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Featured researches published by P. Giommi.


Nature | 1997

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

E. Costa; F. Frontera; J. Heise; M. Feroci; J. J. M. in 't Zand; F. Fiore; M.N. Cinti; D. Dal Fiume; L. Nicastro; M. Orlandini; E. Palazzi; Massimo Rapisarda; G. Zavattini; R. Jager; A. N. Parmar; A. Owens; S. Molendi; G. Cusumano; Maria Concetta Maccarone; S. Giarrusso; A. Coletta; L. A. Antonelli; P. Giommi; J. M. Muller; L. Piro; R. C. Butler

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.


The Astrophysical Journal | 2005

Evidence for a canonical GRB afterglow light curve in the Swift/XRT data

Ja Nousek; Vanessa Mangano; Paul T. O'Brien; P. Giommi; Olivier Godet; S. D. Barthelmy; Mike R. Goad; Sergio Campana; G. Cusumano; J. P. Osborne; A. P. Beardmore; A. Falcone; Jonathan Granot; G. Tagliaferri; Milvia Capalbi; David N. Burrows; Patrizia Romano; C. P. Hurkett; J. A. Kennea; Guido Chincarini; Dirk Grupe; Enrico Ramirez-Ruiz; Sandy Patel; Kim L. Page; Alan A. Wells; Chryssa Kouveliotou; A. Moretti; N. Gehrels

We present new observations of the early X-ray afterglows of the first 27 gamma-ray bursts (GRBs) detected with the Swift X-ray Telescope (XRT). The early X-ray afterglows show a canonical behavior, where the light curve broadly consists of three distinct power law segments. These power law segments are separated by two corresponding break times. On top of this canonical behavior of the early X-ray light curve, many events have superimposed X-ray flares, which are most likely caused by internal shocks due to long lasting sporadx activity of the central engine, up to several hours after the GRB. We find that the initial steep decay is consistent with it being the tail of the prompt emission: from photons that are radiated at large angles relative to our line of sight. The first break in the light curve takes place when the forward shock emission becomes dominant, with the intermediate shallow flux decay likely caused by the continuous energy injection into the external shock. When this energy injection stops, a second break is then observed in the light curve. This energy injection increases the energy of the afterglow shock by at least a factor of f greater than or approx. equal to 4, and augments the already severe requirements for the efficiency of the prompt gamma-ray emission.


The Astrophysical Journal | 2006

Evidence for a canonical gamma-ray burst afterglow light curve in the Swift XRT data

John A. Nousek; C. Kouveliotou; Dirk Grupe; Kim L. Page; Jonathan Granot; Enrico Ramirez-Ruiz; Sandeep K. Patel; D. N. Burrows; Vanessa Mangano; S. D. Barthelmy; A. P. Beardmore; Sergio Campana; Milvia Capalbi; Guido Chincarini; G. Cusumano; A. Falcone; N. Gehrels; P. Giommi; Mike R. Goad; Olivier Godet; C. P. Hurkett; J. A. Kennea; A. Moretti; P. T. O’Brien; J. P. Osborne; Patrizia Romano; G. Tagliaferri; Alan A. Wells

We present new observations of the early X-ray afterglows of the first 27 gamma-ray bursts (GRBs) well observed by the Swift X-Ray Telescope (XRT). The early X-ray afterglows show a canonical behavior, where the light curve broadly consists of three distinct power-law segments: (1) an initial very steep decay (/t � � with 3P � 1 P5), followed by (2) a very shallow decay (0:5P � 2 P1:0), and finally (3) a somewhat steeper decay (1P � 3 P1:5). These power-law segments are separated by two corresponding break times, tbreak;1 P500 s and 10 3 sPtbreak;2P 10 4 s. On top of this canonical behavior, many events have superimposed X-ray flares, which are most likely caused by internal shocks due to long-lasting sporadic activity of the central engine, up to several hours after the GRB. We find that the initial steep decay is consistent with it being the tail of the prompt emission, from photons that are radiated at large angles relative to our line of sight. The first break in the light curve (tbreak;1) takes place when the forward shock emission becomes dominant, with the intermediate shallow flux decay (� 2) likely caused by the continuous energy injection into the external shock. When this energy injection stops, a second break is then observed in the light curve (tbreak;2). This energy injection increases the energy of the afterglow shock by at least a factor of f k4 and augments the already severe requirements for the efficiency of the prompt gamma-ray emission. Subject headingg gamma rays: bursts — radiation mechanisms: nonthermal


Nature | 2006

The association of GRB 060218 with a supernova and the evolution of the shock wave.

