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.
