Precise orbital ephemeris for the Accreting Millisecond Pulsar IGR J17511-3057
ATel #2221; A. Riggio (INAF-OACagliari & Univ. of Cagliari), A. Papitto (INAF-OACagliari & Univ. of Cagliari), L. Burderi (Univ. of Cagliari), T. Di Salvo (Univ. of Palermo), A. D'Aì (Univ. of Palermo), R. Iaria (Univ. of Palermo), M. T. Menna (INAF-OAR)
on 2 Oct 2009; 09:33 UT
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Credential Certification: Alessandro Papitto (email@example.com)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
Referred to by ATel #: 2232
Taking advantage from the precise source position given by Chandra
(ATEL #2215), we report here refined orbital parameters of the newly
discovered Accreting Millisecond Pulsar IGR J17511-3057 (ATEL #2196,
#2197, #2198, #2215, #2216).
We have analysed the RXTE(PCA) public observations (Full and
pseudo-production Data, http://heasarc.gsfc.nasa.gov/docs/xte/SOF/SOF_data_hp.html )
available up to date and spanning from 2009 Sep 13 to 2009 Sep 26.
The pulsation is present in all the data analysed. The pulse profile
was modelled with a fundamental harmonic and a 1st overtone. The
pulsed fraction (not corrected for the background) are of about 12%
and 2%, respectively.
The pulse phase delays of the fundamental do not show a clear
spin-up/down trend, while there is evidence of pulse phase delays
fluctuations with an amplitude of about 0.05 in phase units on
timescales of few days.
The mean spin frequency calculated on all the considered data and
taking into account the positional uncertanty given in ATEL #2215 is
244.83395157(7) Hz, although local deviations up to 4x10^-7 Hz
around this mean value are observed caused by the mentioned phase
The orbital ephemeris derived from our analysis is:
Orbital period: 12487.5126(9) s
Projected semimajor axis: 275.194(3) lt-ms
Time of passage for ascending node: 55088.0320280(5) MJD [TDB]
Eccentricity e: < 6e-5 (2 sigma c.l.)
Unless otherwise stated, errors in parentheses are quoted at the 1
The orbital parameters given here are consistent, within the errors,
with the first RXTE timing reported in Atel #2197, and with the
recent XMM-Newton timing reported in Atel #2220. We appreciate the
RXTE rapid follow-up scheduling and constant monitoring of the
current source outburst.