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Long duration outbursts from the two X-ray bursters AX J1745.6-2901 and GRS 1741.9-2853 suggested by XMM-Newton observations

ATEL # 1058; D. Porquet (Obs. Astronomique de Strasbourg, France), N. Grosso (Obs. Astronomique de Strasbourg, France), A. Goldwurm (APC-Paris & SAp/CEA-Saclay, France), M. Sakano (University of Leicester, UK), G. Belanger (ESAC-ESA, Spain), P. Ferrando (APC-Paris & SAp/CEA-Saclay, France), G. Hasinger (MPE Garching, Germany), B. Aschenbach (MPE Garching, Germany), P. Predhel (MPE Garching, Germany), Y. Tanaka (MPE Garching, Germany), R. Genzel (MPE Garching, Germany), F. Yusef-Zadeh (Dearborn Observatory and Northwestern University, US), R.S. Warwick (University of Leicester, UK), F. Melia (University of Arizona, US)
on 20 Apr 2007; 18:32 UT
Password Certification: Delphine Porquet (Delphine.Porquet@astro.u-strasbg.fr)

Subjects: X-ray, Binaries, Neutron Stars, Transients

From March 31 to April 4, 2007, three observations were performed by XMM-Newton as part of a multi-wavelength observation campaign of SgrA* and its neighboring X-ray transient sources. We here report the detection of two bright transient sources in outburst during these observations.

The first source is located at RA=17h45m35.7, Dec=-29d01m35.3s (J2000) with a typical uncertainty of 1.5" radius, i.e., about 90"-SW from SgrA*. This source is at only 2.1" from Swift J174535.5-290135.6 (with an estimated uncertainty of 6" radius) which was detected by the Swift X-Ray Telescope (XRT) in late February 2006 (ATEL #753), and simultaneously detected with JEM-X aboard INTEGRAL (ATEL #756). It is also at 2.4" from CXOGC J174535.6-290133 (with an estimated uncertainty of 0.3" radius; Muno et al. 2003, ApJ, 622, L113), and at 35.6" from AX J1745.6-2901 (with an estimated uncertainty of 24" radius). This latter ASCA source is an eclipsing X-ray burster with an eclipse period of 8.356+/-0.008 h (Maeda et al. 1996, PASJ, 48, 417). We observed seven deep eclipses from the XMM-Newton source with a period consistent with the period of AX J1745.6-2901, as well as a type-I X-ray burst. A renewed activity of Swift J174535.5-290135.6 has been reported by Swift and INTEGRAL on mid-February 2007 (ATEL #1005, #1006). Therefore, our XMM-Newton observations would indicate an outburst duration of at least 7 weeks for this transient.

The second source is located at RA=17h45m02.3, Dec=-28d54m51.6s (J2000) with a typical uncertainty of 1.5" radius, i.e., about 9.9'-NW from SgrA*. This source is at only 1.6", 31.8", and 48.8" from CXOGC J174502.3-285450 (with an estimated uncertainty of 0.3" radius), AX J1745.0-2855 (with an estimated uncertainty of 40" radius), and GRS 1741.9-2853 (with an estimated uncertainty of 45" radius), respectively. We observed two type-I X-ray bursts, which is consistent with the bursting behaviour of GRS 1741.9-2853. A renewed activity of this source in X-rays has been reported on mid-February 2007 by Swift/XRT (ATEL #1006), INTEGRAL/JEM-X (ATEL #1007), and Chandra (ATEL #1013). Therefore, our XMM-Newton observations would suggest an outburst duration of at least 7 weeks for this transient. However, our last XMM-Newton observation, obtained on April 3-4, 2007, indicates that XMM-Newton/EPIC count rate decreased by about a factor of 2.5 in less than one day.

The determination of the accurate X-ray fluxes of these bright sources, both affected by strong pile-up, will be published later.


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