Microquasars are promising candidates to emit high-energy gamma-rays.
Moreover, statistical studies show that variable EGRET sources at low galactic
latitudes could be associated with the inner spiral arms. The variable nature
and the location in the Galaxy of the high-mass microquasars, concentrated in
the galactic plane and within 55 degrees from the galactic center, give to
these objects the status of likely counterparts of the variable low-latitude
EGRET sources. We consider in this work the two most variable EGRET sources at
low-latitudes: 3EG J1828+0142 and 3EG J1735-1500, proposing a microquasar model
to explain the EGRET data in consistency with the observations at lower
energies (from radio frequencies to soft gamma-rays) within the EGRET error
box.Comment: (1)Universitat de Barcelona, (2)Instituto Argentino de
  Radioastronomia (3) Facultad de Ciencias Astronomicas y Geofisicas
  (4)Lawrence Livermore National Laboratory 6 pages, 2 figures. Presented as a
  poster at the V Microquasar Workshop, Beijing, June 2004. Accepted for
  publication in the Chinese Journal of Astronomy & Astrophysic

Combi J. A.

D F Torres

Filliatre P.

G E Romero

Ghisellini G.

Hartman R. C.

J M Paredes

Nolan P. L.

Punsly B.

Romero G. E.

V Bosch-Ramon

Chinese Journal of Astronomy and Astrophysics

English

arXiv

Microquasars are promising candidates to emit high-energy gamma-rays. Moreover, statistical studies show that variable EGRET sources at low galactic latitudes could be associated with the inner spiral arms. The variable nature and the location in the Galaxy of the high-mass microquasars, concentrated in the galactic plane and within 55 degrees from the galactic center, give to these objects the status of likely counterparts of the variable low-latitude EGRET sources. We consider in this work the two most variable EGRET sources at low-latitudes: 3EG J1828+0142 and 3EG J1735-1500, proposing a microquasar model to explain the EGRET data in consistency with the observations at lower energies (from radio frequencies to soft gamma-rays) within the EGRET error box.Instituto Argentino de RadioastronomíaFacultad de Ciencias Astronómicas y Geofísica

Bosch Ramon, Valentí

Paredes, J. M.

Romero, Gustavo Esteban

Torres, Diego F.

LAReferencia - Red Federada de Repositorios Institucionales de Publicaciones Científicas Latinoamericanas

