{
  "bibcode": "2014GCN.16877....1M",
  "body": "A. Maselli (INAF-IASFPA), K. L. Page (U. Leicester), H. A. Krimm\n(CRESST/GSFC/USRA) and S. R. Oates (IAA-CSIC, MSSL-UCL) report on behalf\nof the Swift team:\n\nAt 04:44:43 on 2014 October 02, the Swift Burst Alert Telescope (BAT)\ntriggered on what appears to be the Be star HD 305560 (GCN Circ. #16874).\n\nUsing the data set from T-239 to T+963 sec from the recent telemetry\ndownlink, we report further analysis of the BAT data. The BAT\nground-calculated position is RA, Dec = 161.562, -60.604 which is\nequivalent to\n\nRA(J2000)  =  10h 46m 15.0s\nDec(J2000) = -60d 36' 13.9\"\n\nwith an uncertainty of 3.1 arcmin (radius, sys+stat, 90% containment).\nThe partial coding was 53%.\n\nThe mask-weighted light curve shows that the source entered the field of\nview during a slew at around T-100 seconds and that the count rate was\nrelatively flat through the duration of the event data. In the 15-50 keV\nrange, the count rate during this period averaged 0.04 +/- 0.005\nct/s/cm^2. Examination of the BAT transient monitor images before the\ntrigger shows no detection in earlier intervals going back to 2014\nSeptember 01, the most recent observation ending 13 minutes before the\ntrigger.\n\nObservations made after the burst response interval show the source fading\nrapidly in the BAT monitor 15-50 keV band.  By 09:36:32.0 UT, the rate was\ndown to 0.005 +/- 0.003 ct/s/cm^2 and by 10:49:28.0, the source had faded\nto a level consistent with background. This rapid fading is not consistent\nwith the typical behaviour of a high-mass X-ray binary system in outburst.\n\nThe time-averaged spectrum from T+0.00 to T+320.00 sec is best fit by a\nsimple power-law model.  The power law index of the time-averaged spectrum\nis 2.42 +/- 0.39.  The fluence in the 15-150 keV band is 1.0 +/- 0.2 x\n10^-6 erg/cm2. The 1-sec peak photon flux measured from T+0.00 sec in the\n15-150 keV band is 0.1 +/- 0.0 ph/cm2/sec.  All the quoted errors are at\nthe 90% confidence level.\n\nThe results of the batgrbproduct analysis are available at\nhttp://gcn.gsfc.nasa.gov/notices_s/614193/BA/\n\nThe Swift X-Ray Telescope (XRT) started observing HD 305560 at T0+424 s\n(where T0 corresponds to the time at which HD 305560 entered the BAT\nfield of view). Using data from the whole available dataset we found a\nbright, uncatalogued X-ray source located at RA, Dec 161.6173, -60.5644\nwhich is equivalent to\n\nRA(J2000)  =  10h 46m 28.14s\nDec(J2000) = -60d 33' 51.7\"\n\nwith an uncertainty of 3.6 arcseconds (radius, 90% confidence). This\nlocation is 2.9 arcmin from the BAT ground-calculated position, within the\nBAT error circle, and is 2.5 arcsec from the SIMBAD position of the Be\nstar HD 305560.\n\nInitially, the soft X-ray 0.3-10 keV count rate was at the level of ~15\nct/s; then, after reaching a peak of 20 ct/s (corresponding to\n1.8e-9 erg/cm^2/s, observed) at ~T0+540 s, it was followed by a moderate\ndecay, reaching a count rate of ~6 ct/s by ~1.2 ks after the trigger.\nThe second snapshot of XRT data started at T0+5.7 ks, with the soft\nX-ray emission showing a flaring phase, with the count rate rapidly\nrising from ~0.6 ct/s to ~18 ct/s at T0+6.4 ks and keeping at that\ncount rate level until this snapshot concluded, at T0+6.9 ks. Data\ncollected at T0+11.5 ks caught the source in an evident decaying phase\nwith a count rate of ~7.6 ct/s down to 0.6 ct/s when the\nobservation concluded, at T0+18.4 ks.\n\nThe XRT data collected between T0+424 s and 18.4 ks can be fitted with a\nhard power-law (Gamma = 0.81 +0.07/-0.12) plus an optically thin thermal\ncomponent (kT = 0.45 +/- 0.15 keV), with a high absorbing column of (3.4\n+0.7/-0.4)x10^22 cm^-2. Time-slicing the XRT spectra provides no strong\nevidence for changes in these temperatures during this interval.\n\nBecause of the brightness of the optical source (V~9.8 mag), the\nUV/Optical Telescope (UVOT) data are saturated in all 6 optical and UV\nfilters and have therefore not been analysed in detail.\n\nThis information has also been posted as ATel 6526.",
  "circularId": 16877,
  "createdOn": 1412279727000,
  "email": "klp5@leicester.ac.uk",
  "subject": "Swift observations of HD 305560",
  "submitter": "Kim Page at U.of Leicester  <klp5@leicester.ac.uk>"
}