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A photospheric radius-expansion burst observed from XTE J1701-407 by INTEGRAL: an update on distance

ATel #2814; J. Chenevez (DTU Space, Denmark), M. Falanga (ISSI, Switzerland), S. Brandt (DTU Space, Denmark), D. Galloway (Monash University, Australia), E. Kuulkers (ESA/ISOC, Spain), A. Cumming (Mc Gill University, Canada), H. Schatz (Michigan State University, USA), N. Lund (DTU Space, Denmark), T. Ooestbroek (ESA/ESTEC, The Netherlands), C. Ferrigno (ISDC, Switzerland)
on 24 Aug 2010; 17:24 UT
Credential Certification: Jerome CHENEVEZ (jerome@dsri.dk)

Subjects: X-ray, Neutron Star, Transient

Referred to by ATel #: 3604, 3654, 12617

On 2010-08-22 00:56:19 the INTEGRAL Burst Alert System (IBAS) triggered on an event ((GCN 11132, Gotz & Ferrigno, 2009) from the known burst source XTE J1701-407 (Falanga et al., A&A 496, 333, 2009; Linares et al., MNRAS 392, L11, 2009) during an observation of the field around SNR RXJ1713.7-3946 (PI R. Terrier).
As part of our monitoring of long thermonuclear X-ray bursts with INTEGRAL, we have analysed both the JEM-X and ISGRI data covering this event, and we identify it as another type I (thermonuclear) X-ray burst. The duration of the burst was about 3 minutes (3-30 keV), with an exponential decay time of 118s. The peak flux was about 4 Crab (1e-7 erg/cm2/s) in the 3-30 keV energy band (JEM-X) and 0.35 Crab (3.4 e-9 erg/cm2/s) in the 18-40 keV band (IBIS/ISGRI). The JEM-X light curve shows evidence for photosperic radius expansion, with a 2s precursor starting about 4s before the main burst.
The time resolved spectral analysis of the burst allows us to measure the unabsorbed bolometric peak flux of (1.5 +/-0.2)e-7 erg/cm2/s. Assuming that the burst reached the empirically-measured Eddington limit of L_Edd=3.8e38 erg/s (Kuulkers et al.2003), we derive the distance to the source to be 5.0 +/- 0.4 kpc, which is slightly lower than the previous estimated distance of 6.2 kpc by Falanga et al. (2009).

Recent RXTE PCA monitoring observations of 4U 1701-407 (see also Markwardt et al. ATel #1569) indicate that the source is beginning a new outburst. Indeed, we estimate the source flux in the hour preceeding the burst to be (2.1 +/-0.3)e-9 erg/cm2/s extrapolated between 0.3-100 keV. At the source distance this translates to a persistent bolometric luminosity of about 6.3e36 erg/s, which is close to the luminosity (8.3e36 erg/s) the source had at the moment of its previous long burst (Falanga et al., 2009).

Light curves of the burst can be obtained from the following adress: ftp://ftp.spacecenter.dk/pub/Jerome/Science/XTE_J1701-407/