A multifrequency study of possible relic lobes in giant radio sources

1 MB·English

by  Sagar Godambe

Mon.Not.R.Astron.Soc.000,1–??() Printed24January2009 (MNLATEXstylefilev1.4)
A multifrequency study of possible relic lobes in giant
radio sources
⋆
Sagar Godambe1,2 , C. Konar3, D.J. Saikia1 and Paul J. Wiita4,5
1 National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Post Bag 3, Ganeshkhind, Pune 411007, India
9 2 Department of Physics, The University of Utah, Salt Lake City,UT 84112-0830, USA
0 3 Inter-UniversityCentre for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune 411007, India
0 4 Department of Physics and Astronomy, Georgia State University, PO Box 4106, Atlanta, Georgia 30302-4106, USA
2 5 School of Natural Sciences, Institute for Advanced Study, Princeton, NewJersey, 08540, USA

n
a
J
Accepted. Received
4
2

ABSTRACT
]
O We present low-frequency observations with the Giant Metrewave Radio Tele-
scope (GMRT) of three giant radio sources (GRSs, J0139+3957, J0200+4049 and
C
J0807+7400) with relaxed diffuse lobes which show no hotspots and no evidence of
.
h jets. The largest of these three, J0200+4049, exhibits a depression in the centre of
p the western lobe, while J0139+3957 and J0807+7400 have been suggested earlier by
- Klein et al. and Lara et al. respectively to be relic radio sources. We estimate the
o
ages of the lobes. We also present Very Large Array (VLA) observations of the core
r
t of J0807+7400, and determine the core radio spectra for all three sources. Although
s
a theradiocoressuggestthatthesourcesarecurrentlyactive,weexplorethepossibility
[ that the lobes in these sources are due to an earlier cycle of activity.

1 Key words: galaxies: active – galaxies: individual (J0139+3957, J0200+4049 and
v J0807+7400)– galaxies: nuclei – radio continuum: galaxies
6
3
8
3
1. 1 INTRODUCTION Telescope (GMRT)andtheVeryLargeArray(VLA),Jam-
0 rozyetal.(2008)haveestimatedtheirmedianagetobe∼20
Giant radio sources (GRSs) are defined to be those which
09 haveaprojectedlinearsize>∼1Mpc(Ho=71kms−1Mpc−1, Mlikyerlywthoilbeethaeliorwmeredliimanitssizinecies∼th1e3r0a0dkiopce.mTishseiosnpeicstorfatleangneoist
Ω =0.27,Ω =0.73, Spergeletal.2003), andprovideuse-
: m vac seen all theway to the nuclear region, and there could also
v ful insights towards understanding the late stages of evolu-
be re-acceleration of particles in the lobes. For the smaller
i tion of radio sources and probing the external environment
X sourcesalargenumberofstudiesofspectralageshavebeen
onMpcscalesatdifferentredshifts(e.g.Gopal-Krishna,Wi-
r made.Forexample,forasampleof3CRsourceswithame-
a ita & Saripalli 1989; Subrahmanyan & Saripalli 1993; Sub- dian size of 342 kpc studied by Leahy, Muxlow & Stephens
rahmanyan, Saripalli & Hunstead 1996; Mack et al. 1998;
(1989) using the Multi-Element Radio Linked Interferome-
Ishwara-Chandra & Saikia 1999; Kaiser & Alexander 1999;
ter Network (MERLIN) at 151 MHz and the VLA at 1500
Blundell, Rawlings & Willott 1999 and references therein;
MHz, thespectral age was found tohavea median valueof
Schoenmakers et al. 2000, 2001; Konar et al. 2004, 2008;
∼8Myr.Similargradientsinspectralindexacrossthelobes
Machalski et al. 2007, 2008; Jamrozy et al. 2008).
havealsobeenseeninsmallersourcessuchasthosestudied
There havebeen many attempts to determine theages
by Liu, Pooley & Riley (1992) which have a median linear
of double-lobed radio sources including the GRSs. Most
size of 103 kpc and a median age of ∼1.7 Myr. There is a
lobes of GRSs exhibit a steepening in spectral index from
cleartrendforthespectralagetoincreasewithsize,whichis
the outer peaks towards the nuclear region, allowing an es-
broadlyconsistentwiththeexpectationsofdynamicalmod-
timate of the spectral age, similar to what has been done
els of the propagation of jets in an external medium (e.g.
for double-lobed radio sources of smaller dimensions. For a
Falle1991;Kaiser&Alexander1997;Jeyakumaretal.2005
sample of GRSs observed with the Giant Metrewave Radio
and references therein).
