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Short-term X-ray/gamma-ray variability from PSR B1259-63

ATel #6248; P. Bordas (Max-Planck-Institut fur Kernphysik), V. Zabalza (Department of Physics and Astronomy, University of Leicester), C. Romoli (Dublin Institute for Advanced Studies), D. Khangulyan (Institute of Space and Astronautical Science/JAXA) and G. Puehlhofer (Institut fur Astronomie und Astrophysik, Universitat Tuebingen)
on 19 Jun 2014; 14:06 UT
Credential Certification: Pol Bordas (pol.bordas@mpi-hd.mpg.de)

Subjects: X-ray, Gamma Ray, Binary, Neutron Star, Pulsar

 
We have monitored PSR B1259-63 with Swift-XRT during its recent 
periastron passage, including the first and second neutron star 
crossings of the companion's circumstellar disk, the periastron passage 
itself (t_p) on May 4th 2014, and the expected onset of the gamma-ray 
flare (see ATels #6204, #6216, #6225 and #6231). A preliminary analysis 
of the Swift-XRT data shows the double-peak structure around t_p as 
observed in previous periastron passages, with the highest flux observed 
during the second disk-crossing on May 22nd (t_p +18d, ATel #6198). 
After this, the source X-ray flux (0.3-10 keV) has decayed steadily, 
dropping down to 2.13e-11 erg/cm2/s at t_p+30d. 
 
From June 2nd to June 12th (t_p +29d and +39d, respectively) the 
descending trend halted, and a slight increase in the X-ray flux is 
observed, from 2.43(18)e-11 erg/cm2/s to 2.51(9)e-11 erg/cm2/s. Enhanced 
gamma-ray emission has also been reported (see ATels above). On 
subsequent days, from June 13th to June 14th, a sharp X-ray "dip" has 
been observed, in which the X-ray flux dropped down to about 1.48e-11 
erg/cm2/s. Later on, from June 15th to June 18th, the X-ray flux seems 
to have recovered, displaying again values at the level of 2.14e-11 
erg/cm2/s. 
 
We also analysed Fermi-LAT data on the source from previous nights. A 
sharp decrease of the gamma-ray flux is observed, from a value of 2.1e-6 
ph/cm2/s on June 12th (t_p + 38d) to 0.77e-6 ph/cm2/s on June 14th-15th 
(2-day binning, t_p + 40d-41d), whereas the flux during June 14th-15th 
is below the detection limit (TS < 25) on a daily interval. A binned 
likelihood analysis over a square region of 30x30 degrees with the IRFs 
"P7REP_SOURCE_V15" has been employed, with the source list extracted 
from the 2FGL catalog. The lightcurve was computed by fixing first the 
background sources performing a likelihood analysis over a time period 
going from June 3rd to June 16th. We then left free to vary the 
parameters for PSR B1259-63 during daily bins. The behaviour seen in the 
daily lightcurve seems to be in agreement with the flare detected in 
2011. 
 
We encourage multi-wavelength observations of PSR B1259-63 to follow up 
and better characterize the variability of the source on short-term 
time-scales. 
 
---- Swift-XRT results: ---- 
 
obs-ID  MJD  t-t_p(d)  flux(1e-11 erg/cm2/s)  flux-e  Gamma Gamma-e         
 
 18    56767.17  -14.3   2.58   0.20   1.41   0.09  
 19    56774.96   -6.5   1.88   0.09   1.60   0.06  
 20    56781.96    0.5   1.41   0.07   1.73   0.06  
 21    56783.89    2.4   1.38   0.14   1.94   0.12  
 22    56784.09    2.6   1.38   0.11   1.77   0.10  
 23    56786.15    4.7   1.19   0.12   1.89   0.13  
 24    56794.60   13.1   2.56   0.59   1.86   0.29  
 25    56796.84   15.4   3.76   0.19   1.57   0.06  
 26    56799.43   17.9   4.58   0.16   1.75   0.04  
 27    56802.50   21.0   3.45   0.14   1.75   0.05  
 28    56805.69   24.2   3.14   0.14   1.55   0.05  
 29    56810.93   29.4   2.15   0.17   1.53   0.09  
 30    56811.06   29.6   2.27   0.20   1.74   0.11  
 32    56815.10   33.6   2.35   0.13   1.55   0.06  
 33    56819.29   37.8   2.49   0.11   1.50   0.05  
 35    56820.46   39.0   2.40   0.22   1.49   0.11  
 36    56821.85   40.4   2.03   0.17   1.54   0.10  
 37    56822.85   41.4   1.48   0.15   1.73   0.12  
 38    56823.29   41.8   2.54   0.31   1.25   0.14  
 39    56824.58   43.1   2.07   0.14   1.60   0.08  
 40    56825.61   44.1   1.75   0.32   1.86   0.22  
 41    56826.13   44.7   2.18   0.32   1.39   0.17 
 
Note: column densities N_H = 0.50 have been assumed throughout. 
 
We thank the Swift Team for implementing the ToO observations of PSR B1259-63 
at a short notice. We also thank the LAT team for scheduling pointed observations  
the source and acknowledge the use of public data available at the Fermi 
Science Support Center.