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Correction on Chandra Detection of Pulsations from GRO J1744-28

ATel #5896; Deepto Chakrabarty (MIT), Peter G. Jonker (SRON), Craig B. Markwardt (NASA/GSFC)
on 18 Feb 2014; 10:09 UT
Credential Certification: Deepto Chakrabarty (deepto@space.mit.edu)

Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar

Referred to by ATel #: 5904

We recently reported the detection of coherent X-ray pulsations from GRO J1744-28 using data from the Chandra/HRC-I taken on 2014 February 16 (ATel #5895). In that report, we stated that the timing accuracy of our event data could be as poor as 120 ms, owing to the effects of the HRC wiring error described in the Chandra Proposer's Observatory Guide. This is incorrect, as we did not account for the overall background rate in the detector, including untelemetered (vetoed) events. (For a detailed discussion, see http://asc.harvard.edu/cal/Hrc/timing_200304.html ) With the background events included, the timing accuracy should be no worse than around 4 ms, which is negligible compared to the 467 ms pulse period of GRO J1744-28. Thus, the HRC wiring error should have no significant effect on the pulse timing measurements we reported.

We note that this corrected description does not change any of the source parameters that we reported previously.

We thank Jules Halpern for pointing out our error.