GCN Circular 2478

GRB031203: ROSAT upper limits suggest XMM-S1 source as the transient

S. Campana, G. Tagliaferri, G. Chincarini, S. Covino, 
D. Fugazza (INAF-OAB), L. Stella (INAF-OAR)

We analysed ROSAT PSPC archival data of Zeta Puppis 
(rp200663n00, on-time 55 ks).
The two XMM-Newton sources (Santos-Lleo & Calderon 
GCN #2464) found in the INTEGRAL error box of GRB 031203 
are within the inner rib of the PSPC.
ROSAT did not detect the two sources.

Using XIMAGE/sosta (and correcting for the exposure map), 
we obtained a 3 sigma upper limit of 
 1.3E-03 c/s on S1 and of  
 1.1E-03 c/s on S2.
The column density of this field is 6x1021 cm-2.
Assuming a power law spectrum with photon index between 
1-2, we can extrapolate (using PIMMS) XMM-Newton rates of 
1.9E-02 - 3.5E-02 c/s for S1 and 
1.5E-02 - 2.9E-02 c/s for S2.

The XMM-Newton sources have been estimated to have a rate of:
S1  0.10+/-0.015 c/s (error at 3 sigma)
S2  0.04+/-0.010 c/s (error at 3 sigma).

If our assumptions on the spectrum are correct, 
we note that the XMM-Newton count rate of S1 is 
not compatible with the ROSAT PSPC upper limit,
suggesting that S1 is an X-ray variable source.