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Fermi and Swift observations of correlated and high-energy activity from the FSRQ TXS 0059+581

ATel #8981; Stefano Ciprini (ASDC Rome & INFN Perugia, Italy)*, Luigi Pacciani (INAF IAPS, Rome), Giovanna Pivato (INFN and University of Pisa)*, (*) on behalf of the Fermi Large Area Telescope Collaboration
on 23 Apr 2016; 13:55 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@asdc.asi.it)

Subjects: Optical, Ultra-Violet, X-ray, Gamma Ray, >GeV, AGN, Blazar, Quasar

The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope, has observed hard-spectrum gamma rays from a source positionally consistent with the FSRQ TXS 0059+581 (also known as GB6 J0102+5824, 7C 0059+5808, 5BZU J0102+5824 and 3FGL J0102.8+5825) with radio coordinates (J2000), R.A.: 15.69068 deg, Dec.: 58.40309 deg (Johnston et al. 1995, AJ, 110, 880). TXS 0059+581 has a redshift z=0.644 (Sowards-Emmerd et al. 2005, ApJ, 626, 95) and is monitored by the MOJAVE program (Lister & Homan 2005, AJ, 130, 1389).

Preliminary analysis indicates that on April 17, 2016, TXS 0059+581 was in an active state with a daily averaged gamma-ray flux (E>100MeV) of (0.2+/-0.1) X 10^-6 photons cm^-2 s^-1, and a corresponding photon spectral index (E>100MeV) of 1.7+/-0.3 compared to the average index of 2.094+/-0.035 in the 3FGL catalog (Acero et al. 2015, ApJS 218, 23). Preliminary analysis also indicates that the most energetic photons coincident with TXS 0059+581 and detected on April 17, have energies of 32.6 GeV and 88.0 GeV. High-level gamma-ray flux was previously reported in January 2012 (ATel#3864).

The high-energy activity was significantly detected above 10 GeV in the interval between April 6 and 19, 2016, following the analysis of the LAT data with the prescription of Pacciani et al. 2014, ApJ, 790, 45. The corresponding time-averaged HE flux (E>10GeV) of (3.9+/-1.6) X 10^-9 photons cm^-2 s^-1 is about 22 times greater than the (E>10GeV) flux reported in the 3FGL catalog. The averaged (E>100MeV) photon spectral index for this interval is in line with the hard photon index observed on April 17.

A high-urgency follow-up ToO Swift observation was performed on April 18, and April 21, 2016. Swift XRT data were taken in Photon Counting mode. The X-ray spectrum (0.3-10 keV) can be fit by an absorbed power law model with an HI column density set to the Galactic value of 3.5 X 10^21 cm^-2 (Kalberla et al. 2005, A&A, 440, 775). The unabsorbed flux of April 18 was (3.5+/-0.9)X10^-12 erg cm^-2 s^-1, comparable to the peak X-ray flux detected by Swift XRT on April 2, 2008. The corresponding photon spectral index 2.1+/-0.3 suggests the possibility of both a synchrotron-tail and inverse Compton (IC) contribution to the X-ray spectrum, in agreement with the spectral hardening observed by the LAT. The unabsorbed (0.3-10 keV) flux of April 21 was (4.8+/-0.8)X10^-12 erg cm^-2 s^-1, and the corresponding photon spectral index of 1.1+/-0.4 could be originated by a single, IC, component.

Simultaneous Swift UVOT observations obtained using all the filters (Poole et al. 2008, MNRAS, 383, 627) are given in observed magnitudes. April 18 19:26-21:18 UTC: V=16.44+/-0.06, B=17.32+/-0.06, U=17.00+/-0.06, UV-W1=17.9+/-0.1, UV-M2=18.6+/-0.1, UV-W2=18.5+/-0.1. April 21 03:16-05:05 UTC: V=16.2+/-0.1, B=17.45+/-0.08, U=17.1+/-0.1, UV-W1=17.4+/-0.2, UV-W2=19.2+/-0.2. The values for April 18 are 1.5 to 2 magnitudes brighter than the archival UVOT observations.

The time-correlated gamma-ray/X-ray/UV/optical behavior confirms the source identification of 3FGL J0102.8+5825 with the FSRQ TXS 0059+581.

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. In consideration of the ongoing activity of this source we encourage multiwavelength observations. For this source the contact persons are L. Pacciani (luigi.pacciani@iaps.inaf.it), S. Ciprini (stefano.ciprini@asdc.asi.it) and G. Pivato (giovanna.pivato@pi.infn.it).

The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.

We thank the Swift Team for making these observations possible, in particular B. Sbarufatti as the Swift Observatory Duty Scientist.