* Astronomy

Blobrana · L

RE: XTE J1807-294

Blobrana · L

Title: Precise determination of orbital parameters in system with slowly drifting phases: application to the case of XTE J1807-294
Authors: A. Riggio, T. Di Salvo, L. Burderi, R. Iaria, A. Papitto, T. Menna, G. Lavagetto

We describe a timing technique that allows to obtain precise orbital parameters of an accreting millisecond pulsar in those cases in which intrinsic variations of the phase delays (caused e.g. by proper variation of the spin frequency) with characteristic timescale longer than the orbital period do not allow to fit the orbital parameters over a long observation (tens of days). We show under which conditions this method can be applied and show the results obtained applying this method to the 2003 outburst observed by RXTE of the accreting millisecond pulsar XTE J1807-294 which shows in its phase delays a non-negligible erratic behavior. We refined the orbital parameters of XTE J1807-294 using all the 90 days in which the pulsation is strongly detected and the method applicable. In this way we obtain the orbital parameters of the source with a precision more than one order of magnitude better than the previous available orbital solution, a precision obtained to date, on accreting millisecond pulsars, only for XTE J1807-294 analyzing several outbursts spanning over seven years and with a much better statistics.

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XTE J1807-294.kmz
Google Sky file

-- Edited by Blobrana at 17:08, 2008-01-12

Blobrana · L

The millisecond X-rays pulsar XTE J1807-294, was discovered by XTE on February 21.
It is a binary system. The companion has a minimum mass of about 7 Jupiters, and an orbital period of 40.1 minutes .

RA = 18:07:00.0 and Dec = -29:24:30

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Title: Studies of orbital parameters and pulse profile of the accreting millisecond pulsar XTE J1807-294
Authors: M.G.F.Kirsch, K.Mukerjee, M.G.Breitfellner, S.Djavidnia, M.J. Freyberg, E.Kendziorra and M.J.S. Smith

The accreting millisecond pulsar XTE J1807-294 was observed as a Target of Opportunity (ToO) by XMM-Newton on March 22, 2003 after its discovery on February 21, 2003 by RXTE. The source was detected in its bright phase with an observed average count rate of 33.3 cts s^1 in the EPIC-pn camera in the 0.510 keV energy band (3.7mCrab). Using the earlier established best-fit orbital period of 40.0741±0.0005 minutes from the RXTE observations and considering a circular binary orbit as first approximation, we derived a value of 4.8±0.1 lt-ms for the projected orbital radius of the binary system and an epoch of the orbital phase of MJD52720.67415(16). The barycentric mean spin period of the pulsar was derived as 5.2459427±0.0000004 ms. The pulsars spin-pulse profile showed a prominent (1.5ms FWHM) pulse, with energy and orbital phase dependence in the amplitude and shape. The measured pulsed fraction in four energy bands was found to be 3.1±0.2% (0.53.0 keV), 5.4±0.4% (3.06.0 keV), 5.1±0.7% (6.010.0 keV) and 3.7±0.2%(0.510.0 keV), respectively. Studies of spinprofiles with orbital phase and energy showed significant increase in its pulsed fraction during the second observed orbit of the neutron star, gradually declining in the subsequent two orbits, which was associated with sudden but marginal increase in mass accretion. From our investigations of orbital parameters and estimation of other properties of this compact binary system, we conclude that XTE J1807-294 is very likely a candidate for a millisecond radio pulsar.

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