New outbursts of two faint X-ray transients (GRS 1741.9-2853 and XMM J174457-2850.3) located in the Galactic center region

ATel #512; R. Wijnands, T. Maccarone, J. Miller-Jones, M. van der Klis (U. Amsterdam), M. Rupen, (NRAO/GSFC), J. in 't Zand (SRON-Utrecht), Q. D. Wang (U. Massachusetts), J. Grindlay, D. Steeghs (CfA), R. Fender, R. Cornelisse (U. Southampton), E. Kuulkers (ISOC, ESA/ESAC), C. B. Markwardt (U. Maryland, NASA/GSFC), J. Homan (MIT)
on 6 Jun 2005; 19:56 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: Rudy Wijnands (rudy@space.mit.edu)

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The Galactic Center region was observed in a series of 7 pointings with the Chandra X-ray Observatory on 5 June 2005 01:44-13:08 UTC. During these observations we found that the two faint X-ray transients GRS 1741.9-2853 (e.g., Muno et al. 2003, ApJ 598, 474, and references therein) and XMM J174457-2850.3 (Sakano et al. 2005, MNRAS 357, 1211) were in outburst again.

GRS 1741.9-2853 is a neutron star X-ray transient and was detected during our observations at a 2-10 keV flux of approximately 1E-10 erg/s/cm^2 (assuming absorbed power-law spectral shape with a Galactic column density of 9.7E22 cm^-2 and a power-law index of 1.88; see Muno et al. 2003).

XMM J174457-2850.3 is a faint X-ray transient that has not been classified yet and that was found at a 2-10 keV flux of approximately 9E-11 erg/s/cm^2 (assuming an absorbed power-law spectral shape with a Galactic column density of 5.9E22 cm^-2 and a power-law index of 1.0; see Sakano et al. 2005).

These low flux levels demonstrate that both transients are very faint with 2-10 keV X-ray luminosities of 7-8 E35 erg/s (assuming a distance of 8 kpc).

We urge follow-up observations at X-ray, infrared, and radio wavelengths of these enigmatic X-ray transients.

Our Chandra observations are part of a X-ray monitoring campaign (PI: Wijnands) of the Galactic center region (approximately 1.7 square degrees centered on Sgr A*) using both the Chandra X-ray Observatory and the XMM-Newton telescope. The purpose of these observations is to search for outbursts of faint X-ray transients (with 2-10 keV X-ray luminosities between 1E34 and 1E36 erg/s) which cannot be detected by other monitoring X-ray satellites due to sensitivity limits and/or confusion problems. The next set of observations will be performed around 9-10 September 2005 (XMM-Newton), in the week of 17 October 2005 (Chandra), and around 28 February 2006 (XMM-Newton).