G. Finnegan

University College Dublin

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Trends

Author Order

Document Type

Co-Authors

A. Cesarini

University of Urbino

M. Pohl

University of Potsdam

D. Kieda

University of Utah

H. Krawczynski

Washington University in St. Louis

A. J. Weinstein

Iowa State University

W. Benbow

Center for Astrophysics Harvard & Smithsonian

L. Ciupik

Adler Planetarium

P. Kaaret

Marshall Space Flight Center

L. Fortson

University of Minnesota

G. Gyuk

Adler Planetarium

Cooperative Institutions

Centre National de la Recherche Scientifique

197

National Institute for Astrophysics

143

Max Planck Institute for Physics

108

Max Planck Society

108

University of Turku

107

ETH Zurich

Commissariat à l'Énergie Atomique et aux Énergies Alternatives

University of Würzburg

Kavli Institute for Particle Astrophysics and Cosmology

Universitat de Barcelona

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Field

VERITAS OBSERVATIONS OF DAY-SCALE FLARING OF M 87 IN 2010 APRIL

The Astrophysical Journal (2012)

E. Aliu T. Arlen T. Aune M. Beilicke W. Benbow

VERITAS has been monitoring the very-high-energy (VHE; >100GeV) gamma-ray activity of the radio galaxy M87 since 2007. During 2008, flaring activity on a timescale of a few days was observed with a peak flux of (0.70 +- 0.16) X 10^{-11} cm^{-2} s^{-1} at energies above 350GeV. In 2010 April, VERITAS detected a flare from M87 with peak flux of (2.71 +- 0.68) X 10^{-11} cm^{-2} s^{-1} for E>350GeV. The source was observed for six consecutive nights during the flare, resulting in a total of 21 hr of good quality data. The most rapid flux variation occurred on the trailing edge of the flare with an exponential flux decay time of 0.90^{+0.22}_{-0.15} days. The shortest detected exponential rise time is three times as long, at 2.87^{+1.65}_{-0.99} days. The quality of the data sample is such that spectral analysis can be performed for three periods: rising flux, peak flux, and falling flux. The spectra obtained are consistent with power-law forms. The spectral index at the peak of the flare is equal to 2.19 +- 0.07. There is some indication that the spectrum is softer in the falling phase of the flare than the peak phase, with a confidence level corresponding to 3.6 standard deviations. We discuss the implications of these results for the acceleration and cooling rates of VHE electrons in M87 and the constraints they provide on the physical size of the emitting region.

Flare

Spectral index

10.1088/0004-637x/746/2/141

Cite

Citations (50)

THE JUNE 2008 FLARE OF MARKARIAN 421 FROM OPTICAL TO TeV ENERGIES

The Astrophysical Journal (2008)

I. Donnarumma V. Vittorini S. Vercellone E. Del Monte M. Feroci

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

Cite

Citations (100)

DISCOVERY OF VERY HIGH ENERGY GAMMA-RAY RADIATION FROM THE BL LAC 1ES 0806+524

The Astrophysical Journal (2008)

V. A. Acciari E. Aliu T. Arlen M. A. Bautista M. Beilicke

The high-frequency-peaked BL Lacertae object 1ES 0806+524, at redshift z = 0.138, was observed in the very high energy (VHE) gamma-ray regime by VERITAS between 2006 November and 2008 April. These data encompass the two- and three-telescope commissioning phases, as well as observations with the full four-telescope array. 1ES 0806+524 is detected with a statistical significance of 6.3 standard deviations from 245 excess events. Little or no measurable variability on monthly timescales is found. The photon spectrum for the period 2007 November to 2008 April can be characterized by a power law with photon index 3.6 ± 1.0stat ± 0.3sys between ∼ 300 GeV and ∼ 700 GeV. The integral flux above 300 GeV is (2.2 ± 0.5stat ± 0.4sys) × 10−12 cm−2 s−1 which corresponds to 1.8% of the Crab Nebula flux. Non-contemporaneous multiwavelength observations are combined with the VHE data to produce a broadband spectral energy distribution that can be reasonably described using a synchrotron--self-Compton model.

BL Lac object

Crab Nebula

Spectral energy distribution

10.1088/0004-637x/690/2/l126

Cite

Citations (54)

Erratum: VERITAS deep observations of the dwarf spheroidal galaxy Segue 1 [Phys. Rev. D85, 062001 (2012)]

Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D, Particles, fields, gravitation, and cosmology (2015)

E. Aliu S. Archambault T. Arlen T. Aune M. Beilicke

Dwarf spheroidal galaxy

10.1103/physrevd.91.129903

Cite

Citations (19)

Detection of Pulsed Gamma Rays Above 100 GeV from the Crab Pulsar

Science (2011)

E. Aliu T. Arlen T. Aune M. Beilicke W. Benbow

This detection constrains the mechanism and emission region of gamma-ray radiation in the pulsar’s magnetosphere.

