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GCN Circular 21612

LIGO/Virgo G298048: Possible X-ray detection with Swift
2017-08-20T08:42:40Z (7 years ago)
Phil Evans at U of Leicester <>
P.A. Evans (U. Leicester), J.A. Kennea (PSU), S.B. Cenko (NASA/GSFC), B. Sbarufatti (INAF-OAB/PSU), S. Campana (INAF-OAB), E. Troja (NASA/GSFC/UMCP) S.D. Barthelmy (NASA/GSFC), A.P. Beardmore (U. Leicester), A.A. Breeveld (UCL-MSSL), D.N. Burrows (PSU), , G. Cusumano (INAF-IASF PA), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V.D'Elia(ASDC), S.W.K. Emery (UCL-MSSL), P. Giommi (ASI), C. Gronwall (PSU), H.A. Krimm (CRESST/GSFC/USRA), N.P.M. Kuin (UCL-MSSL), A.Y. Lien (GSFC/UMBC), F.E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB), J.A. Nousek (PSU), S.R. Oates (U. Warwick), P.T. O'Brien (U. Leicester), J.P. Osborne (U. Leicester), C. Pagani (U. Leicester), K.L. Page (U.Leicester), D.M. Palmer (LANL), M. Perri (ASDC), J.L. Racusin (NASA/GSFC), M.H. Siegel (PSU), G. Tagliaferri (INAF-OAB), A. Tohuvavohu (PSU) report on behalf of the Swift team:

Swift has continued to monitor the position of the likely EM counterpart to the LVC trigger G298048. We have now collected a total of 19.3 ks at the position of the optical source first reported by Coulter et al. (LVC GCN 21529).

In the summed data a faint X-ray source is detected at a position of (RA,Dec)=194.45112, -23.3845 degrees which is equivalent to:
RA (J2000.0) = 13h 09m 48.27s
Dec (J2000.0) = -23d 23��� 04.3���

with an uncertainty of 6.4 arcsec (radius, 90% confidence). This source is 11.3 arcsec from the position reported by Coulter et al.

The mean count rate is  6.5 (+2.8,-2.2) e-4 ct/sec which corresponds to a 0.3-10 keV flux of 2.6 (+1.1, -0.9) e-14 erg/cm^2/s. Assuming a distance of 42.5 Mpc (D���Elia et al., LVC Circ. 21592) this corresponds to a luminosity of 5.6 (+2.4, -1.9)e39 erg/s. In the data binned per Swift pointing, the peak detection is at ~twice this level.

At the current time we do not have sufficient statistics to confirm whether the object is variable. We also note that, given the probable radio emission from the host (Alexander, Fong & Berger, LVC Circ. 21548) the host may be a weak AGN, at the current time we cannot rule out the possibility that the X-rays come from the host galaxy rather than the optical afterglow.

Further observations are planned.
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