2009A&A...501.1031K

PSRJ1846-0258 is a young rotation-powered pulsar with one of the highest surface magnetic field strengths, located in the centre of SN-remnant Kes-75. In June 2006 a magnetar-like outburst took place. Using multi-year RXTE and INTEGRAL observations covering the epoch of the outburst, we aim to study the temporal and spectral characteristics of PSRJ1846-0258 over a broad ∼3-300keV energy range to derive constraints on theoretical scenarios aiming to explain this schizophrenic behaviour. We explored all publically available RXTE observations of PSRJ1846-0258 to generate accurate ephemerides over the period January 30, 2000-November 7, 2007. Phase-folding procedures yielded pulse profiles for RXTE PCA (∼3-30keV), RXTE HEXTE (∼15-250keV) and INTEGRAL ISGRI (∼20-300keV). The pulsed spectrum over the full ∼3-300keV energy range was derived, as well as the total spectrum (including the pulsar wind nebula) over the 20-300keV band with the ISGRI. The timing, spatial, and spectral analyses were applied for epochs before, during, and after the magnetar-like outburst to study the evolution of the high-energy characteristics. ISGRI detected PSRJ1846-0258/Kes-75 before outburst during 2003-2006 with a power-law-shape spectrum over the 20-300keV energy range with photon index Γ=1.80±0.06 and energy flux (20-300keV) of (6.62±0.35)x10^–11erg/cm²/s. More than 90 days after the onset of the outburst, still during the decay phase, the same spectral shape was measured (Γ=1.75_–0.31^+0.27) with an indication for a 52% (2.3σ) enhanced total emission, while one year after the outburst the hard X-ray non-thermal emission of PSRJ1846-0258/Kes-75 was found to be back to its pre-outburst values. PCA monitoring of PSRJ1846-0258 before the outburst yielded phase-coherent ephemerides confirming the earlier derived breaking index of the spindown. During the outburst, incoherent solutions have been derived. We show that the radiative outburst was triggered by a major spin-up glitch near MJD 53883±3 with a glitch size Δν/ν in the range (2.0-4.4)x10^–6. Using all pre-outburst observations of ISGRI and HEXTE for the first time pulse profiles have been obtained up to 150keV with a broad single asymmetric pulse. The pulse shape did not vary with energy over the 2.9-150keV energy range, nor did it change during the magnetar-like outburst. The time-averaged pre-outburst ∼3-300keV pulsed spectrum measured with the PCA, HEXTE, and ISGRI was fitted with a power-law model with Γ=1.20±0.01. A fit with a curved power-law model gives an improved fit. Around 150keV the pulsed fraction approaches 100%. For the first 32 days of the magnetar-like outburst, the 3-30keV pulsed spectrum can be represented with two power laws, a soft component with index Γ_s=2.96±0.06 and a hard component with the pre-outburst value Γ_h ∼1.2. Above ∼9 keV, all spectra during outburst are consistent with the latter single power-law shape with index ∼1.2. The 2-10 keV flux increased by a factor ∼5 and the 10-30 keV flux increased with only 35%. After ∼120 days the soft outburst and the enhancement of the hard non-thermal component both vanish. The varying temporal and spectral characteristics of PSRJ1846-0258 can be explained in a scenario of a young high-B-field pulsar in which a major glitch triggered a sudden release of energy. Resonant cyclotron upscattering could subsequently generate the decaying/cooling soft pulsed component measured during outburst between 3 and 10keV. The (variation in the) non-thermal hard X-ray component can be explained with synchrotron emission in a slot-gap or outer-gap pulsar model.