-
A. Bulgarelli,
C. Pittori,
F. Lucarelli, E. Striani,
F. Gianotti,
M. Trifoglio,
S. Sabatini,
M. Tavani,
F. Verrecchia,
A. Trois, [......],
P. Picozza,
M. Prest,
P. Lipari,
D. Zanello,
P. W. Cattaneo,
A. Rappoldi,
P. Santolamazza,
S. Colafrancesco,
P. Giommi,
L. Salotti
[show abstract]
[hide abstract]
ABSTRACT: AGILE is detecting an intense gamma-ray emission above 100 MeV from a
source of Galactic coordinates (l, b) = (70.3 2.5) ± 1.2
deg (95% stat. c.l. and systematic error) (1-day integration).
Integrating from 2010-03-24 02:24 UT to 2010-03-25 01:01 UT, a maximum
likelihood analysis yields a detection at a significance level of about
5 sigma, and a flux above 250 10-8 ph/cm2/s (E > 100 MeV).
The Astronomer's Telegram. 02/2010; 2512:1.
-
S. Sabatini,
M. Tavani, E. Striani,
A. Bulgarelli,
V. Vittorini,
G. Piano,
E. Del Monte,
M. Feroci,
F. de Pasquale,
M. Trifoglio, [......],
S. Vercellone,
A. Zambra,
D. Zanello,
C. Pittori,
F. Verrecchia,
P. Santolamazza,
P. Giommi,
S. Colafrancesco,
L. A. Antonelli,
L. Salotti
[show abstract]
[hide abstract]
ABSTRACT: Cygnus X-1 is the archetypal black hole (BH) binary system in our Galaxy. We report the main results of an extensive search for transient gamma-ray emission from Cygnus X-1 carried out in the energy range 100 MeV - 3 GeV by the AGILE satellite, during the period 2007 July - 2009 October. The total exposure time is about 300 days, during which the source was in the "hard" X-ray spectral state. We divided the observing intervals in 2 or 4 week periods, and searched for transient and persistent emission. We report an episode of significant transient gamma-ray emission detected on 2009, October 16 in a position compatible with Cygnus X-1 optical position. This episode, occurred during a hard spectral state of Cygnus X-1, shows that a 1-2 day time variable emission above 100 MeV can be produced during hard spectral states, having important theoretical implications for current Comptonization models for Cygnus X-1 and other microquasars. Except for this one short timescale episode, no significant gamma-ray emission was detected by AGILE. By integrating all available data we obtain a 2$\sigma$ upper limit for the total integrated flux of $F_{\gamma,U.L.} = 3 \times 10^{-8} \rm ph cm^{-2} s^{-1}$ in the energy range 100 MeV - 3 GeV. We then clearly establish the existence of a spectral cutoff in the energy range 1-100 MeV that applies to the typical hard state outside the flaring period and that confirms the historically known spectral cutoff above 1 MeV. Comment: Accepted for publication by ApJ on the 9th of Feb 2010, 5 pages, 3 figures
02/2010;
-
A Pellizzoni,
A Trois,
M Tavani,
M Pilia,
A Giuliani,
G Pucella,
P Esposito,
S Sabatini,
G Piano,
A Argan, [......],
F Verrecchia,
V Vittorini,
A Zambra,
D Zanello,
P Giommi,
S Colafrancesco,
A Antonelli,
L Salotti,
N D'Amico,
G F Bignami
[show abstract]
[hide abstract]
ABSTRACT: Pulsars are known to power winds of relativistic particles that can produce bright nebulae by interacting with the surrounding medium. These pulsar wind nebulae are observed by their radio, optical, and x-ray emissions, and in some cases also at TeV (teraelectron volt) energies, but the lack of information in the gamma-ray band precludes drawing a comprehensive multiwavelength picture of their phenomenology and emission mechanisms. Using data from the AGILE satellite, we detected the Vela pulsar wind nebula in the energy range from 100 MeV to 3 GeV. This result constrains the particle population responsible for the GeV emission and establishes a class of gamma-ray emitters that could account for a fraction of the unidentified galactic gamma-ray sources.