In the course of our study of GRSs, a number of these
⋆ E-mail: [email protected] objects appeared to have diffuse lobes of emission without
(SG); [email protected] (CK); [email protected] (DJS); any prominent peaks of emission towards the outer edges
[email protected](PJW) of the lobes. Unlike Fanaroff-Riley Class I sources, these
(cid:13)c RAS
2 Godambe et al.
3 OBSERVATIONAL RESULTS
Table 1.Observinglog
The GMRT images of the three sources, J0139+3957,
Teles- Array Obs. Sources Obs. J0200+4049 and J0807+7400, at the different frequencies
cope Conf. Freq. Date
are presented in Figs. 1, 2 and 3 respectively, while the ob-
MHz
servational parameters andsome oftheobserved properties
(1) (2) (3) (4) (5)
are presented in Table 2, which is arranged as follows. Col-
GMRT 239 J0139+3957 2007Jun02 umn 1: Name of the source; column 2: frequency of obser-
GMRT 334 J0139+3957 2005Jan28 vations in units of MHz; columns 3-5: themajor and minor
GMRT 605 J0139+3957 2007Jun02 axes of the restoring beam in arcsec and its position angle
GMRT 1287 J0139+3957 2003Aug19
(PA) in degrees; column 6: the rms noise in units of mJy
VLAa D 4841 J0139+3957 2000Jul24 beam−1;column7:theintegratedfluxdensityofthesource
GMRT 239 J0200+4049 2007Dec29
in mJy estimated byspecifying an area enclosing theentire
GMRT 333 J0200+4049 2004Dec25
source. We examined the change in flux density by speci-
GMRT 605 J0200+4049 2007Dec29
GMRT 1289 J0200+4049 2004Nov25 fying different areas and found the difference to be within
GMRT 239 J0807+7400 2005Jan07 a few per cent. The flux densities at different frequencies
GMRT 334 J0807+7400 2004Dec07 have been estimated over similar areas. Columns 8, 11 and
GMRT 605 J0807+7400 2005Jan07 14: component designation, where W, C and E denote the
GMRT 1289 J0807+7400 2005Jan17 western,coreandeasterncomponentsrespectively;columns
VLAb B 1385 J0807+7400 1995Nov19 9and10, 12and13,and15and16:thepeakandtotalflux
VLAb D 1435 J0807+7400 1993Nov01 densitiesofeachofthecomponentsinunitsofmJybeam−1
VLAb C 1685 J0807+7400 1996Feb19
and mJy respectively. The superscript g indicates that the
VLAb C 4860 J0807+7400 1996Feb19
flux densities have been estimated from a two-dimensional
a ImagepublishedbyKonaretal.(2004). Gaussian fit to thecore component.
b ArchivaldatafromtheVLA.
do not have any jets and the radio emission could be from
relic lobes. We have chosen three of these sources, namely 4 DISCUSSION AND RESULTS
J0139+3957, J0200+4049 and J0807+7400, for a detailed
The integrated flux densities of the sources from our mea-
investigation using the GMRT. Two of these, J0139+3957
surements as well as those from the literature are listed in
andJ0807+7400, havebeensuggested earlier toberelicra-
Table 3, which is self-explanatory, while some of the phys-
dio sources by Klein et al. (1995) and Lara et al. (2001)
ical properties of the sources are listed in Table 4 which is
respectively.Inthispaperwepresenttheresultsofmultifre-
arrangedasfollows.Column1:sourcename;Column2:red-
quencyobservationsofthesethreesourcesatlowfrequencies
shift;columns3and4:thelargestangularsizeinarcsecand
withtheGMRT,attempttoestimatetheirspectralagesand
the corresponding projected linear size in kpc; column 5:
explorethepossibility that theselobes might berelics from the luminosity at 1.4 GHz in logarithmic units of W Hz−1;
anearliercycleofactivity.Wealsopresentthecorefluxden-
columns 6 and 10: lobe designation where W and E denote
sities of J0807+7400 from archival VLA data, and the core
the western and eastern lobes respectively; columns 7 and
spectra of thethreesources.
11:breakfrequency,ν ,witherrorsinunitsofGHz;columns
B
8and12:magneticfield,B ,inunitsofnT;columns9and
eq
13: spectral ages of the lobes with errors in units of Myr.
