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Register a new userDiscovery of a New Pulsar Wind Nebula in the Large Magellanic Cloud
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We present new high-resolution radio and X-ray observations of the supernova remnant (SNR) B0453-685 in the Large Magellanic Cloud, carried out with the Australia Telescope Compact Array and the Chandra X-ray Observatory respectively. Embedded in the SNR shell is a compact central nebula producing both flat-spectrum polarized radio emission and non-thermal X-rays; we identify this source as a pulsar wind nebula (PWN) powered by an unseen central neutron star. We present a new approach by which the properties of a SNR and PWN can be used to infer upper limits on the initial spin period and surface magnetic field of the unseen pulsar, and conclude that this star was an initial rapid rotator with current properties similar to those of the Vela pulsar. As is the case for other similarly-aged sources, there is currently an interaction taking place between the PWN and the SNRs reverse shock.
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Rossi X-Ray Timing Explorer observations of the Small Magellanic Cloud have revealed a previously unknown transient X-ray pulsar with a pulse period of 95s. Provisionally designated XTE SMC95, the pulsar was detected in three Proportional Counter Array observations during an outburst spanning 4 weeks in March/April 1999. The pulse profile is double peaked reaching a pulse fraction ~0.8. The source is proposed as a Be/neutron star system on the basis of its pulsations, transient nature and characteristically hard X-ray spectrum. The 2-10 keV X-ray luminosity implied by our observations is > 2x10^37 erg/s which is consistent with that of normal outbursts seen in Galactic systems. This discovery adds to the emerging picture of the SMC as containing an extremely dense population of transient high mass X-ray binaries.
We report the discovery of a new Small Magellanic Cloud Pulsar Wind Nebula (PWN) at the edge of the Supernova Remnant (SNR)-DEM S5. The pulsar powered object has a cometary morphology similar to the Galactic PWN analogs PSR B1951+32 and the mouse. It is travelling supersonically through the interstellar medium. We estimate the Pulsar kick velocity to be in the range of 700-2000 km/s for an age between 28-10 kyr. The radio spectral index for this SNR PWN pulsar system is flat (-0.29 $pm$ 0.01) consistent with other similar objects. We infer that the putative pulsar has a radio spectral index of -1.8, which is typical for Galactic pulsars. We searched for dispersion measures (DMs) up to 1000 cm/pc^3 but found no convincing candidates with a S/N greater than 8. We produce a polarisation map for this PWN at 5500 MHz and find a mean fractional polarisation of P $sim 23$ percent. The X-ray power-law spectrum (Gamma $sim 2$) is indicative of non-thermal synchrotron emission as is expected from PWN-pulsar system. Finally, we detect DEM S5 in Infrared (IR) bands. Our IR photometric measurements strongly indicate the presence of shocked gas which is expected for SNRs. However, it is unusual to detect such IR emission in a SNR with a supersonic bow-shock PWN. We also find a low-velocity HI cloud of $sim 107$ km/s which is possibly interacting with DEM S5. SNR DEM S5 is the first confirmed detection of a pulsar-powered bow shock nebula found outside the Galaxy.
We report on a peculiar X-ray binary pulsar IKT1 = RXJ0047.3-7312 observed with XMM-Newton in Oct. 2000. The X-ray spectrum is described by a two-component spectrum. The hard component has a broken power-law with respective photon indices of 0.2 and 1.8, below and above the break energy at 5.8 keV. The soft component can be modeled by a blackbody of kT = 0.6 keV. The X-ray flux shows a gradual decrease and periodic variations of about 4000 s. The averaged flux in 0.7-10.0 keV is 2.9x10^-12 ergs/cm^2/s, which is ~10 times brighter than that in a ROSAT observation in Nov. 1999. In addition to the 4000-s variation, we found coherent pulsations of 263 +/- 1 s. These discoveries strengthen the Be/X-ray binary scenario proposed by the ROSAT and ASCA observations on this source, and confirm that most of the hard sources in the Small Magellanic Cloud are X-ray binary pulsars. A peculiar property of this XBP is that the coherent pulsations are found only in the soft component, and the folded light curve shows a flat top shape with a sharp dip. We discuss the nature of this XBP focusing on the peculiar soft component.
We report on a discovery of a diffuse nebula containing a pointlike source in the southern blowout region of the Cygnus Loop supernova remnant, based on Suzaku and XMM-Newton observations. The X-ray spectra from the nebula and the pointlike source are well represented by an absorbed power-law model with photon indices of 2.2+/-0.1 and 1.6+/-0.2, respectively. The photon indices as well as the flux ratio of F_nebula/F_pointlike ~ 4 lead us to propose that the system is a pulsar wind nebula, although pulsations have not yet been detected. If we attribute its origin to the Cygnus Loop supernova, then the 0.5-8 keV luminosity of the nebula is computed to be 2.1e31 (d/540pc)^2 ergs/s, where d is the distance to the Loop. This implies a spin-down loss-energy E_dot ~ 2.6e35 (d/540pc)^2 ergs/s. The location of the neutron star candidate, ~2 degrees away from the geometric center of the Loop, implies a high transverse velocity of ~1850 (d/540pc)(t/10kyr)^{-1} km/s, assuming the currently accepted age of the Cygnus Loop.
We report the discovery of a possible symbiotic star, in the Large Magellanic Cloud (LMC). The object under consideration here, designated as RP 870, was detected during the course of a comprehensive H$alpha$ survey of the LMC by Reid & Parker (2012). The spectrum of RP 870 showed high ionization emission lines of He I, He II and [O III] and molecular absorption bands of TiO $lambda$$lambda$6180, 7100. The collective signatures of a hot component (high excitation/ionization lines) and of a cool component (TiO molecular bands) are seen in RP 870, from which we propose it as a symbiotic star. Since known symbiotic systems are rare in the LMC, possibly less than a dozen are known, we thought the present detection to be interesting enough to be reported.
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