IceCube-190730A: Swift XRT and UVOT Follow-up and prompt BAT Observations
ATel #12985; Marcos Santander (U. Alabama), Azadeh Keivani (Columbia U.), Aaron Tohuvavohu (Penn State U.)
on 2 Aug 2019; 17:00 UT
Credential Certification: Marcos Santander (jmsantander@ua.edu)
Subjects: X-ray, Neutrinos, AGN, Quasar
The Neil Gehrels Swift Observatory observed the field of the ICECUBE_Astrotrack_Gold astrophysical neutrino candidate event IceCube-190730A (revision 1, ATel #12967) on two epochs: the first one beginning on July 30, 21:57:43 UT, about 1.1 hours after the neutrino detection, and a follow-up exposure starting on August 1, 00:49:52 UT. The neutrino 50% localization region contains the FSRQ PKS 1502+106 (z ~ 1.84), which is listed in the 3FHL Fermi-LAT catalog of hard-spectrum gamma ray sources, and the Seyfert 1 galaxy Markarian 841 (z ~ 0.03).
Swift-XRT collected a total exposure of 1.8 ks in PC mode over the two epochs. Data were reduced using the online tools described in Evans et al. 2014 (ApJS, 210, 8). Photon spectra for both sources were extracted in the 0.3-10 keV range and fitted with an absorbed power-law function. Unabsorbed fluxes were obtained using a Galactic column density of 2.52 x 10^20 cm^-2 from Willingale et al. 2013 (MNRAS 431, 1). The best-fit spectral values for both sources are given below for the combined XRT exposure.
Source Index Unabsorbed flux (erg cm^-2 s^-1)
PKS 1502+106 1.3 +/- 0.5 7.5 (+3.7, -2.5) x 10^-13
Markarian 841 1.7 +/- 0.1 1.9 (+0.2, -0.1) x 10^-11
We compare these values with those listed for the sources in the 1SXPS catalog (Evans et al. 2013, ApJS 210, 1). For PKS 1502+106 the flux is lower than the 1SXPS value (1.62 +/- 0.06 x 10^-12 erg cm^-2 s^-1) while the photon index is consistent. For Markarian 841 the flux and photon index are consistent with the 1SXPS values at the 1-2 sigma level.
Simultaneous Swift-UVOT observations were performed on both epochs. Magnitude values are given below for both sources, which have been corrected for Galactic extinction using values from Schlafly & Finkbeiner 2011 (ApJ 737, 103). As found by MASTER (ATel #12971), ZTF (ATel #12974) and Keel (ATel #12983) no indication of a substantial outburst was found in these observations when compared with SDSS photometry.
Epoch 1 (July 30):
Source Filter Exposure Magnitude
PKS 1502+106 UVM2 978 s 18.24 +/- 0.09
Markarian 841 UVM2 978 s 13.02 +/- 0.02
Epoch 2 (August 1):
PKS 1502+106 U 807 s 18.01 +/- 0.06
Markarian 841 U 807 s 13.42 +/- 0.02
At the neutrino arrival time the localization region was outside the coded BAT field-of-view, but above the Earth-limb with respect to the spacecraft. Within T0-200s to T0+75s no significant detections (SNR > 4 sigma) were found in a targeted search of the BAT raw light curves with time-bins of 64 ms, 1 s, and 1.6 s. We find no evidence for the possible transient reported by INTEGRAL (GCN. 25232) but note that the typical 4-sigma BAT upper limit for GRBs outside the coded field-of-view is above the flux reported by the INTEGRAL team.
We wish to thank the Swift Team for making these observations possible, in particular N. Klingler as the Swift Observatory Duty Scientist.
