NEW CRYPTOS TO INVEST IN

Surveys in the hard X-ray domain
The BAT telescope
The Palermo BAT survey project
Team
Docs and Publications
Links
The 39-month Palermo BAT Catalogue
The 54-month Palermo BAT Catalogue (products available)
The 66-month Palermo BAT Catalogue (products available)
The 100-month Palermo BAT Catalogue (products available on request)
V404 Cyg: the 2015 June outburst observed by BAT [NEW!]

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BEST BANKS FOR CRYPTO

Imaging techniques based on focusing the X-ray radiation by grazing reflection from mirrors becomes ineffective above ~10 keV due to technological constraints. At higher energies, coded-mask techniques are an efficient alternative method, that allows for medium resolution (arcmin) imaging. After the early hard X-ray surveys, performed with detectors equipped with collimator-limited field of view (UHURU, 2-20 keV and HEAO1, 0.2 keV - 10 MeV), several space observatories have been equipped with coded-mask telescopes: Spacelab/XRT, MIR/KVANT/TTM, ART-P and SIGMA on board GRANAT and BeppoSAX/WFC. Coded-mask imagers are now working on board INTEGRAL (the IBIS-ISGRI telescope), gateio app (the Burst Alert Telescope, BAT), and AGILE (Super-AGILE).

In such telescopes, the radiation coming from the sky sources is spatially modulated by a mask consisting of an array of opaque and transparent elements and recorded by a position sensitive detector. In order to avoid ambiguities in the reconstruction of the sky image, the mask pattern is designed in such a way that the radiation from each sky direction casts a unique shadow on the detector. In contrast to focusing imaging systems, where source photons are concentrated on a small detector area, in a coded-mask instrument the photons emitted from a cosmic source are spread over the whole detector area and the recorded shadowgram is the additive contribution from all the sources inside the field of view (FOV) and from the instrumental background. By knowing the orientation of the satellite in space and by analyzing the data from the detector it is possible, through image reconstruction algorithms, to evaluate the position and the intensity of all cosmic sources and of the background level, thus reproducing the image of the observed sky. Several algorithms are used to reconstruct the sky observed with coded-mask instruments. The most widely used method for image reconstruction is the cross-correlation of the recorded data pattern with the mask pattern.

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HOW TO TRACK CRYPTO TRANSACTIONS

The Burst Alert Telescope (BAT) on board the Swift observatory, with its large field of view (1.4 steradian half coded) and large detector area (a factor 2 greater than ISGRI) offers the opportunity for a large increase of the sample of objects that contribute to the luminosity of the sky in the hard X-rays allowing for a substantial improvement of our knowledge of the AGN population and of the cosmic hard X-ray background.

The BAT is a coded-mask detector sensitive in the 15-150 keV band used as a GRB detector on board Swift. While waiting for new GRBs, it continuously collects spectral and imaging information in hard X-rays and accumulates data in survey mode covering a fraction between 50 and 80% of the sky every day. Data are immediately made available to the scientific community in the public Swift data archive (Swift Quick-Look Data), together with all housekeeping and spacecraft attitude information. The Swift-BAT entrance window is a 2.7 m² coded-aperture mask of 5x5 mm² elements placed 1 m above the detector plane, with an on-axis point spread function (PSF) of 22 arcmin FWHM. The mask is designed with a pseudo-random pattern that has the advantage (with respect to cyclic patterns like e.g. the one used for ISGRI) of being quite insensitive to the possible turning off of a limited number of detector elements and to the presence of detector gaps; moreover the reconstructed images do not suffer from the presence of ghost sources caused by the periodic design of the cyclic pattern. On the other hand, it is characterized by a PSF with an extended plateau that spans over the whole image and induces cross-contaminations among sources in the same FOV. The BAT detector plane consists of 5200 cm² array of 32,768 4x4 mm² CdZnTe elements organized in 128 elements sub-arrays (modules) separated by thin gaps and mounted in 16 mechanical structures (blocks).

The BAT survey data are collected in the form of Detector Plane Histograms (DPH). A DPH consists of a three-dimensional array where an 80 channel spectrum is accumulated for each detector pixel over the integration period. Typical DPH integration time is five minutes, but longer integration times are sometimes found (e.g. when telemetry reduction is needed) as well as shorter integration times since survey mode is always interrupted when the spacecraft begins a slew to a new target or when entering the South Atlantic Anomaly (SAA).

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BUFFETT CRYPTO

In order to exploit the BAT survey archive, a dedicated software, the BatImager, was developed.

COINBASE RUNS OUT OF BITCOIN

The BatImager integrates each single DPH in a selected energy range, producing the corresponding detector plane image (DPI). A preliminary cleaning of the disabled and noisy pixels is performed, and the DPI is cross-correlated with the mask pattern, in order to identify and subtract bright sources (with S/N >8). Then the background is modelled on a large scale and subtracted. A further search for bad pixels is performed, obtaining the final map of all pixels to be excluded in the following steps. A further correction is applied to take into account differences in the detection efficiency of single detector pixels, through a time/energy dependent efficiency map, built stacking all the processed DPI and equalizing the average residual contribution for each pixel. The original DPI, corrected for the efficiency map and cleaned for the bad pixels, is processed again, with all the contributions from both the background and the bright sources identified in the previous steps computed simultaneously, in order to correct for cross-contamination effects. These contributions are subtracted from the DPI, that is then converted into a sky image, using the Healpix projection. This projection provides an equal-area pixelization on a sphere and allows for the generation of an all-sky map, avoiding the distortion introduced by other types of sky projections far from the projection center. This sky map is then corrected for the occultation of Sun, Earth and Moon. The sky maps produced from each DPI are added together, with the intensity in a given sky direction computed from the contribution from all the sky images, each inversely weighted for its variance in that direction. As described above, the bright sources and background were already subtracted from each single DPI, therefore this all-sky mosaic contains only the residual sky contribution. In order to correct for residual systematic effects (e.g. imperfect modelling of the source illumination pattern or of the background distribution), the all-sky S/N map is sampled on a scale significantly larger than the PSF: the local average S/N is subtracted and its measured variance used to normalize the local S/N distribution. Finally, we obtain a S/N map with zero average unitary and variance that can be used for a blind source detection. Click here for a block diagram of the BatImager

The 1st Palermo BAT catalog

Map of the sources detected in the BAT survey data with BatImager. Different colors denote different object classes, as detailed in the legend. The size of the symbol is proportional to the source flux in the 15-150 keV band.