time-Resolving Observatory for Broadband Energy X-rays High Energy Modular Array and Wide Field Monitor detectors: concept and design

Preliminary study of the multi—physics design for the support structure of LEM—X space mission

In this modern space exploration era, the lunar site offers new opportunities such as the deployment of an X—ray observatory capable of observing half of the sky simultaneously, but also may allowing access to the entire solid angle by exploiting the rotation of the moon around its own axis.The Lunar Electromagnetic Monitor in X—rays (LEM—X) is an All Sky Monitor for the X—ray band (2–50 keV) based on the concept of coded aperture camera. The basic element is the camera of the Wide Field Monitor and the concept is to realize a ”dome” composed of N identical modules that observe different directions, thus covering an overall simultaneous field of view of 2π in the sky. In this paper, we describe the preliminary study of a support structure for that camera, the design solutions adopted for the most important thermo—mechanical drivers, which have been elaborated and used for the demonstration of compliance to the system requirements with the environment. In particular, we reported some different thermal and mechanical scenario of this preliminary structure and the optimization of critical components with innovative and accurate fem analysis.

Near to long-term forecasts in x-ray and gamma-ray bands: Are we entering the era of dark matter astronomy?

We assess Galactic Dark Matter (DM) sensitivities to photons from annihilation and decay using the spatial and kinematic information determined by state-of-the-art simulations in the Latte suite of Feedback In Realistic Environments (FIRE-2). For kinematic information, we study the energy shift pattern of DM narrow emission lines predicted in FIRE-2 and discuss its potential as DM-signal diagnosis, showing for the first time the power of symmetric observations around $l=0^{\circ}$. We find that the exposures needed to resolve the line separation of DM to gas by XRISM at $5\sigma$ to be large, $\gtrsim 4$ Ms, while exposures are smaller for Athena ($\lesssim 50$ ks) and Lynx ($\lesssim 100$ ks). We find that large field-of-view exposures remain the most sensitive methods for detection of DM annihilation or decay by the luminosity of signals in the field of view dominating velocity information. The $\sim$4 sr view of the Galactic Center region by the Wide Field Monitor (WFM) aboard the eXTP mission will be highly sensitive to DM signals, with a prospect of $\sim 10^5$ to $10^6$ events from the 3.5 keV line in a 100 ks exposure, with the range dependent on photon acceptance in WFM's field of view. We also investigate detailed all-sky luminosity maps for both DM annihilation and decay signals - evaluating the signal-to-noise for a DM detection with realistic X-ray and gamma-ray backgrounds - as a guideline for what could be a forthcoming era of DM astronomy.

EXTP perspectives for the νMSM sterile neutrino dark matter model

We discuss the potential of the eXTP X-ray telescope, in particular its Spectroscopic Focusing Array (SFA), Large Area Detector (LAD) and Wide Field Monitor (WFM) for the detection of a signal from keV-scale decaying dark matter. We show that the sensitivity of the eXTP is sufficient to improve existing constraints on the mixing angle of the neutrino Minimal extension of the Standard Model ($\nu$MSM) by a factor of 5-10 within the dark matter mass range 2-50 keV, assuming 1% level of systematic uncertainty. We assert that the eXTP will be able to probe previously inaccessible range of $\nu$MSM parameters and serve as a precursor for the Athena mission in decaying dark matter searches.

OBSERVACIÓN DE METEOROS DE DOS ESTACIONES CON MINI-MEGATORTORA Y FAVOR UN SISTEMA DE MONITOREO EN CAMPO AMPLIO

Here we present the results of our four years long observations of meteors with Mini-MegaTORTORA wide-field monitoring system with sub-second temporal resolution. Over this period, we detected and catalogued more than 175000 faint meteors with magnitudes down to 8-10 mag and angular velocities up to 40 deg/s. Recently, we started double-station observations using Mini-MegaTORTORA together with reconstructed FAVOR camera on 3.8 km baseline. This setup allows to observe tens of faint meteors per night. We present the preliminary results of such observations.

The enhanced X-ray Timing and Polarimetry mission—eXTP

In this paper we present the enhanced X-ray Timing and Polarimetry mission - eXTP. eXTP is a space science mission designed to study fundamental physics under extreme conditions of density, gravity and magnetism. The mission aims at determining the equation of state of matter at supra-nuclear density, measuring effects of QED, and understanding the dynamics of matter in strong-field gravity. In addition to investigating fundamental physics, eXTP will be a very powerful observatory for astrophysics that will provide observations of unprecedented quality on a variety of galactic and extragalactic objects. In particular, its wide field monitoring capabilities will be highly instrumental to detect the electro-magnetic counterparts of gravitational wave sources. The paper provides a detailed description of: (1) the technological and technical aspects, and the expected performance of the instruments of the scientific payload; (2) the elements and functions of the mission, from the spacecraft to the ground segment.

