Gamma-ray Burst 160409A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #19296
  P. A. Evans (U. Leicester) reports on behalf of the Swift team:
  Swift has initiated a ToO observation of the Swift/BAT GRB 160409A. Automated analysis of the XRT data will be presented online at http://www.swift.ac.uk/ToO_GRBs/00020604
  Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. These are not necessarily related to the Swift/BAT event. Any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration.
  Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).
  This circular is an official product of the Swift-XRT team.
• GCN Circular #19304
  GRB 160409A found in Swift BAT ground analysis
  P.A. Evans (U. Leicester), J.P. Osborne (U Leicester), K. L. Page (U Leicester), and D.M. Palmer (LANL) report on behalf of the Swift Team
  At 05:54:14 UT on 2016-04-09 BAT triggered and located GRB 160409A (trigger #682162). Swift did not immediately slew to this source because its location approximately matched a known source (4U 1916-053) in its on-board catalog. The BAT on-board calculated location is RA, dec 289.705,-5.390 which is

  RA(J2000) = 19h 18m 49s
  Dec(J2000) = -5d 23' 24"
  

  with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex peak structure with a duration of about 30 sec. The peak count rate was ~1300 counts/sec (15-350 keV), at ~2 sec after the trigger.
  The catalogued source, 4U 1916-053, is identified by Simbad as being the LXB V* V1405 Aql. However, this object is 9 arcminutes from the BAT position, and well outside the error circle. BAT has detected a burst from that source (1.1 arcmin offset from the V1405 Aql location) in April 2006. During the 6-minute accumulation that overlaps the trigger, SAX J2103.5+4545 is detected (at lower significance and correspondingly larger position uncertainty) with a 3.3 arcmin offset. Therefore we can confidently state that this trigger did not come from the location of V1405 Aql and is due to a different source.
  A Swift Target of Opportunity was requested and XRT began observing the field at 00:34:58 UT on 2016-04-12, which is 2.8 days after the BAT trigger. No unknown sources were detected in the 3 kiloseconds of data, although two known sources and possible scattered X-rays from V1405 Aql were seen. No new sources were detected in UVOT down to a limiting magnitude of 21.3 in white.
  Qualitatively, about half of long GRBs would be visible in a 3 ks XRT observation at that delay after the trigger, so the non-detection of an afterglow does not rule out a GRB.
• GCN Circular #19305
  A.P. Beardmore (U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), T.G.R. Roegiers (PSU), L.M. McCauley (PSU), J.A. Kennea (PSU), S.L. Gibson (U. Leicester) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team:
  Swift-XRT has performed follow-up observations of the Swift/BAT-detected burst GRB 160409A, collecting 3.0 ks of Photon Counting (PC) mode data between T0+240.0 ks and T0+246.7 ks.
  No uncatalogued X-ray sources have been detected inside or close to the Swift/BAT error region. The 3-sigma upper limit in the field ranges from ~0.004 to ~0.005 ct s^-1, corresponding to a 0.3-10 keV observed flux of 1.7e-13 to 2.1e-13 erg cm^-2 s^-1 (assuming a typical GRB spectrum).
  A previously-catalogued X-ray source has been detected inside or close to the Swift/BAT error region, however because it is a catalogued object it is unlikely to be the afterglow.
  An uncatalogued was detected, however this was too far from the GRB position to be the afterglow.
  The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at http://www.swift.ac.uk/ToO_GRBs/00020604.
  This circular is an official product of the Swift-XRT team.
• GCN Circular #19312
  D. Frederiks, S. Golenetskii, R.Aptekar, P. Oleynik, M. Ulanov, D. Svinkin, A. Tsvetkova, A.Lysenko, A. Kozlova, and T. Cline, on behalf of the Konus-Wind team, report:
  The long-duration GRB 160409A (Swift-BAT ground detection: Evans et al., GCN 19304) triggered Konus-Wind at T0=21254.430 s UT (05:54:14.430).
  The KW light curve shows single structure-less pulse with a total duration of ~35 s. The emission is visible up to ~7 MeV.
  The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB160409_T21254/
  As observed by Konus-Wind, the burst had a fluence of 1.8(-0.3,+0.3)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+4.846 s, of 1.5(-0.2,+0.2)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range).
  The time-averaged spectrum (measured from T0 to T0+24.832 s) is best fit in the 20 keV - 15 MeV range by the cutoff power law with the following model parameters: the photon index alpha = -0.68(-0.16,+0.18), and the peak energy Ep = 209(-18,+22) keV, chi2 = 107/98 dof. Fitting this spectrum with the GRB (Band) function yields the same alpha and Ep with an upper limit on beta of -2.1
  The spectrum near the peak count rate (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 15 MeV range by the cutoff power law with the following model parameters: the photon index alpha = -0.72(-0.17,+0.19), and the peak energy Ep = 252(-26,+32) keV, chi2 = 122/98 dof. Fitting this spectrum with the GRB (Band) function yields the same alpha and Ep with an upper limit on beta of -2.0
  All the quoted errors are at the 1 sigma confidence level. All the quoted values are preliminary.