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IceCube-171106A: Swift observations

ATel #10942; A. Keivani (PSU), D. B. Fox (PSU), J. J. DeLaunay (PSU), J. A. Kennea (PSU), P. A. Evans (U. Leicester), D. F. Cowen (PSU), J. P. Osborne (U. Leicester), and F. E. Marshall (GSFC) report on behalf of the Swift-IceCube collaboration:
on 10 Nov 2017; 00:24 UT
Credential Certification: Azadeh Keivani (azastron@gmail.com)

Subjects: X-ray, Blazar, Transient

Swift has observed the field of IceCube-171106A (Rev 0; subsequently updated to Rev 1, GCN #22105), utilizing the on-board 19-point tiling pattern to cover a region centered on RA,Dec (J2000) = (340.0d,+7.4d), with a radius of ~0.8°. Swift-XRT collected ~750 s per field of PC mode data per tile. The observations were taken between 21:51:12 UT on Nov 6 and 11:52:10 UT on Nov 7 (i.e. from 11.5 ks to 62.0 ks after the neutrino trigger), and covered 2.1 deg2. Fourteen X-ray sources are detected in the observations, of which five lie within the refined neutrino localization.

Of the fourteen identified sources, two correspond to known X-ray emitters, X1 to 1RXS J224124.3+071253, and X3 to UGC 12138. Two further sources, X4 and X14, have positions consistent with ROSAT Faint Source Catalog objects.

Five further sources have potential counterparts from the SIMBAD database. X2 matches to HD 215109; detection of this optically bright star may be due to optical loading rather than bona fide X-ray emission. X5 matches to 87GB 223537.9+070825 (5BZQJ2238+0724 in BZcat), which is a flat-spectrum radio quasar and known blazar, not previously reported to emit in X-rays. X6 matches to PMN J2243+0716, a radio-bright quasar. X8 matches to the GALEX "blue object" source 2690384041306227301. X10 matches to WISE J224206.68+073148.3, a known BL Lac-type blazar. Observing X-ray emission (or in the case of HD 215109, an optical loading detection) at the level seen here from any of these sources would not be remarkable.

Given the recent observation of high-energy gamma-ray activity from TXS 0506+056, potentially associated with the IceCube-170922A (GCN #21916, ATels #10791 and #10817), we note in particular the two X-ray luminous blazars within the neutrino localization, 87GB 223537.9+070825 and WISE J224206.68+073148.3.

Identified sources:

 
Source	RA		Dec		r_90	R_x**	Catalog/Notes 
========================================================================== 
  X1*	22:41:24.15	+07:12:57.6	4.1"	61(9)	1RXS J224124.3+071253  
  X2	22:42:48.20	+06:40:14.2	4.4"	82(3)	HD 215109 (optical loading) 
  X3	22:40:17.14	+08:03:13.4	2.1"	410(3)	UGC 12138 
  X4	22:41:20.34	+06:48:58.7	5.4"	32(9)	1RXS J224122.2+064851 
  X5*	22:38:10.41	+07:24:12.8	5.2"	30(8)	87GB 223537.9+070825 
  X6	22:43:05.82	+07:16:34.7	5.7"	9(5)	PMN J2243+0716 
  X7	22:37:54.30	+07:22:02.9	6.8"	? 
  X8	22:38:59.95	+07:02:43.7	6.3"	4(4)	GALEX 2690384041306227301 
  X9*	22:38:47.59	+07:22:24.8	6.1"	? 
  X10*	22:42:06.68	+07:31:52.6	7.4"	7(4)	WISE J224206.68+073148.3 
  X11	22:40:15.96	+07:48:42.2	5.9"	9(4) 
  X12	22:40:26.17	+06:50:14.3	5.9"	4(4) 
  X13	22:38:21.18	+08:04:20.7	4.9"	3(5) 
  X14*	22:39:52.53	+07:11:57.1	6.7"	9(5)	1RXS J223951.8+071132 
========================================================================== 
* inside the refined 90%-confidence neutrino localization 
** R_x indicate count rate in units of counts ks-1.  

Excluding identified sources, the 3σ upper limit on the count rate in the rest of the field is 0.01 ct s-1, which corresponds to a 0.3-10 keV flux of 4.1e-13 erg cm-2 s-1 for a typical AGN spectrum (NH=3e20 cm-2, Γ=1.7). Overlaps between the different tiles account for 0.5 deg2: in these regions the 3σ upper limit is 0.009 ct s-1, corresponding to 3.7e-13 erg cm-2 s-1.

The neutrino localization was in the Swift BAT's field of view from 404 s to 117 s prior to the neutrino alert time. There were no triggered GRBs during this time. Using the 287 s survey exposure (starting at 18:32:55 UT on 2017 Nov 06) we searched for any hard X-ray emission inside the 90%-confidence neutrino localization. We found no point source and set a 4σ upper limit on the fluence during that time period of 5e-7 erg cm-2 (15-150 keV) assuming a photon index of -2.