Sergio Campana; Vanessa Mangano; Alexander J. Blustin; Peter J. Brown; David N. Burrows; Guido Chincarini; J. R. Cummings; G. Cusumano; M. Della Valle; Daniele Malesani; P. Meszaros; John A. Nousek; M. J. Page; Takanori Sakamoto; Eli Waxman; Bing Zhang; Z. G. Dai; Neil Gehrels; Stefan Immler; F. E. Marshall; K. Mason; A. Moretti; Paul T. O'Brien; Julian P. Osborne; Kim L. Page; Patrizia Romano; Pwa Roming; Gianpiero Tagliaferri; L. R. Cominsky; P. Giommi

Although the link between long Gamma Ray Bursts (GRBs) and supernovae (SNe) has been established, hitherto there have been no observations of the beginning of a supernova explosion and its intimate link to a GRB. In particular, we do not know however how a GRB jet emerges from the star surface nor how a GRB progenitor explodes. Here we report on observations of the close GRB060218 and its connection to SN2006aj. In addition to the classical non-thermal emission, GRB060218 shows a thermal component in its X-ray spectrum, which cools and shifts into the optical/UV band as time passes. We interpret these features as arising from the break out of a shock driven by a mildly relativistic shell into the dense wind surrounding the progenitor. Our observations allow us for the first time to catch a SN in the act of exploding, to directly observe the shock break-out and to provide strong evidence that the GRB progenitor was a Wolf-Rayet star.Although the link between long γ-ray bursts (GRBs) and supernovae has been established, hitherto there have been no observations of the beginning of a supernova explosion and its intimate link to a GRB. In particular, we do not know how the jet that defines a γ-ray burst emerges from the stars surface, nor how a GRB progenitor explodes. Here we report observations of the relatively nearby GRB 060218 (ref. 5) and its connection to supernova SN 2006aj (ref. 6). In addition to the classical non-thermal emission, GRB 060218 shows a thermal component in its X-ray spectrum, which cools and shifts into the optical/ultraviolet band as time passes. We interpret these features as arising from the break-out of a shock wave driven by a mildly relativistic shell into the dense wind surrounding the progenitor. We have caught a supernova in the act of exploding, directly observing the shock break-out, which indicates that the GRB progenitor was a Wolf–Rayet star.


The Astrophysical Journal | 2006

The early x-ray emission from grbs

P. T. O’Brien; R. Willingale; Julian P. Osborne; Mike R. Goad; Kim L. Page; S. Vaughan; E. Rol; A. P. Beardmore; Olivier Godet; C. P. Hurkett; Alan A. Wells; Bing Zhang; Shiho Kobayashi; David N. Burrows; John A. Nousek; J. A. Kennea; A. Falcone; Dirk Grupe; Neil Gehrels; S. D. Barthelmy; John K. Cannizzo; J. R. Cummings; J. E. Hill; Hans A. Krimm; Guido Chincarini; Gianpiero Tagliaferri; Sergio Campana; A. Moretti; P. Giommi; Matteo Perri

We present observations of the early X-ray emission for a sample of 40 gamma-ray bursts (GRBs) obtained using the Swift satellite, for which the narrow-field instruments were pointed at the burst within 10 minutes of the trigger. Using data from the Burst Alert Telescope and the X-Ray Telescope, we show that the X-ray light curve can be well described by an exponential that relaxes into a power law, often with flares superimposed. The transition time between the exponential and the power law provides a physically defined timescale for the burst duration. In most bursts, the power law breaks to a shallower decay within the first hour, and a late emission hump is observed, which can last for many hours. In other GRBs the hump is weak or absent. The observed variety in the shape of the early X-ray light curve can be explained as a combination of three components: prompt emission from the central engine, afterglow, and the late hump. In this scenario, afterglow emission begins during or soon after the burst, and the observed shape of the X-ray light curve depends on the relative strengths of the emission due to the central engine and that of the afterglow. There is a strong correlation such that those GRBs with stronger afterglow components have brighter early optical emission. The late emission hump can have a total fluence equivalent to that of the prompt phase. GRBs with the strongest late humps have weak or no X-ray flares.


