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Swift follow-up of the newly discovered burster millisecond pulsar IGR J17511-3057

ATel #2198; E. Bozzo (ISDC), C. Ferrigno (ISDC/IAAT), E. Kuulkers (ESA/ESAC, Spain), M. Falanga (ISSI Bern), J. Chenevez, S. Brandt (National Space Institute, Denmark), V. Beckmann (APC, France), A. Bird (Southampton, UK), A. Domingo (LAEFF/INTA, Spain), K. Ebisawa (ISAS, Japan), P. Jonker (SRON, The Netherlands), P. Kretschmar (ESA/ESAC, Spain), C. Markwardt (GSFC, USA), T. Oosterbroek (ESA/ESTEC, The Netherlands), A. Paizis (INAF-IASF, Italy), D. Risquez (LAEFF/INTA, Spain), C. Sanchez-Fernandez (ESA/ESAC, Spain), S. Shaw (Southampton, UK), R. Wijnands (UvA, The Netherlands)
on 14 Sep 2009; 12:37 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Nami Mowlavi (Nami.Mowlavi@obs.unige.ch)

Subjects: X-ray, Neutron Star, Transient

Referred to by ATel #: 2199, 2215, 2216, 2220, 2221, 2232, 7288

Following the discovery of the new hard X-ray transient IGR J17511-3057 by INTEGRAL (Atel #2196) and its classification as a millisecond pulsar by RXTE (Atel #2197), a Swift ToO was performed.

Swift/XRT observed IGR J17511-3057 on 2009-09-13 at 19:53:31 for a total exposure time of 4 ks. The first 2.5 ks were accumulated in window timing (WT) mode. A thermonuclear type-I X-ray burst was discovered in the WT light curve of the source at 2009-09-14 00:51:37 UTC with an exponential decay time of ~12.5 s. This burst is most likely a He burst.

The WT 0.5-10 keV X-ray spectrum is well described (reduced chi^2 of 1.08 for 283 dof) by applying an absorbed cut-off power-law model. We obtained an absorption column density of (0.6+/-0.1)E22 cm^(-2), compatible with the Galactic absorption in the direction of the source, a cut-off energy of 3.3+/-0.6 keV, and a power-law photon index of 0.2+/-0.2. The absorbed 0.5-10 keV X-ray flux is 6.0e-10 ergs/cm^2/s.

The latest 1.5 ks were accumulated by Swift/XRT in photon counting (PC) mode. These data were strongly affected by pile up, due to the high source count rate. The PC spectrum is thus only poorly determined and the results of the fit provided values of the parameters in agreement with those of the WT spectrum. By using the PC data and the XRTCENTROID tool, we determined a newly improved source position at:

RA: 17:51:09.0

DEC: -30:57:40.0

The 90 % confidence error circle is 3.5 arcsec.

More detailed analysis of the Swift/XRT data are in progress. We thanks the Swift team for the rapid follow up on this source.