X-Raying the MOJAVE Sample of Compact Extragalactic Radio Jets
X-Raying the MOJAVE Sample of Compact Extragalactic
Radio Jets
M. Kadler∗,†, G. Sato∗, J. Tueller∗, R. M. Sambruna∗, C. B. Markwardt∗,
P. Giommi∗∗ and N. Gehrels∗
∗Astrophysics Science Division, NASA’s Goddard Space Flight Center, Greenbelt, MD 20771, USA
†NASA Postdoctoral Research Associate
∗∗ASI Science Data Center, ESRIN, I-00044 Frascati, Italy
Abstract. The MOJAVE sample is the first large radio-selected, VLBI-monitored AGN sample for which complete X-ray
spectral information is being gathered. We report on the status of Swift survey observations which complement the available
archival X-ray data at 0.3-10 keV and in the UV with its XRT and UVOT instruments. Many of these 133 radio-brightest
AGN in the northern sky are now being observed for the first time at these energies. These and complementary other multi-
wavelength observations provide a large statistical sample of radio-selected AGN whose spectral energy distributions are
measured from radio to gamma-ray wavelengths, available at the beginning of GLAST operations in 2008. Here, we report
the X-ray spectral characteristics of 36 of these previously unobserved MOJAVE sources. In addition, the number of MOJAVE
sources detected by the BAT instrument in the hard X-ray band is growing: we report the detection of five new blazars with
Keywords: galaxies: active — galaxies: jets — galaxies: individual (NRAO 140, PKS B 1222+216, PKS B 1510−089, 3C 345, PKS
B 2126−158)
PACS: 95.85.Bh, 95.85.Nv, 95.85.Pw, 98.54.Cm
X-RAY OBSERVATIONS OF MOJAVE AND RELEVANCE FOR GLAST
Radio-loud core-dominated (RLCDs) active galactic nuclei (AGN) are an important class of extragalactic supermassive
black-hole systems whose bright compact radio cores can be imaged at milliarcsecond resolution with Very-Long-
Baseline Interferometry (VLBI). The vast majority of all RLCDs are blazars, BL Lac objects and flat-spectrum
radio quasars, but also some Seyfert and broad-line radio galaxies exhibit bright compact radio cores with powerful
relativistic jets. Since 1994, the VLBA 2 cm Survey [1] and its follow-up MOJAVE ([4], and Lister 2007, these
proceedings) have been monitoring the structural changes in the jets of more than 200 AGN with bright compact
radio cores. At present, the MOJAVE monitoring regularly observes 192 objects, including a flux-density limited,
radio-selected, statistically complete sub sample of the 133 radio-brightest compact extragalactic jets in the northern
sky: the MOJAVE sample1.
Compact radio jets of blazars, typically show ejections of relativistic plasma every few months to years related to
the formation of new jet component that travel at superluminal speeds of up to ∼ 30 c down the jet. On the other hand,
blazars are known to be bright and rapidly variable gamma-ray sources. The connection of jet-formation events to
the broadband-SED variability of blazars is an important aspect of both the MOJAVE and GLAST project and calls
for multi-wavelength coordination with other large surveys at intermediate observing wavelengths. In order to be able
to react swiftly to gamma-ray flares detected by GLAST, to plan and coordinate multiwavelength observations, it is
important to gather broadband SED information about the objects of interest in advance to the arrival of first GLAST
data. In our case of a radio-selected AGN sample that is continuously monitored with VLBI and single-dish telescopes
(see Fuhrmann et al., these proceedings), Swift with its optical/UV (UVOT) and X-ray (XRT) capabilities, is ideally
suited to provide these SED data to connect the radio and gamma-ray bands.
1 See the program website for a detailed description of the selection criteria and a regularly updated list of the full sample:
http://www.physics.purdue.edu/astro/MOJAVE/
http://arxiv.org/abs/0704.1465v1
http://www.physics.purdue.edu/astro/MOJAVE/
Swift X-Ray Survey of the MOJAVE Sample
An archival X-ray spectral survey of all publicly available data for MOJAVE sources has been conducted by [2].
