Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe gamma-ray flaring properties of the blazar 3C 454.3
126
0
0.0
(
0
)
Authors
S. Vercellone
Ask ChatGPT about the research
No Arabic abstract
3C 454.3 is the most variable and intense extragalactic gamma-ray blazar detected by AGILE and Fermi during the last 4 years. This remarkable source shows extreme flux variability (about a fact or of 20) on a time-scale of 24-48 hours, as well as repeated flares on a time-scale of more than a year. The dynamic range, from the quiescence up to the most intense gamma-ray super-flare, is of about two orders of magnitude. We present the gamma-ray properties of 3C 454.3, comparing both the characteristics of flares at different levels and their multi-wavelength behavior. Moreover, an interpretation of both the long- and short-term properties of 3C 454.3 is reviewed, with particular emphasis on the two gamma-ray super-flares observed in 2009 and 2010, when 3C 454.3 became the brightest source of the whole gamma-ray sky.
rate research
Read More
We present the gamma-ray data of the extraordinary flaring activity above 100 MeV from the flat spectrum radio quasar 3C 454.3 detected by AGILE during the month of December 2009. 3C 454.3, that has been among the most active blazars of the FSRQ type since 2007, was detected in the gamma-ray range with a progressively rising flux since November 10, 2009. The gamma-ray flux reached a value comparable with that of the Vela pulsar on December 2, 2009. Remarkably, between December 2 and 3, 2009 the source more than doubled its gamma-ray emission and became the brightest gamma-ray source in the sky with a peak flux of F_{gamma,p} = (2000 pm 400) x 10^-8 ph cm^-2 s^-1 for a 1-day integration above 100 MeV. The gamma-ray intensity decreased in the following days with the source flux remaining at large values near F simeq (1000 pm 200) x 10^-8 ph cm^-2 s^-1 for more than a week. This exceptional gamma-ray flare dissipated among the largest ever detected intrinsic radiated power in gamma-rays above 100 MeV (L_{gamma, source, peak} simeq 3 x 10^46 erg s^-1, for a relativistic Doppler factor of {delta} simeq 30). The total isotropic irradiated energy of the month-long episode in the range 100 MeV - 3 GeV is E_{gamma,iso} simeq 10^56 erg. We report the intensity and spectral evolution of the gamma-ray emission across the flaring episode. We briefly discuss the important theoretical implications of our detection.
Since 2005, the blazar 3C 454.3 has shown remarkable flaring activity at all frequencies, and during the last four years it has exhibited more than one gamma-ray flare per year, becoming the most active gamma-ray blazar in the sky. We present for the first time the multi-wavelength AGILE, SWIFT, INTEGRAL, and GASP-WEBT data collected in order to explain the extraordinary gamma-ray flare of 3C 454.3 which occurred in November 2010. On 2010 November 20 (MJD 55520), 3C 454.3 reached a peak flux (E>100 MeV) of F_gamma(p) = (6.8+-1.0)E-5 ph/cm2/s on a time scale of about 12 hours, more than a factor of 6 higher than the flux of the brightest steady gamma-ray source, the Vela pulsar, and more than a factor of 3 brighter than its previous super-flare on 2009 December 2-3. The multi-wavelength data make a thorough study of the present event possible: the comparison with the previous outbursts indicates a close similarity to the one that occurred in 2009. By comparing the broadband emission before, during, and after the gamma-ray flare, we find that the radio, optical and X-ray emission varies within a factor 2-3, whereas the gamma-ray flux by a factor of 10. This remarkable behavior is modeled by an external Compton component driven by a substantial local enhancement of soft seed photons.
Recent detection of suborbital gamma-ray variability of Flat Spectrum Radio Quasar (FSRQ) 3C 279 by Fermi Large Area Telescope (LAT) is in severe conflict with established models of blazar emission. This paper presents the results of suborbital analysis of the Fermi/LAT data for the brightest gamma-ray flare of another FSRQ blazar 3C 454.3 in November 2010 (MJD 55516-22). Gamma-ray light curves are calculated for characteristic time bin lengths as short as 3 min. The measured variations of the 0.1-10 GeV photon flux are tested against the hypothesis of steady intraorbit flux. In addition, the structure function is calculated for absolute photon flux differences and for their significances. Significant gamma-ray flux variations are measured only over time scales longer than ~5h, which is consistent with the standard blazar models.
We focus on the exceptional flaring activity of 3C 454.3 in November 2010 and we discuss a theoretical framework addressing all data in their overall evolution. For two weeks the source has shown a plateau of enhanced GeV emission preceding a sudden major flare lasting about 3 days before decaying. The gamma-ray flare onset is abrupt (about 6 hours), and is characterized by a prominent Compton dominance with the GeV flux exceeding the pre-flare values by a factor of 4-5, whereas the optical and X-ray fluxes increased only by a factor 2. We explore two alternatives. Case 1, with high-energy emission originating within the BLR; and Case 2, with most of it produced outside. We show that Case 1 has considerable problems in explaining the whole set of multifrequency data. Case 2, instead, leads to a consistent and interesting interpretation based on the enhanced inverse Compton radiation that is produced as the jet crashes onto a mirror cloud positioned at few parsec from the BH. This model explains the gamma-ray vs. optical/X-ray behavior of 3C 454.3, including the otherwise puzzling phenomena such as the prominent orphan optical flare, and the enhanced line emission with no appreciable gamma-ray counterpart that preceded the GeV flare. It also accounts for the delayed onset of the latter on top of the long plateau. Our modelling of the exceptional 3C 454.3 gamma-ray flare shows that, while emission inside the canonical BLR is problematic, major and rapid variations can be produced at parsec scales with moderate bulk Lorentz factors $Gammaapprox 15$.
Opacity-driven shifts of the apparent VLBI core position with frequency (the core shift effect) probe physical conditions in the innermost parts of jets in active galactic nuclei. We present the first detailed investigation of this effect in the brightest gamma-ray blazar 3C454.3 using direct measurements from simultaneous 4.6-43 GHz VLBA observations, and a time lag analysis of 4.8-37 GHz lightcurves from the UMRAO, CrAO, and Metsahovi observations in 2007-2009. The results support the standard Konigl model of jet physics in the VLBI core region. The distance of the core from the jet origin r_c(nu), the core size W(nu), and the lightcurve time lag DT(nu) all depend on the observing frequency nu as r_c(nu)~W(nu)~ DT(nu)~nu^-1/k. The obtained range of k=0.6-0.8 is consistent with the synchrotron self-absorption being the dominating opacity mechanism in the jet. The similar frequency dependence of r_c(nu) and W(nu) suggests that the external pressure gradient does not dictate the jet geometry in the cm-band core region. Assuming equipartition, the magnetic field strength scales with distance r as B = 0.4(r/1pc)^-0.8 G. The total kinetic power of electron/positron jet is about 10^44 ergs/s.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
