PoS(NLS1)024

25 Pages·2011·0.3 MB·English

Evidence of powerful relativistic jets in narrow-line
Seyfert 1 galaxies
P
o
S
(
LuigiFoschini† N
∗
INAFOsservatorioAstronomicodiBrera,ViaE.Bianchi46,23807,Merate(Italy)
L
E-mail: [email protected]
S
1
In 2008, the Fermi Gamma-raySpace Telescope has revealed– for the first time – high-energy
(E>100MeV)g raysfromafewNarrow-LineSeyfert1Galaxies(NLS1s). Later,in2009and )
2010, two multifrequencycampaigns on one of these sources, PMN J0948+0022(z=0.585), 0
definitelyconfirmedthepresence,insourcesofthistype,ofarelativisticjetverysimilarandwith
2
comparablepowertothoseinblazars.However,thesesourcesareneitherblazarsnorradiogalax-
4
ies,asprovenbytheiropticalspectrumandbytheirverycompactradiomorphology. Moreover,
sinceNLS1saregenerallyhostedinspiralgalaxies,thiscastsasignificantdoubtontheparadigm
ofthe correlationbetweenjets andellipticalhostgalaxies. Thesefindingsposeintriguingchal-
lenges to the currentknowledgeof jet systems and on how these structuresare generated. The
currentstatusoftheresearchesinthisfieldisreviewedandongoingworkisoutlined.
Narrow-LineSeyfert1GalaxiesandtheirplaceintheUniverse
April4-6,2011
Milano,Italy
Speaker.
∗
†Iwouldliketothankfortheinteresting,useful,andamusingdiscussionsG.Ghisellini,L.Maraschi,andF.Tavec-
chio.ThanksalsotoS.Komossafortheeditorialhandlingofthismanuscript.
(cid:13)c Copyrightownedbytheauthor(s)underthetermsoftheCreativeCommonsAttribution-NonCommercial-ShareAlikeLicence. http://pos.sissa.it/
RelativisticjetsinNLS1 LuigiFoschini
1. Introduction
Narrow-Line Seyfert 1 Galaxies (NLS1s) constitute a class of active galactic nuclei (AGNs)
withpeculiar characteristics. Beforethisworkshop, IwasawarethatNLS1swereveryinteresting
sources, but now, after the conclusion of the meeting and having heard several interesting talks, I
haveunderstood thatNLS1sareevenmoreinteresting andspecialthanIcouldhavethought(1).
RichardPoggeinhistalk[89]hasoutlined25yearsofNLS1sstudies,fromthefirstinteresting
notes(e.g. [27,42]),totheawarenessofthediscoveryofanewclassofAGNs[85]. Severalauthors
havepointed outthattheobserved features atdifferent wavelengths suggest thatNLS1sareAGNs
P
with relatively low masses, high accretion rates, and possibly young (e.g. [14, 16, 17, 50, 76,
o
88]; see the updates [18, 51, 75, 87]). NLS1s generally do not display strong activity at radio
S
frequencies, butasmallpercentofthem( 7%)donotfollowthisrule[65].
∼
The first radio-loud NLS1, PKS 0558 504 (z=0.137), was discovered in 1986 [91]. Later, (
−
in the early 2000s, a few more sources of this type were discovered [52, 84, 106, 65] and there N
was already a first (unsuccessful) attempt to detect very high-energy g rays (E >400 GeV) from
L
these sources with the Whipple Cˇerenkov telescope. More radio-loud NLS1s were found with
S
early surveys both radio- and optically-selected [101, 104]. Although, in some cases, the flat or
1
invertedradiospectrumandhighbrightnesstemperaturesuggestedthepresenceofarelativisticjet
[106, 30], in other cases there was no direct indication of beaming [65]. Moreover, these sources )
had a very compact radio morphology, making it difficult to trace the components searching for 0
superluminal motion [30]. Other indications of a possible presence of a relativistic jet came from
2
optical-to-X-ray studiesofvariability [37].
