Swift reports an outburst of the HMXB RX J1037.5-5647
ATel #3936; H. A. Krimm (CRESST/GSFC/USRA), J. A. Kennea (PSU), S. T. Holland (CRESST/GSFC/USRA), S. D. Barthelmy (GSFC), W. Baumgartner (CRESST/GSFC/UMBC), J. Cummings (CRESST/GSFC/UMBC), N. Gehrels (GSFC), C. B. Markwardt (GSFC), D. Palmer (LANL), T. Sakamoto (CRESTT/GSFC/UMBC), G. Skinner (CRESST/GSFC/UMD), M. Stamatikos (OSU/GSFC), J. Tueller (GSFC), T. Ukwatta (MSU)
on 21 Feb 2012; 01:19 UT
Credential Certification: Hans A. Krimm (Hans.Krimm@nasa.gov)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
The hard X-ray transient monitor of the Swift Burst Alert Telescope (BAT) has detected a hard X-ray outburst from the persistent Be/NS X-ray binary pulsar RX J1037.5-5647 (aka 4U 1036-56).
In the current epoch, RX J1037.5-5647 was first detected by the BAT in the 15-50 keV band on 2012 February 3 (MJD 55960) at a rate of 0.004 +/- 0.0008 counts/sec/cm2 (~20 mCrab). It peaked at 0.0067 +/- 0.0019 counts/sec/cm2 (~30 mCrab) on 2012 Feb. 6, remaining detectable through Feb. 13, but since that time it has been undetectable (1-sigma upper limit of 0.001 counts/sec/cm2).
A 2982-second Swift target of opportunity observation was performed starting at 19:02:18 on 2012 Feb. 17. The XRT observed in Photon Counting mode and a UVOT-enhanced position was determined at:
RA (J2000): 10 37 35.34 (159.39725 deg)
Dec (J2000): -56 47 57.5 (-56.79930 deg)
90% Error radius: 2.1"
which is consistent with the source position reported in Liu, van Paradijs & van den Heuvel (2000; Astron. Astrophys., Suppl. Ser., 147, 25)
The XRT spectral fit parameters were (Cstat = 438 for 538 dof):
N_H = 2.53 +/- 0.55 x 10^22 cm^-2
Gamma = 0.62 +/- 0.23
Unabsorbed flux (0.3-10 keV) = 9.2 +/- 0.60 x 10^-11 erg/s/cm2
There is no evidence of any lines or other deviations from a smooth spectrum. We can compare this flux to that measured with XMM Newton in 2009 when the source was in a low-luminosity state, as reported by La Palombara et al (2009; A&A 505, 947). At that time the flux was 4 X 10^-12 erg/s/cm2. If we use the same conversion as La Palombara, we derive that the current luminosity is ~2.8 X 10^35 erg/s. Comparing to Figure 6 in the La Palombara paper, we see that the current luminosity is comparable to the brightest ever measured for this source.
The BAT rate becomes 3.3 X 10^-9 erg/cm2/s in the 14-195 keV band when converted to flux using the XRT power law index. This is significantly higher than either the average flux for RX J1037.5-5647 in the 58-month BAT hard X-ray survey: 18.07 X 10-12 erg/cm2/s and also the peak rate is higher than any of the peaks seen in the BAT survey light curve (http://swift.gsfc.nasa.gov/docs/swift/results/bs58mon/SWIFT_J1037.6-5649).
The XRT flux shows variability which roughly matches the pulse period of 853.4 sec. (We did not perform timing analysis on these data at this stage.)
Swift/BAT Hard X-ray transient monitor page for RX J1037.5-5647