GCN Circular 45808

Subject

EP#01709320865: Swift-XRT observations

Event

EP261003a

Date

2026-10-05T08:58:28Z (13 hours ago)

Edited On

2026-10-05T13:50:46Z (8 hours ago)

From

Phil Evans at U of Leicester <pae9@star.le.ac.uk>

Edited By

Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov>

Via

P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi  (INAF-IASFPA) , A.P.
Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N.
Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA),
P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro
(INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato
(INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the
Swift-XRT team:

Swift-XRT has performed follow-up observations of the Einstein Probe/WXT-detected
source EP#01709320865, collecting 847 s of Photon Counting (PC) mode data between
T0+15 ks and T0+16 ks after the trigger. We have detected 1 source.  This has been
automatically classified as an uncatalogued X-ray source.

Uncatalogued X-ray sources
--------------------------

  Source 1 (SWIFT J203008.6-125641):
  ==================================
    RA (J2000.0):   307.5359  =  20 30 08.62
    Dec (J2000.0):  -12.9448  =  -12 56 41.3
    Error:	    6.2 (arcsec, radius, 90% confidence).
    Detect flag:    GOOD
    Distance:	    52 arcsec from the Einstein Probe/WXT position.
    Mean rate:	    0.0156 [+0.0064, -0.0051] ct s^-1
    Mean flux:	    (6.0 [+2.4, -1.9])e-13 erg cm^-2 s^-1
    Peak rate:	    0.0156 [+0.0064, -0.0051] ct s^-1
    Peak flux:	    (6.0 [+2.4, -1.9])e-13 erg cm^-2 s^-1
    ECF:	    3.82e-11 erg cm^-2 ct^-1
		      assuming NH=4.73e+20 cm^-2, gamma=1.84
		      determined from a spectral fit.
    RASS UL:	    5.5e-02 ct s^-1 (converted to XRT; 0.3-10 keV)
		      so the source is not above this 3-sigma upper limit.
    There is no evidence for fading.

All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with
catalogues and upper limits  from other missions, we assumed a power-law spectrum
with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated.

The results of the XRT-team automatic analysis of the XRT observations, including a
position-specific upper limit calculator, are available at
https://www.swift.ac.uk/EP/EP_FIELD00091.

This circular is an official product of the Swift-XRT team.