4
The definitive proof of the existence of relativistic jets in NLS1s arrived after the launch
of the Fermi Gamma-ray Space Telescope (hereafter Fermi) in 2008 June. Already after a few
months of operation, there was the first detection at g rays (E > 100 MeV) of a NLS1: it was
PMNJ0948+0022 (z=0.5846) [1, 38]. This discovery immediately triggered amultiwavelength
(MW) campaign (2009 March-July), which confirmed that the g -ray emission was indeed as-
sociated with the NLS1 and that the MW behavior was typical of a relativistic jet, like those
in blazars [3, 48]. The NLS1 had a peak in the g -ray flux on April 1, 2009, with a value of
4 10 7 ph cm 2 s 1 and then declined, followed by a similar trend at all the wavelengths,
− − −
∼ ×
while radio emission increased reaching the peak about a couple of months later. In 2010 July,
PMNJ0948+0022 underwent amuchstronger outburst, reaching thepowerof 1048 erg/s inthe
∼
0.1 100 GeV band and this event was preceded by a significant change in the radio polarization
−
angle, which occurred about one year before [39]. It is worth noting the extreme power at g rays
together with the lack of extended radio structures. One basic question, stressed by G. Ghisellini,
isindeed: wheresuchgreatpowerhasgone?
Thisisjustoneofthemanyproblemsopened bythediscovery ofhigh-energy g -rayemission
from NLS1s, but many others are present. Iam not able yet to say what is the effective impact of
this discovery in our knowledge of AGNsand relativistic jets. I am still in the phase of searching
andcollectinginformationstobetterunderstandthepropertiesofthesesources,comparewithother
known AGNs, and try to infer some useful knowledge. Although there is a handful of g -NLS1s,
1Seetheworkshopproceedingsathttp://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=126.
2
RelativisticjetsinNLS1 LuigiFoschini
0
0 2
2
5
5 1
Number of sources 101 umber or sources 10
N
5
5
P
0 0.2 0.4 0.6 0
redshift 500 1000 1500 2000
FWHM Hb [km/s] o
Figure1: SampleofNLS1s:(leftpanel)Redshiftdistribution;(rightpanel)FWHMHb distribution. S
(
N
in the present work I would like to report about an early study of their MW properties and the
L
comparison withradio-quiet objects andwithbrightg -rayblazars.
S
1
2. Sample selection
)
0
Ratherobviously, Iperformed theearlysearchforhigh-energy g raysfromNLS1sin2008by
2
startingwithasamplebuiltwiththemostradio-loudobjects. Thecoreofthissamplewasthelistof
veryradio-loud sources ofYuanetal. [104], whichwereoptically selected fromtheSloan Digital 4
Sky Survey (SDSS)andhadtheradio loudness R= f /f >100. Somesources withthe
1.4GHz 440nm
same R prescription were found in the literature and added to the sample [41, 65, 84, 105, 107].
Thislistwascomposedof29veryradio-loudNLS1s,whichresultedin4detectionsathigh-energy
g raysafteroneyearofFermioperations [4].
Now,inorder tomakeamoreextended work, Ihave relaxed the prescription on Rand added
also less radio-loud and even radio-quiet (although not silent) NLS1s from the FIRST Bright
Quasars Survey (FBQS) [101]. Therefore, the sample studied in the present work is composed
of 76 NLS1s, of which 45 are from the FBQS [101], 23 are from the SDSS [104] and 8 are from
literature [41,65,84,105,107](seeTablesA1andA2intheAppendix). Theradio-quiet (R<10)
subsample iscomposed of30sources, whiletheradio-loud one(R>20) has39objects; 7NLS1s
ofthepresent listareradio-intermediate (10<R<20). Thedistributions ofzandFWHMHb are
displayed in Fig. 1. The measurements of the FWHM Hb are taken from the available literature
([41,65,84,101,104,105,107]).
