Discovery of $\gamma $-ray emission from a steep radio spectrum ...

Discovery of γ-ray emission from a steep radio spectrum NLS1 B3 1441+476 Neng-Hui Liao1 , Yun-Feng Liang1,2 , Shan-Shan Weng3 , Min-Feng Gu4 , Yi-Zhong Fan1

arXiv:1510.05584v1 [astro-ph.HE] 19 Oct 2015

1

Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, China 2

University of Chinese Academy of Sciences, Yuquan Road 19, Beijing 100049, China 3

4

Department of Physics, Nanjing Normal University, Nanjing, China

Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences,80 Nandan Road, Shanghai 200030, China

[email protected] (NHL); [email protected] (YFL); [email protected] (YZF) ABSTRACT Narrow line Seyfert 1 galaxies (NLS1s) usually do not host relativistic jet and the γ-ray NLS1s are expected to be rare. All γ-ray NLS1s reported to date have flat radio spectra and the jets are found to be closely aligned. No γ-ray mis-aligned NLS1 has been predicted before. In this work we analyze the first seven-year F ermi/Large Area Telescope (LAT) data of a steep radio spectrum NLS1 B3 1441+476 and report the first detection of γ-rays in such a kind of objects. No rapid variability is observed from radio to γ rays and additionally low core dominance (. 0.7) and Compton dominance (. 1) are found. B3 1441+476 has a compact radio morphology and a radio spectrum turnover at ∼ 100MHz. A radiation model successfully reproducing some steep-spectrum radio quasars can reasonably fit the spectral energy distribution of B3 1441+476. All these facts strongly suggest that B3 1441+476 hosts a mis-aligned and plausibly underdeveloped relativistic jet, which provides a valuable target to reveal the formation and evolution of relativistic jets in NLS1s. Subject headings: galaxies: active – galaxy: jet – Quasars: individual:B3 1441+476– radiation mechanisms: non-thermal

1. INTRODUCTION Active galactic nuclei (AGNs, Urry & Padovani 1995) powered by accretion of material onto super-massive black holes (SMBHs) are the most luminous and persistent sources of electromagnetic radiation in the universe. In the pre-F ermi/LAT (Large Area Telescope; Atwood et al. 2009)

–2– era, it was known that γ-rays from AGNs are produced in blazars and radio galaxies (Hartman et al. 1999). Thanks to the successful operation of F ermi/LAT, a new class of γ-ray AGNs, the radioloud narrow-line Seyfert 1 galaxies (RLNLS1s), has been firmly established (Abdo et al. 2009a, b; Ackermann et al. 2015). NLS1s are characterized by a narrow width of the broad Blamer emission lines with FWHM (Hβ) < 2000 km s−1 , along with strong optical FeII lines and weak forbidden lines (e.g. Pogge 2000). NLS1s are thought to have small black hole masses (between 105 and 108 M⊙ ) and accretion systems with Eddington ratios larger than ∼0.1, indicative of an early stage of AGN activity (e.g. Boroson & Green 1992; Collin & Kawaguchi 2004), while normal radioloud AGNs, such as blazars and radio galaxies, tend to have higher central BH mass and lower Eddington ratios (Sikora et al. 2007). RLNLS1s are likely hosted by late-type galaxies while other radio-loud AGNs tend to be in early-type galaxies (e.g. Collin & Kawaguchi 2004). The detection of the MeV−GeV γ rays of the RLNLS1s provides the direct evidence for the presence of a closely aligned relativistic jets in these systems (Abdo et al. 2009a, 2009b; Yuan et al. 2008), which seems to be at odds with the paradigm that a fully developed relativistic jet could happen only in elliptical galaxies (e.g. Marscher 2010). So far, γ-ray emissions have been detected in several RLNLS1s by F ermi/LAT (Abdo et al. 2009a, b; Ackermann et al. 2015; D’Ammando et al. 2012, 2015; Yao et al. 2015). They all show flat radio-spectrum which is a distinct character of blazars (Foschini et al. 2015). And evidence of significantly Doppler beaming effect has been found for all these sources, such as: superluminal motion of jet component (D’Ammando et al. 2012), very high radio brightness temperature (e.g. Yuan et al. 2008; Gallo et al. 2006), high radio core dominance parameter (e.g. Foschini et al. 2015), and rapid variability in γ-ray and optical/infarad bands (Jiang et al. 2012; Paliya et al. 2013, 2014). Comparing to γ-ray blazars, γ-ray NLS1s tend to have lower γ-ray luminosities, which may be due to their small black hole masses (e.g. Chen & Bai 2010). In contrast, γ-ray emission from the steep radio spectrum radio loud NLS1s, whose jets are widely believed to be mis-aligned, has not been discovered yet. Because of their large jet inclination angles, the γ−ray emission is expected to be significantly suppressed by the Doppler beaming effect. That is why no γ-ray mis-aligned NLS1 has been predicted before. Nevertheless, γ-ray misaligned NLS1s, if exist, are very important because they offer a different perspective than flat radio spectrum sources for approaching high-energy phenomena. The study of mis-aligned γ-ray NLS1s can also shed light on the disk-jet connection and are helpful to understand the unified scheme of radio loud AGNs. B3 1441+476 is one of two NLS1s and is very radio loud (R=1331, Yuan et al. 2008) together with a steep radio spectrum between 151 MHz and 4.85 GHz (αrad = 0.60, Gu et al. 2015, throughout this work we refer to a spectral index α as the energy index such that Fν ∝ ν −α , corresponding to a photon index Γph = α + 1). The target exhibits typical NLS1 behaviors with a

