GRB 151231A

Last updated: 01/12/2016

The figure below shows the 3\,\sigma error box of the GRB localized by the InterPlanetary Network (IPN), and all galaxies in the GLADE catalog within a \pm\, 0.2^{\circ} environment from its edges along both axes. Numbers in the plot indicate distances of the galaxies in megaparsecs.

For more details about the GRB and its localization, check out the corresponding GCN Circular where the GRB data was taken from.

Symbols in the plot represent different methods for distance measurement:

blue + distance calculated from spectroscopic redshift (2MPZ)
green x distance calculated from photometric redshift (2MPZ)
red ☐ distance estimated with a random forest machine learning technique based on 2MASS J, H, and Ks magnitudes (GLADE)
orange O distance derived using various other methods (GWGC or HyperLEDA; see GLADE documentation for more details)

We use cosmological parameters H_0=70 \ \mathrm{km}\ \mathrm{s}^{-1}\ \mathrm{Mpc}^{-1}}, \Omega_{\mathrm{M}}=0.3 and \Omega_{\Lambda}=0.7 when calculating a distance from redshift.
Sky area near the 90% error box of 151231A

We have identified 25 galaxies inside the error box. distances of these galaxies are 176 Mpc, 239 Mpc, 245 Mpc, 247 Mpc, 250 Mpc, 251 Mpc, 254 Mpc, 261 Mpc, 263 Mpc, 267 Mpc, 268 Mpc, 271 Mpc, 278 Mpc, 291 Mpc, 301 Mpc, 310 Mpc, 338 Mpc, 348 Mpc, 349 Mpc, 406 Mpc, 504 Mpc, 522 Mpc, 577 Mpc, 635 Mpc and 829 Mpc.

This event was classified as a long GRB. Nevertheless, assuming that the event is a short GRB, we can identify 8 galaxies outside the error box from which a pair of merging neutron stars (BNSs) could have kicked out from to reach a position inside the GRB error box. Parameters of these galaxies are listed in the table below. Note that we have identified these galaxies as the ones being within a 100 kpc radius outside the GRB error box. According to Fong & Berger 2013, 95% of all binary neutron stars kicked out from a galaxy should merge within a 100 kpc range around its host.

D [Mpc] α [deg] R [kpc] P [%]

D [Mpc]: Distance of the galaxy in Mpc.
α [deg]: Angular distance of the galaxy from the error box in degrees.
R [kpc]: Projected distance of the galaxy from the error box in kpc.
P [%]: Probability that a BNS kicked out from the galaxy reaches a projected distance R before the merger. We calculated P using the observed distribution of projected physical offsets of short GRBs from their host galaxies, shown in Fig. 5 of Fong & Berger 2013. Note, that in order to have a BNS merge inside the error box with probability P, one must assume that the kick occurred towards the closest point of the error box from the galaxy center.

Click HERE if you want to download all GLADE parameters of galaxies shown in the figure. Each row in the linked ascii file correspond to a galaxy indicated in the plot. For an explanation on what different columns represent, click HERE.