Science 02/2010; 327(5966):663-5. · 31.20 Impact Factor
-
S. Vercellone,
F. D'Ammando,
V. Vittorini,
I. Donnarumma,
G. Pucella,
M. Tavani,
A Ferrari,
C. M. Raiteri,
M. Villata,
P. Romano, [......],
A. Lahteenmaki,
V. M. Larionov,
P. Leto,
R. Ligustri,
E. Lindfors,
J M Lopez,
A. P. Marscher,
R. Mujica,
M. Nikolashvili,
K. Nilsson
[show abstract]
[hide abstract]
ABSTRACT: We report on 18 months of multiwavelength observations of the blazar 3C 454.3 (Crazy Diamond) carried out in July 2007-January 2009. We show the results of the AGILE campaigns which took place on May-June 2008, July-August 2008, and October 2008-January 2009. During the May 2008-January 2009 period, the source average flux was highly variable, from an average gamma-ray flux F(E>100MeV) > 200E-8 ph/cm2/s in May-June 2008, to F(E>100MeV)~80E-8 ph/cm2/s in October 2008-January 2009. The average gamma-ray spectrum between 100 MeV and 1 GeV can be fit by a simple power law (Gamma_GRID ~ 2.0 to 2.2). Only 3-sigma upper limits can be derived in the 20-60 keV energy band with Super-AGILE. During July-August 2007 and May-June 2008, RXTE measured a flux of F(3-20 keV)= 8.4E-11 erg/cm2/s, and F(3-20 keV)=4.5E-11 erg/cm2/s, respectively and a constant photon index Gamma_PCA=1.65. Swift/XRT observations were carried out during all AGILE campaigns, obtaining a F(2-10 keV)=(0.9-7.5)E-11 erg/cm2/s and a photon index Gamma_XRT=1.33-2.04. BAT measured an average flux of ~5 mCrab. GASP-WEBT monitored 3C 454.3 during the whole 2007-2008 period from the radio to the optical. A correlation analysis between the optical and the gamma-ray fluxes shows a time lag of tau=-0.4 days. An analysis of 15 GHz and 43 GHz VLBI core radio flux observations shows an increasing trend of the core radio flux, anti- correlated with the higher frequency data. The modeling SEDs, and the behavior of the long-term light curves in different energy bands, allow us to compare the jet properties during different emission states, and to study the geometrical properties of the jet on a time-span longer than one year. Comment: Accepted for publication in ApJ. Adapted Abstract. 17 pages, 19 Figures, 5 Tables
02/2010;
-
M. Tavani,
A Giuliani,
A. W. Chen,
A. Argan,
G. Barbiellini,
A. Bulgarelli,
P. Caraveo,
P W Cattaneo,
V. Cocco,
T. Contessi, [......],
V. Vittorini,
A. Zambra,
D. Zanello,
C. Pittori,
F. Verrecchia,
P. Santolamazza,
P. Giommi,
S. Colafrancesco,
L. A. Antonelli,
L. Salotti
[show abstract]
[hide abstract]
ABSTRACT: The Supernova Remnant (SNR) IC 443 is an intermediate-age remnant well known for its radio, optical, X-ray and gamma-ray energy emissions. In this Letter we study the gamma-ray emission above 100 MeV from IC 443 as obtained by the AGILE satellite. A distinct pattern of diffuse emission in the energy range 100 MeV-3 GeV is detected across the SNR with its prominent maximum (source "A") localized in the Northeastern shell with a flux F = (47 \pm 10) 10^{-8} photons