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

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The SED of the EC and SSC emission, as well as the seed photon SED, are computed. ... IC emission is dominated by SSC scattering, reaching EGRET energies. ... – PowerPoint PPT presentation

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

1
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
2
Outline of the talk

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

3
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).

4
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)
5
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)
6
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.

7
(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)

8
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)
9
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)
10
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)
11
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.

12
(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.