For all the lobes listed in Table 2 we have fitted the
2 OBSERVATIONS AND ANALYSES
observed spectra for the Jaffe & Perola (1973, JP) model
Both the GMRT and the VLA observations were made in usingtheSYNAGEpackage(Murgia1996;Murgiaetal.1999)
the standard fashion, with each target source observation toestimatethebreakfrequencylistedincolumns7and11of
interspersed with observations of the phase calibrator. The Table 4. Since theintegrated spectra at low frequencies are
primaryfluxdensitycalibrator wasanyoneof3C48, 3C147 usually determined from a larger number of measurements
and3C286withallfluxdensitiesbeingonthescaleofBaars thanthoseoftheindividuallobesofemission,wehavefixed
et al. (1977). The total observing time on each source is a thevalueofαinj fromafittotheintegratedspectrumusing
few hours for the GMRT observations while for the VLA the SYNAGE package. However, because of the very diffuse
observations the time on source ranges up to 10 minutes. extended emission in these sources, several measurements
All the data were analysed in the standard fashion using even at low frequencies appear to have missed a significant
the NRAO AIPS package. All the data were self calibrated amountofthetotalfluxdensity.Thehighlydiscrepantmea-
to producethe best possible images. surementshavenotbeenusedinthefinalfitsforestimating
The observing log for both the GMRT and the VLA αinj, where the typical error in αinj is within about ±0.1.
observations is given in Table 1 which is arranged as fol- For a sample of GRSs studied earlier (Konar et al. 2008;
lows. Columns 1 and 2 show the name of the telescope and Jamrozy et al. 2008), the values of αinj estimated for the
the array configuration for the VLA observations; column lobeswhen possiblearesimilar, within theuncertainties, to
3 shows the frequency of the observations in MHz, while those estimated from the integrated spectra. Therefore this
columns 4 and 5 list the sources observed and the dates of procedurehasbeenadoptedforallthethreesourcesconsid-
theobservations, respectively. eredhere.Wealsoexaminedthespectralindeximagesofthe
(cid:13)c RAS,MNRAS000,1–??
A multifrequency study of possible relic lobes 3
J0139+3957 GMRT 334 MHz
J0139+3957 GMRT 239 MHz
39 59 00
39 59 00
58 30
58 30
DECLINATION (J2000) 5576 33000000 DECLINATION (J2000) 5576 33000000
00 00
55 30 55 30
01 39 45 40 35 30 25 20 15 01 39 45 40 35 30 25 20 15
RIGHT ASCENSION (J2000) RIGHT ASCENSION (J2000)
Cont peak flux = 2.1068E-01 Jy/beam Cont peak flux = 9.8188E-02 Jy/beam
Levs = 1.100E-02 * (-1, 1, 2, 4, 8, 16) Jy/beam Levs = 8.000E-03 * (-1, 1, 2, 4, 8) Jy/beam
J0139+3957 GMRT 605 MHz J0139+3957 GMRT 1287 MHz
39 59 00 39 59 00
58 30 58 30
DECLINATION (J2000) 57 300000 DECLINATION (J2000) 57 300000
56 30 56 30
00 00
55 30 55 30
01 39 45 40 35 30 25 20 15 01 39 45 40 35 30 25 20 15
RIGHT ASCENSION (J2000) RIGHT ASCENSION (J2000)
Cont peak flux = 4.1817E-02 Jy/beam Cont peak flux = 3.1963E-02 Jy/beam
Levs = 6.500E-04 * (-1, 1, 2, 4, 8, 16, 32, 64) Jy/beam Levs = 2.500E-04 * (-1, 1, 2, 4, 8, 16, 32, 64, 128) Jy/beam
Figure 1. GMRT images of J0139+3957 at 239, 334, 605 and 1287 MHz. The image at 1287 MHz has been reproduced from Konar
et al. (2004). In this figure as well as in all the other images of the sources, the peak brightness and the contour levels in units of Jy
beam−1 aregivenbeloweachimage.Inalltheimagestherestoringbeamsareindicatedbyellipses;thevaluesarethoselistedinTable
2unlessmentionedotherwiseinthecaption. The+signindicatesthepositionoftheopticalhostgalaxy.
Table 2.Theobservational parametersandobservedpropertiesofthesourcesfromtheGMRTimages.
