E. Costa

Discovery of an X-ray afterglow associated with the γ-ray burst of 28 February 1997

Establishing the nature of γ-ray bursts is one of the greatest challenges in high-energy astrophysics. The distribution of these bursts is isotropic across the sky, but inhomogeneous in space, with a deficit of faint bursts. It is currently unknown whether γ-ray bursts are produced in our Galaxy or at cosmological distances. The detection and identification of counterparts at other wavelengths are seen as crucial for resolving the origin of the events. Here we report the detection by the Beppo-SAX satellite of an X-ray ‘afterglow’, associated with the γ-ray burst of 28 February 1997 (GRB970228; ref. 3)—the first such detection for any γ-ray burst. The X-ray transient was found to contain a significant fraction of the total energy of the γ-ray burst and, following the initial detection eight hours after the main burst, faded within a few days with a power-law decay function. The rapid locating of this γ-ray burst instigated a multi-wavelength observational campaign that culminated in the identification of a fading optical transient in a position consistent with the X-ray transient reported here.The invention is a three-piece contact assembly for an electrical connector. The contact assembly is characterized by an inner sleeve (10) captivated between a forward outer sleeve (20) and a rear outer sleeve (30) to eliminate deformation and relative movement between the sleeves of a contact assembly.

An Unusual Supernova in the Error Box of the Gamma-Ray Burst of 25 April 1998

The discovery of afterglows associated with γ-ray bursts at X-ray, optical and radio wavelengths and the measurement of the redshifts of some of these events, has established that γ-ray bursts lie at extreme distances, making them the most powerful photon-emitters known in the Universe. Here we report the discovery of transient optical emission in the error box of the γ-ray burst GRB980425, the light curve of which was very different from that of previous optical afterglows associated with γ-ray bursts. The optical transient is located in a spiral arm of the galaxy ESO184-G82, which has a redshift velocity of only 2,550u2009kmu2009s−1 (ref. 6). Its optical spectrum and location indicate that it is a very luminous supernova, which has been identified as SN1998bw. If this supernova and GRB980425 are indeed associated, the energy radiated in γ-rays is at least four orders of magnitude less than in other γ-ray bursts, although its appearance was otherwise unremarkable: this indicates that very different mechanisms can give rise to γ-ray bursts. But independent of this association, the supernova is itself unusual, exhibiting an unusual light curve at radio wavelengths that requires that the gas emitting the radio photons be expanding relativistically,.on April 25.90915 UT with one of the Wide Field Cameras(WFCs) and the Gamma Ray Burst Monitor (GRBM) on board BeppoSAX, and with the Burst andTransient Source Experiment (BATSE) on board the Compton Gamma Ray Observatory (CGRO).The BATSE burst profile consists of a single wide peak. The burst flux rose in ∼ 5 s to amaximum flux of (3.0± 0.3)×10

Discovery of the peculiar supernova 1998bw in the error box of GRB 980425

The discovery of afterglows associated with γ-ray bursts at X-ray, optical and radio wavelengths and the measurement of the redshifts of some of these events, has established that γ-ray bursts lie at extreme distances, making them the most powerful photon-emitters known in the Universe. Here we report the discovery of transient optical emission in the error box of the γ-ray burst GRB980425, the light curve of which was very different from that of previous optical afterglows associated with γ-ray bursts. The optical transient is located in a spiral arm of the galaxy ESO184-G82, which has a redshift velocity of only 2,550u2009kmu2009s−1 (ref. 6). Its optical spectrum and location indicate that it is a very luminous supernova, which has been identified as SN1998bw. If this supernova and GRB980425 are indeed associated, the energy radiated in γ-rays is at least four orders of magnitude less than in other γ-ray bursts, although its appearance was otherwise unremarkable: this indicates that very different mechanisms can give rise to γ-ray bursts. But independent of this association, the supernova is itself unusual, exhibiting an unusual light curve at radio wavelengths that requires that the gas emitting the radio photons be expanding relativistically,.on April 25.90915 UT with one of the Wide Field Cameras(WFCs) and the Gamma Ray Burst Monitor (GRBM) on board BeppoSAX, and with the Burst andTransient Source Experiment (BATSE) on board the Compton Gamma Ray Observatory (CGRO).The BATSE burst profile consists of a single wide peak. The burst flux rose in ∼ 5 s to amaximum flux of (3.0± 0.3)×10