I have also considered, as a comparison, a subsample of the bright g -ray blazars detected by
Fermi during its early months of operations [2]. The subsample of 34 AGNs has been defined on
thebasisoftheavailabilityofSwiftoptical(Bfilter)andX-raydata[44,45]. Radiodataweretaken
from the Faint Images of the Radio Sky at Twenty Centimenters (FIRST), as for the NLS1s (see
next Section). It is worth noting that the original selection of these blazars was done on the basis
of the high detection significance (>10s , [2]), so this is not a flux-limited sample. On the other
hand, alsothesampleofNLS1sisnotfluxlimited.
3
RelativisticjetsinNLS1 LuigiFoschini
3. MultiwavelengthData
For all the sources in Table A1, I gathered the data from radio to g rays from the publicly
available archives and data servers (Table A2). All the data were corrected for the absorption due
to the Galactic hydrogen, transformed – when necessary – into flux density at specific frequency
(radio: 1.4GHz;optical: 440nm;X-rays: 1keV;g rays: 100MeV),K-correctedbymultiplyingthe
fluxdensitywiththefactor(1+z)a 1,havingassumedthefollowingvaluesofa =0,a = 0.5
− r o
−
(see [104]), a X =1, and a g =1.5 (see [4]). Thecorresponding luminosities have been calculated
withinaL CDMcosmology withH0=70kms−1 Mpc−1 andW L =0.73[64].
P
o
3.1 Radiodata
S
RadiodataweretakenfromtheVLA(VeryLargeArray)FIRST(FaintImagesoftheRadioSky
(
atTwentyCentimenters2)survey[11], operated at1.4GHz. Onlytwosources wereinskyregions
N
not covered by the FIRST: PMN J0134 4258 and PKS 0558 504. In both cases, I extended to
− −
1.4GHzthefluxdensity measuredat4.8GHz[103]byadopting aflatradiospectrum (a =0). L
r
S
3.2 Opticaldata
1
Most of the optical data in the B filter band (440 nm) were taken from the Sloan Digital Sky )
Survey (SDSS3). The ugriz system was converted into theUBVRI one by using the formulae re- 0
portedin[24]. WhenthesourcewasnotinaregioncoveredbytheSDSS,Iusedthemeasurements
2
oftheUSNavalObservatory (USNO)B1Catalog[81]. ForPKS0558 504, Ireferto[82].
− 4
TheobservedmagnitudeshavebeendereddenedbyusingtheA calculatedfromtheN mea-
V H
surements oftheLeiden-Argentine-Bonn Survey[62]andtheextinction lawsby[22].
Most of the sources are quasar-like and, therefore, the host galaxy contribution is negligible.
Forthelowestredshiftsources, Iestimatedthatthehostgalaxycontributed atmaximumbya10%
influx,byassuming aspiralhostofSatype4.
3.3 X-raydata
IhaveusedtheROSATBrightandFaintSourceCatalogues(5)[98,99],whicharebasedonan
all-skysurveyinthe0.1 2.4keVenergyband. Whenthereisnodetection,Icalculateda3s upper
−
limit byusing the available exposure atthesource position. Inafewcases, although there wasno
detectionwithROSAT,theNLS1waslaterdetectedwithothersatellites(e.g. PKS1502+036with
Swift,[4]). However,forthesakeofhomogeneity, Ihavepreferred tokeeptheupperlimit.
The count rates were then dereddened and converted into physical units (c.g.s.) by means
of WebPIMMS(6), having frozen the N to the Galactic value ([62]) and the photon index of the
H
power-lawmodelto2.
2http://sundog.stsci.edu/index.html
3http://www.sdss.org/
4AS0typewouldbefainter.See[96].
