Aims. We present the time-resolved optical emission of gamma-ray bursts GRB 060904B and GRB 070420 during their prompt and early afterglow phases. Methods. We used time resolved photometry from ...optical data taken by the TAROT telescope and time resolved spectroscopy at high energies from the Swift spacecraft instrument. Results. The optical emissions of both GRBs are found to increase from the end of the prompt phase, passing to a maximum of brightness at $t_{\rm peak}=9.2$ min and 3.3 min for GRB 060904B and GRB 070420 respectively and then decrease. GRB 060904B presents a large optical plateau and a very large X-ray flare. We argue that the very large X-flare occurring near tpeak is produced by an extended internal engine activity and is only a coincidence with the optical emission. GRB 070420 observations would support this idea because there was no X-flare during the optical peak. The nature of the optical plateau of GRB 060904B is less clear and might be related to the late energy injection.
Context. Our knowledge of the intrinsic properties of short duration Gamma-Ray Bursts has relied, so far, only upon a few cases for which the estimate of the distance and an extended, multiwavelength ...monitoring of the afterglow have been obtained. Aims. We carried out multiwavelength observations of the short GRB 061201 aimed at estimating its distance and studying its properties. Methods.We performed a spectral and timing analysis of the prompt and afterglow emission and discuss the results in the context of the standard fireball model. Results. A clear temporal break was observed in the X-ray light curve about 40 min after the burst trigger. We find that the spectral and timing behaviour of the X-ray afterglow is consistent with a jet origin of the observed break, although the optical data can not definitively confirm this and other scenarios are possible. No underlying host galaxy down to R ~ 26 mag was found after fading of the optical afterglow. Thus, no secure redshift could be measured for this burst. The nearest galaxy is at $z = 0.111$ and shows evidence of star formation activity. We discuss the association of GRB 061201 with this galaxy and with the ACO S 995 galaxy cluster, from which the source is at an angular distance of 17'' and 8.5', respectively. We also test the association with a possible undetected, positionally consistent galaxy at z ~ 1. In all these cases, in the jet interpretation, we find a jet opening angle of 1–2 degrees.
We present the long-term monitoring of the high-mass X-ray binary GX 301-2 performed with the SuperAGILE (SA) instrument on-board the Astro-rivelatore Gamma ad Immagini LEggero (AGILE) mission. The ...source was monitored in the 20-60 keV energy band during the first year of the mission from 2007 July 17 to 2008 August 31, covering about one whole orbital period and three more pre-periastron (PP) passages for a total net observation time of about 3.7 Ms. The SA data set represents one of the most continuous and complete monitoring at hard X-ray energies of the 41.5 days long binary period available to date. The source behavior was characterized at all orbital phases in terms of hard X-ray flux, spectral hardness, spin-period history, pulsed fraction, and pulse shape profile. We also complemented the SA observations with the soft X-ray data of the Rossi X-Ray Timing Explorer/All-Sky Monitor. Our analysis shows a clear orbital modulation of the spectral hardness, with peaks in correspondence with the PP flare and near phase 0.25. The hardness peaks, we found, could be related with the wind-plus-stream accretion model proposed in order to explain the orbital light-curve modulation of GX 301-2. Timing analysis of the pulsar spin period shows that the secular trend of the ~680 s pulse period is consistent with the previous observations, although there is evidence of a slight decrease in the spin-down rate. The analysis of the hard X-ray-pulsed emission also showed a variable pulse shape profile as a function of the orbital phase, with substructures detected near the passage at the periastron, and a clear modulation of the pulsed fraction, which appears in turn strongly anticorrelated with the source intensity.
Since its early phases of operation, the AGILE mission is successfully observing Gamma Ray Bursts (GRBs) in the hard X-ray band with the SuperAGILE imager and in the MeV range with the ...Mini-Calorimeter. Up to now, three firm GRB detections were obtained above 25
MeV and some bursts were detected with lower statistical confidence in the same energy band. When a GRB is localized, either by SuperAGILE or Swift/BAT or INTEGRAL/IBIS or Fermi/GBM or IPN, inside the field of view of the Gamma Ray Imager of AGILE, a detection is searched for in the gamma ray band or an upper limit is provided. A promising result of AGILE is the detection of very short gamma ray transients, a few ms in duration and possibly identified with Terrestrial Gamma-ray Flashes. In this paper we show the current status of the observation of Gamma Ray Bursts and Terrestrial Gamma-ray Flashes with AGILE.
The AGILE Mission Barbiellini, G.; Argan, A.; Boffelli, F. ...