Crab Pulsar

Gamma-Ray Astronomy

10.1126/science.1208192

Cite

Citations (193)

La cirugía de cataratas no afecta a los sistemas de reconocimiento de iris en los aeropuertos

Gaceta óptica: Órgano Oficial del Colegio Nacional de Ópticos-Optometristas de España (2009)

G. Finnegan

IRIS (biosensor)

Source

Cite

Citations (0)

THE 2010 VERY HIGH ENERGY γ-RAY FLARE AND 10 YEARS OF MULTI-WAVELENGTH OBSERVATIONS OF M 87

The Astrophysical Journal (2012)

A. Abramowski F. Acero F. Aharonian A. G. Akhperjanian G. Anton

The giant radio galaxy M 87 with its proximity (16 Mpc), famous jet, and very massive black hole ((3 − 6) × 109 M☉) provides a unique opportunity to investigate the origin of very high energy (VHE; E > 100 GeV) γ-ray emission generated in relativistic outflows and the surroundings of supermassive black holes. M 87 has been established as a VHE γ-ray emitter since 2006. The VHE γ-ray emission displays strong variability on timescales as short as a day. In this paper, results from a joint VHE monitoring campaign on M 87 by the MAGIC and VERITAS instruments in 2010 are reported. During the campaign, a flare at VHE was detected triggering further observations at VHE (H.E.S.S.), X-rays (Chandra), and radio (43 GHz Very Long Baseline Array, VLBA). The excellent sampling of the VHE γ-ray light curve enables one to derive a precise temporal characterization of the flare: the single, isolated flare is well described by a two-sided exponential function with significantly different flux rise and decay times of τrised = (1.69 ± 0.30) days and τdecayd = (0.611 ± 0.080) days, respectively. While the overall variability pattern of the 2010 flare appears somewhat different from that of previous VHE flares in 2005 and 2008, they share very similar timescales (∼day), peak fluxes (Φ>0.35 TeV ≃ (1–3) × 10−11 photons cm−2 s−1), and VHE spectra. VLBA radio observations of 43 GHz of the inner jet regions indicate no enhanced flux in 2010 in contrast to observations in 2008, where an increase of the radio flux of the innermost core regions coincided with a VHE flare. On the other hand, Chandra X-ray observations taken ∼3 days after the peak of the VHE γ-ray emission reveal an enhanced flux from the core (flux increased by factor ∼2; variability timescale <2 days). The long-term (2001–2010) multi-wavelength (MWL) light curve of M 87, spanning from radio to VHE and including data from Hubble Space Telescope, Liverpool Telescope, Very Large Array, and European VLBI Network, is used to further investigate the origin of the VHE γ-ray emission. No unique, common MWL signature of the three VHE flares has been identified. In the outer kiloparsec jet region, in particular in HST-1, no enhanced MWL activity was detected in 2008 and 2010, disfavoring it as the origin of the VHE flares during these years. Shortly after two of the three flares (2008 and 2010), the X-ray core was observed to be at a higher flux level than its characteristic range (determined from more than 60 monitoring observations: 2002–2009). In 2005, the strong flux dominance of HST-1 could have suppressed the detection of such a feature. Published models for VHE γ-ray emission from M 87 are reviewed in the light of the new data.

Flare

10.1088/0004-637x/746/2/151

Cite

Citations (159)

VERITAS Observations of Galactic Sources

Bulletin of the American Physical Society (2010)

G. Finnegan

Source

Cite

Citations (0)

DISCOVERY OF TeV GAMMA-RAY EMISSION FROM TYCHO ’S SUPERNOVA REMNANT

The Astrophysical Journal Letters (2011)

V. A. Acciari E. Aliu T. Arlen T. Aune M. Beilicke

We report the discovery of TeV gamma-ray emission from the Type Ia supernova remnant (SNR) G120.1+1.4, known as Tycho's supernova remnant. Observations performed in the period 2008-2010 with the VERITAS ground-based gamma-ray observatory reveal weak emission coming from the direction of the remnant, compatible with a point source located at $00^{\rm h} \ 25^{\rm m} \ 27.0^{\rm s},\ +64^{\circ} \ 10^{\prime} \ 50^{\prime\prime}$ (J2000). The TeV photon spectrum measured by VERITAS can be described with a power-law $dN/dE = C(E/3.42\;\textrm{TeV})^{-\Gamma}$ with $\Gamma = 1.95 \pm 0.51_{stat} \pm 0.30_{sys}$ and $C = (1.55 \pm 0.43_{stat} \pm 0.47_{sys}) \times 10^{-14}$ cm$^{-2}$s$^{-1}$TeV$^{-1}$. The integral flux above 1 TeV corresponds to $\sim 0.9%$ percent of the steady Crab Nebula emission above the same energy, making it one of the weakest sources yet detected in TeV gamma rays. We present both leptonic and hadronic models which can describe the data. The lowest magnetic field allowed in these models is $\sim 80 \mu$G, which may be interpreted as evidence for magnetic field amplification.

Crab Nebula

10.1088/2041-8205/730/2/l20

Cite

Citations (171)

A connection between star formation activity and cosmic rays in the starburst galaxy M82

Nature (2009)

V. A. Acciari E. Aliu T. Arlen T. Aune M. A. Bautista

10.1038/nature08557

Cite

Citations (243)