Absorption of high-energy gamma rays in Cygnus X-3

Cerutti, Benoît; Dubus, G.; Malzac, J.; Szostek, A.; Belmont, R.; Zdziarski, A. A.; Henri, G.

doi:10.1051/0004-6361/201116581

Cited by 41 publications

(60 citation statements)

References 48 publications

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“…Particles would then be accelerated by an internal shock formed in the collision of a fast jet with a previously existing slower outflow. Notably, Cerutti et al (2011) estimate a similar distance (in units of R g ) of the γ-ray source for Cyg X-3, where the γ-ray emission is related with hard/soft state transitions (e.g. Corbel et al 2012) occurring at L/L Edd similar to that of NGC 4945.…”

Section: Discussionmentioning

confidence: 69%

The X-/γ-Ray Correlation in NGC 4945 and the Nature of Its γ-Ray Source

Wojaczyński

Niedźwiecki

2017

ApJ

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We report hints for the correlation between the X-ray and γ-ray emission in the nearby galaxy NGC 4945, which harbors both an active galactic nucleus and a nuclear starburst region. We have divided the Fermi/LAT observations of NGC 4945 into two datasets, comprising events detected during the low (L) and high (H) level of X-ray emission from the active nucleus of this galaxy, determined using the Swift/BAT light curve. Both datasets contain an equal amount of 3.8 years of LAT data and NGC 4945 is detected with a similar statistical significance of ∼ 15σ in L and 14σ in H. However, the slope of the γ-ray spectrum hardens with the increase of the X-ray flux, with the photon index Γ = 2.47 ± 0.07 in L and 2.11 ± 0.08 in H. The change is confirmed by a systematic variation of the spectral energy distribution as well as a substantial reversal of the γ-ray signal in significance maps for low and high γ-ray energies. The X/γ-ray correlation indicates that the γ-ray production is dominated by the active nucleus rather than by cosmic rays interacting with the interstellar medium. We discuss possible locations of the γ-ray source. We also compare NGC 4945 with other starburst galaxies detected by LAT and we note similarities between those with active nuclei, e.g. unlikely high efficiencies of γ-ray production in starburst scenario, which argues for a significant contribution of their active nuclei to the γ-ray emission.

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Section: Discussionmentioning

confidence: 69%

The X-/γ-Ray Correlation in NGC 4945 and the Nature of Its γ-Ray Source

Wojaczyński

Niedźwiecki

2017

ApJ

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“…The simultaneous strong soft X-ray emission from the disk and γ-ray emission from the jet preceding the intense radio outbursts are consistent with a scenario in which the hot thermal corona "dissolves" and the accretion power from the disk directly charges the jet, emitting γ-rays and, subsequently, radio outbursts (via synchrotron processes) far from the compact object. The γ-ray detections of Cygnus X-3 provide new constraints on emission models for this powerful X-ray binary, indicating that hybrid-Comptonization mechanisms (Coppi 1999) alone cannot account for the γ-ray fluxes detected by AGILE and Fermi above 100 MeV, unless we assume unrealistic physical parameters (Cerutti et al 2011). This implies that the corona cannot be the site of the γ-ray emission.…”

Section: Discussionmentioning

confidence: 99%

“…We assumed that the distribution of the disk photons is fully isotropized by the stellar wind in the observer frame. This implies that the γ-ray photosphere (i.e., where τ γγ 1) has a radius of ∼10 10 cm (Cerutti et al 2011). With these assumptions, 13 Our modeling is a simplification: we assume that the bump in the X-ray emission during the "hypersoft" state can be modeled with a simple BB component, which is a very good approximation for our purposes.…”

Section: A Leptonic Scenariomentioning

confidence: 99%

“…The peak γ-ray isotropic luminosity detected above 100 MeV is L γ ∼ 10 36 erg s −1 (for a distance of 7−10 kpc). The γ-ray emission is most likely associated with a relativistic jet (Tavani et al 2009a;Abdo et al 2009;Dubus et al 2010;Cerutti et al 2011;Zdziarski et al 2012a), but the radiative process (leptonic or hadronic) is uncertain.…”

Section: Introductionmentioning

confidence: 99%

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The AGILE monitoring of Cygnus X-3: transient gamma-ray emission and spectral constraints

