Gamma-ray Burst 150402A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #17661
  J. R. Cummings (CPI) and D. M. Palmer (LANL) on behalf of the Swift-BAT science team:
  At 00:37:46 Swift-BAT triggered on GRB 150402A (trigger# 636865). Image attempts were prematurely terminated by a preplanned slew. A significant source was found in ground analysis at RA, Dec 173.658, +40.992, which is

  RA (J2000)  11h 34m 37.9s
  Dec (J2000) 40d 59' 33"
  

  with an estimated uncertainty radius of 2.5 arcmin (90% containment).
  The lightcurve shows two symmetrical peaks, each about 5 seconds long, the second harder and brighter. The counting rate in BAT of the brighter peak was about 1500 counts/sec. T90 was about 14 +- 2 seconds.
  A Swift TOO has been requested in order to locate the afterglow.
• GCN Circular #17662
  P. A. Evans (U. Leicester) reports on behalf of the Swift team:
  Swift has initiated a ToO observation of the Swift/BAT GRB 150402A. Automated analysis of the XRT data will be presented online at http://www.swift.ac.uk/ToO_GRBs/00020486
  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 #17663
  Owen Littlejohns (ASU), Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM), Chris Klein (UCB), Ori Fox (UCB), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (ORAU/GSFC), Eleonora Troja (GSFC), Enrico Ramirez-Ruiz (UCSC), Jos=E9 A. de Diego (UNAM), Leonid Georgiev (UNAM), Jes=FAs Gonz=E1lez (UNAM), Carlos Rom=E1n-Z=FA=F1= iga (UNAM), Neil Gehrels (GSFC), and Harvey Moseley (GSFC) report:
  We observed the field of GRB 150402A (Cummings, et al., GCN 17661) with the Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the 1.5m Harold Johnson Telescope at the Observatorio Astron=F3mico Nacional on Sierra San Pedro M=E1rtir from 2015/04 3.02 to 2015/04 10.92 UTC (26.39 to 34.29 hours after the BAT trigger), obtaining a total of 3.16 hours exposure in the r and i bands.
  Currently, there is only one source detected by the Swift/XRT within the Swift/BAT error circle (Evans, GCN 17662).

    RA(J2000)  =3D  11h 34m 34.0s
    Dec(J2000) =3D +40d 58' 37.8"
  

  This source has an error circle of 6.2 arcseconds. We detect no uncatalogued transient inside the error circle for this source. In comparison with the SDSS DR9, we obtain the following upper limits (3-sigma):

    r     > 22.75
    i     > 22.68
  

  These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB.
  We thank the staff of the Observatorio Astron=F3mico Nacional in San Pedro M=E1rtir.
• GCN Circular #17664
  H. A. Krimm (CRESST/GSFC/USRA), M. De Pasquale (INAF-IASFPA), N. P. M. Kuin (UCL-MSSL), J. R. Cummings (CPI), J. Kennea (PSU), A. Y. Lien (GSFC/UMBC), K. Page (U. Leicester) report on behalf of the Swift team
  Further observations of GRB 150402A (Cummings and Palmer, GCN 17661) were carried out by the Swift observatory (Evans, GCN 17662). We collected 4.8 ks of Photon Counting (PC) mode data between T0+108.4 ks and T0+121.6 ks, where T0 is the time of the BAT trigger. One uncatalogued X-ray source has been detected inside or close to the Swift/BAT error region, it is below the RASS limit and shows no definitive signs of fading. Therefore, at the present time we cannot confirm this as the afterglow. Details of this source are given below:

     RA (J2000.0):  173.5883  =3D  11h 34m 21.19s
     Dec (J2000.0): +40.9398  =3D  +40 56=E2=80=B2 23.3=E2=80=B2=E2=80=B2
     Error: 4.6 arcsec (radius, 90% conf.)
     Count-rate: (3.5 =C2=B1 1.1)e-3 ct s^-1
     Flux: (1.7 =C2=B1 0.5)e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)
  

  One catalogued source was also detected too far from the BAT GRB position to be a likely afterglow candidate. The UVOT observed in the uvw1 filter. Close to the XRT position a star is seen in the DSS, which shows no evidence of an additional fading source contributing to the emission. The GRB upper limit is uvw1 > 18.63. Revised analysis of the BAT data yields a refined position of

     RA (J2000):  173.604 =3D 11h 34m 25.1s
     Dec (J2000): +40.988 =3D 40d 59' 18"
  

  with an estimated uncertainty radius of 3.0 arcmin (90% containment). Mask-weighted data is available from T-2.0 to T+8.0 sec, which does not cover the entire burst, but we estimate T90 from the un-weighted data to be 14.4 +- 1.6 sec (estimated error including systematics). The available light curve shows two peaks, each about 4 seconds long. The time-averaged spectrum from T+0.0 to T+8.1 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.29 +- 0.47. The fluence in the 15-150 keV band is 1.5 +- 0.4 x 10^-7 erg/cm2. All the quoted errors are at the 90% confidence level. No further observations of this source are currently planned.
• GCN Circular #17685
  M. De Pasquale (INAF-IASF Palermo) and H. Krimm (CRESST/GSFC/USRA)
  Further 9.9 ks of XRT observations of GRB150402A (Cummings et al., GCN circ. 17661), taken between T0+643.2 and T0+673.6 ks, show that the uncatalogued X-ray source detected in the BAT error region (Krimm et al., GCN circ. 17664) is still detected at a count rate of 3.9e-3 ct s^-1, showing no fading with respect to previous observations. We therefore conclude that this source is not the X-ray afterglow of GRB150402A. The 3 sigma upper limit calculated at the centre of the BAT error circle is 3.7e-3 ct s^-1.
  This circular is an official product of XRT team.