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Outburst of XMMU J054134.7-682550 in the LMC

ATEL # 1169; D.M. Palmer (LANL), D. Grupe (PSU), H. A. Krimm (GSFC/USRA)
on 6 Aug 2007; 17:21 UT
Distributed as an Instant Email Notice (Transients)
Password Certification: David M. Palmer (

Subjects: Optical, X-ray, Binaries, Black Holes, Neutron Stars, Transients

Routine scanning of the Swift-BAT data on 2007-08-03 found a previously undetected source at a level of ~50 mCrab, with an earliest detection at 10-20 mCrab on 2007-07-14.

A ToO with Swift on 2007-08-03 shows a strong source at
XRT position (J2000):
RA = 5h 41m 33.90s Dec = -68d 25' 50.2" (unc. 3.5")
UVOT Position (J2000):
RA = 5h 41m 34.32s Dec = -68d 25' 48.3" (unc. 1.0")
These positions are consistent with each other and with the location of the probable HMXB source XMMU J054134.7-682550 in the Large Magellanic Cloud (Liu et al 2005, A&A, 442, 1135L). This source is also seen in the ROSAT All Sky Survey at a flux lower than the XRT flux by a factor of 3500.

The XRT WT mode data (230s) can be fitted by an absorbed broken power law with the absorption column density fixed to the Galactic value (2.46e21 cm^-2; Dickey & Lockman 1990). The broken power law parameters are: Gamma-1 = 3.33+/-0.25, E-break = 1.60+0.20/-0.14, and Gamma-2 = 1.67+0.84/-0.45. The observed 0.3-10.0 keV flux is 4.48e-10 ergs s-1 cm-2. Using a distance of 52 kpc to the LMC gives a luminosity of 1.45e38 erg/s in this energy band.

The UVOT detection using the UVW1 has a magnitude of 12.32, not corrected for Galactic reddening (E(B-V)=0.075; Schlegel et al. 1998).

No further pointed observations are planned, but BAT will continue to monitor the source when it is in its field of view, and may trigger an automatic observation if it becomes substantially brighter. The BAT light curve, frequently updated, is available at

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R. E. Rutledge , Editor
ATEL Mirror v1.0 Updates