Nature | 2011

Relativistic jet activity from the tidal disruption of a star by a massive black hole

David N. Burrows; J. A. Kennea; G. Ghisellini; Vanessa Mangano; Bing Zhang; Kim L. Page; M. Eracleous; Patrizia Romano; T. Sakamoto; A. Falcone; J. P. Osborne; Sergio Campana; A. P. Beardmore; Alice A. Breeveld; M. M. Chester; R. Corbet; S. Covino; J. R. Cummings; Paolo D'Avanzo; Valerio D'Elia; P. Esposito; P. A. Evans; Dino Fugazza; Jonathan Mark Gelbord; Kazuo Hiroi; S. T. Holland; Kuiyun Huang; Myungshin Im; G. L. Israel; Young-Beom Jeon

Supermassive black holes have powerful gravitational fields with strong gradients that can destroy stars that get too close, producing a bright flare in ultraviolet and X-ray spectral regions from stellar debris that forms an accretion disk around the black hole. The aftermath of this process may have been seen several times over the past two decades in the form of sparsely sampled, slowly fading emission from distant galaxies, but the onset of the stellar disruption event has not hitherto been observed. Here we report observations of a bright X-ray flare from the extragalactic transient Swift J164449.3+573451. This source increased in brightness in the X-ray band by a factor of at least 10,000 since 1990 and by a factor of at least 100 since early 2010. We conclude that we have captured the onset of relativistic jet activity from a supermassive black hole. A companion paper comes to similar conclusions on the basis of radio observations. This event is probably due to the tidal disruption of a star falling into a supermassive black hole, but the detailed behaviour differs from current theoretical models of such events.D. N. Burrows , J. A. Kennea , G. Ghisellini , V. Mangano , B. Zhang , K. L. Page , M. Eracleous , P. Romano , T. Sakamoto , A. D. Falcone , J. P. Osborne , S. Campana , A. P. Beardmore , A. A. Breeveld , M. M. Chester , R. Corbet , S. Covino , J. R. Cummings , P. D’Avanzo , V. D’Elia , P. Esposito , P. A. Evans , D. Fugazza, J. M. Gelbord , K. Hiroi , S. T. Holland , K. Y. Huang , M. Im, G. Israel , Y. Jeon , Y.-B. Jeon , N. Kawai , H. A. Krimm , P. Mészáros , H. Negoro , N. Omodei , W.K. Park , J. S. Perkins , M. Sugizaki , H.-I. Sung , G. Tagliaferri , E. Troja , Y. Ueda, Y. Urata, R. Usui , L. A. Antonelli , S. D. Barthelmy , G. Cusumano , P. Giommi , F. E. Marshall , A. Melandri , M. Perri , J. L. Racusin , B. Sbarufatti , M. H. Siegel , & N. Gehrels 21


Nature | 2011

Relativistic jet activity from the tidal disruption of a star by a massive black hole [Discovery of the onset of rapid accretion by a dormant massive black hole]

D. N. Burrows; J. A. Kennea; G. Ghisellini; Vanessa Mangano; Bin-Bin Zhang; Kim L. Page; M. Eracleous; Patrizia Romano; T. Sakamoto; A. Falcone; J. P. Osborne; S. Campana; A. P. Beardmore; Alice A. Breeveld; M. M. Chester; R. Corbet; S. Covino; J. R. Cummings; Paolo D'Avanzo; Valerio D'Elia; P. Esposito; P. A. Evans; Dino Fugazza; Jonathan Mark Gelbord; Kazuo Hiroi; S. T. Holland; Kuiyun Huang; Myungshin Im; G. L. Israel; Young-Beom Jeon

Supermassive black holes have powerful gravitational fields with strong gradients that can destroy stars that get too close, producing a bright flare in ultraviolet and X-ray spectral regions from stellar debris that forms an accretion disk around the black hole. The aftermath of this process may have been seen several times over the past two decades in the form of sparsely sampled, slowly fading emission from distant galaxies, but the onset of the stellar disruption event has not hitherto been observed. Here we report observations of a bright X-ray flare from the extragalactic transient Swift J164449.3+573451. This source increased in brightness in the X-ray band by a factor of at least 10,000 since 1990 and by a factor of at least 100 since early 2010. We conclude that we have captured the onset of relativistic jet activity from a supermassive black hole. A companion paper comes to similar conclusions on the basis of radio observations. This event is probably due to the tidal disruption of a star falling into a supermassive black hole, but the detailed behaviour differs from current theoretical models of such events.D. N. Burrows , J. A. Kennea , G. Ghisellini , V. Mangano , B. Zhang , K. L. Page , M. Eracleous , P. Romano , T. Sakamoto , A. D. Falcone , J. P. Osborne , S. Campana , A. P. Beardmore , A. A. Breeveld , M. M. Chester , R. Corbet , S. Covino , J. R. Cummings , P. D’Avanzo , V. D’Elia , P. Esposito , P. A. Evans , D. Fugazza, J. M. Gelbord , K. Hiroi , S. T. Holland , K. Y. Huang , M. Im, G. Israel , Y. Jeon , Y.-B. Jeon , N. Kawai , H. A. Krimm , P. Mészáros , H. Negoro , N. Omodei , W.K. Park , J. S. Perkins , M. Sugizaki , H.-I. Sung , G. Tagliaferri , E. Troja , Y. Ueda, Y. Urata, R. Usui , L. A. Antonelli , S. D. Barthelmy , G. Cusumano , P. Giommi , F. E. Marshall , A. Melandri , M. Perri , J. L. Racusin , B. Sbarufatti , M. H. Siegel , & N. Gehrels 21