Source Freq. Beamsize rms SI Cp Sp St Cp Sp St Cp Sp St
MHz ′′ ′′ ◦ mJy mJy mJy mJy mJy mJy mJy mJy
/b /b /b /b
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16)
J0139+3957 239 14.3 12.9 278 2.85 6415 W 211 3609 E 143 2728
334 13.9 8.6 308 2.58 5434 W 103 3403 E 75 2044
605 6.3 4.9 74 0.16 2643 W 42 1445 Cg 38 74 E 42 1249
1287 6.2 3.8 37 0.05 1201 W 4.5 600 Cg 34 35 E 10 579
J0200+4049 239 20.5 12.6 58 0.83 9129 W 25 4788 E 25 4543
333 10.2 8.2 68 0.28 10000 W 8.4 5028 Cg 9.5 14.8 E 8.1 5183
605 5.4 5.3 88 0.13 5014 W 2.3 2733 Cg 8.4 9.6 E 2.5 2384
1289 3.7 2.5 316 0.12 C 6.4 8.9
J0807+7400 239 41.8 32.0 312 1.5 929 W 74 404 E 80 557
334 13.2 9.5 63 0.32 937 W 6.2 396 Cg 40 45 E 8.8 493
605 7.0 5.7 346 0.08 433 W 14 192 Cg 19 22 E 20 238
1289 9.6 9.3 83 0.05 169 W 11 81 Cg 8.5 11.6 E 7.4 87
C:Valuesofcorefluxdensitieslistedherehavebeenestimatedfromimageswiththeresolutionsgivenhere.Estimatesbymappingwith
aloweruv-cutoffarelistedlater,alongwithvaluesfromthe literature.
(cid:13)c RAS,MNRAS000,1–??
4 Godambe et al.
J0200+4049 GMRT 333 MHz
0 5 10
40 54
52
)
0
0 50
0
2
J
(
N
O
TI 48
A
N
LI
C
E 46
D
44
42
02 01 00 00 45 30 15 00 01 59 45
RIGHT ASCENSION (J2000)
Cont peak flux = 1.0118E-02 Jy/beam
Levs = 1.100E-03 * (-1, 1, 2, 4, 8, 16) Jy/beam
J0200+4049 GMRT 605 MHZ
J0200+4049 GMRT 239 MHz
40 54
40 54
52
52
N (J2000) 50 ON (J2000) 50
TIO 48 ATI 48
A N
LIN CLI
C E
DE 46 D 46
44 44
42 42
02 01 00 00 45 30 15 00 01 59 45 02 01 00 00 45 30 15 00 01 59 45
RIGHT ASCENSION (J2000) RIGHT ASCENSION (J2000)
Cont peak flux = 1.5548E-01 Jy/beam Cont peak flux = 2.3373E-02 Jy/beam
Levs = 2.500E-02 * (-1, 1, 2, 4, 8, 16) Jy/beam Levs = 2.000E-03 * (-1, 1, 2, 4, 8, 16) Jy/beam
Figure 2. GMRT imageof J0200+4049 at 333 MHzis showninthe upper panel. The 239-MHzimageconvolved to aresolution of 45
arcsec,andthe605-MHzimageconvolved totheresolutionof the333-MHzimageareshowninthelowerpanels.
(cid:13)c RAS,MNRAS000,1–??
A multifrequency study of possible relic lobes 5
J0807+7400 GMRT 239 MHz
74 02 30
0) 00
0
0
J2 01 30
N (
TIO 00
A
N 00 30
LI
C
E 00
D
73 59 30
00
08 08 15 00 07 45 30 15 00 06 45 30 15 00
RIGHT ASCENSION (J2000)
Cont peak flux = 2.0759E-01 Jy/beam
Levs = 6.000E-03 * (-1, 1, 2, 4, 8) Jy/beam
J0807+7400 GMRT 334 MHz
74 02 30
0) 00
0
0
J2 01 30
N (
O 00
TI
A
N 00 30
LI
EC 00
D
73 59 30
00
08 08 15 00 07 45 30 15 00 06 45 30 15 00
RIGHT ASCENSION (J2000)
Cont peak flux = 2.2712E-01 Jy/beam
Levs = 1.200E-03 * (-1, 1, 2, 4, 8, 16, 32) Jy/beam
J0807+7400 GMRT 605 MHz
74 02 30
0) 00
0
0
J2 01 30
N (
O 00
TI
NA 00 30
LI
EC 00
D
73 59 30
00
08 08 15 00 07 45 30 15 00 06 45 30 15 00
RIGHT ASCENSION (J2000)
Cont peak flux = 1.9586E-02 Jy/beam
Levs = 3.200E-04 * (-1, 1, 2, 4, 8, 16, 32, 64) Jy/beam
J0807+7400 GMRT 1289 MHz
74 02 30
0) 00
0
0
J2 01 30
N (
O 00
TI
A
N 00 30
LI
EC 00
D
73 59 30
00
08 08 15 00 07 45 30 15 00 06 45 30 15 00
RIGHT ASCENSION (J2000)
Cont peak flux = 7.3649E-02 Jy/beam
Levs = 2.000E-04 * (-1, 1, 2, 4, 8, 16, 32, 64) Jy/beam
Figure 3.GMRTimagesofJ0807+7400 at239,334,605and1289MHz.
