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RXTE high energy flare follow-up observation of the Crab Nebula

ATel #2872; Nikolai Shaposhnikov (UMD/CRESST/NASA/GSFC), Keith Jahoda (NASA/GSFC), Jean Swank (NASA/GSFC), Tod Strohmayer (NASA/GSFC), Craig Markwardt (NASA/GSFC), Martin Weisskopf (NASA/MSFC)
on 25 Sep 2010; 15:26 UT
Credential Certification: Nikolai Shaposhnikov (nikolai.v.shaposhnikov@nasa.gov)

Subjects: X-ray, Pulsar

Following the detection of increased gamma ray emission from a location consistent with the Crab nebula by AGILE (Atel #2855) and FERMI/LAT (Atel #2861) RXTE performed a dedicated pointing observation on September 24, 2010 14:45 UT.  Analysis of the PCU2 data has not shown any significant changes in the the overall spectral properties. A fit with the absorbed (N_H = 0.34 * 1022 cm-2 fixed) power law yielded the photon index of 2.128+/-0.002 and normalization at 1 keV of 10.96+/-0.06 which translates to unabsorbed fluxes of 3.7e-8 erg/cm2/s between 2 and 30 keV. The corresponding values observed during the previous observation on September 10, 2010 are 2.132+/-0.003 and 11.06+/-0.06 respectively.  This values are consistent with observed deviations of the Crab spectrum from the calibration parameters on the order of a few percent. The PCA detector response is calibrated to produce the Crab power law index of 2.11 and 1keV normalization of 11.0 which corresponds to 2-30 PCA/PCU2 flux of 3.82e-8 erg/cm2/s. Fourier analysis shows 9% fractional rms level and the harmonics components identical to the historically observed in Crab pulsar power spectrum in the whole PCA energy range (2-60 keV). Therefore, the flux and pulsed properties seen by the PCA have not changed significantly on the timescale of days. Our results are consistent with the reports of no significant changes in Crab properties in X-rays and IR (Atels #2856, #2858, #2866, #2867, #2868) during the recent gamma-ray flare. RXTE daily observations are currently scheduled through September 30, 2010 to follow any possible evolution of the source properties.