Issue |
A&A
Volume 411, Number 1, November III 2003
Special letters issue on: first science with integral
|
|
---|---|---|
Page(s) | L395 - L398 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361:20031421 | |
Published online | 17 November 2003 |
Letter to the Editor
First IBIS results on the high energy emission of Cygnus X-2 *
1
CNR-Istituto di Astrofisica Spaziale e Fisica Cosmica, Area Ricerca Roma 2/Tor Vergata, via del Fosso del Cavaliere, 100 00133 Roma, Italy
2
CNR-Istituto di Astrofisica Spaziale e Fisica Cosmica, Sezione di Palermo, via Ugo La Malfa 153, 90146 Palermo, Italy
Corresponding author: L. Natalucci, lorenzo@rm.iasf.cnr.it
Received:
17
July
2003
Accepted:
12
September
2003
The bright low-mass X-ray binary Cyg X-2 was in the field of
view of the IBIS telescope during the early Cygnus region
observations, executed during the INTEGRAL Performance
Verification Phase.
The data presented are spanning about one week and cover
the rising edge of one of the two peaks of the ≈82 day
cycle of the Cyg X-2 light curve. The IBIS data in the energy
range 20-40 keV exhibit flux variation correlated with the
RXTE/ASM light curve. Two different main exposures,
separated by ≈5 days are found to be characterized by
sensibly different spectra, with significant softening and
higher X-ray luminosity in the second part, coincident with
the long-term cycle peak.
At high energies, both measured spectra are very steep. The ratio
of the 30-45 keV and 20-30 keV detected fluxes is ≈0.30,
against a value of 0.95 expected for a Crab-like spectrum. No
positive detection exists for keV, with a flux upper limit (
) of ~
erg cm-2 s-1
in the 45-100 keV band.
Key words: binaries: individual / stars:individual:Cyg X-2 / stars: neutron / X-rays: binaries
© ESO, 2003
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.