(cid:13)c RAS,MNRAS000,1–??
6 Godambe et al.
sources,butduetothelargediffusenatureofthelobesand
Table 3.Thetotal fluxdensities
differentuvcoveragesatdifferentfrequencies,ageestimates
Source Freq. Flux Error References using the integrated spectra of the lobes were found to be
density more reliable. While estimating αinj, the core flux density
MHz mJy mJy has been subtracted from thetotal fluxdensity.
(1) (2) (3) (4) (5) Theminimumenergymagneticfieldhasbeenestimated
by integrating the spectrum from a frequency correspond-
J0139+3957 26.3 64960 6086 9
74 17821 2673 1 ingtoaminimumLorentzfactor, γmin∼10for therelativis-
151 10800 756 10 tic electrons to an upper limit of 100 GHz, which corre-
178 4773 596 11 sponds to a Lorentz factor ranging from a few times 104
239 6415 962 P to 105 depending on the estimated magnetic field strength
325 4750 100 15 (seeHardcastleetal.2004;Crostonetal.2005;Konaretal.
334 5434 815 P 2008). Then, under assumptions that (i) the magnetic field
408 3890 195 12 strength in a given lobe is constant throughout the energy-
605 2643 264 P
loss process, (ii) the particles injected into the lobe have
1287 1201 120 P
a constant power-law energy spectrum, and (iii) the time-
1400 798 16 15
scale of isotropization of the pitch angles of the particles
1400 802 80 2
is short compared with theirradiative lifetime, thespectral
1460 1037 104 3
4841 203 20 4 age, τspec, hasbeen estimated from
4850 262 30 15
1100455500 110165 47 16,1185 τspec=50.3B2B+1/B22 {νbr(1+z)}−1/2[Myr], (1)
iC
J0200+4049 26.3 52780 6000 9 whereBiC=0.318(1+z)2isthemagneticfieldstrengthequiv-
74 5519 828 1 alent to the cosmic microwave background radiation. Here
151 12080 846 10 B,themagnetic fieldstrength of thelobes, and BiC areex-
178 2997 450 12 pressed in units of nT, ν is the spectral break frequency
br
239 9129 1369 P in GHz above which the radio spectrum steepens from the
325 2980 80 15 initial power-law spectral index,αinj, given by S∝ν−αinj.
327 4360 184 17
333 10000 1500 P
408 4390 219 3
4.1 J0139+3957
605 5014 501 P
1400 292 29 2
Thelarge-scale structureshowing therelaxed lobes(Fig. 1)
1400 220 10 17
hasbeen reportedearlier byanumberofauthors(e.g. Hine
1400 1261 126 6
1979; Vigotti et al. 1989). Klein et al. (1995) presented Ef-
1460 1359 136 3
felsberg observations of the source and suggested it to be
4850 180 27 7
4850 292 35 15 onewithpossiblereliclobesofemission.Konaretal.(2004)
4850 418 10 17 reportedGMRTandVLAobservationsat1287at4841MHz
10450 95 11 15 respectively and found that the spectral index of the entire
10550 95 2 17,18 sourcebetween1.3and4.8GHzis1.34whilethatofthecore
is0.8.InFig.4,weshowthefitstotheintegratedspectraof
J0807+7400 38 3300 900 13 theentiresourceaswellasthewesternandeasternlobesus-
151 1220 90 14
ingtheinjectionspectralindex,αinj=1.00,determinedfrom
239 929 139 P
the fit to the entire source after subtracting the core flux
334 937 141 P
density.Thespectralages forthewestern andeasternlobes
605 433 43 P
using our measurements have been found to be 12+10 and
1289 169 17 P −1
1400 155 16 2 5.3+−229.2 Myr respectively (Table 4).
