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We report on the discovery and analysis of the transient X-ray pulsar CXO/XMMU J073709.13+653544 detected in the 2004 August-October Chandra and XMM observations of the nearby spiral galaxy NGC2403. The source exhibits X-ray pulsations with a period P~18 s, a nearly sinusoidal pulse shape and pulsed fraction 46-70%. The source shows a rapid decrease of the pulsation period from 18.25 s on Aug. 9 to 17.93 s on Sep. 12 and possibly 17.56 s on Oct. 3, 2004. The X-ray spectra of the source are hard and are well fitted with an absorbed simple power law of photon index 0.9~1.2. The X-ray properties of the source and the absence of an optical/UV counterpart allow us to identify CXO/XMMU J073709.13+653544 as accreting X-ray pulsar in NGC2403. The maximum unabsorbed luminosity of the source in the 0.3-7 keV range, ~2.6x10e38 erg/s at 3.2 Mpc, is at least 260 times higher than its quiescent luminosity. The corresponding luminosity in the 0.3-100 keV energy range could be as high as ~1.2x10e39 erg/s, assuming the typical pulsar energy spectrum with high-energy cut-off at 10-20 keV. The rate of decrease of the pulsation period of the source (-10e-7 s/s) is one of the fastest observed among accreting pulsars. The evolution of the pulsation period suggests that it is dominated by the intrinsic spin-up of the compact object. The accretion rate implied by X-ray luminosity of CXO/XMMU J073709.13+653544 could account for the observed spin-up rate, assuming that the X-ray source is powered by disk accretion onto highly magnetized neutron star. Based on the transient behavior and overall X-ray properties of the source, we conclude that it could be an X-ray pulsar belonging to either a Be binary system or a low-mass system similar to GRO J1744-28.
IGR J18483-0311 was discovered with INTEGRAL in 2003 and later classified as a supergiant fast X-ray transient. It was observed in outburst many times, but its quiescent state is still poorly known. Here we present the results of XMM-Newton, Swift, a
We present the XMM-Newton observations obtained during four revolutions in Spring and Summer 2004 of CXOGC J174540.0-290031, a moderately bright transient X-ray source, located at only 2.9 from SgrA*. We report the discovery of sharp and deep X-ray e
We describe X-ray observations with Chandra and XMM-Newton of 18 galaxy groups (M_group ~ 1-6x10^13 Msolar, z~0.05) from the Zurich Environmental Study (ZENS). We aim to establish the frequency and properties, unaffected by host galaxy dilution and o
We present Chandra and XMM-Newton observations of the composite star-forming/Seyfert galaxy IRAS20051-1117. The X-ray imaging and spectral properties reveal the presence of an active nucleus. The Chandra image shows a strong nuclear point source (L(2
On 2003 September 17 INTEGRAL discovered a bright transient source 3 degrees from the Galactic Center, IGR J17544-2619. The field containing the transient was observed by XMM-Newton on 2003 March 17 and September 11 and 17. A bright source, at a posi