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INTEGRAL detects increased activity from 4U 0115+63

ATel #331; J. A. Zurita Heras (ISDC, Versoix), S. E. Shaw (Southampton; ISDC, Versoix), I. Kreykenbohm (IAA, Tubingen), P. Kretschmar (ISDC, Versoix; MPE, Garching), Diego Gotz (IASF, Milano), S. Mereghetti (IASF, Milano), A. Lutovinov (IKI, Moscow), G. Palumbo (Bologna), T. Oosterbroek (ESTEC, Noordwijk), C. Budtz-Jorgensen (DSRI, Copenhagen), P. Ubertini (IASF, Roma)
on 13 Sep 2004; 16:58 UT
Credential Certification: Jerome Rodriguez (jrodriguez@cea.fr)

Subjects: X-ray, Gamma Ray, Binary, Pulsar

During a Galactic Plane Scan on September 12th 2004, the INTEGRAL gamma ray observatory detected the high mass X-ray binary 4U 0115+63. Increased activity was first noticed by the IBAS gamma ray burst detection software at 14:53 UTC, leading to the generation of three alerts (1978-79-80). The source was visible in the ISGRI field of view until 16:24 UTC.

The source was also visible in the JEM-X x-ray monitor in one Science window (2 ksec observation starting at 15:31 UTC) leading to the following estimated fluxes:

JEM-X: 3-10 keV ~500 mCrab; 10-30 keV ~750 mCrab
ISGRI: 20-60 keV ~400 mCrab; 60-200 keV ~25 mCrab.

Those values correspond to an increase of a factor 10 to the fluxes reported in Atel#326 from Lutovinov et al. 14 days earlier.

Spectral extraction was possible from the JEM-X observation. No cyclotron line features were seen, although only a 2 ksec observation was available for JEM-X in this preliminary analysis.

Pulsed analysis of the ISGRI data, in the 15-40 keV band, clearly shows a periodic signal of 3.614 +/- 0.003 s, which is in agreement with published values and identifies the flux as being from the associated pulsar, PSR B0115+63.4.