The LOFT mission concept

The Large Observatory For x-ray Timing (LOFT) is a mission concept exploiting a novel detector solution and constitutes the base for a series of subsequent projects in various states of advancement. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument and the uniquely large field of view of its wide field monitor, LOFT will be able to study the behavior of matter in extreme conditions such as the strong gravitational field in the innermost regions close to black holes and neutron stars and the supra-nuclear densities in the interiors of neutron stars. The science payload is based on a Large Area Detector (LAD, >8m2 effective area, 2–30 keV, 240 eV spectral resolution, 1 degree collimated field of view) and a Wide Field Monitor (WFM, 2–50 keV, 4 steradian field of view, 1 arcmin source location accuracy, 300 eV spectral resolution). The WFM is equipped with an on-board system for bright events (e.g., GRB) localization. The trigger time and position of these events are broadcast to the ground within 30 s from discovery. In this paper we present the structure of the mission concept.

Transient X-ray Binaries in the Magellanic Clouds and Milky Way

AbstractThis contribution gave three examples of X-ray transients in the Magellanic Clouds and the Milky Way that have been observed as part of the SALT Transients Large Programme. The transients (SMC X-3, MAXI J1957+032 and ASASSN-16oh) have been triggered from both space-based wide-field monitoring facilities (Swift/XRT, MAXI) and ground-based ones (ASASSN, the All Sky Automated Survey for SN), providing insights into the physics of super-Eddington accretion onto neutron stars and white dwarfs, and also into the long-term properties of accreting millisecond X-ray pulsars.

Discovery of a Rapid, Luminous Nova in NGC 300 by the KMTNet Supernova Program

Abstract We present the discovery of a rapidly evolving transient by the Korean Microlensing Telescope Network Supernova Program (KSP). KSP is a novel high-cadence supernova survey that offers deep (∼21.5 mag in BV I bands), nearly continuous wide-field monitoring for the discovery of early and/or fast optical transients. KSP-OT-201509a, reported here, was discovered on 2015 September 27 during the KSP commissioning run in the direction of the nearby galaxy NGC 300, and stayed above detection limit for ∼22 days. We use our BV I light curves to constrain the ascent rate, −3.7(7) mag day−1 in V, decay timescale, days, and peak absolute magnitude, mag. We also find evidence for a short-lived pre-maximum halt in all bands. The peak luminosity and light-curve evolution make KSP-OT-201509a consistent with a bright, rapidly decaying nova outburst. We discuss constraints on the nature of the progenitor and its environment using archival Hubble Space Telescope (HST)/ACS images and conclude with a broad discussion on the nature of the system.

EXPLORING THE TRANSIENT RADIO SKY WITH VLITE: EARLY RESULTS

ABSTRACT We report on a search for radio transients at 340 MHz with the Jansky Very Large Array Low-band Ionosphere and Transient Experiment (VLITE). Between 2015 July 29 and September 27, operating in commensal mode, VLITE imaged approximately 2800 pointings covering 12,000 deg2 on the sky, sampling timescales ranging from tens of seconds to several hours on a daily basis. In addition, between 2015 February 25 and May 9, VLITE observed 55 epochs of roughly 2–4 hr each toward the COSMOS field. Using existing radio source catalogs, we have searched all of the daily VLITE images for transients, while for the COSMOS field we compared individual images and the summed image to search for new sources in repeated observations of the same field. The wide range of timescales makes VLITE sensitive to both coherent and incoherent transient source classes. No new transients are found, allowing us to set stringent upper limits on transients at milli-jansky levels and at low frequencies where comparatively few such surveys have been carried out to date. An all-sky isotropic surface density of bursting radio transients with similar rates, durations, and intensities as the unusual transient GCRT J1745−3009, discovered in wide-field monitoring toward the Galactic center, is ruled out with high confidence. The resulting non-detections allows us to argue that this is a coherent source, whose properties most resemble the growing class of nulling pulsars. We end with a discussion of the future prospects for the detection of transients by VLITE and other experiments.

Untriggered search for rapid optical transients with Mini-MegaTORTORA wide-field monitoring system

AbstractHere we report ongoing efforts for an untriggered search of rapid optical transients of various astrophysical and non-astrophysical origins on time scales down to fractions of a second with Mini-MegaTORTORA. Mini-MegaTORTORA is a novel 9-channel wide-field optical monitoring system in operation since 2014 at Special Astrophysical Observatory on Russian Caucasus.