This so-called 2cm-X-Sample currently contains 50 out of 133 MOJAVE sources. 17 additional sources have been
observed by Swift before the beginning of our project. This still leaves us with 66 of the radio brightest blazars in the
northern sky having never been observed with an X-ray spectroscopic mission above 2 keV.
We have started a program to observe all the so-far unobserved MOJAVE sources with the Swift XRT as part of the
Swift blazar key project. This will produce the first statistically complete large radio-selected sample of blazars and
other RLCDs. The observations will complete the data base of the 2 cm-X-Sample of photon indices, source-intrinsic
absorbing column densities and X-ray luminosities. It will allow for the first time statistically robust radio/X-ray
correlation analyses of these quantities with relativistic jet parameters from VLBI observations. In addition, because
of the ongoing MOJAVE monitoring observations, the Swift data will naturally yield to an unprecedented set of quasi-
simultaneous broadband SED data from the radio, optical/UV and X-ray regime.
New X-ray spectra for 36 MOJAVE sources:. Our program started in November 2006. At the time of writing
(March 2007), 94 objects have been observed. We concentrate here on completed observations (i.e., >∼ 10 ksec) of
sources from the statistically complete MOJAVE sample of the 133 radio-brightest, compact AGN in the northern sky.
The XRT data were acquired mainly in Photon Counting (PC) mode. We used the program XSELECT to extract
source and background counts from the cleaned event lists processed at Swift Science Data Center (SDC). The source
spectrum is calculated from a circular region with the radius of 47 arcsec, while the background region is selected as
an annulus of the outer radius of 150 arcsec and the inner radius of 70 arcsec. A pile-up correction is applied when the
count rate exceeds 0.6 counts/s by excluding the central area of 7 arcsec radius. RLCDs are found to have comparably
simple X-ray spectra, typically well-approximated by an absorbed power law. Therefore, we performed a spectral fit to
the time-averaged spectra with an absorbed power-law model. As of March 2007, we have completed the observations
of 36 out of 66 previously unobserved MOJAVE sources. In Table 1, we report for the first time the basic X-ray spectral
characteristics of these objects in the (0.3− 10)keV band. Errors quoted are at the 90% confidence level.
All 36 objects have been detected with the XRT in 10 ksec exposures. In some cases of either very low X-ray flux
or peculiar spectral or temporal source behavior, we have obtained follow-up observations to improve the photon
statistics or to trace source variability over a longer time range. We find an average value of Γave = 1.8, with a standard
deviation of 0.2 similar to values of ∼ 1.6–1.7, which are typically found in the old 2 cm-X-Sample ([2] and in prep.).
The absorbing column densities determined have been compared to the expected Galactic absorption values from the
LAB survey [3]. Significant excess absorption was found in 9 sources (< 1021 cm−2 in all cases; compare Table 1).
New hard X-ray detections of five blazars with BAT:. The Burst Alert Telescope (BAT) is the hard X-ray instru-
ment on-board Swift and is a continuously operating all-sky hard X-ray monitor and survey instrument [5]. Prior to the
beginning of our program, 17 blazars were detected by BAT (Tueller et al., in prep.). These sources were found via
“blind search” of the whole sky, using a sliding-cell detection method (BATCELLDETECT), requiring at least ∼ 5σ sig-
nificance of each individual source. We have conducted a search of the BAT data base, based on the first nine months of
observations, aiming for those MOJAVE sources for which our Swift XRT fill-in observations did yield an extrapolated
(14− 195)keV flux above or close to ∼ 10−11 erg s−1 cm−2. This criterion was met for 19 objects which we assign a
ranking number, according to the value of the extrapolated flux (rank 1 for the highest to rank 19 for the lowest extrap-
olated flux). We found significant excess flux at the positions of five blazars: NRAO 140 (Rank 1, Fextrapol. = 4.73×
10−11 erg s−1 cm−2, 5.1σ ), PKS B 1510−089 (Rank 2, Fextrapol.= 3.68×10−11 erg s−1 cm−2, 4.0σ ), PKS B 2126−158
(Rank 3, Fextrapol. = 3.40× 10
−11 erg s−1 cm−2, 3.4σ ), 3C 345 (Rank 6, Fextrapol. = 2.61× 10−11 erg s−1 cm−2, 3.7σ ),
and PKS B 1222+216 (Rank 19, Fextrapol. = 9.36 × 10
−12 erg s−1 cm−2, 3.8σ ). A deeper analysis of the hard X-
ray properties of these blazars is currently being performed. Tentative signals (. 3σ ) are found at the position
of the 5th-ranked source PKS B 1127−145, the 10th-ranked source PKS B 0403−132, and the 16th-ranked source
PKS B 2008−159.
