Edgardo Costa

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The gamma–ray burst of 1997 February 28 was localized using the arrival– time analysis method with the Ulysses, BeppoSAX, and WIND spacecraft. The result is a ±31.5(3σ) wide annulus of possible arrival directions which intersects both the position of the burst determined independently by the SAX Wide Field Camera, and the position of a fading X-ray source(More)
The well-known Crab Nebula is at the center of the SN1054 supernova remnant. It consists of a rotationally powered pulsar interacting with a surrounding nebula through a relativistic particle wind. The emissions originating from the pulsar and nebula have been considered to be essentially stable. Here, we report the detection of strong gamma-ray (100(More)
We report on the prompt X– and γ–ray observations of GRB990712 with the BeppoSAX Gamma-Ray Burst Monitor and Wide Field Camera No. 2. Due to Sun constraints, we could not perform a follow-up observation with the BeppoSAX Narrow Field Instruments. The light curve of the prompt emission shows two pulses and a total duration of about 40 s in X-rays. In(More)
We present ground-based optical observations of GRB 020124 starting 1.6 hours after the burst, as well as subsequent Very Large Array (VLA) and Hubble Space Telescope (HST) observations. The optical afterglow of GRB 020124 is one of the faintest afterglows detected to date, and it exhibits a relatively rapid decay, Fν ∝ t−1.60±0.04, followed by further(More)
We report the discovery of a transient equivalent hydrogen column density with an absorption edge at approximately 3.8 kiloelectron volts in the spectrum of the prompt x-ray emission of gamma-ray burst (GRB) 990705. This feature can be satisfactorily modeled with a photoelectric absorption by a medium located at a redshift of approximately 0.86 and with an(More)
The study of astronomical objects using electromagnetic radiation involves four basic observational approaches: imaging, spectroscopy, photometry (accurate counting of the photons received) and polarimetry (measurement of the polarizations of the observed photons). In contrast to observations at other wavelengths, a lack of sensitivity has prevented X-ray(More)
Strong electric discharges associated with thunderstorms can produce terrestrial gamma-ray flashes (TGFs), i.e., intense bursts of x rays and γ rays lasting a few milliseconds or less. We present in this Letter new TGF timing and spectral data based on the observations of the Italian Space Agency AGILE satellite. We determine that the TGF emission above 10(More)
Optical Transients from gamma-ray burst sources, in addition to offering a distance determination, convey important information on the physics of the emission mechanism, and perhaps also about the underlying energy source. As the gamma-ray phenomenon is extremely diverse, with time scales spanning several orders of magnitude, some diversity in optical(More)
We report on Hubble Space Telescope (HST) observations of the optical transient (OT) discovered in the error box of the gamma-ray burst GRB970508. The object was imaged on 1997 June 2 with the Space Telescope Imaging Spectrograph (STIS) and Near-Infrared Camera and Multi-Object Spectrometer (NICMOS). The observations reveal a point-like source with R = 23.1(More)
Trigonometric parallaxes, proper motions and VJ (RI )KC photometry are given for 25 stars (of which one is a zeroparallax control field) targeted by the Cerro Tololo Inter-American Observatory Parallax Investigation (CTIOPI), a widely scoped program aimed at discovering and characterizing nearby stars. The trigonometric parallaxes and proper motions(More)