1465 152 15 5 The existence of a possible steep-spectrum core was
4850 46 7 8 noted earlier (e.g. Hine 1979; Klein et al. 1995). Similar-
4850 38 6 7 resolution observationsof about 5arcsec between 1.4 and 5
GHz(Fomalont & Bridle1978; Gregorini et al.1988; Bondi
P: Present paper 1: VLA Low-frequency Sky Survey (VLSS;
et al. 1993; Klein et al. 1995) also yield a core spectral in-
http://lwa.nrl.navy.mil/VLSS; 2: NRAO VLA Sky Survey
(NVSS; Condon et al. 1998); 3: Vigotti et al. 1989; 4: Konar et dex of ∼0.8. This is consistent with the 10.6 GHz value of
al.2004; 5:Laraet al.2001; 6: White &Becker 1992; 7: Becker, 4±1 mJy (Mack et al. 1994). Saripalli et al. (1997) find the
White & Edwards 1991; 8: Gregory & Condon 1991; 9: Viner & core to be a compact source with a flux density of 20±5
Erickson 1975; 10: Hales, Baldwin & Warner 1993; 11: Pilking- mJyfrom VLBIobservationsat 1.67 GHzwitharesolution
ton & Scott 1965; 12: Gower, Scott & Wills 1967; 13: Hales et of 25 mas. The core flux densities from our low-frequency
al.1995; 14: Hales et al. 1991; 15. Schoenmakers et al. 2000; 16. measurements, byputtinga lower uvlimit tominimise any
Macketal.1994;17.Vigottietal.1999;18.Gregorinietal.1998.
contamination from extended emission, along with values
fromtheliteraturearelistedinTable5.Thespectrum(Fig.
5) shows clearly that while the high frequency spectrum is
steep, it flattensbelow about a GHz.
(cid:13)c RAS,MNRAS000,1–??
A multifrequency study of possible relic lobes 7
1000
1000
1000
100
100 100
J0139+3957: Integrated - Core J0139+3957: West Lobe J0139+3957: East Lobe
1 10 100 1000 10 100 1000 100 1000
Figure 4.Thefitstothespectraoftheentiresourceaftersubtracting thecontributionofthecore(leftpanel),western(middlepanel)
andeastern(rightpanel)lobesofJ0139+3957 usingthe SYNAGEpackage.
1000
1000
1000
100
100
J0200+4049: Integrated - Core J0200+408: West Lobe J0200+408: East Lobe
100
1 10 100 1000 10 100 1000 10 100 1000
Figure 6.The fits tothe spectra of the entire sourceafter subtracting the contribution of the core (leftpanel), as wellas the western
(middlepanel)andeastern(rightpanel)lobesofJ0200+4049 usingtheSYNAGEpackage.
100 (2004).Thelatteralsoreportthedetectionofaradiocoreat
4.8GHzwithafluxdensityof2.6mJy,andacompactcom-
ponent to the east which is coincident with a faint galaxy
seen in the Digital Sky Survey (DSS) image. Our images
mJy) (wFeisgt.er2n)lsohboew,wehviicdheniscecloefaralydseepernesisniotnhein33t3h-eMcHenztirmeaogfet.hIet
nsity ( 10 isalso seen at239 MHzwherethedataisofpoorer quality,
e
ux d and at 605 MHz which require more short-spacing data to
Fl produce a better image. The GMRT image at 1289 MHz is
not shown here since only the core and the unrelated com-
pact source to theeast (see Konar et al. 2004) were visible.
The flux density of the source appears to have been
1
1000 10000 under-estimated in the 74-MHz VLSS image and at 178
Frequency (MHz) MHz in the 4C survey, possibly due to the large extent of
Figure 5.Thespectrum oftheradiocoreofJ0139+3957. the diffuse low-brightness lobes of emission. The values at
these frequencies lie significantly below the fit to the inte-
grated spectrum (Fig. 6). For example the flux density at
178 MHz is only ∼3 Jy while it has been estimated to be
4.2 J0200+4049
approximately 12 Jy at 151 MHz. The flux density values
The double lobed structure has been imaged earlier by a at 74 and 178 MHz have not been considered in the fit to
numberofauthors(Vigottietal.1989;Gregorinietal.1988; the integrated spectrum of the source. The injection spec-
Schoenmakersetal.2000),andsomeofthediffuseemission tral index has been estimated to be0.73. The spectral ages
isalsovisibleintheNVSSimagereproducedbyKonaretal. estimated for the western and eastern lobes using our mea-
(cid:13)c RAS,MNRAS000,1–??
