Chandra Observation of the Anomalous X-ray Pulsar 1E 1841-045

We present the results from the {\it Chandra} ACIS CC mode observation of an anomalous X-ray pulsar (AXP) 1E 1841-045. This is the first observation in which the pulsar spectrum in wide energy range is spatially discriminated from the surrounding SNR, Kes 73. Like other AXPs, the phase-integrated spectrum is fitted well with power-law plus blackbody model. The spectral parameters are $\Gamma = 2.0 \pm 0.3$, $kT_{\rm BB} = 0.44 \pm 0.02$ keV, and $N_H = 2.54^{+0.15}_{-0.13} \times 10^{22} {\rm cm}^{-2}$. This photon index is significantly flatter than the other AXPs, and resemble to soft gamma-ray repeaters (SGRs) in the quiescent state. The pulse profile is double-peaked, and we found that the second peak has significantly hard spectrum. The spectra of all phases are consistent with power-law plus blackbody model with constant temperature and photon index. When fitted with two blackbody model, we obtained similarly good fit. These results can be interpreted that there are two emission regions with different energy spectra.Comment: 4 pages, 4 figures, accepted for publication in PASJ Letter

Pulse Profile Change Possibly Associated with a Glitch in an Anomalous X-Ray Pulsar 4U 0142+61

We report a glitch-like pulse frequency deviation from the simple spin-down law in an anomalous X-ray pulsar (AXP) 4U 0142+61 detected by ASCA observations. We also found a significant pulse profile change after the putative glitch. The glitch parameters resemble those found in another AXP 1RXS J170849.0$-$400910, in the Vela pulsar, and in other radio pulsars. This suggests that the radio pulsars and AXPs have the same internal structure and glitch mechanism. It must be noted, however, that the pulse frequency anomaly can also be explained by a gradual change of the spin-down rate ($\dot{P}$) without invoking a glitch.Comment: 14 pages, 4 figures, accepted by Ap

Recurrent Outbursts and Jet Ejections Expected in Swift J1644+57: Limit-Cycle Activities in a Supermassive Black Hole

The tidal disruption event by a supermassive black hole in Swift J1644+57 can trigger limit-cycle oscillations between a supercritically accreting X-ray bright state and a subcritically accreting X-ray dim state. Time evolution of the debris gas around a black hole with mass M=10^{6} {\MO} is studied by performing axisymmetric, two-dimensional radiation hydrodynamic simulations. We assumed the $\alpha$-prescription of viscosity, in which the viscous stress is proportional to the total pressure. The mass supply rate from the outer boundary is assumed to be ${\dot M}_{\rm supply}=100L_{\rm Edd}/c^2$, where $L_{\rm Edd}$ is the Eddington luminosity, and $c$ is the light speed. Since the mass accretion rate decreases inward by outflows driven by radiation pressure, the state transition from a supercritically accreting slim disk state to a subcritically accreting Shakura-Sunyaev disk starts from the inner disk and propagates outward in a timescale of a day. The sudden drop of the X-ray flux observed in Swift J1644+57 in August 2012 can be explained by this transition. As long as ${\dot M}_{\rm supply}$ exceeds the threshold for the existence of a radiation pressure dominant disk, accumulation of the accreting gas in the subcritically accreting region triggers the transition from a gas pressure dominant Shakura-Sunyaev disk to a slim disk. This transition takes place at $t {\sim}~50/({\alpha}/0.1)$ days after the X-ray darkening. We expect that if $\alpha > 0.01$, X-ray emission with luminosity $\gtrsim 10^{44}$ ${\rm erg}{\cdot}{\rm s}^{-1}$ and jet ejection will revive in Swift J1644+57 in 2013--2014.Comment: 6 pages, 4 figures, accepted for publication in PASJ Letter