We present optical, X-ray, high energy ($\lessapprox 30$ GeV) and very high energy ($\gtrapprox 100$ GeV; VHE) observations of the high-frequency peaked blazar Mrk 421 taken between 2008 May 24 and June 23. A high energy $\gamma$-ray signal was detected by AGILE with \sqrt{TS}=4.5 on June 9--15, with $F(E>100 \mathrm{MeV})= 42^{+14}_{-12}\times 10^{-8}$ photons cm$^{-2}$ s$^{-1}$. This flaring state is brighter than the average flux observed by EGRET by a factor of $\sim$3, but still consistent with the highest EGRET flux. In hard X-rays (20-60 keV) SuperAGILE resolved a 5-day flare (June 9-15) peaking at $\sim$ 55 mCrab. SuperAGILE, RXTE/ASM and Swift/BAT data show a correlated flaring structure between soft and hard X-rays. Hints of the same flaring behavior are also detected in the simultaneous optical data provided by the GASP-WEBT. A Swift/XRT observation near the flaring maximum revealed the highest 2-10 keV flux ever observed from this source, of 2.6 $\times 10^{-9}$ erg cm$^{-2}$ s$^{-1}$ (i.e. > 100 mCrab). A peak synchrotron energy of $\sim$3 keV was derived, higher than typical values of $\sim$0.5-1 keV. VHE observations with MAGIC and VERITAS on June 6-8 show the flux peaking in a bright state, well correlated with the X-rays. This extraordinary set of simultaneous data, covering a twelve-decade spectral range, allowed for a deep analysis of the spectral energy distribution as well as of correlated light curves. The $\gamma$-ray flare can be interpreted within the framework of the synchrotron self-Compton model in terms of a rapid acceleration of leptons in the jet.

Flare

Spectral energy distribution

10.1088/0004-637x/691/1/l13

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Citations (100)

An X-Ray Burst from a Magnetar Enlightening the Mechanism of Fast Radio Bursts

arXiv (Cornell University) (2020)

M. Tavani C. Casentini A. Ursi F. Verrecchia A. Addis

Fast radio bursts (FRBs) are short (millisecond) radio pulses originating from enigmatic sources at extragalactic distances so far lacking a detection in other energy bands. Magnetized neutron stars (magnetars) have been considered as the sources powering the FRBs, but the connection is controversial because of differing energetics and the lack of radio and X-ray detections with similar characteristics in the two classes. We report here the detection by the AGILE satellite on April 28, 2020 of an X-ray burst in coincidence with the very bright radio burst from the Galactic magnetar SGR 1935+2154. The burst detected by AGILE in the hard X-ray band (18-60 keV) lasts about 0.5 seconds, it is spectrally cutoff above 80 keV, and implies an isotropically emitted energy ~ $10^{40}$ erg. This event is remarkable in many ways: it shows for the first time that a magnetar can produce X-ray bursts in coincidence with FRB-like radio bursts; it also suggests that FRBs associated with magnetars may emit X-ray bursts of both magnetospheric and radio-pulse types that may be discovered in nearby sources. Guided by this detection, we discuss SGR 1935+2154 in the context of FRBs, and especially focus on the class of repeating-FRBs. Based on energetics, magnetars with fields B ~ $10^{15}$ G may power the majority of repeating-FRBs. Nearby repeating-FRBs offer a unique occasion to consolidate the FRB-magnetar connection, and we present new data on the X-ray monitoring of nearby FRBs. Our detection enlightens and constrains the physical process leading to FRBs: contrary to previous expectations, high-brightness temperature radio emission coexists with spectrally-cutoff X-ray radiation.

Magnetar

Fast radio burst

10.48550/arxiv.2005.12164

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Citations (44)

GRB 130427A: high energy gamma-ray detection by AGILE.

GCN (2013)

F. Verrecchia C. Pittori A. Giuliani M. Marisaldi F. Longo

Source

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Citations (7)

Study of theγ-ray source 1AGL J2022+4032 in the Cygnus region

Astronomy and Astrophysics (2010)

A. Chen G. Piano M. Tavani A. Trois G. Dubner

Identification of gamma-ray-emitting Galactic sources is a long-standing problem in astrophysics. One such source, 1AGL J2022+4032, coincident with the interior of the radio shell of the supernova remnant Gamma Cygni (SNR G78.2+2.1) in the Cygnus Region, has recently been identified by Fermi as a gamma-ray pulsar, LAT PSR J2021+4026. We present long-term observations of 1AGL J2022+4032 with the AGILE gamma-ray telescope, measuring its flux and light curve. We compare the light curve of 1AGL J2022+4032 with that of 1AGL J2021+3652 (PSR J2021+3651), showing that the flux variability of 1AGL J2022+4032 appears to be greater than the level predicted from statistical and systematic effects and producing detailed simulations to estimate the probability of the apparent observed variability. We evaluate the possibility that the gamma-ray emission may be due to the superposition of two or more point sources, some of which may be variable, considering a number of possible counterparts. We consider the possibility of a nearby X-ray quiet microquasar contributing to the flux of 1AGL J2022+4032 to be more likely than the hypotheses of a background blazar or intrinsic gamma-ray variabilty of LAT PSR J2021+4026.

10.1051/0004-6361/201015279

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Citations (16)

The Large Observatory for X-ray Timing (LOFT)

Experimental Astronomy (2011)

M. Feroci L. Stella M. van der Klis T. J. L. Courvoisier M. Hernanz

Spectral resolution

10.1007/s10686-011-9237-2

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Citations (195)

GRB 131108A: AGILE/GRID observation.

GCN (2013)

A. Giuliani F. Longo F. Verrecchia C. Pittori M. Marisaldi

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Citations (2)

Correction to: SERENA: Particle Instrument Suite for Determining the Sun-Mercury Interaction from BepiColombo

Space Science Reviews (2021)

S. Orsini S. Livi Herbert Lichtenegger S. Barabash A. Milillo

Planetary science

Mercury

10.1007/s11214-021-00809-8

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Citations (7)

Science with the new generation high energy gamma- ray experiments

arXiv (Cornell University) (2007)

Marcelo A. Alvarez D. DʼArmiento G. Agnetta A. Alberdi L. A. Antonelli

This Conference is the fifth of a series of Workshops on High Energy Gamma- ray Experiments, following the Conferences held in Perugia 2003, Bari 2004, Cividale del Friuli 2005, Elba Island 2006. This year the focus was on the use of gamma-ray to study the Dark Matter component of the Universe, the origin and propagation of Cosmic Rays, Extra Large Spatial Dimensions and Tests of Lorentz Invariance.

Component (thermodynamics)

High energy

10.48550/arxiv.0712.1548

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Citations (0)

GRB 090408b: IPN triangulation.

GRB Coordinates Network (2009)

S. Golenetskii R. Aptekar D. Frederiks E. Mazets V. Pal'Shin

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AGILE detection of C-class solar flares at the beginning of the new solar cycle 25