The prompt emission of GRB990712 with BeppoSAX: evidence of a transient x-ray emission feature

We report on the prompt X- and γ-ray observations of GRB 990712 with the BeppoSAX Gamma-Ray Burst Monitor and Wide Field Camera 2. As a result of 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 γ-rays, the event is even shorter. The 2-700 keV spectral emission with time shows a discontinuity in the peak energy Ep of the EF(E) spectrum: Ep is above our energy passband during the first pulse and goes down to ~10 keV during the second pulse. Another peculiarity is noted in this event for the first time: the evidence of a 2 s duration emission feature during the tail of the first pulse. The feature is consistent with either a Gaussian profile with centroid energy of 4.5 keV or a blackbody spectrum with kTbb ~ 1.3 keV. We discuss the possible origin of the feature. The most attractive possibility is that we are observing the thermal emission of a baryon-loaded expanding fireball when it becomes optically thin.

Time variability of Gamma Cassiopeiae in X-rays

Observations par le satellite EXOSAT, de la source RX 4U 0053+60 (γ Cas), revelant des oscillations dans le flux RX avec une periode denviron 6000 t. La source montre egalement une variabilite chaotique sur des echelles de temps pouvant aller jusqua quelques dizaines de secondes. Ces observations sous-tendent lhypothese que la source RX est une etoile a neutrons dans une large orbite autour de letoile Be γ Cas

Multicolor photometry of the GRB970508 optical remnant

We report results of follow-up multicolor photometry of the optical variable source that is a probable remnant of the gamma-ray burst GRB970508 discovered by the BeppoSAX satellite [3]. Observations were carried out in Johnson-Kron-Cousins BVRcIc system with the 1-m and 6-m telescopes of SAO RAS. Between the 2nd and the 5th day after the burst a fading of the remnant is well fitted with an exponential law in all four bands. During this period the ‘broadband spectrum’ of the object was unchanged and can be approximated by a power-law, Fν∝ν−1.1. After the 5th day the decline of brightness is slowed down. In the Rc band until the 84th day, the light curve can be described by a power-law relation, F∝t−1.179(±0.016).

XMM-Newton observations of the field of γ-ray burst 980425

Abstract The error box of GRB980425 has been observed by XMM- Newton in March 2002, with the aim of measuring the late epoch X-ray emission of the supernova 1998bw and of clarifying its supposed association with the GRB itself. We present here the preliminary results obtained with the EPIC PN camera. Our observations confirm the association between SN 1998bw and GRB980425. The EPIC PN measurement of the SN 1998bw flux is significantly below the extrapolation of the power-law temporal trend fitted to the BeppoSAX points and implies a faster temporal decay. We propose different physical interpretations of the SN X-ray light curve, according to whether it is produced by one or more radiation components.

Initial results from the high energy experiment PDS aboard BeppoSAX

The high energy experiment PDS is one of the Narrow Field Instruments aboard the X-ray astronomy satellite BeppoSAX. It covers the energy band from 15 to 300 keV. Here we report results on its in-flight performance and observations of galactic and extragalactic X-ray sources obtained during the Science Verification Phase of the satellite: in particular Crab, Cen X−3, 4U1626−67 and PKS2155−305.

Response function of the Gamma-Ray Burst Monitor (GRBM) onboard the BeppoSAX satellite

Preliminary results of a study aimed to the determination of the response function, in direction and energy, of the Gamma-Ray Burst Monitor (GRBM) onboard the BeppoSAX satellite are presented. The study has been carried out by means of Monte Carlo techniques, taking into account on-ground calibration before launch, and the Crab spectrum measured during the flight. The derived response matrix will be used to evaluate properties (e.g., direction, spectrum, fluence) of all Gamma-Ray Bursts detected with the GRBM.

The Prompt and Afterglow Emission of GRB 001109 Measured by BeppoSAX

We present here preliminary results of BeppoSAX measurements of the prompt (2–700 keV) and afterglow (0.1 – 10 keV) emission of the ‘dark’ GRB 001109. The burst light curves show indication of pulse broadening with the decrease of the energy band and its average spectrum is well described by the standard Band function from X to gamma‐rays. The X‐ray afterglow emission shows a monotonic power‐law decay and its spectrum can be satisfactorily fitted with a photo‐electrically absorbed power‐law. Both the decay index and the photon index are inside the range of common values found in GRBs afterglows. More detailed data analysis and interpretation is in progress.