Department of Astronomy, University of Padova

Department of Physics, University of Padova

INAF-Astronomical Observatory of Padova

Paola Mucciarelli

In collaboration with:• Zampieri, Turolla, Treves, Falomo, Chieregato, Kaaret & di Stefano.

The UltraLuminous X-ray source NGC 1313 X-2

NGC1313 X-2: X-ray properties NGC1313 is a nearby spiral

galaxy hosting two ULXs, NGC1313 X-1 and X-2, and the interacting supernova 1978K.

NGC1313 X-2 is a well known ULX, variable on a timescale of months.

Assuming that at maximum the source radiates at the Eddington limit, a mass of 50 M⊙ is derived for the compact remnant.

NGC1313 X-2

NGC1313 X-1

MODEST-6, August 29-31, 2005

♣ The XMM spectrum shows statistical evidence for a MCD component with kT=0.2 keV (Miller et al. 2003 ,Zampieri et al. 2004)

MBH~ 90f4 M

NGC1313 X-2: optical counterpartNGC 1313 X-2 optical counterpart was identified in an ESO 3.6m R band image, using the Chandra position with an uncertainty of 0.7 (Zampieri et al., 2004).

In archive ESO VLT (BVR) band images the counterpart is resolved in two distinct point-like sources, C1 and C2, separated by 0.7”(Mucciarelli et al., in prep.).Taking into account Galactic absorption: C1: R=23.5, (B-V)

0=-0.2

(V-R)0=-0.2

C2: R=23.4, (B-V)0>1.0

(V-R)0=0.4

(R-I)0=0.2(from Liu et al. 2005)

MODEST-6, August 29-31, 2005

Both object are nor an AGN (absence of redshifted emission lines and very high fX/fR) neither foreground stars.

C1: BO-O9 main sequence star of 20M

in NGC 1313 C2: G supergiant of about 10M in NGC

1313

Conclusions

MODEST-6, August 29-31, 2005

Two optical counterparts are detected (on VLT images) inside the Chandra error box of the ULX

NGC 1313 X-2.

Irrespectively of wich of the two objects is the actual counterpart, NGC 1313 X-2 appears to be a high mass X-ray binary with a massive donor star.

At the present stage, there seems to be no compelling argument to rule out any of the two

object C1 and C2 as possible counterpart.

Follow up optical spectroscopy under optimal seeing conditions and with the slit along the line of conjunction C1-C2 is crucial to disentangle the

emission from the two objects.

Theoretical modelling may also help to distinguish the counterpart

(Patruno & Zampieri, in prep.)