5http://www.xray.mpe.mpg.de/cgi-bin/rosat/rosat-survey
6http://heasarc.gsfc.nasa.gov/Tools/w3pimms.html
4
RelativisticjetsinNLS1 LuigiFoschini
Name RA Dec err(dist) F0.1−100GeV G TS |t| S/N
1H0323+342 51.25 +34.20 0.12(0.07) 6.0 0.7 2.87 0.09 164 <2.7 4.0
± ±
SBS0846+513 132.45 +51.19 0.11(0.05) 0.51 0.15 2.0 0.1 52 12 8 4.7
± ± ±
PMNJ0948+0022 147.253 +0.385 0.07(0.02) 13.7 0.7 2.85 0.04 1081 <0.8 5.4
± ±
FBQSJ1102+2239 165.70 +22.63 0.37(0.10) 2.0 0.6 3.1 0.2 32 25 12 2.9
± ± ±
SDSSJ124634.65+023809.0 191.83 +2.53 0.47(0.21) 1.7 0.7 3.1 0.3 15 32 15 2.1
± ± ±
PKS1502+036 226.257 +3.457 0.05(0.02) 7.0 0.6 2.71 0.07 411 1.3 0.5 6.6
± ± ±
PKS2004 447 302.002 44.504 0.08(0.07) 1.2 0.3 2.3 0.1 44 6.2 1.7 12
− − ± ± ±
Table 1: SummaryofFermi/LATdetectionsofg -NLS1sbasedon30monthsofdata. Thenewdetections
areemphasizedinitalic.Thecolumns“RA”and“Dec”(J2000)indicatethepositionoftheg -raysource.The
column“err(dist)”istheerrorat95%confidencelevel[deg]and,betweenparentheses,thereisthedistance P
[deg]oftheg -raycentroidfromtheradiocoordinates. Thethreefollowingcolumnsindicate–respectively
o
– the integrated g -ray flux in the 0.1 100 GeV energy band [10 8 ph cm 2 s 1], the photon index of
− − −
the power-lawmodelusedto fittheg −photons,andtheteststatistic (TS,see [78]forits definition),where S
√TS s .Thetwolatestcolumns,t andS/N,displaythecharacteristictimescale[days]ofdoubling/halving (
∼
fluxandthesignificanceofthefluxchange[s ],respectively.
N
L
3.4 g -raydata S
1
I have retrieved all the publicly available data of the Large Area Telescope (LAT, [9]) on-
)
board Fermiincluded intheperiod2008August500:00UTCto2011February200:00UTC,i.e.
0
about 30 months of data (7). The analysis was performed by using the LAT Science Tools
v. 9.18.6and the corresponding background and instrument response files (8). The adopted 2
techniques arequitestandard andaredescribed withmoredetailsinotherpapers(e.g. [1,3,4]). 4
First, I have searched for new detections by integrating all the 30 months of data. To take
into account the possible contaminating sources inside the 10 radius of interest centered on the
◦
NLS1under examination, Istarted modeling the sources in the firstFermi catalog [5]. If, after an
inspection of the results of the first analysis run, I found some new contaminating sources, then I
added them tothe listofmodeled sources andrepeated therun. Theiteration stops whennomore
newly contaminating sources were found. In addition to the confirmation of the already known
g -NLS1s[4],Ihavefoundthreenewcandidates. Theresults aresummarizedinTable1.
I have also studied the variability at g rays of these sources, by producing light curves in the
0.1 100 GeV energy band with different binnings (1, 2, and 3 days) and taking as good the bins
−
withdetectionsatlevelTS>10( 3s ). Theobtainedcurvesconsistofanumberofbinsspanning
∼
from a few points to 87 in the case of PMNJ0948+0022, the brightest g -NLS1. A few examples
oflight curves areshowninFig.2. Itisworthnoting thecaseofSBS0846+513, one ofthethree
newlydiscoveredg -NLS1sreportedinthiswork: thesourcewasdiscoveredsinceitbecameactive
during the latest months. AsIwill show also later, this means that the discovery of new g -NLS1s
ultimately depends onthestatusofactivityofthesource.