Astronomy & astrophysics,
08/2009, Letnik:
502, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Context. AGILE is an Italian Space Agency mission dedicated to observing the gamma-ray Universe. The AGILE's very innovative instrumentation for the first time combines a gamma-ray imager (sensitive ...in the energy range 30 MeV–50 GeV), a hard X-ray imager (sensitive in the range 18–60 keV), a calorimeter (sensitive in the range 350 keV–100 MeV), and an anticoincidence system. AGILE was successfully launched on 2007 April 23 from the Indian base of Sriharikota and was inserted in an equatorial orbit with very low particle background. Aims. AGILE provides crucial data for the study of active galactic nuclei, gamma-ray bursts, pulsars, unidentified gamma-ray sources, galactic compact objects, supernova remnants, TeV sources, and fundamental physics by microsecond timing. Methods. An optimal sky angular positioning (reaching 0.1 degrees in gamma-rays and 1–2 arcmin in hard X-rays) and very large fields of view (2.5 sr and 1 sr, respectively) are obtained by the use of Silicon detectors integrated in a very compact instrument. Results. AGILE surveyed the gamma-ray sky and detected many Galactic and extragalactic sources during the first months of observations. Particular emphasis is given to multifrequency observation programs of extragalactic and galactic objects. Conclusions. AGILE is a successful high-energy gamma-ray mission that reached its nominal scientific performance. The AGILE Cycle-1 pointing program started on 2007 December 1, and is open to the international community through a Guest Observer Program.
We report the detection by the Astrorivelatore Gamma a Immagini Leggero (AGILE) satellite of terrestrial gamma ray flashes (TGFs) obtained with the minicalorimeter (MCAL) detector operating in the ...energy range 0.3–100 MeV. We select events typically lasting a few milliseconds with spectral and directional selections consistent with the TGF characteristics previously reported by other space missions. During the period 1 June 2008 to 31 March 2009 we detect 34 high‐confidence events showing millisecond durations and a geographical distribution peaked over continental Africa and Southeast Asia. For the first time, AGILE‐MCAL detects photons associated with TGF events up to 40 MeV. We determine the cumulative spectral properties of the spectrum in the range 0.5–40 MeV, which can be effectively described by a Bremsstrahlung spectrum. We find that both the TGF cumulative spectral properties and their geographical distribution are in good agreement with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) results.
The Italian Space Agency Science Data Center (ASDC) is a facility with several responsibilities including support to all the ASI scientific missions as for management and archival of the data, acting ...as the interface between ASI and the scientific community and providing on-line access to the data hosted. In this poster we describe the services that ASDC provides for SuperAGILE, in particular the ASDC public web pages devoted to the dissemination of SuperAGILE scientific results. SuperAGILE is the X-Ray imager onboard the AGILE mission, and provides the scientific community with orbit-by-orbit information on the observed sources. Crucial source information including position and flux in chosen energy bands will be reported in the SuperAGILE public web page at ASDC. Given their particular interest, another web page will be dedicated entirely to GRBs and other transients, where new event alerts will be notified and where users will find all the available informations on the GRBs detected by SuperAGILE.
We report on a multiwavelength observation of the blazar 3C 454.3 (which we dubbed crazy diamond) carried out on November 2007 by means of the astrophysical satellites AGILE, International Gamma-Ray ...Astrophysics Laboratory (INTEGRAL), Swift, the Whole Earth Blazar Telescope (WEBT) Consortium, and the optical-NIR telescope Rapid Eye Mount (REM). Thanks to the wide field of view of the AGILE satellite and its prompt alert dissemination to other observatories, we obtained a long (three weeks), almost continuous gamma -ray coverage of the blazar 3C 454.3 across 14 decades of energy. This broadband monitoring allows us to study in great detail light curves, correlations, time lags, and spectral energy distributions (SEDs) during different physical states. Gamma-ray data were collected during an AGILE pointing toward the Cygnus Region. Target of Opportunity (ToO) observations were performed to follow up the gamma -ray observations in the soft and hard X-ray energy bands. Optical data were acquired continuously by means of a preplanned WEBT campaign and through an REM ToO repointing. 3C 454.3 is detected at a ~19 sigma level during the three-week observing period, with an average flux above 100 MeV of F E > 100 MeV = (170 ± 13) X 10-8 photons cm-2 s-1. The gamma -ray spectrum can be fitted with a single power law with photon index Gamma GRID = 1.73 ± 0.16 between 100 MeV and 1 GeV. We detect significant day-by-day variability of the gamma -ray emission during our observations, and we can exclude that the fluxes are constant at the 99.6% (~2.9 sigma ) level. The source was detected typically around 40 deg off-axis, and it was substantially off-axis in the field of view of the AGILE hard X-ray imager. However, a five-day long ToO observation by INTEGRAL detected 3C 454.3 at an average flux of about F 20-200 keV = 1.49 X 10-3 photons cm-2 s-1with an average photon index of Gamma IBIS = 1.75 ± 0.24 between 20-200 keV. Swift also detected 3C 454.3 with a flux in the 0.3-10 keV energy band in the range (1.23-1.40) X 10-2 photons cm-2 s-1 and a photon index in the range Gamma XRT = 1.56-1.73. In the optical band, both WEBT and REM show an extremely variable behavior in the R band. A correlation analysis based on the entire data set is consistent with no time lags between the gamma -ray and the optical flux variations. Our simultaneous multifrequency observations strongly indicate that the dominant emission mechanism between 30 MeV and 30 GeV is dominated by inverse Compton scattering of relativistic electrons in the jet on the external photons from the broad line region.
The X-ray afterglow of the short GRB 061201 clearly showed an early steepening of the light curve 0.7 hours after the burst with post break decay index consistent with d2~2. We discuss some possible ...interpretations of this feature. Despite the optical afterglow was clearly detected, no underlying galaxy was found down to R'26 mag.
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