Collective effects of stellar winds and unidentified gamma-ray sources Diego F. Torres THE...
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Collective effects of stellar winds and unidentified gamma-ray sources
Diego F. Torres
THE MULTI-MESSENGER APPROACH TO UNIDENTIFIED GAMMA-RAY SOURCES
http://europa.ieec.fcr.es/english/recerca/map
Institut de Ciencies de l’Espai, Barcelona, Spain
Diego F. Torres dtorres@ ieec.uab.es http://europa.ieec.fcr.es/english/recerca/map
2 things discussed in the conference
Observational discovery of TeV sources without lower energy counterparts (not even GeV), e.g., Funk
Possibility of –at least two- explanations (Aharonian) Fastest diffusion of higher energy hadrons and follow-up interaction in
molecular clouds a bit separated from the accelerator Effect of stellar winds
(single stellar winds Torres et al. 2004, ApJ Letters) (collective stellar winds, this talk)
Diego F. Torres dtorres@ ieec.uab.es http://europa.ieec.fcr.es/english/recerca/map
1999 – 2001 Observations 112 hr June - September 2002 Observations 137 hr
Unidentified TeV sources: The HEGRA source in Cygnus
Aharonian et al. 05
Diego F. Torres dtorres@ ieec.uab.es http://europa.ieec.fcr.es/english/recerca/map
Making a long story short: no counterpart is identified
Butt et al. 05
Diego F. Torres dtorres@ ieec.uab.es http://europa.ieec.fcr.es/english/recerca/map
Butt, et al. 2003
110 cataloged OB stars in Cyg OB2 shown as a surface density plot (stars per 4 arcmin2). Note that many stars in Cyg OB2 remain uncataloged – the total number of OB stars alone is expected to be ~2600 (Knodlseder 2002). Although the extinction pattern towards Cyg OB2 may control the observed surface density of OB stars, our analysis assumes that the observed distribution of OB stars tracks the actual distribution. The thick contours show the location probability (successively, 50%, 68%, 95%, and 99%) of the non-variable EGRET source 3EG 2033+4118. The red circle outlines the extent of the TeV source.
Enhancement of stellar density at the HEGRA TeV source
Butt et al. 05
Diego F. Torres dtorres@ ieec.uab.es http://europa.ieec.fcr.es/english/recerca/map
HESS J1303-631: first serendipitous discovery during monitoring of the PSR B1259. [A&A 439 (2005) 1013]
Still unidentified. Extended source.
In correspondence the OB association Cen OB1 that contain al least 20 O stars and 1 WR star.
Also no known counterpart at lower freq yet.
Unidentified TeV sources: HESS J1303
Aharonian et al. 05
Diego F. Torres dtorres@ ieec.uab.es http://europa.ieec.fcr.es/english/recerca/map
Hadronic -rays from stellar associations: needed ingredients
High-energy accelerated particles (up to hundreds TeV)
Collective effects of strong stellar winds & SNe at the association core
supperbubble large scale shock CR acceleration
(see, e.g., Montmerle 1979; Casse & Paul 1980; Bykov & Fleishman 1992a,b; Bykov 2001)
Dense enough target medium
(for p-p interactions 0 ) Proposed target: collective winds of OB stars
near the acceleration region
Diego F. Torres dtorres@ ieec.uab.es http://europa.ieec.fcr.es/english/recerca/map
Winds of massive OB stars: basic observational facts
O and B stars lose a significant fraction of their mass in stellar winds with terminal velocities of order 103 km s-1.
With mass loss rates as high as M ~ 510-7 – 110-5 M◦ yr-1 the density at the base of the wind can reach 10-12 g cm-3 (e.g., Lamers & Cassinelli 1999, Ch.2).
Such winds are also permeated by significant magnetic fields, that can reach mG or even higher at tenths of pc from the surface (Surface magnetic field B ~ 10-100 G, Donati et al. 2001, 2002)
.
