Hard X-ray INTEGRAL observations of the Crab Nebula during its gamma-ray flare

ATel #4869; E. Jourdain (IRAP/CNRS), L. Natalucci (INAF/IAPS)
on 7 Mar 2013; 15:53 UT
Credential Certification: Lorenzo Natalucci (Lorenzo.Natalucci@iasf-roma.inaf.it)

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The INTEGRAL mission is observing the Crab nebula since 2013-03-02 06:56 UTC (Rev 1268 -1269), during its enhanced gamma-ray activity (ATel#4855, #4856 and #4867) and including a pre-flare period.

The IBIS/ISGRI average rates during Rev 1268, in 4 energy bands before and during the flare are:
   20-40 keV       40-60 keV      60-100 keV      100-200 keV
158.29+/-0.17  56.22+/-0.10   41.18+/-0.11   22.95+/-0.10   pre-flare
158.96+/-0.15  55.70+/-0.08   40.05+/-0.09   22.90+/-0.09   flare

where the flare integration period is the same reported in ATel#4856.

We performed a spectral analysis of the SPI data in the period 2013-03-02 08:43 to 2013-03-05 14:13 UTC, up to 300 keV using a broken power law model. The best fit values are similar to those usually observed :
alpha1=2.07, alpha2=2.27 (the energy break is fixed to 100 keV)
F(100 keV)=6.6x10^-4 ph/(cm^2 s keV).

Splitting the above data set into 4 time intervals and analyzing the corresponding spectra, allows to establish that the Crab spectrum (shape and normalization) is stable during the whole period, i.e. before and during the gamma-ray flare.

INTEGRAL observations will continue up to 2013-03-07 22:06, while the E > 100 MeV flux is still high.