8 Godambe et al.
Table 4.Physicalpropertiesofthesources
Source Redshift LAS l P1.4 Cmp. νB Beq Spec. Cmp. νB Beq Spec.
age age
′′ kpc WHz−1 GHz nT Myr GHz nT Myr
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13)
J0139+3957 0.2107 370 1259 26.16 W 16+−41.13.3 0.81 12+−110 E 119+−212106 0.66 5.3+−229.2
J0200+4049 0.0827 920 1414 25.34 W 0.73+−00..0250 0.20 143+−255 E 0.64+−00..0147 0.18 151+−255
J0807+7400 0.1204 555 1190 24.76 W 5.0−+247.0.7 0.15 46+−5278 E 2.8+−51..63 0.20 64+−2247
Table 5.CorefluxdensitiesofJ0139+3957
Teles- Resolution Date Freq. S Ref.
cope ′′ MHz mJy
(1) (2) (3) (4) (5) (6)
GMRT ∼10 2007Jun02 239 39.3±6 P
GMRT ∼10 2005Jan28 334 38.3±6 P
GMRT ∼5 2007Jun02 605 41.0±4 P
GMRT ∼5 2003Aug19 1287 35.0±4 2
VLA ∼5 1982Sep 1465 33.0±3 1
Cambridge ∼5 1977Oct 2695 24.0±2 5
VLA ∼15 2000Jul24 4841 12.0±1 2
VLA 4.9 1989Jul 4885 12.0±1 4
VLA ∼2 1977Mar-May 4900 13.0±2 6
Effelsberg 69 1990−1991 10550 4.0±1 3
P:Presentpaper;1:Gregorinietal.1988; 2:Konaretal.2004;3:Macketal.1994;4:Bondietal.1993;5:Hine1979;
6:Fomalont&Bridle1978
100 4.3 J0807+7400
This source is a giant low-power radio galaxy, the weak-
est of our three GRSs. Observations at 1.4 GHz by Lara et
al. (2001) show a compact core component and a weak and
mJy) extendedhalo-likeemissionelongatedintheeast-westdirec-
ensity ( 10 toinolnywthitehcnoroeecvoidmepnocneeonftewitahservjiseitbsleo.rLhaortaspeottas.l.A(t2040.91)GsHugz-,
d
ux gested that this object could be a relic FR II radio galaxy
Fl
wherehotspotregionsarenolongerpresent.OurGMRTim-
ages at low frequenciesshow thediffuselobes and bridgeof
emission. The spectral ages of thelobes usingour measure-
mentsare46+57 and64+24 Myrforthewesternandeastern
1 −28 −27
1000 10000 lobes respectively (Table 4; Fig. 8).
Frequency (MHz)
The core has a flat spectral index at high frequencies
Figure 7.Thespectrum oftheradiocoreofJ0200+4049. but appears to have a steep radio spectrum with a spectral
index of ∼0.6 at lower frequencies (Fig. 9), possibly due to
unresolved jet/lobe structure from more recent activity.
surementsare143+25 and151+25 Myrrespectively(Table4;
−5 −5
Fig.6),whicharethelargestamongstthethreesourcesdis-
5 CONCLUDING REMARKS
cussedhere.Moreaccuratemeasurementsofthefluxdensity
at both low and high frequencies would help determine the Wehavepresentedlow-frequencyGMRTobservationsofthe
break frequency more reliably. The lobes are relaxed with lobes of emission of three giant radio sources, J0139+3957,
a depression in surface brightness in the western lobe. This J0200+4049 and J0807+7400, with diffuse lobes of emis-
clearly suggests that the lobes are no longer being fed with sion, but no hotspots and no jets from the nuclear region.
energy from thenucleus. Kleinetal.(1995)hadearliersuggestedJ0139+3957tocon-
Thecorefluxdensitiesestimatedbyimagingwithlower sist of relic lobes, while Lara et al. (2001) suggested that
uv limits to minimise contamination by extended emission J0807+7400 is a relic FRII radio source. We have tried to
arelistedinTable6.Althoughthehigh-frequencyspectrum explore this theme by examining the structure and spectra
appears to be fairly steep, with a spectral index of ∼0.8 of all three sources over a large frequency range. Although
between1289 and4841 MHz,thespectrumappearstoturn these three sources do not have hotspots, their structures
overat low frequencies (Fig. 7). are not similar to the FRI sources which are characterised
(cid:13)c RAS,MNRAS000,1–??
A multifrequency study of possible relic lobes 9
Table 6.CorefluxdensitiesofJ0200+4049
Teles- Resolution Date Freq. S Ref.
cope ′′ MHz mJy
(1) (2) (3) (4) (5) (6)
GMRT ∼11 2007Dec29 239 7.6±1.1 P
GMRT ∼7 2004Dec25 333 9.5±1.4 P
GMRT ∼5 2007Dec29 605 9.2±0.9 P
GMRT ∼3 2004Nov25 1289 7.9±0.8 P
VLA ∼12 2000Jul24 4841 2.6±0.3 1
P:Presentpaper;1:Konaretal.2004
1000
100
100
100
J0807+7400: Integrated - Core J0807+7400: West Lobe J0807+7400: East Lobe
10
10 100 1000 100 1000 100 1000
Figure 8. The fits to the spectra of the entire source after subtracting the contribution of the core (left panel) as well as the western
(middlepanel)andeastern(rightpanel)lobesofJ0807+7400 usingtheSYNAGEpackage.
