Swift Observations of the Be/X-ray Transient System 1A 1118-615

We report results of Swift observations for the high mass Be/X-ray binary system 1A 1118-615, during an outburst stage in January, 2009 and at a flaring stage in March, 2009. Using the epoch-folding method, we successfully detected a pulsed period of 407.69(2) sec in the outburst of January and of 407.26(1) sec after the flare detection in March. We find that the spectral detection for the source during outburst can be described by a blackbody model with a high temperature (kT ~ 1-3 keV) and a small radius (R ~ 1 km), indicating that the emission results from the polar cap of the neutron star. On the other hand, the spectra obtained after the outburst can further be described by adding an additional component with a lower temperature (kT ~ 0.1-0.2 keV) and a larger emission radius (R ~ 10-500 km), which indicates the emission from around the inner region of an accretion disk. We find that the thermal emission from the hot spot of the accreting neutron star dominates the radiation in outburst; the existence of both this X-ray contribution and the additional soft component suggest that the polar cap and the accretion disk emission might co-exist after the outburst. Because the two-blackbody signature at the flaring stage is a unique feature of 1A 1118-615, our spectral results may provide a new insight to interpret the X-ray emission for the accreting neutron star. The time separation between the three main outbursts of this system is ~17 years and it might be related to the orbital period. We derive and discuss the associated physical properties by assuming the elongated orbit for this specific Be/X-ray transient.Comment: 9 pages, 3 figures and 4 tables; accepted by MNRA

Investigation of CTA 1 with Suzaku Observation

We report on an 105 ks Suzaku observation of the supernova remnant CTA 1 (G119.5+10.2). The Suzaku soft X-ray observation was carried out with both timing mode and imaging mode. A ~ 10' extended feature, which is interpreted as a bow-shock component of the pulsar wind nebula (PWN), is revealed in this deep observation for the first time. The nebular spectrum can be modelled by a power-law with a photon index of ~ 1.8 which suggests a slow synchrotron cooling scenario. The photon index is approximately constant across this extended feature. We compare and discuss our observations of this complex nebula with previous X-ray investigations. We do not obtain any significant pulsation from the central pulsar in the soft (0.2-12 keV) and hard (10-60 keV) X-ray data. The non-detection is mainly due to the loss of the precise imaging ability to accurately determine the source contribution. The spectra of XIS and HXD can be directly connected without a significant spectral break according to our analysis. Future observations of NuSTAR and Astro-H would be able to resolve the contamination and provide an accurate hard X-ray measurement of CTA 1.Comment: 9 pages, 7 figures, accepted by MNRA

The X-ray Properties of the Energetic Pulsar PSR J1838-0655

We present and interpret several new X-ray features of the X-ray pulsar PSR J1838-0655. The X-ray data are obtained from the archival data of CHANDRA, RXTE}, and SUZAKU. We combine all these X-ray data and fit the spectra with different models. We find that the joint spectra are difficult to fit with a single power law; a broken power-law model with a break at around 6.5 keV can improve the fit significantly. The photon index changes from $\Gamma$ = 1.0 (below 6.5 keV) to $\Gamma$ = 1.5 (above 6.5 keV); this indicates a softer spectral behaviour at hard X-rays. The X-ray flux at 2-20 keV is found to be 1.6x10^{-11} ergs cm^{-2} s^{-1}. The conversion efficiency from the spin-down luminosity is ~ 0.9% at 0.8-10 keV, which is much higher than that (~ 10^{-3}% - 10^{-4}%) of the pulsars that show similar timing properties. We discuss non-thermal radiation mechanisms for the observed high X-ray conversion efficiency and find that emission from the magnetosphere of a greatly inclined rotator is the most favorable interpretation for the conversion rate and the pulse profiles at X-ray bands. A line feature close to 6.65 keV is also detected in the spectra of SUZAKU/XIS; it might be the K$_\alpha$ emission of highly ionised Fe surrounding the pulsar.Comment: 8 pages, 6 figures and 1 tabl

Multi-Wavelength Observations Of A New Redback Millisecond Pulsar 4FGL J1910.7-5320

We present the study of multi-wavelength observations of an unidentified Fermi Large Area Telescope (LAT) source, 4FGL J1910.7-5320, a new candidate redback millisecond pulsar binary. In the 4FGL 95% error region of 4FGL J1910.7-5320, we find a possible binary with a 8.36-hr orbital period from the Catalina Real-Time Transient Survey (CRTS), confirmed by optical spectroscopy using the SOAR telescope. This optical source was recently independently discovered as a redback pulsar by the TRAPUM project, confirming our prediction. We fit the optical spectral energy distributions of 4FGL J1910.7-5320 with a blackbody model, inferring a maximum distance of 4.1 kpc by assuming that the companion fills its Roche-lobe with a radius of R = 0.7R_sun. Using a 12.6 ks Chandra X-ray observation, we identified an X-ray counterpart for 4FGL J1910.7-5320, with a spectrum that can be described by an absorbed power-law with a photon index of 1.0+/-0.4. The spectrally hard X-ray emission shows tentative evidence for orbital variability. Using more than 12 years of Fermi-LAT data, we refined the position of the {\gamma}-ray source, and the optical candidate still lies within the 68% positional error circle. In addition to 4FGL J1910.7-5320, we find a variable optical source with a periodic signal of 4.28-hr inside the 4FGL catalog 95% error region of another unidentified Fermi source, 4FGL J2029.5-4237. However, the {\gamma}-ray source does not have a significant X-ray counterpart in a 11.7 ks Chandra observation, with a 3-{\sigma} flux upper limit of 2.4*10^-14 erg cm^-2 s^-1 (0.3-7 keV). Moreover, the optical source is outside our updated Fermi-LAT 95% error circle. These observational facts all suggest that this new redback millisecond pulsar powers the {\gamma}-ray source 4FGL J1910.7-5320 while 4FGL J2029.5-4237 is unlikely the {\gamma}-ray counterpart to the 4.28-hr variable.Comment: Accepted for publication in Ap