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Swift detection of an ~500s period in MAXI J1409-619

ATEL # 3060; J. A. Kennea (PSU), P. Curran (CEA/Saclay), H. Krimm (CRESST/GSFC/USRA), P. Romano, V. Mangano (INAF-IASFPA), P. A. Evans (U Leicester), K. Yamaoka (Aoyama Gakuin U) and D. N. Burrows (PSU)
on 1 Dec 2010; 1:40 UT
Distributed as an Instant Email Notice (Transients)
Password Certification: Jamie A. Kennea (kennea@astro.psu.edu)

Subjects: X-ray, Transients
Referred to by ATEL #: 3067, 3069, 3070

At 15:35UT on November 30th, 2010 Swift/BAT triggered on an outburst from MAXI J1409-619 (Mangano et al., GCN #11428), and it was observed by Swift for a total of 2ks in a combination of PC and WT mode. MAXI J1409-619 was first discovered by MAXI on October 18th, 2010 (Yamaoka et al., ATEL #2959) and followed up by Swift, which accurately localized and confirmed the new transient (Kennea et al., ATEL #2962).

The XRT PC mode data reveal an enhanced emission state over the previous detection, with a mean flux of 7 x 10^-10 erg/s/cm^2 (0.3-10 keV, uncorrected for absorption), ~7 times brighter than the flux reported by Swift on October 20th, 2010 (Kennea et al., ATEL#2962).

The PC mode pile-up corrected light-curve reveals a sinusoidal periodicity, not previously detected, with a period of 503 +/- 10 s. 4 clear cycles are seen in the second orbit consisting of 1.9ks of PC mode data taken between 16:55 and 17:28UT, with a sinusoidal peak-to-trough modulation of 42% of the mean flux.

RXTE observations taken October 22-23, 2010 (Yamaoka et al, ATEL #2969) reported no detection of this periodicity, and we have analyzed the previous Swift/XRT data using the Lomb-Scargle method and have also found no evidence of this periodicity. Therefore this periodicity is a transient feature, most likely due to the accretion event that triggered BAT. We suggest that this periodicity is the rotation period of the compact object in MAXI J1409-619, most likely a neutron star, and that MAXI J1409-619 is a candidate HMXB system.


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