–3– broad Hβ emission line with a width (FWHM) of (1848±113) km s−1 , along with R4570 ∼ 1.5 and [OIII]λ5007/Hβ ∼ 0.3 (Yuan et al. 2008). The central BH mass is estimated as ∼ 107.4 M⊙ and the Eddington ratio is given as 0.34 (Berton et al., 2015). In this paper, we analyze the LAT data of NLS1 B3 1441+476 and report the discovery of its γ-ray emission. This work is organized as follows: in Section 2 the routines of Fermi/LAT and Swift data analysis are introduced; in Section 4 we summarize our results with some discussion.

2. DATA ANALYSIS 2.1. LAT Data Analysis The Fermi/LAT (Atwood et al. 2009) is a pair-conversion γ-ray telescope sensitive to photon energies greater than 20 MeV. It has a large peak effective area (∼8000 cm2 for 1 GeV photons), viewing ≃ 2.4 sr of the full sky with angular resolution (68% containment radius) better than 1◦ at 1 GeV. In its routine survey mode, LAT performs a complete and uniform coverage of the sky in every 3 hours. The latest Pass 8 data used in this paper were collected during the first 7-year operation from 2008 August 4th to 2015 August 4th. Photon events belonging to evclass 128 and evtype 3 with the energy ranging from 500 MeV to 500 GeV were considered. Because the angular resolution of LAT increases rapidly with the energy in the sub-GeV energy range, 500 MeV is chosen to avoid significant contamination from the background. The updated standard ScienceTools software package version v10r0p5 with the instrument response functions of P8R2 SOURCE V6 was adopted throughout the data analysis. For the LAT background files, we used gll iem v06.fit as the galactic diffuse model and iso P8R2 SOURCE V6 v06.txt for the isotropic diffuse emission template 1 . The entire data set was filtered with gtselect and gtmktime tasks by following the standard analysis threads2 . The unbinned likelihood algorithm (Mattox et al. 1996) implemented in the gtlike task was used to extract the flux and spectrum. All sources from the Fermi LAT third source catalog (3FGL, Acero et al. 2015) within 16◦ of the target were included. The flux and spectral parameters of sources within 6◦ region of interest (ROI) together with normalization factors of the two diffuse backgrounds were set free, while parameters of other sources were fixed at the 3FGL values. Firstly, we added a γ-ray source with Powerlaw spectral template corresponding to B3 1441+476 1

http://fermi.gsfc.nasa.gov/ssc/data/access/lat/BackgroundModels.html

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http://fermi.gsfc.nasa.gov/ssc/data/analysis/scitools/

