Chandra non-detection of the newly discovered Millisecond X-ray Pulsar SWIFT J1756.9-2508
ATel #1133; A. Papitto (INAF-OARoma/Univ. Roma Tor Vergata), T. Di Salvo (Univ. Palermo), L. Burderi (Univ. Cagliari), E. Gallo (UCSB), M. T. Menna (INAF-OARoma), A. Riggio (Univ. Cagliari), M. I. Krauss (MIT), D. Chakrabarty (MIT), A. Antonelli (INAF-OARoma), E. Bozzo (INAF-OARoma/Univ. Roma Tor Vergata), M. Burgay (INAF-OACagliari), N. D'Amico (INAF-OACagliari), R. Iaria (Univ. Palermo) G. L. Israel (INAF-OARoma), A. Possenti (INAF-OACagliari), V. Testa (INAF-OARoma)
on 7 Jul 2007; 03:53 UT
Credential Certification: Alessandro Papitto (firstname.lastname@example.org)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
We report on the non detection of the neutron star
transient SWIFT J1756.9-2508 during a 11ks Chandra/ACIS-I DDT observation
performed on 2007-07-06 (starting at 01:25:11 UT). This recently discovered
X-ray source, which harbors the eighth known Millisecond X-ray Pulsar, was
found in outburst on 2007 June 7.
Based on the observed decay rate (ATels #1105, #1107, #1108, #1111, #1114,
#1117), the source is expected to have reached quiescence at the time of
the observation reported here.
Only one photon was recorded over the energy range
0.3-8.0 keV inside a
circular region centered at the
Swift/XRT position (ATel 1111) with a 3.5 arcsec radius. Applying the
prescription for small number statistics by Gehrels (1986),
we derive a conservative upper limit of 4.3e-4 count/sec (95%) for the
Depending on the assumed spectral shape, we can thus set upper limits on
the source unabsorbed flux. For a blackbody model with kT = 0.2-0.3 KeV,
we derive F(0.3-8) = 0.4-1.4E-13 erg/cm2/s, while F(0.3-8)= 0.2-1.3E-13
erg/cm2/s for a
power law model with photon index varying in the range 1-3.
In both cases, the nH was fixed to the respective best fitting values for
the first Swift/XRT observation (ATEL #1111).
We thank the Chandra X-ray Center Team and in particular the Director Dr.Harvey
Tananbaum for having made this DDT observation possible.