Astronomy and Astrophysics | 2009

Roma-BZCAT: A multifrequency catalogue of Blazars

E. Massaro; P. Giommi; Cristina Leto; P. Marchegiani; A. Maselli; Matteo Perri; S. Piranomonte; S. Sclavi

We present a new catalogue of blazars based on multi-frequency surveys and on an extensive review of the literature. Blazars are classified as BL Lacertae objects, as flat spectrum radio quas ars or as blazars of uncertain/transitional type. Each object is identified by a root name, coded as BZB, BZQ and BZU for these three subclasses respectively, and by its coordinates. This catalogue i s being built as a tool useful for the identification of the extragala ctic sources that will be detected by present and future experiments for X and gamma-ray astronomy, like Swift, AGILE, Fermi-GLAST and Simbol-X. An electronic version is available from the ASI Science Data Center web site at http://www.asdc.asi.it/bzcat.


Nature | 2005

An origin for short gamma-ray bursts unassociated with current star formation.

S D Barthelmy; G Chincarini; D N Burrows; N Gehrels; S. Covino; A. Moretti; P Romano; Paul T. O'Brien; C L Sarazin; C Kouveliotou; Mike R. Goad; S Vaughan; G Tagliaferri; Bing Zhang; L. A. Antonelli; Sergio Campana; J R Cummings; P D'Avanzo; Melvyn B. Davies; P. Giommi; D Grupe; Y Kaneko; J A Kennea; A King; Shiho Kobayashi; A Melandri; P. Meszaros; J A Nousek; S Patel; T Sakamoto

Two short (< 2 s) γ-ray bursts (GRBs) have recently been localized and fading afterglow counterparts detected. The combination of these two results left unclear the nature of the host galaxies of the bursts, because one was a star-forming dwarf, while the other was probably an elliptical galaxy. Here we report the X-ray localization of a short burst (GRB 050724) with unusual γ-ray and X-ray properties. The X-ray afterglow lies off the centre of an elliptical galaxy at a redshift of z = 0.258 (ref. 5), coincident with the position determined by ground-based optical and radio observations. The low level of star formation typical for elliptical galaxies makes it unlikely that the burst originated in a supernova explosion. A supernova origin was also ruled out for GRB 050709 (refs 3, 31), even though that burst took place in a galaxy with current star formation. The isotropic energy for the short bursts is 2–3 orders of magnitude lower than that for the long bursts. Our results therefore suggest that an alternative source of bursts—the coalescence of binary systems of neutron stars or a neutron star-black hole pair—are the progenitors of short bursts.


Nature | 2005

An unexpectedly rapid decline in the X-ray afterglow emission of long gamma-ray bursts.

Gianpiero Tagliaferri; Mike R. Goad; Guido Chincarini; A. Moretti; Sergio Campana; David N. Burrows; Matteo Perri; S. D. Barthelmy; N. Gehrels; Hans A. Krimm; Takanori Sakamoto; Pawan Kumar; P. Meszaros; Shiho Kobayashi; Bing Zhang; L. Angelini; P. L. Banat; A. P. Beardmore; Milvia Capalbi; S. Covino; G. Cusumano; P. Giommi; Olivier Godet; J. E. Hill; J. A. Kennea; Vanessa Mangano; David C. Morris; John A. Nousek; Paul T. O'Brien; Julian P. Osborne

‘Long’ γ-ray bursts (GRBs) are commonly accepted to originate in the explosion of particularly massive stars, which give rise to highly relativistic jets. Inhomogeneities in the expanding flow result in internal shock waves that are believed to produce the γ-rays we see. As the jet travels further outward into the surrounding circumstellar medium, ‘external’ shocks create the afterglow emission seen in the X-ray, optical and radio bands. Here we report observations of the early phases of the X-ray emission of five GRBs. Their X-ray light curves are characterised by a surprisingly rapid fall-off for the first few hundred seconds, followed by a less rapid decline lasting several hours. This steep decline, together with detailed spectral properties of two particular bursts, shows that violent shock interactions take place in the early jet outflows.

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