AGILE gamma-ray detection ofEta Carinae

M. Corcoran on behalf of the AGILE Team

IAU Symposium, August 2009

AGILE Satellite AGILE Satellite (IABG, (IABG, MunichMunich16 June,16 June, 2006)2006)

350 kg satellite350 kg satellite

Gamma-ray astrophysics missions(above 30 MeV)

June 11, 2008NASAFERMI

April 23, 2007ASIAGILE

Apr. 1991 – Jun. 2000NASACGRO

Aug. 1975 – Apr. 1982ESACOS–B

Nov. 1972 – July 1973NASASAS-2

The AGILE Payload: the most compact

instrument for high-energy astrophysics

It combines for the first time a gamma-ray

imager (30 MeV- 30 GeV)

with a hard X-ray imager (18-60 keV) with

large FOVs (1-2.5 sr) and optimal angular

resolution

FERMI/GLAST AGILE

A quick comparison

10 %50 %Energy resolution(~ 400 MeV)

whole sky1/5sky coverage

~ 8000-10000500Aeff (10 GeV) (cm2)

2.52.5FOV (sr)

3o - 4o

< 1o

4o - 5o

< 1o

PSF (68 % cont. radius)

100 MeV

1 GeV

~ 2000-2500~400Aeff (100 MeV) (cm2)

FERMI/LATAGILE

a comparison: 1-day exposure

~ (1-2) 107

cm2 sec~ 2 107

cm2 sec1-day exposure (30 degreeoff-axis, 100 MeV)

~ 0.16~ 0.5Source livetime fraction

variablefixedAttitude

whole sky1/5sky coverage

2.52.5FOV (sr)

FERMI(LAT)

AGILE(GRID)

Galactic Center

Cygnus Region Carina Region

AGILE gamma-ray emission above 100 MeV

AGILE study of the Galactic plane• Galactic Center region• Cygnus region• Carina region• Crux region

AGILE accumulated a large exposure in the Carina Region, equivalent to ~ 5 months of effective livetime for an exposure of 109 cm2 sec and flux sensitivity of 10-7 ph. cm-2s-1 above 100 MeV.

Several old and new gamma-ray sources are detected, some are time variable

Detection of Eta Carinae (average flux of a few 10-7 ph. cm-2s-1 above 100 MeV.

The CARINA REGION (MW observations)

X-Ray images

CHANDRA XMM-Newton ASCA

Hamaguchi et al. 2007 ApJ 663, 522

Hubble Space TelescopeIRAS far-IR multicolor image

(from N. Smith 2009 Handb. Star Form. Regions II p.138)

AGILE gamma-ray map on same scale

UV rays & winds of numberless young hot stars produce a wealth of spectacular nebular structures

Eta Carinae

AGILE integrated gamma-ray map above 100 MeV of the Carina Region

AGILE integrated gamma-ray map above 100 MeV of the Carina Region

IRAS far-IR emission from the Carina Region

AGILE discovery of gamma-ray emission from a sourcecoincident with Eta Carinae

(integrated intensity map above 100 MeV)

AGILE study of the Eta Car region

(Tavani et al., 2009)

AGILE’s good angular resolution above 100 MeV resolves satisfactorily the region near Eta Car.

3 gamma-ray sources within a few degrees squared.

the Eta Carinae gamma-ray counterpart is well separated from the anomalous X-ray pulsar AXP 1E 1048.1 – 5937 and from the unidentfied INTEGRAL source IGR J10447-6027.

Detection of Eta Carinae (pre-periastron)(average flux of F = 40 x 10-8 ph. cm-2s-1 above 100 MeV during the 2008 pointings).

Detection of a (relatively soft) gamma-ray flare on October 12-13, 2008

AGILE –Carina Region at 400 MeV

AGILE-GRID, Eta Carinae at 400 MeV

Eta Carinae average gamma-ray properties

• 7.8-sigma detection above 100 MeV

• (l,b) = (287.6, -0.7) ± 0.3 ± 0.1

• F = (37 ± 5) x 10-8 ph. cm-2 s-1

• L = 3.4 x 1034 erg/s (2.3 kpc dist)

Gamma-ray emission from Eta Carinae

The source was positively detected during several individual observing runs showing a roughly constant gamma-ray flux over the whole observations period. The October 2008 maximum is due to a flare (see next slides) rather than to a flux increase before periastron as in X-rays.

Transient gamma-ray emission from EtaCarinae (12-13 Oct., 2008)

10-11 Oct.

16-17 Oct.14-15 Oct.

12-13 Oct.

The 11-13th October, 2008 Eta Car gamma-ray flare

11-13 Ott 08

2 days integration maps - counterclockwise

5.2 detection(l,b) = 288.0, -0.4 ± 0.6F = (270 ± 65) x 10-8 ph/cm2/sL =3 x 1035 erg/s (2.3 kpc dist)

a relatively “soft” flare(100 MeV vs 400 MeV maps)

> 400 MeV> 100 MeV

The gamma-ray flare of Oct 11-13, 2008 is mainly due to photons of energy lower than 400 MeV.

The keV to MeV Energy Spectrum of Eta Carinae

SAX MECS

AGILE

INTEGRAL

Although data are not simultaneous, it is interesting to note that the average AGILE spectrum together with the INTEGRAL historical spectrum is in qualitative agreement with expectations based on inverse Compton and/or pion decay models of gamma-ray emission from colliding wind binaries (Raimeret al, 2006)

Oct 2008 Flare

average emission

Summary on the Eta Car region

Detection of Eta Carinae (pre-periastron)(average flux of F = 40 x 10-8 ph. cm-2s-1 above 100 MeV during the 2008 pointings).

Detection of a gamma-ray flare from Eta Carinae (Oct. 12-13, 2008)(F = 270 x 10-8 ph. cm-2s-1 above 100 MeV).

Very weak or absent emission near periastron(AGILE ToO observation, Jan. 9-17, 2009)

Weak or absent emission detected above 100 MeV during an AGILE pointing in April 2009.

ConclusionsAGILE detected a point source centered on the object Eta Carinae

identification with the Eta Carinae is supported by:

• Eta Car is a very massive and powerful CW binary system • it is the strongest and hardest 2-10 and 22-100 KeV source in the

field • the two nearby hard X-ray sources detected by INTEGRAL are

outside the AGILE error box• it has a non-thermal X-ray excess (BSAX, INTEGRAL, SUZAKU)• time variability both in X- and gamma-rays • no alternative identification so far

This is the first remarkable detection above 100 MeV of a colliding wind binary system, confirming the efficient particle acceleration and highly non-thermal nature of the strong shock in a CWB.