You will be presented with the full text of a science research paper. Please write an abstract for this paper. Your response should include the abstract and no additional text.

Paper text:
the low - hard state of accreting black holes is characterized by the presence of a hot corona around the compact object .
figure [ fig : geometria ] shows a scheme of the main components of the system . for this geometry ,
we assume a spherical corona with a radius @xmath0 and an accretion disk that penetrates the corona up to a radius @xmath1 .
we suppose that the corona is homogeneous and in steady state .
we assume that the luminosity of the corona is 1 % of the eddington luminosity of the black hole . for a corona characterized by the parameters of table [ tab_1 ] , this yields @xmath2 erg s@xmath3 .
the corona is composed of a two - temperature plasma , with an electron temperature @xmath4 k and an ion temperature @xmath5 k ( e.g. ref . ) .
this is a consequence of electron cooling being more efficient than proton .    in the low - hard state
we can assume the system is in a steady state .
we then consider equipartition of energy between the different components of the system and obtain the values of the relevant physical parameters .
the x - rays emission of the corona is characterized by a power law with an exponential cut - off at high energies , @xmath6 in accordance with what is observed in cygnus x-1 ( e.g. ref . ) , we adopt @xmath7 and @xmath8 kev .
table [ tab_1 ] shows the values of the parameters in our model .
the injection function for relativistic protons and electrons is a power - law in the energy of the particles @xmath9 , which is the consequence of diffusive particle acceleration by shock waves in the coronal plasma .
typical spectral indices are @xmath10 ( ref . ) .
the normalization constant @xmath11 can be obtained from the total power injected in relativistic protons and electrons , @xmath12 .
this power @xmath13 was assumed to be a fraction of the luminosity of the corona , @xmath14 , with @xmath15 .
the way in which energy is divided between hadrons and leptons is unknown , but different scenarios can be taken into account by setting @xmath16 .
we consider models with an injection dominated by protons in which @xmath17 and models with @xmath18 .
the injected particles will lose their energy by different radiative processes .
there are three relevant processes of interaction of relativistic electrons with magnetic , matter and photon fields in this scenario : synchrotron radiation , inverse compton scattering , and relativistic bremsstrahlung . for protons
there are also three relevant processes : synchrotron radiation , proton - proton inelastic collisions and photohadronic interactions .
these interactions produce pions , which then decay producing muons .
we also consider the energy loss of these particles ; the processes for charged pions are the same as for protons and for muons the same as for electrons .
we consider two mechanisms of particle escape from the corona : advection and diffusion . in the case of advection , particles fall onto the compact object at a mean radial velocity @xmath19 ( ref . ) .
therefore the advection rate is    @xmath20    in the case of diffusion , we consider that the corona is static and diffusion of relativistic particles occurs in the bohm regime .
the diffusion coefficient is @xmath21 , where @xmath22 is the giroradius of the particle .
the diffusion rate is    @xmath23    figure [ fig : perdidas ] shows the cooling rates for different processes of energy loss , along with the acceleration and escape rates , for each type of particle considered . under the physical conditions previously described , the main channel of energy loss for electrons is synchrotron radiation . for protons ,
both @xmath24 and @xmath25 interactions are relevant .
however , in the model with advection , most protons fall into the black hole before radiating their energy . for pions ,
the main channel of energy loss is @xmath26 interaction , but an important fraction of pions decay before cooling . on the contrary , muons with energies above @xmath27
ev cool mostly by inverse compton scattering .
+    the maximum energy that a relativistic particle can attain depends on the acceleration mechanism and the different processes of energy loss .
the acceleration rate @xmath28 for a particle of energy @xmath29 in a magnetic field @xmath30 is given by    @xmath31    where @xmath32 is a parameter that characterizes the efficiency of the acceleration .
we have fixed @xmath33 , which describes an efficient acceleration .
in order to obtain the spectral energy distributions produced by the different radiative processes , we solve the transport equation for each kind of particle .
we calculate the seds of different processes following ref .
( ) as standard reference .
we also calculate the radiation emitted by secondary pairs , which are injected mainly by photon - photon annihilations .
+    figure [ fig : seds ] shows all contributions to the total luminosity for different advection regimes and for different values of the parameter @xmath34 .
luminosities produced by hadrons and muons are higher in models with diffusion .
this is because in models with advection an important fraction of protons and pions are swallowed by the black hole , while with diffusion these particles are able to lose their energy before falling into the compact object or escaping .    finally , we take into account the effects of photon - photon attenuation .
the absorption can be quantified through the opacity @xmath35 .
if the initial gamma - ray luminosity is @xmath36 , the attenuated luminosity @xmath37 after the photon travels a distance @xmath38 is @xmath39 .
figure [ fig : todas ] shows the attenuated luminosity for each set of parameters , the spectrum of cygnus x-1 as observed by comptel ( ref . ) , and the sensitivity of different instruments .
notice that in addition of accounting for the mev tail observed by comptel , a high energy bump with luminosities @xmath40 erg s@xmath3 is expected at @xmath41 tev .
the existence of the high - energy tail in the spectrum detected by comptel and reproduced by our model was recently confirmed by observations with integral satellite ( ref . ) .
on one hand , the sed predicted by the model with an injection dominated by protons and diffusion reproduces the observations of cygnus x-1 . on the other hand ,
our model predicts a high energy emission , above 1 tev , that might be detectable by instruments like magic ii or cta in the near future .
this research was supported by anpcyt through grant pict-2007 - 00848 bid 1728/oc - ar and by the ministerio de educacin y ciencia ( spain ) under grant aya 2007 - 68034-c03 - 01 , feder funds .
cygnus x-1 was the first x - ray source widely accepted to be a black hole candidate and remains among the most studied astronomical objects in its class . 
 the detection of non - thermal radio , hard x - rays and gamma rays reveals the fact that this kind of objects are capable of accelerating particles up to very high energies .    in order to explain the electromagnetic emission from cygnus x-1 in the low - hard state we present a model of a black hole corona with both relativistic lepton and hadron content . 
 we characterize the corona as a two - temperature hot plasma plus a mixed non - thermal population in which energetic particles interact with magnetic , photon and matter fields . 
 our calculations include the radiation emitted by secondary particles ( pions , muons and electron / positron pairs ) . finally , we take into account the effects of photon absorption . 
 we compare the results obtained from our model with data of cygnus x-1 obtained by the comptel instrument .