[vsnet-grb-info 18008] GRB 160521B: Theoretical estimate of the redshift and urgent need for further x-ray observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19456
SUBJECT: GRB 160521B: Theoretical estimate of the redshift and urgent need for further x-ray observations
DATE:    16/05/24 19:29:15 GMT
FROM:    Remo Rufinni at ICRA  <ruffini at icra.it>

R. Ruffini, Y. Aimuratov, L. Becerra, C.L. Bianco, M. Kovacevic, R.
Moradi, M. Muccino, A.V. Penacchioni, G.B. Pisani, D. Primorac, J.
Rueda, Y. Wang report:


>From preliminary data of GRB 160521B detected by the Fermi satellite (Yu
& Veres, GCN 19443) and from the presence of both gamma-ray (Fermi-GBM,
8 keV - 40 MeV) and GeV emission (Fermi-LAT, 0.1-100 GeV, see Axelsson
et al., GCN 19444) it is likely that this source is a Binary driven
Hypernova (BdHN) at very high redshift.

Following Ruffini et al. 2016 (arXiv:1602.02732), it lies in the BdHN
region of the Ep-Eiso plane for selected values of the redshift above
0.5 (see purple filled circles in Fig.[1]). The observed GeV emission
implies that the source cannot be a XRF.

The current paucity of data of the X-ray afterglow (Page et al., GCN
19448) is surprising and should be further examined up to late times
taking as an example GRB 090423 at z = 8.

Assuming that GRB 160521B is actually a BdHN, we can test the overlap of
its X-ray flux with the prototypical BdHN sources (see Pisani et al.
2013, A&A, 552, L5). In Fig.[2] it is plotted the single available data
point (Page et al., GCN 19448), not yet observed dimming, of GRB 160521B
X-ray luminosity, assuming 20 different values of the redshift from 0.5
(the lowest blue point) to 10 (the highest one) in steps of 0.5.

>From these preliminary data, GRB 160521B is a BdHN with possible
redshift z > 2.5 all the way up to z ~ 10, assuming that the single
observed X-ray data point belongs to the afterglow. A deep search for
the afterglow in the X-ray band is indeed crucial to define the nature
of this source.


[1] http://www.icranet.org/documents/GRB160521b_Fig1.pdf
[2] http://www.icranet.org/documents/GRB160521b_Fig2.pdf