Chin. J. Astron. Astrophys. Vol. 5 (2005), Suppl., 284–288(http:/ www.chjaa.org)Chinese Journal ofAstronomy andAstrophysicsMicroquasar Models for 3EG J1828+0142 and 3EGJ1735−1500V. Bosch-Ramon1 ⋆, J. M. Paredes1, G. E. Romero2,3 and D. F. Torres41 Departament d’Astronomia i Meteorologia, Universitat de Barcelona, Av. Diagonal 647,E-08028 Barcelona, Spain2 Instituto Argentino de Radioastronomı́a, C.C.5, (894) Villa Elisa, Buenos Aires, Argentina3 Facultad de Ciencias Astronómicas y Geof́ısicas, UNLP, Paseo del Bosque, 1900 La Plata,Argentina4 Lawrence Livermore National Laboratory, 7000 East Avenue, L-413, Livermore, CA 94550Abstract Microquasars are promising candidates to emit high-energy gamma-rays. Moreover, statistical studies show that variable EGRET sources at low galac-tic latitudes could be associated with the inner spiral arms. The variable natureand the location in the Galaxy of the high-mass microquasars, concentrated in thegalactic plane and within 55 degrees from the galactic center, give to these ob-jects the status of likely counterparts of the variable low-latitude EGRET sources.We consider in this work the two most variable EGRET sources at low-latitudes:3EG J1828+0142 and 3EG J1735−1500, proposing a microquasar model to explainthe EGRET data in consistency with the observations at lower energies (from radiofrequencies to soft gamma-rays) within the EGRET error box.Key words: X-rays: binaries — Stars: winds, outflows — gamma-rays: observa-tions — gamma-rays: theory1 INTRODUCTIONMicroquasars are X-ray binaries (XRB) that present relativistic jets (Mirabel & Rodriguez1999). In the past decade, microquasars have also been proposed as high energy sources, emittinginto the the gamma-ray regime. For instance, Paredes et al. (2000) proposed LS 5039, a high-mass microquasar, as the counterpart of the source 3EG J1824−1514. Otherwise, variable low-latitude EGRET sources seem to follow a similar distribution to that presented by high-massmicroquasars (Bosch-Ramon et al. 2004), which are concentrated also in the galactic plane, nottoo far away from the galactic center (55 degrees). 3EG J1828+0142 and 3EG J1735−1500 arethe two most variable EGRET sources in the galactic plane (Torres et al. 2001), presentingquite steep spectra (photon indices of 2.76 and 3.24 respectively) and typical luminosities ofabout 1035 erg s−1, adopting a distance of 4 kpc. We have applied a microquasar model to theseparticular cases for checking the proposal of association between microquasars and the variableEGRET sources in the galactic plane.⋆ E-mail: vbosch@am.ub.esAre 3EG J1828+0142 and 3EG J1735-1500 microquasars? 2852 THE VARIABLE EGRET SOURCES IN THE GALACTIC PLANEEGRET sources in the galactic plane are well-correlated with star forming regions (Romero etal. 1999), and log N-log S studies suggest that they are more abundant toward the inner spiralarms (Gehrels et al. 2000, Bhattacharya et al. 2003). Among these sources, there is a subgroupof variable sources (Nolan et al. 2003) that has been proposed to be the EGRET counterparts ofhigh-mass microquasars (Kaufman Bernadó et al. 2002, Bosch-Ramon et al. 2004). High-massmicroquasars are also somehow correlated with star forming regions (Romero et al. 2004). Weare interested now in two particular cases: 3EG J1828+0142 and 3EG J1735−1500, exploringthe possibility that they can be high-mass microquasars.3 GAMMA-RAY EMISSION FROM MICROQUASARS3.1 The ModelWe have developed a semi-analytical model based on an inhomogeneous leptonic jet formedby relativistic particles. Those particles interact with the seed photon fields (synchrotron, star,disk and corona photons) through inverse Compton (IC) effect (see Bosch-Ramon et al. 2004).We have accounted for both the Thomson and the Klein-Nishina regimes of IC interaction(Blumenthal & Gould 1970). The different functions that represent the electron energy distri-bution, the electron energy and the magnetic field within the jet have been parametrized inorder to simulate their evolution along the jet (e.g. Ghisellini et al. 1985, Punsly et al. 2000).3.2 3EG J1828+0142 and 3EG J1735-15003EG J1828+0142 (Hartman et al. 1999) is the second most variable low-latitude non-transientgamma-ray source. Within the error box of this EGRET source, there are several faint non-thermal radio sources (Punsly et al. 2000) and X-ray sources (observed in the ROSAT All SkySurvey) with typical luminosities of about 1033 erg s−1, adopting distances of 4 kpc. Finally,Comptel upper limits (Shu Zhang 2004) are also known, corresponding to luminosities ofabout 1034-1035 erg s−1 in the COMPTEL energy range at the same distance. The error box of3EG J1735−1500 (Hartman et al. 1999), the most variable EGRET source, has been alreadyexplored by Combi et al. (2003), and there are two potential counterparts: a radio galaxy anda compact radio source that presents hard spectrum and flux densities of about 0.3 Jy. Highupper limits at X-ray and COMPTEL energies are imposed from observational data to be (1034-1035 erg s−1). To model the Spectral Energy Distribution (SED) of a microquasar that could bethe origin of the EGRET emission, we account for the known observational data at differentwavelengths. We must note that the observations at different frequencies were not simultaneous.Regarding upper limits at radio and X-ray energies, they have been taken as the fluxes of thebrightest sources within the EGRET error boxes.4 RESULTSThe Figs. 1 and 2 show the computed SED for 3EG J1828+0142 and 3EG J1735−1500 respec-tively. In Tables 1 and 2 the adopted parameters for both systems are listed. These SED respectthe observational constraints and reproduce pretty well the EGRET spectrum. It is worth not-ing that the used EGRET spectrum for comparison with our model is the averaged one for thefour viewing periods. Nevertheless, concerning variability, microquasars can naturally presentthe variable nature observed in these two objects due to several factors: precession of the jet,orbital motion, etc... (i.e. Kaufman Bernado et al. 2002, Bosch-Ramon & Paredes 2004).Regarding the high-mass star emission of these systems, it could be dust-enshrouded, asit has been suggested, for instance, for INTEGRAL obscured sources thought to be XRB and286 V. Bosch-Ramon et al.Table 1 Common parameters for 3EG J1828+0142 and 3EG J1735–1500Parameter ValueJet kinetic luminosity 5×1035 erg s−1Stellar bolometric luminosity 1038 erg s−1Distance from jet’s apex to the compact object ∼ 108 cmInitial jet radius ∼ 107 cmOrbital radius 3×1012 cmViewing angle to jet’s axis 10◦Magnetic field 300 GaussTable 2 Particular Parameters for 3EG J1828+0142 and 3EG J1735–1500Parameter Adopted values for Adopted values for3EG J1828+0142 3EG J1735–1500Jet Lorentz factor 1.5 3Maximum Lorentz factor for electrons in jet (jet frame) 3×103 2.5×103Electron power-law index 1.5 2Total disk/corona luminosity 1032 erg s−1 1033 erg s−1microquasars (i.e. Walter et al. 2003, Combi et al. 2004). This effect can be very important ifthe sources are located in the inner regions of the galactic plane, being strong enough to obscurea high-mass star from IR wavelengths to soft X-rays. Furthermore, emission in the far infraredcan be too weak to be detected by the satellite IRAS (i.e. Filliatre & Chaty 2004).To compute the overall SED presented in the Figs. 1 and 2, we have adopted a strongmagnetic field and a low maximum energy for the electrons (see Tables 1 and 2). For3EG J1828+0142, the synchrotron emission is dominant in the entire EGRET detection range,which reached only several hundreds of MeV. Moreover, the jet is mildly relativistic. In theother hand, 3EG J1735−1500 was detected up to few GeV. For this second case, we have mod-elled the emission up to several hundreds of MeV through synchrotron self-Compton scattering,and through comptonization of coronal seed photons further up. For this second case, the jetLorentz factor has been taken higher than for the first one. For both sources, accounting forX-ray emission must be dim since otherwise it would imply a clear counterpart at