Abstract
The Gas Pixel Detector (GPD) is an X-ray polarimeter to fly onboard IXPE and other missions. To correctly measure the source polarization, the response of IXPE’s GPDs to unpolarized ...radiation has to be calibrated and corrected. In this paper, we describe the way such response is measured with laboratory sources and the algorithm to apply such correction to the observations of celestial sources. The latter allows to correct the response to polarization of single photons, therefore allowing great flexibility in all the subsequent analysis. Our correction approach is tested against both monochromatic and nonmonochromatic laboratory sources and with simulations, finding that it correctly retrieves the polarization up to the statistical limits of the planned IXPE observations.
Abstract
Imaging X-ray Polarimetry Explorer (IXPE) is a Small Explorer mission that was launched at the end of 2021 to measure the polarization of X-ray emission from tens of astronomical sources. ...Its focal-plane detectors are based on the Gas Pixel Detector, which measures the polarization by imaging photoelectron tracks in a gas mixture and reconstructing their initial directions. The quality of the single track, and then the capability of correctly determining the original direction of the photoelectron, depends on many factors, e.g., whether the photoelectron is emitted at low or high inclination with respect to the collection plane or the occurrence of a large Coulomb scattering close to the generation point. The reconstruction algorithm used by IXPE to obtain the photoelectron emission direction also calculates several properties of the shape of the tracks that characterize the process. In this paper we compare several such properties and identify the best one to weight each track on the basis of the reconstruction accuracy. We demonstrate that significant improvement in sensitivity can be achieved with this approach and for this reason it will be the baseline for IXPE data analysis.
Abstract
The Gas Pixel Detector is a gas detector, sensitive to the polarization of X-rays, currently flying onboard the Imaging X-ray Polarimetry Explorer (IXPE)—the first observatory dedicated to ...X-ray polarimetry. It detects X-rays and their polarization by imaging the ionization tracks generated by photoelectrons absorbed in the sensitive volume, and then reconstructing the initial direction of the photoelectrons. The primary ionization charge is multiplied and ultimately collected on a finely pixellated ASIC specifically developed for X-ray polarimetry. The signal of individual pixels is processed independently and gain variations can be substantial, of the order of 20%. Such variations need to be equalized to correctly reconstruct the track shape, and therefore its polarization direction. The method to do such equalization is presented here and is based on the comparison between the mean charge of a pixel with respect to the other pixels for equivalent events. The method is shown to finely equalize the response of the detectors onboard IXPE, allowing a better track reconstruction and energy resolution, and can in principle be applied to any imaging detector based on tracks.
A multi-wavelength pipeline for pulsar searches Pilia, Maura; Trois, Alessio; Bachetti, Matteo ...
Atti della Accademia nazionale dei Lincei. Rendiconti Lincei. Scienze fisiche e naturali,
12/2019, Volume:
30, Issue:
Suppl 1
Journal Article
Peer reviewed
Open access
Pulsar studies in the recent years have shown, more than others, to have benefited from a multi-wavelength approach. The INAF-Astronomical Observatory in Cagliari (INAF-OAC) is a growing facility ...with a young group devoted to pulsar and fast-transient studies across the electromagnetic spectrum. Taking advantage of this expertise, we have worked to provide a suite of multi-wavelength software and databases for the observations of pulsars and compact Galactic objects at the Sardinia Radio Telescope (SRT). In turn, radio pulsar observations at SRT will be made available, in a processed format, to gamma-ray searches using AGILE and FERMI gamma-ray satellites and, in a near future, they will be complementary to polarimetric X-ray observations with IXPE.
Starting in 2016 August, the onboard software configuration of the Astrorivelatore Gamma ad Immagini LEggero (AGILE) MiniCALorimeter (MCAL) was modified in order to increase the instrument trigger ...capabilities for the detection of short duration high-energy transients, such as weak gamma-ray sub-threshold events and short gamma-ray bursts. MCAL is a nonimaging, all-sky detector, operating in the energy range 0.4-100 MeV. This change was carried out in order to make AGILE more competitive in the detection of electromagnetic counterparts to gravitational wave events revealed by the Laser Interferometer Gravitational-Wave Observatory/Virgo experiments. In the 22 months from 2016 August to 2018 May, the new adopted MCAL-GW configuration substantially enhanced the number of MCAL onboard triggers, increasing the total acquisition time of the instrument, and resulted in the detection of 52 bursts, 40 of which have been confirmed by the InterPlanetary Network.