cm^{-2} s^{-1} above 100 MeV. This location is the site of the strongest shock interaction between the SNR blast wave and the dense circumstellar medium. Source "A" is not coincident with the TeV source located 0.4 degree away and associated with a dense molecular cloud complex in the SNR central region. From our observations, and from the lack of detectable diffuse TeV emission from its Northeastern rim, we demonstrate that electrons cannot be the main emitters of gamma-rays in the range 0.1-10 GeV at the site of the strongest SNR shock. The intensity, spectral characteristics, and location of the most prominent gamma-ray emission together with the absence of co-spatial detectable TeV emission are consistent only with a hadronic model of cosmic-ray acceleration in the SNR. A high-density molecular cloud (cloud "E") provides a remarkable "target" for nucleonic interactions of accelerated hadrons: our results show enhanced gamma-ray production near the molecular cloud/shocked shell interaction site. IC 443 provides the first unambiguous evidence of cosmic-ray acceleration by SNRs. Comment: 5 pages, 2 figures; accepted by ApJLetters on Jan 21, 2010
01/2010;
-
M. Marisaldi,
F. Fuschino,
C. Labanti,
M. Galli,
F. Longo,
E. Del Monte,
G. Barbiellini,
M. Tavani,
A. Giuliani,
E. Moretti, [......],
D. Zanello,
L. A. Antonelli,
S. Colafrancesco,
D. Gasparrini,
P. Giommi,
C. Pittori,
B. Preger,
P. Santolamazza,
F. Verrecchia,
L. Salotti
Journal of Geophysical Research-Space Physics. 01/2010; 115.
-
M. Tavani,
A. Giuliani,
A. W. Chen,
A. Argan,
G. Barbiellini,
A. Bulgarelli,
P. Caraveo,
P. W. Cattaneo,
V. Cocco,
T. Contessi, [......],
V. Vittorini,
A. Zambra,
D. Zanello,
C. Pittori,
F. Verrecchia,
P. Santolamazza,
P. Giommi,
S. Colafrancesco,
L. A. Antonelli,
L. Salotti
Astrophysical Journal Letters. 01/2010; 710(2):L151-L155.
-
A Giuliani,
M Tavani,
G Piano,
M Cardillo, E Striani,
S Sabatini,
A Argan,
E E Costa,
Monte Del,
I Donnarumma, [......],
G Barbiellini,
F Longo,
P W Cattaneo,
A Rappoldi,
F D 'ammando,
S Vercellone,
P Lipari,
A Pellizzoni,
M Pilia,
A Trois
PoS. 01/2010;
-
A. Bulgarelli,
F. Gianotti,
M. Trifoglio,
F. Lucarelli,
C. Pittori,
F. Verrecchia,
M. Tavani, E. Striani,
A. Chen,
A. Giuliani, [......],
P. Picozza,
M. Prest,
P. Lipari,
D. Zanello,
P. W. Cattaneo,
A. Rappoldi,
P. Santolamazza,
S. Colafrancesco,
P. Giommi,
L. Salotti
[show abstract]
[hide abstract]
ABSTRACT: AGILE is detecting intense gamma-ray emission above 100 MeV from a new
unidentified source, AGL J2206+6203, with Galactic coordinates (l, b) =
(104.9, 5.1) ± 0.4 deg (95% stat. c.l.) ±
0.1 deg (syst.), and Celestial coordinates R.A. (J2000) = 22 06 49.17,
Dec. (J2000)= 62 03 45.2. Integrating from 2010-01-20 03:46 UT to
2010-01-25 11:15 UT, a maximum likelihood analysis yields a detection
at a significance level larger than 5 sigma, and a flux F = (160+/-50)
10-8 ph/cm2/s (E > 100 MeV).
The Astronomer's Telegram. 12/2009; 2403:1.