100 ness towards the centre of the lobe. However, all three
have detected radio cores, two of which, J0139+3957 and
J0200+4049, have spectra which flatten at lower frequen-
cies, which could be indicative of an active core, while the
mJy) ccoiersessupgegcetsrtuinmgoufnJr0es8o0l7v+ed74e0x0teanpdpeedaersmsitsesieopn.atTlhoewdferteeqcutieonn-
nsity ( 10 of cores suggests that their nuclei are currently active. Al-
e
ux d though these sources do not belong to the classic double-
Fl double radio galaxies, about a dozen or so of which are
presentlyknown(e.g.Saikia,Konar&Kulkarni2006),these
might also represent sources with evidence of episodic nu-
clearactivity.Itwouldbeinterestingtodeterminethestruc-
1 tures of the cores from high-resolution radio observations.
1000 10000
Frequency (MHz) Therelationshipbetweentheturnoverfrequencyandsource
size for GPS objects (O’Dea 1998) shows that the source
Figure 9.Thespectrum oftheradiocoreofJ0807+7400.
sizes are ∼0.5 to 2 kpc for turnover frequencies of ∼1 and
0.4 GHz respectively (see Figs. 5 and 7). Interpreting the
coresas morerecent activity,thetimescales ofepisodic ac-
by jets that expand to form the diffuse lobes of emission. tivity would range from ∼107 to 108 yr.
Also, the luminosities of two of the three sources are above
thedividing line for these two classes of sources.
The spectral ages of the lobes estimated from SYNAGE
ACKNOWLEDGMENTS
fits to the spectra of the lobes, as well as their integrated
spectra,areintherangeof∼5×106to1.5×108yr,theupper Wethank an anonymousreferee for helpful comments. The
rangebeingclosetotimescalesforwhichthelobesarelikely Giant Metrewave Radio Telescope is a national facility op-
toremainvisibleifnotfedwithafreshsupplyofenergyfrom erated by the National Centre for Radio Astrophysics of
theparent galaxy. the Tata Institute of Fundamental Research. We thank the
The structure and spectra suggest that these lobes staffforhelpwiththeobservations.TheNationalRadioAs-
are possibly no longer being fed, with one of the lobes tronomy Observatory is a facility of the National Science
in J0200+4049 exhibiting a depression in surface bright- Foundation operated under co-operative agreement by As-
(cid:13)c RAS,MNRAS000,1–??
10 Godambe et al.
Table 7.CorefluxdensitiesofJ0807+7400
Teles- Resolution Date Freq. S Ref.
cope ′′ MHz mJy
(1) (2) (3) (4) (5) (6)
GMRT ∼13 2005Jan07 239 32.0±5 P
GMRT ∼9 2004Dec07 334 38.4±6 P
GMRT ∼5 2005Jan07 605 19.1±2 P
GMRT ∼3 2005Jan17 1289 12.5±1 P
VLA-B ∼6 1995Nov19 1385 13.4±1 P
VLA-C ∼14 1996Feb19 1685 10.9±1 P
VLA-D ∼45 1993Nov01 1435 10.5±1 P
VLA-B+C ∼12 1995Nov19 1465 14.0±1 1
1996Feb19 1465
VLA-C ∼6 1996Feb19 4860 13.5±1 P
P:Presentpaper;1:Laraetal.2001
sociated Universities Inc. We thank the VLA staff for easy Konar C., Saikia D.J., Ishwara-Chandra C.H., Kulkarni V.K.,
accesstothearchivaldatabase.Thisresearchhasmadeuse 2004,MNRAS,355,845
of the NASA/IPACextragalactic database (NED) which is KonarC.,JamrozyM.,SaikiaD.J.,MachalskiJ.,2008,MNRAS,
operated by the Jet Propulsion Laboratory, Caltech, under 383,525
LaraL.,CottonW.D.,FerettiL.,GiovanniniG.,MarcaideJ.M.,
contractwiththeNationalAeronauticsandSpaceAdminis-
Ma´rquezI.,VenturiT.,2001,A&A,370,409
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LeahyJ.P.,MuxlowT.W.B.,StephensP.W.,1989,MNRAS,239,
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401
LiuR.,PooleyG.,RileyJ.M.,1992,MNRAS,257,545
MachalskiJ.,Chyz˙yK.T.,StawarzL .,KozielD.,2007,A&A,462,
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