On possible counterparts of the Fermi LAT transient J0910-5041

ATel #1822; R. Landi, V. Sguera, L. Bassani (INAF/IASF Bologna), A. Bazzano, A. De Rosa (INAF/IASF Roma), A. J. Dean (Univ. Southampton)
on 30 Oct 2008; 17:08 UT
Credential Certification: Raffaella Landi (landi@iasfbo.inaf.it)

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With reference to the Fermi LAT detection of the transient J0910-5041 located in the Galactic plane (Atel #1788), we report on two Swift/XRT observations of the region performed few days after the gamma-ray discovery.

The X-ray data indicate the presence of only one source (Source n.1) within the 68% gamma-ray error circle at RA(J2000) = 09h 10m 57.52s, Dec(J2000) = -50deg 48m 10.7s (4.6 arcsec uncertainty).

The only other source (Source n.2) detected in the XRT field of view (and located within the 99% Fermi LAT error circle) disappears above 3 keV, indicating a possible stellar origin. It is possibly associated to the faint ROSAT source 1RXS J091143.6-504411.

The spectrum of source n.1 can be described by a simple power law having the following parameters:

Gamma = 1.7 +/- 0.4, 2-10 keV observed flux of (4.4 +/- 0.7) x 10^-13 erg cm^-2 s^-1 on October 17, 2008

Gamma = 0.7 +/- 0.3, 2-10 keV observed flux of (1.3 +/- 0.2) x 10^-12 erg cm^-2 s^-1 on October 18, 2008

This indicates marginal activity in the source. Source n.1 coincides with the Molonglo radio source MGPS J091057-504808 detected at 36 cm with an integrated flux of ~87 mJy; no optical/infrared counterpart is found within the few arcsec radio uncertainty.

We also note that within the 68% Fermi LAT error circle, another bright radio source is listed in the same catalogue as MGPS J091042-504103 with an integrated 36 cm flux of ~193 mJy; within its uncertainty we find a DENIS object with I and J magnitudes of 18.5 and 15.7 respectively.

We encourage further observations of these potential candidates to the MeV source.