-
A A Abdo,
M Ackermann,
M Ajello,
B Anderson,
W B Atwood,
M Axelsson,
L Baldini,
J Ballet,
G Barbiellini,
D Bastieri, [......],
T L Usher,
V Vasileiou,
N Vilchez,
V Vitale,
A P Waite,
P Wang,
B L Winer,
K S Wood,
T Ylinen,
M Ziegler
[show abstract]
[hide abstract]
ABSTRACT: The diffuse galactic gamma-ray emission is produced by cosmic rays (CRs) interacting with the interstellar gas and radiation field. Measurements by the Energetic Gamma-Ray Experiment Telescope (EGRET) instrument on the Compton Gamma-Ray Observatory indicated excess gamma-ray emission greater, > or approximately equal to 1 GeV relative to diffuse galactic gamma-ray emission models consistent with directly measured CR spectra (the so-called "EGRET GeV excess"). The Large Area Telescope (LAT) instrument on the Fermi Gamma-Ray Space Telescope has measured the diffuse gamma-ray emission with improved sensitivity and resolution compared to EGRET. We report on LAT measurements for energies 100 MeV to 10 GeV and galactic latitudes 10 degrees < or = |b| < or = 20 degrees. The LAT spectrum for this region of the sky is well reproduced by a diffuse galactic gamma-ray emission model that is consistent with local CR spectra and inconsistent with the EGRET GeV excess.
Physical Review Letters 12/2009; 103(25):251101. · 7.37 Impact Factor
-
F. Verrecchia, E. Striani,
M. Tavani,
C. Pittori,
P. Santolamazza,
F. Lucarelli,
S. Vercellone,
F. D'Ammando,
I. Donnarumma,
V. Vittorini, [......],
A. Morselli,
P. Picozza,
M. Prest,
P. Lipari,
D. Zanello,
P. W. Cattaneo,
A. Rappoldi,
S. Colafrancesco,
P. Giommi,
L. Salotti
[show abstract]
[hide abstract]
ABSTRACT: AGILE is detecting a significant gamma-ray emission above 100 MeV from a
source consistent with the position of the blazar PKS 1222+216.
Integrating from 2009-12-13 06:00 UT to 2009-12-15 06:00 UT, a quicklook
maximum likelihood analysis of the AGILE-GRID data yields a detection
at a significance level larger than 5 sigma and a source flux above
250e-8 ph/cm2/sec (E > 100 MeV). An increased gamma-ray activity
from a source consistent with the blazar PKS 1222+216 was previously
reported by Fermi/LAT (ATel #2021) on April 16 2009, with a gamma-ray
flux of (46+/-13)e-8 ph/cm2/sec (E > 100MeV), ten times higher than
the average 6 months value.
The Astronomer's Telegram. 11/2009; 2348:1.
-
E. Striani,
S. Vercellone,
F. Verrecchia,
C. Pittori,
P. Santolamazza,
M. Tavani,
F. D'Ammando,
I. Donnarumma,
V. Vittorini,
E. Del Monte, [......],
A. Morselli,
P. Picozza,
M. Prest,
P. Lipari,
D. Zanello,
P. W. Cattaneo,
A. Rappoldi,
S. Colafrancesco,
P. Giommi,
L. Salotti
[show abstract]
[hide abstract]
ABSTRACT: The AGILE Gamma-Ray Imaging Detector (GRID) has been detecting prolonged
flaring gamma-ray emission above 100 MeV from the flat spectrum radio
quasar 3C 454.3. Integrating from 2009-11-26 01:00UT to 2009-12-02
08:30UT, a quick-look maximum likelihood analysis yields a source flux
of about 700e-8 ph/cm2/sec (E > 100 MeV), with a peak in the last 48
hours of the order of 1000e-8 ph/cm2/sec (E > 100 MeV).
The Astronomer's Telegram. 11/2009; 2322:1.