Diego F. Torres dtorres@ ieec.uab.es http://europa.ieec.fcr.es/english/recerca/map
Wind-wind interaction that takes place in a dense stellar cluster or sub-cluster.
The stars are assumed to be uniformly distributed within the outer radius of the cluster.
The material ejected from the stars goes through stellar wind shocks (drawn as circles) and then participates in an outward flow [with mean velocity V(R) and density n(R)] which eventually leaves the cluster and interacts with the surrounding interstellar matter.
The gas within a collective wind
Diego F. Torres dtorres@ ieec.uab.es http://europa.ieec.fcr.es/english/recerca/map
Istropic distribution of stars
Each with a wind velocity and mass loss rate
Mass and momentum conservation
Within the cluster
Ouside the cluster
Algebra + initial and boundary conditions
Numerically solvable set of equations
The gas within a collective windFrom Domingo-Santamaria & Torres, Hadronic Processes in Winds A&A, 448, 613, 2006
Diego F. Torres dtorres@ ieec.uab.es http://europa.ieec.fcr.es/english/recerca/map
The gas within a collective wind
Wind Velocity Wind VelocityWind Density Wind Density
From Domingo-Santamaria & Torres, Hadronic Processes in Winds A&A, 448, 613, 2006
Diego F. Torres dtorres@ ieec.uab.es http://europa.ieec.fcr.es/english/recerca/map
Penetrating the wind: diffusion vs. convection
Approach: comparison between timescales
Diffusion - Convection
Dr
td23 rV
rtc
3
rRVVEBft
trotp
c
d ,,,,, If >1 Convection dominates
If <1 Diffusion dominates
=1 defines Epmin for protons to penetrate the wind
E.g. only protons with energies
will enter into the wind whereas lower energy protons will be convected away wind modulation effect
MeV-GeV -ray emission substantially reduced
Diego F. Torres dtorres@ ieec.uab.es http://europa.ieec.fcr.es/english/recerca/map
Torres, ApJ, 617,
966 (2004)
Numerical modeling of gamma-ray production, diffusion, losses
Diego F. Torres dtorres@ ieec.uab.es http://europa.ieec.fcr.es/english/recerca/map
Effect of modulation
Knock-on emissivity positron emissivity Losses
From Domingo-Santamaria & Torres, Hadronic Processes in Winds A&A, 448, 613, 2006
Diego F. Torres dtorres@ ieec.uab.es http://europa.ieec.fcr.es/english/recerca/map
Effect of modulation II
Differential Flux Integral Flux Opacity
From Domingo-Santamaria & Torres, Hadronic Processes in Winds A&A, 448, 613, 2006
Diego F. Torres dtorres@ ieec.uab.es http://europa.ieec.fcr.es/english/recerca/map
Effect of modulation III
X=not detectable √=detectable
Diego F. Torres dtorres@ ieec.uab.es http://europa.ieec.fcr.es/english/recerca/map
Concluding remarks
Collective effects of winds, related perhaps with unidentified TeV sources?
We have studied collective wind configurations produced by a number of massive stars, and obtained densities and expansion velocities of the stellar wind gas that is to be target for hadronic interactions in several examples.We have computed secondary particle production, electrons and positrons from charged pion decay, electrons from knock-on interactions, and solve the appropriate diffusion-loss equation with ionization, synchrotron, bremsstrahlung, inverse Compton, and expansion losses to obtain expected γ-ray emission from these regions, including in an approximate way the effect of cosmic ray modulation. Examples where different stellar configurations can produce sources for GLAST satellite, and theMAGIC/HESS/VERITAS telescopes in non-uniform ways, i.e., with or without the corresponding counterparts were shown.
Combined observations with GLAST and MAGIC/HESS will tell.
Most models produce no source at GeV energies, even for GLAST
Good candidates: Cygnus OB2 neighbourhood, Westerlund 1, HESS J1303-631