energiesbeyond 1 keV, corona and disk components have been taken to be weak.5 CONCLUSIONSThe possibility of computing a radio-to gamma microquasar SED, at all in accord with observa-tional constraints, suggests that microquasars may be the counterparts of these two particularsources: 3EG J1828+0142 and 3EG J1735−1500. Other possible objects cannot be discardedas possible counterparts (i.e. an isolated black-hole, see Punsly et al. 2000; accreting neutronstars, see Romero et al. 2001; early-type binaries, see Benaglia & Romero 2003; etc...). However,microquasars appear to be attractive candidates due to the presence of a jet with a relativis-tic leptonic population and strong seed photon fields provided by the stellar companion, theaccreting matter and the electrons themselves. In the near future, instruments like AGILEand GLAST will help us to improve the location of unidentified EGRET sources and furtherobservations at lower energies will help us to better constrain the models as well.Are 3EG J1828+0142 and 3EG J1735-1500 microquasars? 287−6 −4 −2 0 2 4 6 8Log (photon energy [eV])2527293133353739Log (εLε [erg/s])IC emissionseed photonsradio emissionsync. ICcor. ICstar ICdisk ICcor.disksync.starradio jet(1)(2)(3)(4)Fig. 1 SED for an unabsorbed broadband microquasar model of the source 3EG J1828+0142.The adopted parameter values are shown in Tables 1 and 2. There are represented the upper limitsat radio (1), X-ray (2) and COMPTEL (3) energies, as well as the EGRET spectrum (4).−6 −4 −2 0 2 4 6 8Log (photon energy [eV])2527293133353739Log (εLε [erg/s])IC emissionseed photonsradio emissionsync. ICcor. ICstar ICdisk ICstarsync.coronadiskradio jet(1)(2)(3)(4)Fig. 2 The same as in Fig. 1 but for the source 3EG J1735+1500.288 V. Bosch-Ramon et al.Acknowledgements V.B-R. and J.M.P. acknowledge partial support by DGI of the Ministeriode Ciencia y Tecnoloǵıa (Spain) under grant AYA-2001-3092, as well as additional supportfrom the European Regional Development Fund (ERDF/FEDER). During this work, V.B-Rhas been supported by the DGI of the Ministerio de Ciencia y Tecnoloǵıa (Spain) under thefellowship FP-2001-2699. G. E. R is supported by Fundación Antorchas and the ArgentineAgencies CONICET and ANPCyT. This research has benefited from a cooperation agreementsupported by Fundación Antorchas. The work of DFT was performed under the auspices of theUS DOE (NNSA), by UC’s LLNL under contract No. W-7405-Eng-48. We thank an anonymousreferee for useful comments on the paper.ReferencesBenaglia P., Romero G. E., 2003, A&A 399, 1121Bhattacharya D., Akyüz A., Miyagi T., Samimi J., Zych A., 2003, A&A 404, 163Blumenthal G. R., Gould R. J., 1970, Rev. Mod. Phys. , 42, 237Bosch-Ramon V., Romero G. E., Paredes J. M., 2004, A&A, 429, 267Bosch-Ramon V., Paredes, J. M., 2004, A&A, 417, 1075Combi J. A., Romero G. E., Paredes J. M., Torres D. F., Ribó M., 2003, ApJ, 588, 731Combi J. A., Ribó M., Mirabel I. F., Sugizaki M., 2004, A&A, 422, 1031Filliatre P., Chaty S., 2004, ApJ, 616, 469Gehrels N., Macomb D. J., Bertsch D. L., Thompson D. J., Hartman R. C., 2000, Nature, 404, 363Ghisellini G., Maraschi L., Treves A., 1985, A&A, 146, 204Hartman R. C., Bertsch D. L., Bloom S. D. et al., 1999, ApJS, 123, 79Kaufman Bernadó M. M., Romero G. E., Mirabel I. F., 2002, A&A, 385, L10Mirabel I. F., Rodŕıguez L. F., 1999, ARA&A, 37, 409Nolan P. L., Tompkins W. F., Grenier I. A., Michelson P. F., 2003, ApJ, 597, 615Paredes J. M., Mart́ı J., Ribó M., Massi M., 2000, Science, 288, 2340Punsly B., Romero G. E., Torres D. F., Combi J. A., 2000, A&A, 364, 552Romero G. E., Benaglia P., Torres D. F., 1999, A&A, 348, 868Romero G. E., Kaufman Bernadó M. M., Combi J. A., Torres D. F., 2001, A&A, 376, 599Romero G. E., Grenier I. A., Kaufman Bernadó M. M., Mirabel I. F., Torres, D. F., 2004, ESA-SP,552, 703Zhang S., Collmar W., Hermsen W., Schnfelder V., 2004, A&A, 421, 983Torres D. F., Romero G. E., Combi J. A., Benaglia P., Andernach H., Punsly B., 2001, A&A, 370, 468Walter R., Rodriguez J., Foschini L., et al., 2003, A&A, 411, 427

