On the nature of unidentified lowlatitude gammaray sources Are they highmass microquasars

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On the nature of unidentified low-latitude
gamma-ray sourcesAre they high-mass
microquasars?
Valentí Bosch-Ramon(1), Gustavo E. Romero(2,3)
Josep M. Paredes(1) (1)Universitat de Barcelona,
Catalonia (Spain) (2)Instituto Argentino de
Radioastronomía, Buenos Aires, Argentina (3)Facult
at de Ciencias Astronómicas y Geofísicas, La
Plata, Argentina
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Outline of the talk

• Introduction
• The unidentified EGRET sources of the galactic
  plane
• Microquasars as high energy emitters
• Conclusions Are variable EGRET sources
  microquasars?

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Introduction

• The population of low-latitude EGRET sources
  seems to be concentrated toward the inner spiral
  arms (i.e. Bhattacharya et al. 2003) GRP I
  (Romero et al. 2004).
• A subgroup of GRP I displays significant
  variability (Torres et al. 2001, Nolan et al.
  2003).
• High-mass microquasars have been proposed as the
  counterparts of the variable EGRET sources of the
  galactic plane (Kaufman Bernadó et al. 2002,
  Romero et al. 2004).
• A detailed microquasar model has been developed
  for high energy emission. EC and SSC models are
  explored (Bosch-Ramon et al. 2004).

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Non-variable sources of GRP I
Log N-Log S diagram for the steady sources of the
GRP I

• We have taken all those sources within 6 of
  galactic latitude that present dubious or no
  variability (from Nolan et al. 2003).
• Log N-Log S analysis shows a much more steeper
  spectrum for this group than for radio pulsars
  (ßrad. Puls. 1, uniform distr.).
• They seem to be concentrated to the inner spiral
  arms, like the entire GRP I.

NS-2.92
(Bosch-Ramon et al. 2004)
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Variable sources of GRP I
Log N-Log S diagram for the variable sources of
the GRP I

• We have taken all those sources within 6 of
  galactic latitude that present significant
  variability (from Nolan et al. 2003).
• For this group, Log N-Log S analysis shows a
  quite steeper spectrum than for radio pulsars
  (ßrad. Puls. 1).
• They seem to be less concentrated to the inner
  spiral arms than the steady sources.
• High-mass microquasars have large proper motions
  (for LS 5039, Ribó et al 2002 for LSI61 303,
  Mirabel et al. 2004)), being born in star
  formation regions and less spread than radio
  pulsars ß steady srcgt ß HMMQgt ß rad. puls.

NS-1.66
(Bosch-Ramon et al. 2004)
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A microquasar model for high energy emission

• We take into account the (high-mass) star, disk,
  coronal and jet synchrotron photon fields.
• The jet is modeled by parametrization of the
  functions that represent the lepton energy
  distribution, the magnetic field strength and the
  particle energy (see i.e. Ghisellini et al. 1985,
  Punsly 1999).
• Electron energy distribution follows a power-law
  N(E)aE-p
• The SED of the EC and SSC emission, as well as
  the seed photon SED, are computed.
• An outer jet model is developed to explore radio
  emission.

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(Mirabel, Fuchs)

• Compact jets
• Radio IR
• X?
• gamma?
• (synchrotron
• IC)

• Donor star
• IR UV
• (thermal)

• Disk
• corona ?
• X IR
• therm non therm

• Large scale ejection
• Radio X ?
• Interaction with environment

• Dust ?
• IR mm
• (thermal)

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A mild microquasar
Computed SED for a broadband spectrum

• Lk1035 erg/s, Gjet2.5 ?10
• B10 G, ?emax104 p2
• Ldisk1037, Lcor1035 Lstar5x1038 erg/s
• IC emission is dominated by coronal up-scattered
  photons, reaching EGRET energies (KN reg.).
• High disk luminosities at soft X-rays, and
  dominant corona at hard X-rays.
• Lradio ltlt LEGRET lt Lx

(Bosch-Ramon et al. 2004)
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An extreme microquasar
Computed SED of a broadband spectrum

• Lk1035 erg/s, Gjet10 ?1
• B10 G, ?emax106 p2
• Ldisk1037, Lcor1035 Lstar5x1038
  erg/s
• Extremely high luminosities at high energies,
  dominant stellar IC photons, reaching TeV
  energies (KN reg.).
• Very soft spectrum due to the steepening of N(E).
  
• Lradioltlt LEGRET lt Lx

(Bosch-Ramon et al. 2004)
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A realistic microquasar
Computed SED of a broadband spectrum

• Lk1036 erg/s, Gjet1.1 ?10
• B200 G, ?emax104 p2
• Ldisk3x1032, Lcor3x1032 Lstar5x1038
  erg/s
• IC emission is dominated by SSC scattering,
  reaching EGRET energies.
• Low luminosities at X-rays, with harder spectrum
  at high-energy gamma-rays (Thomson reg.).
• Lradioltlt Lx lt LEGRET

(Bosch-Ramon et al. 2004)
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Conclusions Are variable EGRET sources
microquasars?

• Variable low-latitude EGRET sources follow a
  galactic distribution similar to that presented
  by microquasars.
• Our microquasar model predicts emission at EGRET
  energies for reasonable parameter values.
• Moreover, in the context of our model, there is a
  rich set of possibilities regarding emission at
  high-energy gamma-rays, and either EC or SSC
  models can not be discarded.

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(conclusions)

• Other objects could be the counterparts (i.e.
  early-type binaries, Benaglia and Romero 2003
  accreting neutron star, Romero et al. 2001
  etc...) though
• Microquasars seem more promising counterparts due
  the presence of jets and photon fields.
• Multi-wavelength observational campaigns (Paredes
  et al. 2004) new gamma-ray instruments
  (INTEGRAL, AGILE, GLAST, HESS, MAGIC)
  theoretical work
  -gt better statistical
  and physical knowledge of microquasars/EGRET
  sources.