Outburst of a new source IGR J08408-4503 detected by INTEGRAL

ATel #813; D. Gotz, S. Schanne, J. Rodriguez (CEA Saclay), J-C. Leyder (IAG Liege and ISDC), A. von Kienlin (MPE Garching), N. Mowlavi (ISDC), S. Mereghetti (IASF Milano)
on 18 May 2006; 15:03 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Jerome Rodriguez (jrodriguez@cea.fr)

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We report the discovery of a new source, IGR J08408-4503, with the ISGRI camera of the IBIS telescope on board the INTEGRAL satellite, during the deep observation of the Vela region on May 15th 2006. The source is detected in a single 1 hour long pointing and inspection of the source light curve on a 100 s time scale reveals a short outburst of 900 s duration starting at 18:25:33 UTC with a peak flux of 250 mCrab in the 20-40 keV energy band.

We analyzed the JEM-X data at the time of the outburst. The source is clearly detected (significance 9 sigma) at a position consistent with the ISGRI one. The best estimated position is RA = 08h 40m 50s, Dec = -45deg 03' 07'' (J2000, +/-2.5 arcmin @90% error).

Although the error box is quite big for optical and infra-red follow-up observations, it is interesting to note the presence in the INTEGRAL error box of a 7th magnitude star located at a distance of 1.7 kpc (HD 74194, a supergiant member of the Vela OB1 association). A preliminary joint JEM-X/ISGRI fit of the peak spectrum, integrated over 300 s, using a black body model, yields a temperature of 4.51 keV and a 4-50 keV flux of about 2x10^-9 erg/cm²/s. If the star and the X-ray object are associated, then the peak luminosity of IGR J08408-4503 is about 10³⁶ erg/s, which rules out a coronal flare as the origin of the X-ray outburst. For this interpretation to be valid, the X-ray source should lie at a very small distance given its peak flux. On the other hand, the short duration of the flare, the detection in the ISGRI energy band, and the peak flux suggest that IGR J08408-4503 is a new member of the class of Supergiant Fast X-ray transients (SF-XRT), similar to IGR J17544-2619, a confirmed SF-XRT, and to IGR J17391-3021/XTE J1739-302, both having O stars as companion. We cannot however exclude IGR J08409-4504 to be a very long and soft GRB, possibly at very high redshift.

Follow-up observations at other wavelengths are encouraged.