INTEGRAL detects pre-outburst flares in EXO 2030+375
ATel #3052; D. Klochkov, A. Santangelo (IAAT), M. Turler, C. Ferrigno, E. Bozzo, (ISDC - University of Geneva), K. Postnov (SAI, Moscow), I. Caballero (CEA Saclay), P. Kretschmar (ESA, Madrid), J. Wilms, V. Grinberg (Dr. Karl Remeis-Observatory), K. Pottschmidt, D. Marcu (UMBC/NASA GSFC)
on 23 Nov 2010; 13:17 UT
Credential Certification: Carlo Ferrigno (Carlo.Ferrigno@unige.ch)
Subjects: X-ray, Gamma Ray, Binary, Neutron Star, Pulsar
During the observations of the Cygnus X region (MJD: 51519-55521,
UTC: 2010-11-18T16:58 - 2010-11-21T08:57), INTEGRAL serendipitously
monitored the onset of a normal outburst of the Be/X-ray binary
EXO 2030+375, associated to a periastron passage. The IBIS/ISGRI
light curve in the 20-40 keV energy range before MJD 55520 is
characterized by a continuous series of flares with intensity of ~100 mCrab.
The typical duration and the recurrence time of the flares are
~0.2-0.3 days.
After MJD 55520, the source flux displayed a remarkable increase,
raising from ~70 to ~100 mCrab. At this time, the recurrence time
between the flares increased, reaching 0.7 days between the last
two flares with peak fluxes of ~150 mCrab. The relative
intensity of the flares with respect to the underlying flux level decreased.
Thus, the flaring activity seems to decline as the outburst develops.
The observed flaring behavior is very similar to that observed in
the Be/XRB A0535+26 during the normal outburst in 2005, both in
the characteristic time scales and relative amplitude of the flares.
This phenomenon was interpreted by Postnov et al. (2008, A&A 408, L21)
as a manifestation of unstable accretion from the layer accumulated
at the magnetospheric boundary during quiescence.
Such pre-outburst flaring behavior is observed for the first time in
EXO 2030+375 and it might indicate similar instabilities at the magnetospheric
radius of the pulsar.
Further INTEGRAL observations of the region are scheduled on
2010-11-24 16:30 and will continue for about six days, thus covering
a significant fraction of this normal outburst.