Then, I have analyzed all the lightcurves searching for flux variations greater than 3s and
calculated thecorresponding timescalet foradoubling/halving flux,definedas:
7http://fermi.gsfc.nasa.gov/cgi-bin/ssc/LAT/LATDataQuery.cgi
8http://fermi.gsfc.nasa.gov/ssc/data/analysis/
5
RelativisticjetsinNLS1 LuigiFoschini
5 PMN J0948+0022 MW 2010
1
(z=0.5846)
MW 2009
m s]−2−1 10
c
h
p
0 −7
1
[
Fg 5
P
o
0
0 200 400 600 800 1000
Time [MJD − 54683] S
(
0 PKS 1502+036
1 N
(z=0.409)
L
s]−1
m −2 S
c
ph 1
0 −7 5
[1 )
Fg
0
2
4
0 200 400 600 800 1000
Time [MJD − 54683]
0
1
8 SBS 0846+513
(z=0.5837)
s]−1
m −2 6
c
h
p
10 −7 4
[
Fg
2
0 200 400 600 800 1000
Time [MJD − 54683]
Figure 2: Examples of Fermi/LAT light curves of NLS1s (0.1 100 GeV; 1 day time bin). (top panel)
−
PMN J0948+0022wasthe firstNLS1 to bedetectedat g rays[1, 38]and wasalso the targetoftwo MW
campaignsin2009[3]and2010[39],whoseperiodsareindicatedwithdashedverticallines;(centerpanel)
PKS1502+036wasdetectedinthefirstyearofoperations[4];(bottompanel)SBS0846+513isanewly
detectedg -NLS1,becauseitbecomesactiveduringthelatestmonths.
6
RelativisticjetsinNLS1 LuigiFoschini
0 0
0 0
0 0
1 1
00 00 Radio−quiet
1 1
0948
g/s] 10 0948 g/s] 10
er er
0 44 1502 0 44
eV [1 1 1246 0846 1102 eV [1 1 1102 15008246
M M
100 0.1 2004 100 0.1 1246 2004
@ 0323 @
L n 01 L n 01 0323
n 0. n 0.
10−3 10−3 Radio−loud P
500 1000 1500 2000 0.01 0.1 1 10 100 1000 104 o
FWHM Hb [km/s] Radio loudness R
Figure 3: Sample of NLS1s: g rays vs FWHM Hb (left panel) and radio loudness (right panel). The S
detectionswith Fermi/LAT are indicated with blue filled circles. The grayarrowsindicate upper limits at
(
5s . Thegreenpointsrefertothe2009MWCampaignofPMNJ0948+0022[3]. Theredstarsareforthe
bright g -ray blazars from the list of [44, 45]. The two dashed vertical lines representthe separation zone N
betweenradio-quietandradio-loudsources. L
S
1
F(t) =2−(t−tt0) (3.1) )
F(t0) 0
Theresultsaredisplayed inTable1. Ihavereported alsothecasesofFBQSJ1102+2239 and 2
SDSS J124634.65+023809.0, although the flux variations are not significant. These are also the 4
two faintest g -NLS1s, with the poorest statistics for the moment. A better analysis will hopefully
bedoneinthefuture,ifthesources willdisplaysomeenhanced activity.
3.5 ThecaseofPMNJ0948+0022
ThecaseofPMNJ0948+0022isworthunderlining: thereareseveralobservations performed
at the time of the discovery of the g -ray emission and during the 2009 and 2010 MW Campaigns
[1, 3, 4, 39]. This offers the possibility to look at the source variations on months time scales
and isareference tounderstand howmuchag -NLS1could change itsposition along thegraphics
prepared with MW data described above. To prepare the data, I considered as reference the time
of the Swift observations, from which I can measure X-ray and optical fluxes. Fermi information
wereextractedfroma4-dayslongsubsetofLATdata,centeredontheSwiftobservation. Theradio
fluxeswereextrapolated fromtheclosestmultifrequency observations byassumingaflatspectrum
(a =0).