Microquasar Models for 3EG J1828+0142 and 3EG J1735-1500

Microquasars are promising candidates to emit high-energy gamma-rays. Moreover, statistical studies show that variable EGRET sources at low galactic latitudes could be associated with the inner spiral arms. The variable nature and the location in the Galaxy of the high-mass microquasars, concentrated in the galactic plane and within 55 degrees from the galactic center, give to these objects the status of likely counterparts of the variable low-latitude EGRET sources. We consider in this work the two most variable EGRET sources at low-latitudes: 3EG J1828+0142 and 3EG J1735-1500, proposing a microquasar model to explain the EGRET data in consistency with the observations at lower energies (from radio frequencies to soft gamma-rays) within the EGRET error box

Bosch i Ramon, Valentí

Paredes i Poy, Josep Maria

Romero, Gustavo E.

Diposit Digital de la Universitat de Barcelona

Microquasar models for 3EG J1828+0142 and 3EG J1735-1500

Crossref

Microquasars are promising candidates to emit high-energy gamma-rays. Moreover, statistical studies show that variable EGRET sources at low galactic latitudes could be associated with the inner spiral arms. The variable nature and the location in the Galaxy of the high-mass microquasars, concentrated in the galactic plane and within 55 degrees from the galactic center, give to these objects the status of likely counterparts of the variable low-latitude EGRET sources. We consider in this work the two most variable EGRET sources at low-latitudes: 3EG J1828+0142 and 3EG J1735-1500, proposing a microquasar model to explain the EGRET data in consistency with the observations at lower energies (from radio frequencies to soft gamma-rays) within the EGRET error box.Fil: Bosch Ramon, Valentí. Universidad de Barcelona; EspañaFil: Paredes, Josep Maria. Universidad de Barcelona; EspañaFil: Romero, Gustavo Esteban. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Torres, Diego F.. Lawrence Livermore National Laboratory; Estados Unido