LOFT — Large Observatory for X-ray Timing

LOFT (the Large Observatory for X-ray Timing), is a mission concept that was considered by ESA as a candidate for an M3 mission and has been studied during an extended > 2-years long assessment phase.The mission was specifically designed to perform fast X-ray timing and probe the status of the matter near black holes and neutron stars. The LOFT scientific payload is composed of a Large Area Detector (LAD) and a Wide Field Monitor (WFM). The LAD is a 10 m2-class pointed instrument with ∼ 15 times the collecting area of the largest past timing missions (as the Rossi XTE) over the 2-30 keV range (30-80 keV expanded), combined with CCD-class spectral resolution, which holds the capability to revolutionise studies of X-ray variability down to the millisecond time scales.Its ground-breaking characteristic is a mass per unit surface in the range of ∼ 10 kg/m2, enabling an effective area of ∼ 10 m2 (at 10 keV) at a reasonable weight. The development of such large but light experiment, with low mass and power per unit area, is now made possible by the recent advancements in the field of large-area silicon drift detectors and capillary-plate X-ray collimators.Although the LOFT mission has not been down-selected for launch in the M3 ESA programme (with launch in 2022-2024), during the assessment phase most ofthe trade off have been closed leading to a robust and well documenteddesign which will be re-proposed in the future ESA calls. In this paper, we will summarize the characteristics of the LAD instrument and brieflydescribe the status of the detectors design.

The effects of hyper-velocity dust-particle impacts on the LOFT Silicon Drift Detectors

Solid-state detectors that operate in orbit are requiredto withstand harsh space environment conditions. Among the variousphenomena able to damage the sensors, X-ray detectors are subjectedto impacts of orbital debris and micrometeoroids whenever, to besensitive to low energy photons, they need to be``directly'' exposed to the sky.The LOFT mission, proposed for the M3 class opportunity of the ESACosmic Vision, has a very-large sensitive area (greater than 10 m2)made of Silicon Drift Detectors (SDD). Moreover, the satellite includesan X-ray Wide-Field Monitor based on the same SDD detectors. Here wepresent the results of a test campaign at the Cosmic Dust AcceleratorFacility at MPIK in Heidelberg aimed at the space qualification of thedetectors with respect to this phenomenon.

The LOFT contribution to GRB science

LOFT is a satellite mission currently in Assessment Phase for the ESA M3 selection. The payload is composed of the Large Area Detector (LAD), with 2–50 keV energy band, a peak effective area of about 10m2 and an energy resolution better than 260 eV, and the Wide Field Monitor (WFM), a coded mask imager with a FOV of several steradians, an energy resolution of about 300 eV and a point source location accuracy of 1 arcmin in the 2–30 keV energy range. Based on preliminary considerations and estimates, we show how the scientific performances of the WFM are particularly suited to investigate the most relevant open issues in the study of GRBs: the physics of the prompt emission, the spectral absorption features by circum-burst material (and hence the nature of the progenitors), the population and properties of XRFs, and the detection and rate of high-z GRBs. Measurements of the early afterglow emission with the Large Area Detector (LAD) may also be possible depending on the mission slewing capabilities and TOO observations policy.

Observing GRBs with theLOFTWide Field Monitor

LOFT (Large Observatory For X-ray Timing) is one of the four candidate missions currently under assessment study for the M3 mission in ESAs Cosmic Vision program to be launched in 2024. LOFT will carry two instruments with prime sensitivity in the 2-30 keV range: a 10 m2 class large area detector (LAD) with a <1° collimated field of view and a wide field monitor (WFM) instrument. The WFM is based on the coded mask principle, and 5 camera units will provide coverage of more than 1/3 of the sky. The prime goal of the WFM is to detect transient sources to be observed by the LAD. With its wide field of view and good energy resolution of <500 eV, the WFM will be an excellent instrument for detecting and studying GRBs and X-ray flashes. The WFM will be able to detect ~150 gamma ray bursts per year, and a burst alert system will enable the distribution of ~100 GRB positions per year with a ~1 arcmin location accuracy within 30 s of the burst.