-
E. Striani,
S. Vercellone,
F. Verrecchia,
C. Pittori,
P. Santolamazza,
M. Tavani,
F. D'Ammando,
I. Donnarumma,
V. Vittorini,
E. Del Monte, [......],
A. Morselli,
P. Picozza,
M. Prest,
P. Lipari,
D. Zanello,
P. W. Cattaneo,
A. Rappoldi,
S. Colafrancesco,
P. Giommi,
L. Salotti
[show abstract]
[hide abstract]
ABSTRACT: The AGILE Gamma-Ray Imaging Detector (GRID) has been detecting an
extraordinary intense gamma-ray emission above 100 MeV from the flat
spectrum radio quasar 3C 454.3. Integrating from 2009-12-02 06:30
UT to 2009-12-03 08:30 UT, a quick-look maximum likelihood analysis
yields a source flux of about (1800 ± 400)e-8 ph/cm2/sec (E >
100 MeV). This flux value greatly exceeds the value reported by AGILE
in ATel #2322, showing a rapid increase (about 80%) of the gamma-ray
flux of 3C 454.3 in the last 24 hours.
The Astronomer's Telegram. 11/2009; 2326:1.
-
S. Vercellone,
M. Fiocchi,
E. Pian,
M. Tavani,
A. Bazzano,
P. Ubertini,
A. Argan,
E. Costa,
F. D'Ammando,
E. Del Monte, [......],
P. Lipari,
D. Zanello,
P. W. Cattaneo,
A. Rappoldi,
S. Colafrancesco,
P. Giommi,
C. Pittori,
P. Santolamazza,
F. Verrecchia,
L. Salotti
[show abstract]
[hide abstract]
ABSTRACT: The INTEGRAL satellite performed a Target of Opportunity observation of
the blazar 3C 454.3 following the detection by the AGILE/GRID (ATel
#2326) and by the Fermi/LAT (ATel #2328) of a gamma-ray super-flare
above 100 MeV on 2009-12-02. Integrating the data from 2009-12-06
16:41 UT to 2009-12-09 07:46 UT, for a net exposure of about 205 ks, we
obtain a detection of the blazar with INTEGRAL/IBIS with a flux F(20-40
keV) = 13 mCrab (9.8E-11 erg/cm2/s), and a flux F(40-100 keV) = 16
mCrab (1.5E-10 erg/cm2/s).
The Astronomer's Telegram. 11/2009; 2344:1.
-
Y. Evangelista,
M. Feroci,
E. Costa,
E. Del Monte,
I. Donnarumma,
I. Lapshov,
F. Lazzarotto,
L. Pacciani,
M. Rapisarda,
P. Soffitta, [......],
V. Vittorini,
A. Zambra,
L. A. Antonelli,
S. Cutini,
C. Pittori,
B. Preger,
P. Santolamazza,
F. Verrecchia,
P. Giommi,
L. Salotti
[show abstract]
[hide abstract]
ABSTRACT: We present the long-term monitoring of the High Mass X-ray Binary GX 301-2 performed with the SuperAGILE instrument on-board the 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 passages for a total net observation time of about 3.7 Ms. The SuperAGILE dataset represents one of the most continuous and complete monitoring at hard X-ray energies of the 41.5 day 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 SuperAGILE observations with the soft X-ray data of the RossiXTE/ASM. Our analysis shows a clear orbital modulation of the spectral hardness, with peaks in correspondence with the pre-periastron 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 about 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 anti-correlated with the source intensity. Comment: 10 pages, 7 figures, 3 tables, accepted for publication in ApJ
11/2009;
-
M Tavani,
A Bulgarelli,
G Piano,
S Sabatini, E Striani,
Y Evangelista,
A Trois,
G Pooley,
S Trushkin,
N A Nizhelskij, [......],
S Vercellone,
A Zambra,
D Zanello,
C Pittori,
F Verrecchia,
P Giommi,
S Colafrancesco,
P Santolamazza,
A Antonelli,
L Salotti
[show abstract]
[hide abstract]
ABSTRACT: Super-massive black holes in active galaxies can accelerate particles to relativistic energies, producing jets with associated gamma-ray emission. Galactic 'microquasars', which are binary systems consisting of a neutron star or stellar-mass black hole accreting gas from a companion star, also produce relativistic jets, generally together with radio flares. Apart from an isolated event detected in Cygnus X-1, there has hitherto been no systematic evidence for the acceleration of particles to gigaelectronvolt or higher energies in a microquasar, with the consequence that we are as yet unsure about the mechanism of jet energization. Here we report four gamma-ray flares with energies above 100 MeV from the microquasar Cygnus X-3 (an exceptional X-ray binary that sporadically produces radio jets). There is a clear pattern of temporal correlations between the gamma-ray flares and transitional spectral states of the radio-frequency and X-ray emission. Particle acceleration occurred a few days before radio-jet ejections for two of the four flares, meaning that the process of jet formation implies the production of very energetic particles. In Cygnus X-3, particle energies during the flares can be thousands of times higher than during quiescent states.