–4– into the initial background model generated from make3FGLxml.py3. Its γ-ray position was initially set as same as its radio position. After we fitted this model, we checked the Test Statistic (TS) value of the target and made a 12◦ × 12◦ scale residual TS map with each pixel size of 0.2◦ . If any γ-ray excess with TS value over 25 appeared in the TS map, we added a new source with Powerlaw spectral template into the background model to account for each excess. γ-ray locations of the target and the new background sources were obtained by task gtfindsrc. Then the updated background model was refitted to obtain the final result.

2.2. Swift Data Analysis The multi-wavelength observatory Swift carries three instruments (Gehrels et al. 2004), including the Burst Alter Telescope (BAT), the X-ray Telescope (XRT), and the UV/Optical Telescope (UVOT). In 2012, the Swift visited the source region 11 times with a total exposure time of ∼ 6.4 ks. All XRT data were taken in the photon-counting mode, and were processed with the task of xrtpipeline. We extracted the X-ray photons at the source position within 30′′ and just obtained 45 counts which are not sufficient for spectral modeling. In this case, the stacked image was analyzed with the X-ray image analysis program, XIMAGE4, and the count rates around the source coordinate were estimated to be of (7.1 ± 1.3) × 10−3 and (5.4 ± 1.2) × 10−3 cts s−1 in 0.2−10 keV and 0.2−2 keV, respectively. Assuming an absorbed power-law model with the column density fixed to 1.47 × 1020 cm−2 (Yuan et al. 2008), we determined the photon index of Γ ∼ 1.9 and the unabsorbed flux in 0.2−10 keV of 2.8 × 10−13 ergs cm−2 s−1 with the help of WebPIMMS 5 . The UVOT has six filters: V, B, U, UVW1, UVM2 and UVW2. When available, extensions are summed within each image using uvotimsum. To determine the source magnitude, we performed aperture photometry for all filters in the sky image using uvotsource with a source extraction region from 5′′ , and the background emissions were extracted from a neighboring sourcefree region. The averaged magnitudes (in AB system) in the six bands were V = 18.03 ± 0.17, B = 18.02 ± 0.10, U = 18.07 ± 0.05, UV W 1 = 18.27 ± 0.06, UM2 = 18.27 ± 0.07, and UV W 2 = 18.29 ± 0.07, respectively. 3

http://fermi.gsfc.nasa.gov/ssc/data/analysis/user

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http://www.swift.ac.uk/analysis/xrt/xrtcentroid.php

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http://heasarc.gsfc.nasa.gov/cgi-bin/Tools/w3pimms/w3pimms.pl

–5– 3.

