X-Ray and Gamma-Ray Polarization in Leptonic and Hadronic Jet Models of Blazars

2013Jul
Affiliations: 1Ohio University, USA, 2North-West University, South Africa

We present a theoretical analysis of the expected X-ray and gamma-ray polarization signatures resulting from synchrotron self-Compton emission in leptonic models, compared to the polarization signatures from proton synchrotron and cascade synchrotron emission in hadronic models for blazars. Source parameters resulting from detailed spectral-energy-distribution modeling are used to calculate photon-energy-dependent upper limits on the degree of polarization, assuming a perfectly organized, mono-directional magnetic field. In low-synchrotron-peaked blazars, hadronic models exhibit substantially higher maximum degrees of X-ray and gamma-ray polarization than leptonic models, which may be within reach for existing X-ray and gamma-ray polarimeters. In high-synchrotron-peaked blazars (with electron-synchrotron-dominated X-ray emission), leptonic and hadronic models predict the same degree of X-ray polarization, but substantially higher maximum gamma-ray polarization in hadronic models than leptonic ones. These predictions are particularly relevant in view of the new generation of balloon-borne X-ray polarimeters (and possibly GEMS, if revived), and the ability of Fermi-LAT to measure gamma-ray polarization at < 200 MeV. We suggest observational strategies combining optical, X-ray, gamma-ray polarimetry to determine the degree of ordering of the magnetic field and to distinguish between leptonic and hadronic high-energy emission.

Comments: Accepted for publication in The Astrophysical Journal

Similar Publications

Magnetic dynamo action caused by the magnetorotational instability is studied in the shearing-box approximation with no imposed net magnetic flux. Consistent with recent studies, the dynamo action is found to be sensitive to the aspect ratio of the box: it is much easier to obtain in tall boxes (stretched in the direction normal to the disk plane) than in long boxes (stretched in the radial direction). Our direct numerical simulations indicate that the dynamo is possible in both cases, given a large enough magnetic Reynolds number. Read More


We present the results of our radio interferometric observations of pulsars at 325 MHz and 610 MHz using the Giant Metrewave Radio Telescope (GMRT). We used the imaging method to estimate the flux densities of several pulsars at these radio frequencies. The analysis of the shapes of the pulsar spectra allowed us to identify five new gigahertz-peaked spectra (GPS) pulsars. Read More


Be/X-ray binaries are the most populous class of High Mass X-ray Binaries. Their X-ray duty cycle is tightly related to the optical companion wind activity, which in turn can be studied through optical spectroscopical dedicated observations. We study optical spectral features of the Be circumstellar disk to test their long-term variability and their relation with the X-ray activity. Read More


The direct observation of gravitational waves with Advanced LIGO offers novel opportunities to test general relativity in strong-field, highly dynamical regimes. One such opportunity is the measurement of gravitational-wave polarizations. While general relativity predicts only two tensor gravitational-wave polarizations, general metric theories of gravity allow for up to four additional vector and scalar modes. Read More


There are at least two formation scenarios consistent with the first gravitational-wave observations of binary black hole mergers. In field models, black hole binaries are formed from stellar binaries that may undergo common envelope evolution. In dynamic models, black hole binaries are formed through capture events in globular clusters. Read More


We investigate the properties of magnetized stars in the propeller regime using axisymmetric numerical simulations. We modelled the propeller regime for stars with realistically large magnetospheres (5-7 stellar radii), so that our results could be applied to different types of magnetized stars, including Classical T Tauri stars, cataclysmic variables, and accreting millisecond pulsars. A wide range of propeller strengths has been studied, from very strong propellers (where the magnetosphere rotates much more rapidly than the inner disk) to very weak propellers (where the magnetosphere rotates only slightly faster than the inner disc. Read More


The repeating FRB 121102, the only FRB with an accurately determined position, is associated with a variable persistent radio source consistent with a low luminosity active galactic nucleus. I suggest that FRB originate in the accretion disc funnels of intermediate mass black holes. Narrowly collimated radiation is emitted along the wandering instantaneous angular momentum axis of accreted matter. Read More


After several decades of extensive research the mechanism driving core-collapse supernovae (CCSNe) is still unclear. A common mechanism is a neutrino driven outflow, but others have been proposed. Among those, a long-standing idea is that jets play an important role in SN explosions. Read More


The wide-area XMM-XXL X-ray survey is used to explore the fraction of obscured AGN at high accretion luminosities, $L_X (\rm 2-10 \, keV) > 10^{44} \, erg \,s ^{-1}$, and out to redshift $z\approx1.5$. The sample covers an area of about $\rm14\,deg^2$ and provides constraints on the space density of powerful AGN over a wide range of neutral hydrogen column densities extending beyond the Compton-thick limit, $\rm N_H\approx10^{24}\,cm^{-2}$. Read More


Tight binaries of helium white dwarfs (He WDs) orbiting millisecond pulsars (MSPs) will eventually "merge" due to gravitational damping of the orbit. The outcome has been predicted to be the production of long-lived ultra-compact X-ray binaries (UCXBs), in which the WD transfers material to the accreting neutron star (NS). Here we present complete numerical computations, for the first time, of such stable mass transfer from a He WD to a NS. Read More