Nature 11/2009; 462(7273):620-3. · 36.28 Impact Factor
-
M. Tavani,
A. Bulgarelli,
G. Piano,
S. Sabatini, E. Striani,
Y. Evangelista,
A. Trois,
G. Pooley,
S. Trushkin,
N. A. Nizhelskij, [......],
S. Vercellone,
A. Zambra,
D. Zanello,
C. Pittori,
F. Verrecchia,
P. Giommi,
S. Colafrancesco,
P. Santolamazza,
A Antonelli,
L. Salotti
[show abstract]
[hide abstract]
ABSTRACT: The study of relativistic particle acceleration is a major topic of high-energy astrophysics. It is well known that massive black holes in active galaxies can release a substantial fraction of their accretion power into energetic particles, producing gamma-rays and relativistic jets. Galactic microquasars (hosting a compact star of 1-10 solar masses which accretes matter from a binary companion) also produce relativistic jets. However, no direct evidence of particle acceleration above GeV energies has ever been obtained in microquasar ejections, leaving open the issue of the occurrence and timing of extreme matter energization during jet formation. Here we report the detection of transient gamma-ray emission above 100 MeV from the microquasar Cygnus X-3, an exceptional X-ray binary which sporadically produces powerful radio jets. Four gamma-ray flares (each lasting 1-2 days) were detected by the AGILE satellite simultaneously with special spectral states of Cygnus X-3 during the period mid-2007/mid-2009. Our observations show that very efficient particle acceleration and gamma-ray propagation out of the inner disk of a microquasar usually occur a few days before major relativistic jet ejections. Flaring particle energies can be thousands of times larger than previously detected maximum values (with Lorentz factors of 105 and 102 for electrons and protons, respectively). We show that the transitional nature of gamma-ray flares and particle acceleration above GeV energies in Cygnus X-3 is clearly linked to special radio/X-ray states preceding strong radio flares. Thus gamma-rays provide unique insight into the nature of physical processes in microquasars. Comment: 29 pages (including Supplementary Information), 8 figures, 2 tables version submitted to Nature on August 7, 2009 (accepted version available at http://www.nature.com/nature/journal/vaop/ncurrent/pdf/nature08578.pdf)
10/2009;
-
I. Donnarumma,
G. Pucella,
V. Vittorini,
F. D'Ammando,
S. Vercellone,
C. M. Raiteri,
M. Villata,
M. Perri,
W P Chen,
R. L. Smart, [......],
E Vallazza,
A. Zambra,
D. Zanello,
C. Pittori,
P. Santolamazza,
F. Verrecchia,
P. Giommi,
L. A. Antonelli,
S. Colafrancesco,
L. Salotti
[show abstract]
[hide abstract]
ABSTRACT: We report on the second AGILE multiwavelength campaign of the blazar 3C 454.3 during the first half of December 2007. This campaign involved AGILE, Spitzer, Swift,Suzaku,the WEBT consortium,the REM and MITSuME telescopes,offering a broad band coverage that allowed for a simultaneous sampling of the synchrotron and inverse Compton (IC) emissions.The 2-week AGILE monitoring was accompanied by radio to optical monitoring by WEBT and REM and by sparse observations in mid-Infrared and soft/hard X-ray energy bands performed by means of Target of Opportunity observations by Spitzer, Swift and Suzaku, respectively.The source was detected with an average flux of~250x10^{-8}ph cm^-2s^-1 above 100 MeV,typical of its flaring states.The simultaneous optical and gamma-ray