Status and perspectives of Mini-MegaTORTORA wide-field monitoring system with high temporal resolution

Here we briefly summarize our long period experience of constructing and operating wide-field monitoring cameras with sub-second temporal resolution to look for optical components of GRBs, fast-moving satellites and meteors. General requirements for hardware for such systems are discussed along with algorithms of real-time detection and classification of various kinds of short optical transients. We also give a status report on the next generation, multi-objective and transforming monitoring system, the MegaTORTORA, whose 6-channel (Mini-MegaTORTORA-Spain) and 9-channel prototypes (Mini-MegaTORTORA-Kazan) we are building now at SAO RAS. This system combines a wide field of view with subsecond temporal resolution in monitoring regime, and is able to reconfigure itself, in a fractions of second, to follow-up mode which has better sensitivity and provides us with multi-color and polarimetric information on detected transients simultaneously.

Status and Perspectives of the Mini-MegaTORTORA Wide-field Monitoring System with High Temporal Resolution

Here we briefly summarize our long-term experience of constructing and operating wide-field monitoring cameras with sub-second temporal resolution to look for optical components of GRBs, fast-moving satellites and meteors. The general hardware requirements for these systems are discussed, along with algorithms for real-time detection and classification of various kinds of short optical transients. We also give a status report on the next generation, the MegaTORTORA multi-objective and transforming monitoring system, whose 6-channel (Mini-MegaTORTORA-Spain) and 9-channel prototypes (Mini-MegaTORTORA-Kazan) we have been building at SAO RAS. This system combines a wide field of view with subsecond temporal resolution in monitoring regime, and is able, within fractions of a second, to reconfigure itself to follow-up mode, which has better sensitivity and simultaneously provides multi-color and polarimetric information on detected transients.

Early Danish GRB Experiments – and some for the Future?

By 1975 the hunt for GRB counterparts had been on for almost ten years without success. Gamma burst instruments of that day provided little or no directional data in themselves. Positions could be extracted only using the time delay technique – potentially accurate but very slow. Triggered by a japanese report of a balloon instrument for GRB studies based on a Rotation Modulation Collimator we at the Danish Space Research Institute started the development of an RMC detector for GRBs, the WATCH wide field monitor.

Heterogeneity and independency of unitary synaptic outputs from hippocampal CA3 pyramidal cells

The variation of individual synaptic transmission impacts the dynamics of complex neural circuits. We performed whole-cell recordings from monosynaptically connected hippocampal neurons in rat organotypic slice cultures using a synapse mapping method. The amplitude of unitary excitatory postsynaptic current (uEPSC) varied from trial to trial and was independent of the physical distance between cell pairs. To investigate the source of the transmission variability, we obtained patch-clamp recordings from intact axons. Axonal action potentials (APs) were reliably transmitted throughout the axonal arbour and showed modest changes in width. In contrast, calcium imaging from presynaptic boutons revealed that the amplitude of AP-evoked calcium transients exhibited large variations both among different boutons at a given trial and among trials in a given bouton. These results suggest that a factor contributing to the uEPSC fluctuations is the variability in calcium dynamics at presynaptic terminals. Finally, we acquired triple whole-cell recordings from divergent circuit motifs with one presynaptic neuron projecting to two postsynaptic neurons. Consistent with the independency of calcium dynamics among axonal boutons, a series of uEPSC fluctuations was not correlated between the two postsynaptic cells, indicating that different synapses even from the same neuron act independently.We conclude that the intra-bouton and inter-bouton variability in AP-induced calcium dynamics determine the heterogeneity and independency of uEPSCs.

Scars of intense accretion episodes at metal-rich white dwarfs

A re-evaluation of time-averaged accretion rates at DBZ-type white dwarfs points to historical, time-averaged rates significantly higher than the currently observed episodes at their DAZ counterparts. The difference between the ongoing, instantaneous accretion rates witnessed at DAZ white dwarfs, which often exceed 1e8 g/s, and those inferred over the past 1e5-1e6 yr for the DBZ stars can be a few orders of magnitude, and therefore must result from high-rate episodes of tens to hundreds of years so they remain undetected to date. This paper explores the likelihood that such brief, intense accretion episodes of gas-phase material can account for existing data. For reasonable assumptions about the circumstellar gas, accretion rates approaching or exceeding 1e15 g/s are possible, similar to rates observed in quiescent cataclysmic variables, and potentially detectable with future x-ray missions or wide-field monitoring facilities. Gaseous debris that is prone to such rapid accretion may be abundant immediately following a tidal disruption event via collisions and sublimation, or if additional bodies impinge upon an extant disk. Particulate disk matter accretes at or near the Poynting-Robertson drag rate for long periods between gas-producing events, consistent with rates inferred for dusty DAZ white dwarfs. In this picture, warm DAZ stars without infrared excesses have rates consistent with accretion from particulate disks that remain undetected. This overall picture has implications for quasi-steady state models of accretion and the derived chemical composition of asteroidal debris in DBZ white dwarfs.