RESULTS

There is a significant γ-ray excess against the background around the radio position of B3 1441+476 (see Figure 1). The TS value of the excess component is ≃ 45.5, corresponding to a significance of 5.9σ. The source is located at a high Galactic latitude (l ≃ 60◦ ), which does not suffer from significant uncertainty of the Galactic diffuse emission. Thus, we check the possible contamination from the γ-ray neighbors. The brightest γ-ray source within the ROI is 3FGL J1454.5+5124 which is about 4.5◦ away from the target with TS value of ≃ 3000. Its photon flux is almost one order of magnitude higher than that of the excess. Noting that the 95% confidence level (C.L.) of LAT point-spread function (PSF) for 500 MeV photons is about 4◦6 , significant contamination from 3FGL J1454.5+5124 is unlikely. The nearest γ-ray source 3FGL J1440.1+4955 with TS value of ≃235 is 2.4◦ away from the target. Since these two sources have comparable photon fluxes and 68% C.L. of LAT PSF for 500 MeV photons is about 1◦ , contamination from 3FGL J1440.1+4955 can be also ignored. Therefore, the detection of γ-ray emission excess is robust. Localization of the central excess is performed by the gtfindsrc task, giving a γ-ray position of R.A. 220.864◦ and DEC. 47.5292◦, with a 95% C. L. error radius of 0.152◦ (547′′ ). Since it is a high Galactic latitude source, radio-loud AGN is supposed to be its ideal counterpart. We seek the potential counterparts through the SIMBAD database7 . Actually, B3 1441+476 is found to be the only radio-loud AGN within the 95% C.L. γ-ray radius with angular separation of 360′′ . Any flat-spectrum radio sources indicative of potential blazar candidates are not found within the 95% C.L. γ-ray radius. The second nearest known radio-loud AGN is a radio galaxy SDSS J144246.29+474129.4 whose angular separation from the γ-ray location is 716′′. And the nearest blazar SDSS J144446.10+474257.7 is 1042′′ away. Furthermore, we investigate infarad colors of B3 1441+476 to check whether it is included in the Wide-field Infrared Survey Explorer (WISE; Wright et al. 2010) γ-ray Strip (WGS, Massaro et al. 2012). It is detected with high S/N in all four bands (W1, W2, W3, W4), with magnitudes in the WISE All-sky Source Catalog of 13.389±0.025, 12.292±0.022, 9.341±0.024 and 6.726±0.052, respectively. The infarad colors of W2-W3 and W1-W2 are given as 2.95 and 1.10, respectively. Therefore, B3 1441+476 indeed occupies the WSG area, similar with other γ-ray NLS1s (Foschini et al. 2015), suggesting it is capable to generate significant γ-ray emission. Motivated by these facts, we conclude that the central significant γ-ray excess is from B3 1441+476. By analyzing the entire 7-year LAT data, we obtain a best-fitting Powerlaw function for B3 6

http://www.slac.stanford.edu/exp/glast/groups/canda/lat Performance.htm

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http://simbad.u-strasbg.fr/simbad/

–6– 1441+476:

dN E = (2.87 ± 0.51) × 10−13 ( )−(2.95±0.24) , (1) dE 1026 MeV with an integrated flux of (6.15 ± 1.13) × 10−10 photons cm−2 s−1 . No significant evidence of spectral curvature is found. Considering its redshift as 0.703 (in this work we take a ΛCDM cosmology with H0 = 70 km s−1 Mpc−1 , Ωm = 0.3, and ΩΛ = 0.7), the average isotropic apparent γ-ray luminosity from 100 MeV to 100 GeV is (1.4 ± 0.6) × 1046 erg s−1 . The γ-ray SED is extracted by dividing the whole data into 5 sub-energy bins. A powerlaw gives an acceptance description to the SED, which well agrees with the entire fit, see Figure 2. A yearly γ-ray light curve has been also extracted, see figure 3a. Because the source is relatively faint in γ rays, we fix the spectral index of each time bin to the value of the average fit. The source is barely detected by LAT in the first four years, that is why it is absent in 3LAC (Ackermann et al. 2015). A detailed three months bin γ-ray light curve has been extracted for the last three years. The peak flux is (2.57 ± 0.82) × 10−9 photons cm−2 s−1 , nearly four times that of the average flux. B3 1441+476 may resemble mis-aligned AGNs that exhibit moderate γ-ray variability at time scale of months (e.g. Liao et al. 2015).