r
A caveat should be noted when comparing optical-to-g -ray data with radio measurements:
indeed, the production of g rays require a compact region, which in turn is also optically thick at
radiofrequencies [13]. Whentheblobexpandsasitmovesoutward,thenitbecomesoptically thin
at radio frequencies, but its g -ray production drops. Thetimelag between the fluxpeaks atg rays
andradiofrequenciesisoftheorderoftwomonthsforPMNJ0948+0022[3,39],comparablewith
the lag observed in blazars (e.g. [66]). For the sake of simplicity, I used the radio measurements
closest to the Swift observations to prepare the graphics presented here, but – as I explained – it
7
RelativisticjetsinNLS1 LuigiFoschini
0
0
0
1
0
0
1
g/s] 10 0948
r
e
4
4
V [10 1 1102 1502
Me 0846 P
0 1 1246
0 0. o
1
@ 2004 S
1 0323
Ln 0
n 0. (
N
3
−
0
1 L
S
10−6 10−5 10−4 10−3 0.01 0.1 1 10
n Ln @ 1.4 GHz [1044 erg/s] 1
Figure4: SampleofNLS1s: g raysvsradio. ThedetectionswithFermi/LATareindicatedwithbluefilled )
circles. Thegrayarrowsindicateupperlimitsat5s . Thegreenpointsrefertothe2009MWCampaignof
0
PMNJ0948+0022[3].Theredstarsareforthebrightg -rayblazarsfromthelistof[44,45].
2
4
is necessary to take into account their different origin. This caveat is relaxed when dealing with
the complete sample of NLS1s, because the observations at different wavelength have been done
during specificsurveys,whichwerenotlinkedintime.
4. Analysisofthesample
WithalltheavailabledatadescribedinthepreviousSection,Ipreparedthegraphicsdisplayed
in Fig. 3 and Figs. 4, 5, 6. I searched for correlations of n Ln at 100 MeV with its corresponding
values at 1.4 GHz, 440 nm, and 1 keV, by using the ASURV Rev. 1.2 software package [67],
which makes use of the algorithms described in detail in [35, 60]. Nothing significant wasfound.
When using only the g -ray detections, there is something interesting, particularly at optical fre-
quencies (Spearman’sr =0.82,P=0.044),but7pointsarenotsufficientforarobustcorrelation.
It is necessary to repeat the analysis when more detections will be available. When adding the 34
bright blazars, itispossible tofindsignificant correlations, butitisobviously duetotheweightof
thelattersample,wherecorrelations arealready known(e.g. [8]).
NocleartrendisvisibleintheFWHMHb oftheg -NLS1swithrespecttotheotherNLS1sof
thesample,aswellasintheradio loudness, exceptforthefactthatalltheg -NLS1sareradio-loud
(Fig. 3). The least radio-loud g -NLS1 is FBQS J1102+2239, with R=32. The source is rather
unknown, but we could expect some degree of variability in the radio loudness, as shown by the
changes ofthepointsofPMNJ0948+0022 (maximumvariationbyafactor2.6).
8
RelativisticjetsinNLS1 LuigiFoschini
0
0
0
1
0
0
1
s] 0 0948
g/ 1
r
e
44 1502
0
1 1
V [ 1102
e P
M 0846
00 0.1 2004 1246 o
1
@
S
1 0323
Ln 0
n 0. (
N
3
−
0
1 L
S
0.1 1 10 100
n Ln @ 440 nm [1044 erg/s] 1
Figure5: SampleofNLS1s:g raysvsoptical.ThedetectionswithFermi/LATareindicatedwithbluefilled )
circles. Thegrayarrowsindicateupperlimitsat5s . Thegreenpointsrefertothe2009MWCampaignof
0
PMNJ0948+0022[3].Theredstarsareforthebrightg -rayblazarsfromthelistof[44,45].
2
4
Quantities NLS1s Blazars+NLS1s
Kendall Spearman Kendall Spearman
Z P r P Z P r P
L100MeVvsL1.4GHz 3.5 5×10−4 0.59 <10−4 9.2 <10−4 0.86 <10−4
L100MeVvsL440nm 1.2 0.23 0.30 9×10−3 8.2 <10−4 0.75 <10−4
L100MeVvsL1keV 1.9 0.052 0.27 0.02 9.1 <10−4 0.76 <10−4
L100MeVvsRL 3.4 8×10−4 0.49 <10−4 8.5 <10−4 0.81 <10−4
Table 2: Summaryofthecorrelationanalysis. ThenumberofpointsfortheNLS1ssampleis76,with69
upperlimitsatg raysand28upperlimitsatX-rays. ThenumberofpointsoftheBlazars+NLS1ssample
is110,withthesamenumberofupperlimits. Pisthechanceprobability.