Paredes, Josep Maria

CONICET Digital

Chin. J. Astron. Astrophys. Vol. 5 (2005), Suppl., 284–288(http:/ www.chjaa.org)Chinese Journal ofAstronomy andAstrophysicsMicroquasar Models for 3EG J1828+0142 and 3EGJ1735−1500V. Bosch-Ramon1 ⋆, J. M. Paredes1, G. E. Romero2,3 and D. F. Torres41 Departament d’Astronomia i Meteorologia, Universitat de Barcelona, Av. Diagonal 647,E-08028 Barcelona, Spain2 Instituto Argentino de Radioastronomı´a, C.C.5, (894) Villa Elisa, Buenos Aires, Argentina3 Facultad de Ciencias Astrono´micas y Geof´ısicas, UNLP, Paseo del Bosque, 1900 La Plata,Argentina4 Lawrence Livermore National Laboratory, 7000 East Avenue, L-413, Livermore, CA 94550Abstract Microquasars are promising candidates to emit high-energy gamma-rays. Moreover, statistical studies show that variable EGRET sources at low galac-tic latitudes could be associated with the inner spiral arms. The variable natureand the location in the Galaxy of the high-mass microquasars, concentrated in thegalactic plane and within 55 degrees from the galactic center, give to these ob-jects the status of likely counterparts of the variable low-latitude EGRET sources.We consider in this work the two most variable EGRET sources at low-latitudes:3EG J1828+0142 and 3EG J1735−1500, proposing a microquasar model to explainthe EGRET data in consistency with the observations at lower energies (from radiofrequencies to soft gamma-rays) within the EGRET error box.Key words: X-rays: binaries — Stars: winds, outflows — gamma-rays: observa-tions — gamma-rays: theory1 INTRODUCTIONMicroquasars are X-ray binaries (XRB) that present relativistic jets (Mirabel & Rodriguez1999). In the past decade, microquasars have also been proposed as high energy sources, emittinginto the the gamma-ray regime. For instance, Paredes et al. (2000) proposed LS 5039, a high-mass microquasar, as the counterpart of the source 3EG J1824−1514. Otherwise, variable low-latitude EGRET sources seem to follow a similar distribution to that presented by high-massmicroquasars (Bosch-Ramon et al. 2004), which are concentrated also in the galactic plane, nottoo far away from the galactic center (55 degrees). 3EG J1828+0142 and 3EG J1735−1500 arethe two most variable EGRET sources in the galactic plane (Torres et al. 2001), presentingquite steep spectra (photon indices of 2.76 and 3.24 respectively) and typical luminosities ofabout 1035 erg s−1, adopting a distance of 4 kpc. We have applied a microquasar model to theseparticular cases for checking the proposal of association between microquasars and the variableEGRET sources in the galactic plane.⋆ E-mail:Are 3EG J1828+0142 and 3EG J1735-1500 microquasars? 2852 THE VARIABLE EGRET SOURCES IN THE GALACTIC PLANEEGRET sources in the galactic plane are well-correlated with star forming regions (Romero etal. 1999), and log N-log S studies suggest that they are more abundant toward the inner spiralarms (Gehrels et al. 2000, Bhattacharya et al. 2003). Among these sources, there is a subgroupof variable sources (Nolan et al. 2003) that has been proposed to be the EGRET counterparts ofhigh-mass microquasars (Kaufman Bernado´ et al. 2002, Bosch-Ramon et al. 2004). High-massmicroquasars are also somehow correlated with star forming regions (Romero et al. 2004). Weare interested now in two particular cases: 3EG J1828+0142 and 3EG J1735−1500, exploringthe possibility that they can be high-mass microquasars.3 GAMMA-RAY EMISSION FROM MICROQUASARS3.1 The ModelWe have developed a semi-analytical model based on an inhomogeneous leptonic jet formedby relativistic particles. Those particles interact with the seed photon fields (synchrotron, star,disk and corona photons) through inverse Compton (IC) effect (see Bosch-Ramon et al. 2004).We have accounted for both the Thomson and the Klein-Nishina regimes of IC interaction(Blumenthal & Gould 1970). The different functions that represent the electron energy distri-bution, the electron energy and the magnetic field within the jet have been parametrized inorder to simulate their evolution along the jet (e.g. Ghisellini et al. 1985, Punsly et al. 2000).3.2 3EG J1828+0142 and 3EG J1735-15003EG J1828+0142 (Hartman et al. 1999) is the second most variable low-latitude non-transientgamma-ray source. Within the error box of this EGRET source, there are several faint non-thermal radio sources (Punsly et al. 2000) and X-ray sources (observed in the ROSAT All SkySurvey) with typical luminosities of about 1033 erg s−1, adopting distances of 4 kpc. Finally,Comptel upper limits (Shu Zhang 2004) are also known, corresponding to luminosities ofabout 1034-1035 erg s−1 in the COMPTEL energy range at the same distance. The error box of3EG J1735−1500 (Hartman et al. 1999), the most variable EGRET source, has been alreadyexplored by Combi et al. (2003), and there are two potential counterparts: a radio galaxy anda compact radio source that presents hard spectrum and flux densities of about 0.3 Jy. Highupper limits at X-ray and COMPTEL energies are imposed from observational data to be (1034-1035 erg s−1). To model the Spectral Energy Distribution (SED) of a microquasar that could bethe origin of the EGRET emission, we account for the known observational data at differentwavelengths. We must note that the observations at different frequencies were not simultaneous.Regarding upper limits at radio and X-ray energies, they have been taken as the fluxes of thebrightest sources within the EGRET error boxes.4 RESULTSThe Figs. 1 and 2 show the computed SED for 3EG J1828+0142 and 3EG J1735−1500 respec-tively. In Tables 1 and 2 the adopted parameters for both systems are listed. These SED respectthe observational constraints and reproduce pretty well the EGRET spectrum. It is worth not-ing that the used EGRET spectrum for comparison with our model is the averaged one for thefour viewing periods. Nevertheless, concerning variability, microquasars can naturally presentthe variable nature observed in these two objects due to several factors: precession of the jet,orbital motion, etc... (i.e. Kaufman Bernado et al. 2002, Bosch-Ramon & Paredes 2004).Regarding the high-mass star emission of these systems, it could be dust-enshrouded, asit has been suggested, for instance, for INTEGRAL obscured sources thought to be XRB and286 V. Bosch-Ramon et al.Table 1 Common parameters for 3EG J1828+0142 and 3EG J1735–1500Parameter ValueJet kinetic luminosity 5×1035 erg s−1Stellar bolometric luminosity 1038 erg s−1Distance from jet’s apex to the compact object ∼ 108 cmInitial jet radius ∼ 107 cmOrbital radius 3×1012 cmViewing angle to jet’s axis 10◦Magnetic field 300GaussTable 2 Particular Parameters for 3EG J1828+0142 and 3EG J1735–1500Parameter Adopted values for Adopted values for3EG J1828+0142 3EG J1735–1500Jet Lorentz factor 1.5 3Maximum Lorentz factor for electrons in jet (jet frame) 3×103 2.5×103Electron power-law index 1.5 2Total disk/corona luminosity 1032 erg s−1 1033 erg s−1microquasars (i.e. Walter et al. 2003, Combi et al. 2004). This effect can be very important ifthe sources are located in the inner regions of the galactic plane, being strong enough to obscurea high-mass star from IR wavelengths to soft X-rays. Furthermore, emission in the far infraredcan be too weak to be detected by the satellite IRAS (i.e. Filliatre & Chaty 2004).To compute the overall SED presented in the Figs. 1 and 2, we have adopted a strongmagnetic field and a low maximum energy for the electrons (see Tables 1 and 2). For3EG J1828+0142, the synchrotron emission is dominant in the entire EGRET detection range,which reached only several hundreds of MeV. Moreover, the jet is mildly relativistic. In theother hand, 3EG J1735−1500 was detected up to few GeV. For this second case, we have mod-elled the emission up to several hundreds of MeV through synchrotron self-Compton scattering,and through comptonization of coronal seed photons further up. For this second case, the jetLorentz factor has been taken higher than for the first one. For both sources, accounting forX-ray emission must be dim since otherwise it would imply a clear counterpart at energiesbeyond 1 keV, corona and disk components have been taken to be weak.5 CONCLUSIONSThe possibility of computing a radio-to gamma microquasar SED, at all in accord with observa-tional constraints, suggests that microquasars may be the counterparts of these two particularsources: 3EG J1828+0142 and 3EG J1735−1500. Other possible objects cannot be discardedas possible counterparts (i.e. an isolated black-hole, see Punsly et al. 2000; accreting neutronstars, see Romero et al. 2001; early-type binaries, see Benaglia & Romero 2003; etc...). However,microquasars appear to be attractive candidates due to the presence of a jet with a relativis-tic leptonic population and strong seed photon fields provided by the stellar companion, theaccreting matter and the electrons themselves. In the near future, instruments like AGILEand GLAST will help us to improve the location of unidentified EGRET sources and furtherobservations at lower energies will help us to better constrain the models as well.Are 3EG J1828+0142 and 3EG J1735-1500 microquasars? 287−6 −4 −2 0 2 4 6 8Log (photon energy [eV])2527293133353739Log (εLε [erg/s])IC emissionseed photonsradio emissionsync. ICcor. ICstar ICdisk ICcor.disksync.starradio jet(1)(2)(3)(4)Fig. 1 SED for an unabsorbed broadband microquasar model of the source 3EG J1828+0142.The adopted parameter values are shown in Tables 1 and 2. There are represented the upper limitsat radio (1), X-ray (2) and COMPTEL (3) energies, as well as the EGRET spectrum (4).−6 −4 −2 0 2 4 6 8Log (photon energy [eV])2527293133353739Log (εLε [erg/s])IC emissionseed photonsradio emissionsync. ICcor. ICstar ICdisk ICstarsync.coronadiskradio jet(1)(2)(3)(4)Fig. 2 The same as in Fig. 1 but for the source 3EG J1735+1500.288 V. Bosch-Ramon et al.Acknowledgements V.B-R. and J.M.P. acknowledge partial support by DGI of the Ministeriode Ciencia y Tecnolog´ıa (Spain) under grant AYA-2001-3092, as well as additional supportfrom the European Regional Development Fund (ERDF/FEDER). During this work, V.B-Rhas been supported by the DGI of the Ministerio de Ciencia y Tecnolog´ıa (Spain) under thefellowship FP-2001-2699. G. E. R is supported by Fundacio´n Antorchas and the ArgentineAgencies CONICET and ANPCyT. This research has benefited from a cooperation agreementsupported by Fundacio´n Antorchas. The work of DFT was performed under the auspices of theUS DOE (NNSA), by UC’s LLNL under contract No. W-7405-Eng-48. We thank an anonymousreferee for useful comments on the paper.ReferencesBenaglia P., Romero G. E., 2003, A&A 399, 1121Bhattacharya D., Akyu¨z A., Miyagi T., Samimi J., Zych A., 2003, A&A 404, 163Blumenthal G. R., Gould R. J., 1970, Rev. Mod. Phys. , 42, 237Bosch-Ramon V., Romero G. E., Paredes J. M., 2004, A&A, 429, 267Bosch-Ramon V., Paredes, J. M., 2004, A&A, 417, 1075Combi J. A., Romero G. E., Paredes J. M., Torres D. F., Ribo´ M., 2003, ApJ, 588, 731Combi J. A., Ribo´ M., Mirabel I. F., Sugizaki M., 2004, A&A, 422, 1031Filliatre P., Chaty S., 2004, ApJ, 616, 469Gehrels N., Macomb D. J., Bertsch D. L., Thompson D. J., Hartman R. C., 2000, Nature, 404, 363Ghisellini G., Maraschi L., Treves A., 1985, A&A, 146, 204Hartman R. C., Bertsch D. L., Bloom S. D. et al., 1999, ApJS, 123, 79Kaufman Bernado´ M. M., Romero G. E., Mirabel I. F., 2002, A&A, 385, L10Mirabel I. F., Rodr´ıguez L. F., 1999, ARA&A, 37, 409Nolan P. L., Tompkins W. F., Grenier I. A., Michelson P. F., 2003, ApJ, 597, 615Paredes J. M., Mart´ı J., Ribo´ M., Massi M., 2000, Science, 288, 2340Punsly B., Romero G. E., Torres D. F., Combi J. A., 2000, A&A, 364, 552Romero G. E., Benaglia P., Torres D. F., 1999, A&A, 348, 868Romero G. E., Kaufman Bernado´ M. M., Combi J. A., Torres D. F., 2001, A&A, 376, 599Romero G. 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Microquasar models for 3EG J1828+0142 and 3EG J1735-1500

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