4. SUMMARY AND DISCUSSION We have detected the γ-ray emission from B3 1441+476. Its γ-ray spectral index (2.95±0.24) is soft, consistent with other γ-ray NLS1s (Ackermann et al. 2015). And so does the γ-ray luminosity. The difference between B3 1441+476 and other γ-ray NLS1s is that the former has a steep radio spectrum. We note that PKS 2004−447 has a flat radio spectrum below 5 GHz but possesses a steep radio spectrum above 8.4 GHz (Healey et al. 2007; Orienti et al. 2012). Its brightness temperature is high (≃ 1014 K; Gallo et al. 2006). Due to its rather weak optical FeII lines, PKS 2004−447 should not be considered as a typical NLS1 (Komossa et al. 2006). Multiwavelength studies have been performed for another steep radio spectrum very radio-loud NLS1 SDSS J143244.91+301435.3, but no γ-ray emission has been detected (Caccianiga et al. 2014). Therefore, B3 1441+476 is the first γ-ray source with both typical NLS1 behaviors and a steep radio spectrum, indicating the presence of a misdirected jet. Let us investigate the multiwavelength variability of B3 1441+476. In the radio wavelength, it has been observed at 1.4 GHz in the NRAO VLA Sky Survey and the Allen Telescope Array Twenty-centimeter Survey, giving the fluxes of 165.8±5.0 and 150.5±4.6 mJy, respectively (Condon et al. 1998; Croft et al. 2010). Variability amplitude of a few percent is suggested between these observations. We also check the infrared variability adopting WISE data. The infrared light curves are constructed from the PSF profile-fit photometric magnitudes after excluding the data whose S/N is marked as “null”, see Figure 3b. We also exclude those data with S/N < 10 for the

–7– W1 and W2 bands, and S/N < 5 for the W3 bands, and those with reduced χ2 of the profile-fit photometries larger than 2. B3 1441+476 had been monitored by the Catalina Real-time Transient Survey (CRTS, Drake et al. 2009; Djorgovski et al. 2011). The Photometry is transformed from the unfiltered instrumental magnitude to Cousins V by V = VCSS + 0.31(B − V)2 + 0.048 . We averaged the values obtained during the same observing night. There are 45 data points in the V band light curve, ranging from 53552 to 56445 MJD, see Figure 3c. We also plot the Swif t/UVOT light curves, including 23 data points and an upper limit, see Figure 3d. For the UV/optical magnitudes, correction of the Galactic extinction using the E(B-V) value of 0.014 from Schlafly & Finkbeiner (2011) and the extinction laws from Cardelli, Clayton & Mathis (1989) have been performed9 . And the magnitudes are transformed to flux densities according to Bessel (2000) and Wright et al. (2010). The χ2 test and the “normalized excess variance” (σN XS ; Edelson et al. 2002) method are adopted to search variability from these light curves. No significant variability is found. The absence of infrared variability is consistent with the variability flag in the WISE All-Sky Source Catalog var flag of “1110”. In X rays, besides of the Swif t/XRT observation, B3 1441+476 had also detected by ROSAT. The Swif t/XRT flux is scaled to energy range of 0.1-2.4 keV, ∼ 2×10−13 erg cm−2 s−1 , which is comparable with the ROSAT flux, 2.5 × 10−13 erg cm−2 s−1 (Yuan et al. 2008). Although moderate variability at time scale of months is suggested in γ rays, no evidence of significant variability is found from radio to X rays. In radio morphology, B3 1441+476 is unresolved in the FIRST image, indicative of an upper limit linear size (LS) of 8.4 kpc. Recently, its 5 GHz Very Long Baseline Array (VLBA) observations have been available (Gu et al. 2015). The total flux density at 5 GHz from the VLBA image is close to that in the single dish GB6 catalog, suggesting that it is compact in the sub-as scale. In mas scale, its radio core is not directly observed, perhaps hidden in the brightest jet component whose brightness temperature is about 1010.3 K (Gu et al. 2015). Therefore, the core dominance (R) of B3 1441+476 is constrained as . 0.67, where the R is defined as the flux ratio between the jet core component and the extended component. Together with its steep radio spectrum, B3 1441+476 distinguishes significantly from all other γ-ray NLS1s (see Figure 4). Moreover, since it is not detected in the Very Large Array Low-frequency Sky Survey Redux catalog (VLSSr, Lane et al. 2014), considering the VLSSr 74 MHz 5σ unpper limit (∼ 0.5 Jy), its radio spectrum shows a clear trend of a turnover around 100 MHz (also see Gu et al. 2015). Given its radio spectrum characters and the compact structure, this NLS1 shares similarity with compact steep-spectrum (CSS) radio sources. 8 9

http://nesssi.cacr.caltech.edu/DataRelease/FAQ2.html#improve

The extinction magnitudes in six UVOT bands are calculated as: AV = 0.04, AB = 0.06, AU = 0.07, AUW1 = 0.10, AUM2 = 0.13, and AUW2 = 0.12.