Among the faintest radio sources, 1H 0323+342 is the closest g -NLS1, so in this case the
low radio luminosity is compensated by the proximity of the source. Indeed, its flux density
is not negligible ( 600 mJy; see Table A1). The two other sources, FBQS J1102+2239 and
∼
SDSSJ124634.65+023809.0, arefarther, withz=0.455 and 0.362, respectively. Theirfluxesare
weak: 2and 38mJy,respectively (seeTableA1),sothereissomedoubt thattheg -raydetec-
∼ ∼
tion couldbeduetochance coincidence(9). Thesesources areanywayradio-loud, clearly because
they are much more faint at optical frequencies. It is worth noting a bright Fermi blazar close to
the position of SDSS J124634.65+023809.0 in the g -ray vs radio loudness graphic (Fig. 3, right
panel), which isOX+169 (z=0.21), although in term of radio power the difference between the
9SDSSJ124634.65+023809.0isalsotheweakestdetectionatg-rayswithTS=15,i.e. 4s .SeeTable1.
∼
9
RelativisticjetsinNLS1 LuigiFoschini
0
0
0
1
0
0
1
s] 0 0948
g/ 1
r
e
44 1502 (S) 1502
0
1 1
V [ 1102
e P
M 1246 0846
0 1
0 0. o
1
@ 2004 S
1
nLn 0.0 0323 (
N
3
−
0
1 L
S
10−3 0.01 0.1 1 10 100 1000
n Ln @ 1 keV [1044 erg/s] 1
Figure6: SampleofNLS1s:g raysvsX-rays.ThedetectionswithFermi/LATareindicatedwithbluefilled )
circles. Thegrayarrowsindicateupperlimitsat5s . Thegreenpointsrefertothe2009MWCampaignof
0
PMNJ0948+0022[3].Theredstarsareforthebrightg -rayblazarsfromthelistof[44,45].Ifthesourceis
notdetectedbyROSAT,thenitisreportedthe3s upperlimit. ThesourcesnotdetectedbothbyROSATand 2
Fermiare indicatedwithlightgrayarrows, whilethe sourcesdetectedby Fermi, butnotby ROSAT are in 4
lightblue.InthecaseofPKS1502+036,thedetectionwithSwift[4]isindicatedwithanopenbluecircle.
twoisaboutoneorderofmagnitude(seeFig.4). Thereareotherblazarswithsuchlowradiofluxes,
at mJy level [74], some of them detected at high-energy g rays [5]. Therefore, although the radio
fluxesofthetwoNLS1sarelow,itisnotunlikelythattheycangeneratehigh-energy photons, asit
happens forblazarswithcomparable fluxes.
Itriedtoestimatethebrightnesstemperature,byusingboththeapproachesbasedonthespec-
tral characteristics [90] and the variability at radio frequencies [100]. In the latter case, there are
twomeasurementsdonebytheFIRST[11]andbytheNRAOVLASkySurvey(NVSS,[25]),which
weredonewithafewyearsoftimeseparation. InthecaseofFBQSJ1102+2239,thereisachange
of about 67% between the measurement performed during the NVSS (1993 Dec 6, 2.7 0.5 mJy)
±
and FIRST(1996 Jan, 1.8 0.1mJy), which results inanestimation ofthe brightness temperature
±
of 1011 K.Instead, SDSSJ124634.65+023809.0 does not show evident indications ofvariabil-
∼
ity, although thetwomeasurements weredoneonmuchlarger timescale (NVSS,36 1mJy,1995
±
Feb 27; FIRST, 38 1 mJy, 1998 July). The brightness temperature is then 5 1010 K. The
± ∼ ×
estimation following[90]andassumingaratherflatspectralindexofa =0.1,givesatemperature
of 7 1010 K in both cases, which is comparable with the values obtained with the variability.
∼ ×
This value obviously increases to exceed 1011 K if the spectral index becomes inverted. These
temperatures are not outstandingly indicative of beamed non-thermal emission, but there is any-
10