Public INTEGRAL TOO observation of V 0332+53 in outburst

ABSTRACT

IBIS/ISGRI image of the High-Mass X-ray Binary V 0332+53 (EXO 0331+530) during its 2004-2005 outburst INTEGRAL IBIS/ISGRI image of the transient X-ray pulsar V 0332+53 during its outburst of December 2004 - January 2005. V 0332+53 is a neutron star orbiting a high-mass companion star located in the disk of our galaxy, the Milky Way at a distance of about 7 kpc. The outburst observed by INTEGRAL reached a flux of about 1 Crab and was the first one detected from this source since 1989. The neutron star spins with a period of 4.375 seconds giving rise to pulsations. Credits: ISDC/R. Walter

INTEGRAL spectrum of the High-Mass X-ray Binary V 0332+53 during its 2004-2005 outburst The combined ISGRI (red), SPI (green) and JEM-X (white) spectrum was fitted with a simple power-law cutting-off at high energy. The residuals at the bottom clearly show 3 cyclotron lines at energies of ~25, ~55 and ~75 keV (Soldi et al., 2005, ATel #382). This confirms the lines discovered with RXTE by Coburn et al. (2005, ATel #381). Credits: ISDC/I. Kreykenbohm

Refined analysis of the cyclotron lines in the INTEGRAL spectra of V 0332+53 during the 2004-2005 outburst INTEGRAL spectra of the transient X-ray pulsar V 0332+53 (=EXO 0331+530) during it's outburst of December 2004 - January 2005. The combined JEM-X (red) and IBIS/ISGRI (blue) spectrum exhibits three beautiful, harmonically spaced cyclotron lines at 25 keV, 51 keV, and 72 keV allowing to determine the magnetic field of the neutron star to B = 2.7 1012 Gauss. The figure shows the analysis of this spectrum: a) data + folded cutoffpl model b) residuals for model without any CRSFs c) after fitting the fundamental 25 keV line d) the fundamental line and the first harmonic at 50 keV have been fitted e) all three lines have been fitted. Credits: ISDC/I. Kreykenbohm

The V 0332+53 system is composed of a Be star and a pulsar with a pulsation period of 4.4 sec detected with EXOSAT by Stella et al. (1985, ApJ 288, L45). The source was first detected with Vela 5B during an outburst in 1973 (Terrell & Priedhorsky, 1984, ApJ 285, L15). A second outburst occured in 1983 and was observed with EXOSAT. A third outburst was detected by the Ginga satellite in 1989 and Quasi-Periodic Oscillations (QPOs) have been detected at a frequency of about 0.05 Hz (Takeshima et al., 1994, ApJ 436, 871).

The current outburst reaches a flux of about 1 Crab in the X-rays (3-10 keV). The V 0332+53 flux increased steadily between the end of November 2004 and New Year 2005 as can be seen on the RXTE All Sky Monitor (ASM) light curve provided by the Massachusetts Institute of Technology (MIT).

A preliminary analysis of the INTEGRAL data at the ISDC produced a high signal to noise very steep spectrum featuring 3 cyclotron lines (Soldi et al., 2005, ATel 382). This is one of the best cyclotron line spectrum ever obtained and confirms the lines discovered with RXTE by Coburn et al. (2005, ATel 381).

The observations of the Target Of Opportunity (TOO) V 0332+53 are public and available for download from our ftp site, with the data location given in the table below.