ABSTRACT
In this work, we propose a new method of computing the Karhunen–Loève Transform (KLT) applied to complex voltage data for the detection and noise level reduction in astronomical signals. We ...compared this method with the standard KLT techniques based on the Toeplitz correlation matrix and we conducted a performance analysis for the detection and extraction of astrophysical and artificial signals via Monte Carlo (MC) simulations. We applied our novel method to a real data study-case: the Voyager 1 telemetry signal. We evaluated the KLT performance in an astrophysical context: our technique provides a remarkable improvement in computation time and MC simulations show significant reconstruction results for signal-to-noise ratio (SNR) down to −10 dB and comparable results with standard signal detection techniques. The application to artificial signals, such as the Voyager 1 data, shows a notable gain in SNR after the KLT.
The on-board data processing of the AGILE satellite Argan, Andrea; Tavani, Marco; Trois, Alessio
Atti della Accademia nazionale dei Lincei. Rendiconti Lincei. Scienze fisiche e naturali,
12/2019, Volume:
30, Issue:
Suppl 1
Journal Article
Peer reviewed
The on-board data processing of the AGILE instrument is a crucial element of its successful operations. We describe the design and implementation of the Payload Data Handling Unit (PDHU) that ...oversees all scientific acquisitions of the AGILE scientific instrument. The PDHU manages data from all four scientific detectors: the Silicon Tracker, the Mini-Calorimeter, the X-ray imager (Super-AGILE), and the anticoincidence system. Specific PDHU tasks are: the Payload scientific and ancillary sub-system control, the operational modes management, the scientific data processing, and the telemetry/telecommands management. The scientific data processing involve the gamma-ray photon filtering and particle background rejection, the X-ray data acquisition, and a gamma-ray Burst acquisition logic with sub-millisecond trigger capability. The AGILE Data Handling system is very flexible and has been successfully implemented for the complex on-board operations of the scientific instrument.
The IXPE instrument calibration equipment Muleri, Fabio; Piazzolla, Raffaele; Di Marco, Alessandro ...
Astroparticle physics,
March 2022, 2022-03-00, Volume:
136
Journal Article
Peer reviewed
Open access
The Imaging X-ray Polarimetry Explorer is a mission dedicated to the measurement of X-ray polarization from tens of astrophysical sources belonging to different classes. Expected to be launched at ...the end of 2021, the payload comprises three mirrors and three focal plane imaging polarimeters, the latter being designed and built in Italy. While calibration is always an essential phase in the development of high-energy space missions, for IXPE it has been particularly extensive both to calibrate the response to polarization, which is peculiar to IXPE, and to achieve a statistical uncertainty below the expected sensitivity. In this paper we present the calibration equipment that was designed and built at INAF-IAPS in Rome, Italy, for the calibration of the polarization-sensitive focal plane detectors on-board IXPE. Equipment includes calibration sources, both polarized and unpolarized, stages to align and move the beam, test detectors and their mechanical assembly. While all these equipments were designed to fit the specific needs of the IXPE Instrument calibration, their versatility could also be used in the future for other projects.
The microquasar Cygnus X-3 underwent a giant radio flare in 2017 April, reaching a maximum flux of ∼16.5 Jy at 8.5 GHz. We present results from a long monitoring campaign carried out with Medicina at ...8.5, 18.6, and 24.1 GHz, parallel to the Metsähovi radio telescope at 37 GHz, from 2017 April 4 to 11. We observe a spectral steepening from to 0.5 (with ) within 6 hr of the epoch of the flare's peak maximum, and rapid changes in the spectral slope in the following days during brief enhanced emission episodes while the general trend of the radio flux density indicated the decay of the giant flare. We further study the radio orbital modulation of Cyg X-3 emission associated with the 2017 giant flare and with six mini-flares observed in 1983, 1985, 1994, 1995, 2002, and 2016. The enhanced emission episodes observed during the decline of the giant flare at 8.5 GHz coincide with the orbital phase (orbital inferior conjunction). On the other hand, the light curves of the mini-flares observed at 15-22 GHz peak at , except for the 2016 light curve, which is shifted 0.5 w.r.t. the other ones. We attribute the apparent phase shift to the variable location of the emitting region along the bent jet. This might be explained by the different accretion states of the flaring episodes (the 2016 mini-flare occurred in the hypersoft X-ray state).
With the specialization of VLSI ASICs for front-end signal processing electronics, the customization of the control back-end electronics (BEE) has become critical to fully deploy the ASIC ...performance. In the context of space operations, with typical constraints on power and reliability, the design and qualification of such integrated systems present significant challenges. In this paper, we review the design and performance of the BEE systems after two years of operations in low Earth orbit (LEO); these systems read out the custom ASICs inside the gas pixel detectors, which are located at the heart of the imaging X-ray polarimetry explorer (IXPE), a NASA-ASI small explorer mission designed to measure X-ray polarization in the 2–8 keV energy range.
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