Massive Engines

By means of multiwavelength analyses I investigate the emission mechanisms and the physical properties of some among the most powerful sources in the Universe, namely flat spectrum radio quasars and gamma-ray bursts.

Black hole mass estimates and AGN torus detections for a homogeneous sample of radio quasars

Castignani & De Zotti 2015, A&A, 573, 125

Castignani, Haardt et al. 2013, A&A, 560, 28

I studied the multi-wavelength properties of a complete sample of ∼ 100 radio sources out to z ∼ 2 belonging to the flat spectrum radio quasar (FSRQ) class, to unveil the nature of their super massive black hole (SMBH) engines.

In Castignani et al. (2013) I estimated masses of SMBHs by fitting a standard model for the SED of the accretion disk. I demonstrated that the method is particularly well suited just for FSRQs and showed that it gives estimates of quality competitive with the best alternative methods. It has the advantage of requiring only photometric rather than the more observationally demanding spectroscopic data.

In Castignani & De Zotti (2015) I investigated the presence, never demonstrated or disproved before, of dusty circum-nuclear tori in FSRQs. The detection of torus emission was shown to be possible in the presence of low luminosity and low peak frequency of the synchrotron emission from the jet; high torus luminosity, close to that of the accretion disk. This adds an important ingredient to the understanding of the physics of these radio sources.

Comparison of black hole (BH) masses estimated from BLR emission lines (y-axis) and the blue bump emission of the accretion disc (x-axis), for a homogeneous sample of K-band (23 GHz) selected flat spectrum radio quasars. The SEDs of some quasars in the sample with evidence of both blue bump and torus emission at WISE frequencies are shown (Castignani et al. 2013, Castignani & De Zotti 2015).

Variability studies in flat spectrum radio quasars and gamma-ray bursts

Castignani, Pian et al. 2017, A&A, 601, 30

Castignani, Guetta et al. 2014, A&A, 565, 60

In Castignani et al. (2017) I investigated the complex multiwavelength variability of PKS 1510-089 (z = 0.36), one of the brightest gamma-ray flat spectrum radio quasar in the Fermi-LAT catalog.

This is one of the first multi-wavelength and multi-epoch studies of this bright blazar.

Variability and multiwavelength analysis by Castignani, Pian et al. (2017) for the bright flat spectrum radio quasar PKS 1510-089. Multiepoch SED, high-energy light curve, and optical vs gamma-ray long-term correlation function showing clear correlation at zero lag.

In Castignani, Guetta et al. (2014) I studied the emission mechanisms of a complete sample of five gamma-ray bursts (GRBs), all detected at very high-energy in GeV by Fermi-LAT. They are thus among the most compact sources and powerful explosions in the Universe. By means of time series analysis for the first time I searched for the presence of time lags between the gamma and hard X-ray light curves of the five GRBs, using the full light curves. My analysis revealed the complexity of the time behavior of the gamma and X-ray light curves and suggests that the delays should be ascribed to intrinsic physical mechanisms.

Results of the variability analysis by Castignani, Guetta et al. (2014) for the five GRBs in the sample.

Left: gamma-ray (Fermi LAT) and hard X-ray (Fermi GBM) light curves

Right: gamma-ray vs hard X-ray Discrete Correlation Function (DCF) showing gamma-ray lags for all five GRBs

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