–8– The fit of SED of B3 1441+476 can constrain the jet emission (see Figure 5). It is interesting to note that the B3 1441+476 tends to have a smaller Compton dominance (CD) value, .1, while CD values of some other γ-ray NLS1s are > 10, even up to 100 (e.g. Abdo et al. 2009a; D’Ammando et al. 2012). Since external inverse Compton (EC) process is likely responsible for the γ-ray emissions of NLS1s (e.g. Sun et al. 2015), CD could be used to constrain the Doppler factor of the jet. Now we can set a constraint as CD = LEC /LSYN = U′ext δ 2 /UB = 1, where U′ext is the energy density of the external emission at the rest frame, UB is the the energy density of magnetic field and δ is the Doppler factor. The external emission can be from the broad line region (BLR) or the dust torus, and the typical energy densities of 3 × 10−2 and 3 × 10−4 erg cm−3 are adopted (Ghisellini et al. 2012), respectively. If we set the typical strength of magnetic field corresponding to the BLR (5 Gauss) or the dust torus model (1 Gauss), a rough constraint of the Doppler factor of B3 1441+476 can be given as . 5. The classic homogeneous lepton radiation model is used to calculate the jet emission. The U′dust is set as 3 × 10−4 erg cm−3 and the minimum energy of the radiation electron γmin is set as 1. Other input parameters include: Doppler factor δ ≃ 6.4; magnetic field intensity B ≃ 0.6 Gauss; energy break of electron distribution of γbr ≃ 980; spectral indexes of electron distribution p1 = 1.8, p2 = 4 and the normalization of the particle number density K ≃ 64. Since no rapid variability is found from radio to γ rays, the radius of the radiation region is set to be 2.9 × 1017 cm, corresponding to a variability timescale of one month, R = ctvar δ(1 + z)−1 . Assuming that one proton corresponds to one relativistic emitting electron and that protons are ‘cold’ in the comoving frame (Celotti & Ghisellini 2008), the power of jet is estimated as ∼ 4×1046 erg s−1 . The calculated jet emission provides an acceptable description of the SED. Note that a similar radiation model applied successfully to a γ-ray SSRQ 3C 275.1 (Liao et al. 2015). In conclusion, motivated by its multiwavelength properties, B3 1441+476 likely hosts mis-aligned jet and is hence the first γ-ray mis-aligned NLS1. Likely the strong relativistic jet and the violent accretion activity are growing up simultaneously. The connection between these two components can be further investigated by analyzing the X-ray and γ-ray light curves of B3 1441+476. Due to the faintness of its X-ray emission, future deep X-ray observation is essential. We also note that the number ratio between γ-ray NLS1s with aligned and mis-aligned jets (∼10) is lower than that between γ-ray blazars and MAGN (∼100), which may be a challenge of the orientation-based unified model. One puzzle remains. There are dozens of flat radio spectrum NLS1s while just a few steep radio spectrum NLS1s, somewhat at odds with the unified scheme of RL-AGN. Two scenarios are proposed to solve this puzzle. It could be just a selection effect if the BLR of NLS1s has a disklike geometry (e.g. Shen & Ho 2014). There is no Doppler broadening and hence the FWHM of permitted lines are narrower than in a normal Seyfert 1 when it is observed pole-on. Otherwise the Doppler broadening is turn-on so it would be classified as a normal radio galaxy. Another scenario is that NLS1s are young galaxies (e.g. Grupe 2000). For young radio sources, their jets are not

