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INTEGRAL detects an new ouburst from Aql X-1

ATel #280; J. Rodriguez (CEA/SAp, France & ISDC Switzerland), D. C Hannikainen (Obs. of Helsinki), N. Mowlavi (ISDC)
on 18 May 2004; 10:57 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Jerome Rodriguez (jrodriguez@cea.fr)

Subjects: Radio, Millimeter, Sub-Millimeter, Far-Infra-Red, Infra-Red, Optical, Ultra-Violet, X-ray, Gamma Ray, Binary, Black Hole, Neutron Star, Transient, Pulsar

Referred to by ATel #: 286

Further to Maitra et al. (Atel #279), we report on the detection of Aql X-1 in the hard X-rays with the INTEGRAL observatory during observations of GRS 1915+105 performed between May 13 and May 15, 2004. The source is significantly detected by the ISGRI detector of the IBIS telescope in the 20-60 keV and 60-200 keV energy ranges at a flux of roughly 110 mCrab in both ranges. Unfortunately Aql X-1 always lies outside the JEM-X field of view. A study of the RXTE/ASM real time data shows that Aql X-1 is at a level of about 50 mCrab in the 1.2-12 keV range. All this suggests that the source is in a hard X-ray state.

Comparison with previous observations (Molkov et al. Atel #259) shows that the source flux has increased by a factor of at least 3 in the lower ISGRI energy range. The long term RXTE/ASM light curve shows, however, that the source returned to a low activity level after the observations of Molkov et al., confirming that it was undergoing a "mini-outburst" event as suggested by contemporaneous optical observations (Ilovaisky & Chevalier Atel #260).

Our INTEGRAL detection and the source state suggest that Aql X-1 is entering one of its normal yearly outbursts as suggested by Maitra et al. Follow-up observations at all wavelengths are strongly encouraged.