Piano

Tavani

Vittorini

et al. 2012

A&A

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We present the AGILE-GRID (Astro-rivelatore Gamma a Immagini LEggero -Gamma-Ray Imaging Detector) monitoring of Cygnus X-3, during the period between November 2007 and July 2009. We report here the whole AGILE-GRID monitoring of Cygnus X-3 in the AGILE "pointing" mode data-taking, to confirm that the γ-ray activity coincides with the same repetitive pattern of multiwavelength emission and analyze in depth the overall γ-ray spectrum by assuming both leptonic and hadronic scenarios. Seven intense γ-ray events were detected in this period, with a typical event lasting one or two days. These durations are longer than the likely cooling times of the γ-ray emitting particles, implying we see continuous acceleration rather than the result of an impulsive event such as the ejection of a single plasmoid that then cools as it propagates outwards. Cross-correlating the AGILE-GRID light curve with both X-ray and radio monitoring data, we find that the main events of γ-ray activity were detected while the system was in soft spectral X-ray states (RXTE/ASM (Rossi X-ray Timing Explorer/All-Sky Monitor) count rate in the 3−5 keV band 3 counts s −1 ), that coincide with local and often sharp minima of the hard X-ray flux (Swift/BAT (Burst Alert Telescope) count rate 0.02 counts cm −2 s −1 ), a few days before intense radio outbursts. This repetitive temporal coincidence between the γ-ray transient emission and spectral state changes of the source turns out to be the spectral signature of γ-ray activity from this microquasar. These γ-ray events may thus reflect a sharp transition in the structure of the accretion disk and its corona, which leads to a rebirth of the microquasar jet and subsequent enhanced activity in the radio band. The γ-ray differential spectrum of Cygnus X-3 (100 MeV-3 GeV), which was obtained by averaging the data collected by the AGILE-GRID during the γ-ray events, is consistent with a power law of photon index α = 2.0 ± 0.2. Finally, we examine leptonic and hadronic emission models for the γ-ray events and find that both scenarios are valid. In the leptonic model -based on inverse Compton scatterings of mildly relativistic electrons on soft photons from both the Wolf-Rayet companion star and the accretion disk -the emitting particles may also contribute to the overall hard X-ray spectrum, possibly explaining the hard non-thermal power-law tail seen during special soft X-ray states in Cygnus X-3.

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“…Such re-energization could be due to a collision between the jet and a dense clump of the W-R wind (Araudo et al 2009). In this scenario, the absence of γ -ray emission at the time of ejection can be explained by absorption within the system (Cerutti et al 2011), although this model must be reconciled with the observations of Tavani et al (2009) and Abdo et al (2009). The re-energization would lead to additional radio emission as the γ -ray-emitting electrons cool, although the Figure 2.…”

Section: Discussionmentioning

confidence: 95%

The 2010 MAY FLARING EPISODE OF CYGNUS X-3 IN RADIO, X-Rays, AND Γ-Rays

Williams¹,

Tomsick²,

Bodaghee³

et al. 2011

ApJ

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In 2009, Cygnus X-3 (Cyg X-3) became the first microquasar to be detected in the GeV γ -ray regime, via the satellites Fermi and AGILE. The addition of this new band to the observational toolbox holds promise for building a more detailed understanding of the relativistic jets of this and other systems. We present a rich data set of radio, hard and soft X-ray, and γ -ray observations of Cyg X-3 made during a flaring episode in 2010 May. We detect a ∼3 day softening and recovery of the X-ray emission, followed almost immediately by a ∼1 Jy radio flare at 15 GHz, followed by a 4.3σ γ -ray flare (E > 100 MeV) ∼1.5 days later. The radio sampling is sparse, but we use archival data to argue that it is unlikely the γ -ray flare was followed by any significant unobserved radio flares. In this case, the sequencing of the observed events is difficult to explain in a model in which the γ -ray emission is due to inverse Compton scattering of the companion star's radiation field. Our observations suggest that other mechanisms may also be responsible for γ -ray emission from Cyg X-3.

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Absorption of high-energy gamma rays in Cygnus X-3

Cited by 41 publications

References 48 publications

The X-/γ-Ray Correlation in NGC 4945 and the Nature of Its γ-Ray Source

The X-/γ-Ray Correlation in NGC 4945 and the Nature of Its γ-Ray Source

The AGILE monitoring of Cygnus X-3: transient gamma-ray emission and spectral constraints

The 2010 MAY FLARING EPISODE OF CYGNUS X-3 IN RADIO, X-Rays, AND Γ-Rays

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