–9– well developed so they becomes almost invisible for current observations. Actually, RL-NLS1s do share a lot of similarities with young radio sources (e.g. Yuan et al. 2008). B3 1441+476 is an ideal source for distinguishing between these two scenarios. As mentioned before, it has a compact radio morphology at as scale (LS . 8 kpc) and steep radio spectrum with a turnover at about 100 MHz (Gu et al. 2015). It could be classified as a CSS. Therefore, for B3 1441+476 the young radio source scenario is preferred. However, extended radio emissions exceeding the typical size of CSS have recently been observed for all the three arbitrarily selected RLNLS1 with enhanced sensitivity (Richards & Lister 2015). A detailed analysis of the optical spectra of CSSs may be useful to check whether they are the parent population of RLNLS1s or not. This research has made use of data obtained from the High Energy Astrophysics Science Archive Research Center (HEASARC), provided by NASA′ s Goddard Space Flight Center. This research has also made use of the NASA/IPAC Extragalactic Database and the NASA/IPAC Infrared Science Archive which are operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research makes use of the SIMBAD database, operated at CDS, Strasbourg, France. The CSS survey is funded by the National Aeronautics and Space Administration under grant no. NNG05GF22G issued through the Science Mission Directorate Near-Earth Objects Observations Program. The CRTS survey is supported by the US National Science Foundation under grants AST-0909182 and AST-1313422. This work was supported in part by 973 Programme of China under grant 2013CB837000, National Natural Science of China under grants 11361140349, 11433009, 11133006 and 11233006, and the Foundation for Distinguished Young Scholars of Jiangsu Province, China (No. BK2012047).

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Fig. 1.— TS map from 500 MeV to 500 GeV for 12◦ × 12◦ region centered at B3 1441+476. It is for the model with diffuse backgrounds and both 3FGL and newly emerging sources subtracted. TS value of the central excess corresponding to B3 1441+476 is consistent with gtlike analysis. Beside of the target whose radio position is marked as green cross, the strongest and the nearest γ-ray neighbors together with new emerging background sources are listed. The map is smoothed with a σ=0.2◦ Gaussian function.

– 13 –

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Fig. 2.— γ-ray SED of B3 1441+476. The red line represents the best fit of the entire 7 years data together with the 1σ uncertainty area. The black squares are the individual fits for sub-energy bins.

– 14 –

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Fig. 3.— Multiwavelength light curves of B3 1441+476. (a) One year bin γ-ray light curve, together with the 7-year averaged flux (solid line) and its 1σ uncertainty (dashed lines). (b) Optical/UV light curves extracted from Swif t/UVOT observations. (c) Optical V band light curve from CRT survey. The two dashed vertical lines represent the time epoch when the γ-ray flux is in the high state. Since there is only one optical data during this epoch, it is impossible to search any connection between optical and γ-ray light curves. (d) Infrared light curves from WISE observations, W4 band light curve is not plotted due to its large error bar.

– 15 –









ORJ5



 













 

















_DUDGLR_ Fig. 4.— Plane of the radio index (from 1.4 to 5 GHz) and R for γ-ray NLS1s. Since no unambiguous radio core flux is found, PKS 2004−447 is not plotted in this plane. Main data of the radio index and R values from 15 GHz VLBA observations are derived from Foschini et al. (2015). For FBQS J1644+2619, its R value is given by the 1.4 GHz VLA observation (Doi et al. 2012). For SDSS J122222.55+041315.7, its R value is calculated based on the 15 GHz VLBA observation (Lister & Homan 2005).

– 16 –

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Fig. 5.— SED of B3 1441+476, together with the synchrotron plus SSC+EC modeling (blue solid line). The green dashed line represents the synchrotron component, the red dash-dotted line represents the SSC component and the blue dotted line corresponds the EC part. Multiwavelength data includes: the radio data (red) are derived from NED; the infrared data (green) are collected from IRSA; the yellow and the pink points represent SDSS and UVOT data respectively; the black point are XRT flux and the the blue ones are LAT fluxes. The UV/optical data are not considered for modeling because they are probably dominated by the accretion disk.