monitoring allowed us to study the time-lag associated with the variability in the two energy bands, resulting in a possible ~1-day delay of the gamma-ray emission with respect to the optical one. From the simultaneous optical and gamma-ray fast flare detected on December 12, we can constrain the delay between the gamma-ray and optical emissions within 12 hours. Moreover, we obtain three Spectral Energy Distributions (SEDs) with simultaneous data for 2007 December 5, 13, 15, characterized by the widest multifrequency coverage. We found that a model with an external Compton on seed photons by a standard disk and reprocessed by the Broad Line Regions does not describe in a satisfactory way the SEDs of 2007 December 5, 13 and 15. An additional contribution, possibly from the hot corona with T=10^6 K surrounding the jet, is required to account simultaneously for the softness of the synchrotron and the hardness of the inverse Compton emissions during those epochs. Comment: 13 pages, 8 figures, 2 tables, Accepted for publication in ApJ
10/2009;
-
E. Striani,
F. Verrecchia,
C. Pittori,
M. Tavani,
F. D'Ammando,
I. Donnarumma,
S. Vercellone,
V. Vittorini,
E. Del Monte,
Y. Evangelista, [......],
P. Picozza,
M. Prest,
P. Lipari,
D. Zanello,
P. W. Cattaneo,
A. Rappoldi,
P. Santolamazza,
S. Colafrancesco,
P. Giommi,
L. Salotti
[show abstract]
[hide abstract]
ABSTRACT: During the current AGILE pointing centered near the Galactic Center, the
AGILE Gamma-Ray Imaging Detector (GRID) has detected significant
gamma-ray emission above 100 MeV from a gamma-ray source positionally
consistent with the blazar PKS 1830-211. Integrating from
2009-10-12 00:03 UT to to 2009-10-13 04:57 UT, a maximum likelihood
analysis shows a detection at a significance level above 5 sigma, with
a source flux reaching a gamma-ray flux of (160+/-50) e-8 ph/cm2/sec
above 100 MeV.
The Astronomer's Telegram. 09/2009; 2242:1.
-
A Giuliani,
F. Fuschino,
G. Vianello,
M. Marisaldi,
S. Mereghetti,
M. Tavani,
S. Cutini,
G. Barbiellini,
F. Longo,
E. Moretti, [......],
V. Vittorini,
A. Zambra,
D. Zanello,
C. Pittori,
F. Verrecchia,
P. Santolamazza,
P. Giommi,
S. Colafrancesco,
L. A. Antonelli,
L. Salotti
[show abstract]
[hide abstract]
ABSTRACT: Short gamma-ray bursts (GRBs), typically lasting less than 2 s, are a special class of GRBs of great interest. We report the detection by the AGILE satellite of the short GRB 090510 which shows two clearly distinct emission phases: a prompt phase lasting ~ 200 msec and a second phase lasting tens of seconds. The prompt phase is relatively intense in the 0.3-10 MeV range with a spectrum characterized by a large peak/cutoff energy near 3 MeV, in this phase, no significant high-energy gamma-ray emission is detected. At the end of the prompt phase, intense gamma-ray emission above 30 MeV is detected showing a power-law time decay of the flux of the type t^-1.3 and a broad-band spectrum remarkably different from that of the prompt phase. It extends from sub-MeV to hundreds of MeV energies with a photon index alpha ~ 1.5. GRB 090510 provides the first case of a short GRB with delayed gamma-ray emission. We present the timing and spectral data of GRB 090510 and briefly discuss its remarkable properties within the current models of gamma-ray emission of short GRBs. Comment: Accepted by the Astrophysical Journal Letters on September 11, 2009
08/2009;