The rank distribution demonstrates that our method preferentially picks up those blazars that are just below the BAT
detection threshold of a few times 10−11 erg s−1 cm−2. The fact that a significant signal is registered at the position
of the relatively faint source PKS B 1222+216 but not from comparably bright objects like the 4th-ranked source
PKS B 0723−08 suggests that X-ray variability and spectral breaks above 10 keV may play an important role. We
expect to detect more MOJAVE sources with BAT in the future, in particular with increased sensitivity in later stages
of the BAT mission.
TABLE 1. X-ray spectral fitting parameter of MOJAVE sources
Source
IAU B 1950
Exposure
[ksec]
Photon
Index
[1022 cm−2]
NH,Gal
[1022 cm−2]
χ2red/dof F(0.3−10)keV
[erg s−1 cm−2]
0016+731 8950 1.75+0.23
−0.21 0.25
+0.08
−0.07 0.19 0.59/22 3.30×10
0202+149 8983 1.92+1.43
−1.02 < 0.65 0.05 0.74/3 3.04×10
0224+671 4C +67.05 12112 1.89+0.39
−0.34 0.58
+0.25
−0.19 0.40 0.44/9 1.23×10
0336−019 CTA 26 10653 1.94+0.31
−0.27 0.08
+0.07
−0.06 0.06 1.27/11 1.17×10
0403−132 9503 1.56+0.14
−0.13 0.06
+0.04
−0.03 0.04 0.78/37 5.02×10
0529+075 19537 1.86+0.19
−0.18 0.30
+0.19
−0.18 0.17 1.36/31 1.92×10
0529+483 9124 1.28+0.79
−0.63 < 0.37 0.25 0.87/2 9.21×10
1124−186 9515 1.99+0.45
−0.36 0.07
+0.08
−0.06 0.04 1.26/8 9.71×10
1150+812 11244 1.74+0.45
−0.39 < 0.07 0.05 1.24/6 8.48×10
1324+224 13330 1.78+0.19
−0.17 0.07
+0.05
−0.04 0.02 0.86/24 2.01×10
1417+385 11730 2.11+0.52
−0.41 0.08
+0.10
−0.07 0.01 0.46/5 5.56×10
1504−167 12571 1.80+0.70
−0.54 < 0.22 0.07 0.64/7 3.34×10
1538+149 4C +14.60 9527 2.28+0.49
−0.40 0.12
+0.09
−0.07 0.03 0.60/11 1.17×10
1546+027 9657 1.76+0.17
−0.16 0.07
+0.04
−0.04 0.07 1.03/31 3.45×10
1606+106 4C +10.45 49342 1.43+0.10
−0.09 0.04
+0.02
−0.02 0.04 0.93/73 1.92×10
1611+343 DA 406 9789 1.77+0.34
−0.27 < 0.11 0.01 0.74/9 1.18×10
1637+574 10140 1.91+0.14
−0.13 0.05
+0.03
−0.03 0.01 0.90/40 3.95×10
1638+398 NRAO 512 12267 1.49+0.29
−0.23 < 0.04 0.01 1.17/5 7.58×10
1726+455 10722 2.04+0.36
−0.31 0.15
+0.08
−0.07 0.02 1.23/12 1.20×10
1730−130 NRAO 530 9912 1.46+0.32
−0.29 0.29
+0.14
−0.11 0.18 0.98/12 2.18×10
1739+522 4C +51.37 10304 1.55+0.23
−0.20 0.07
+0.06
−0.05 0.03 0.72/18 2.30×10
1741−038 9927 1.72+0.34
−0.31 0.41
+0.18
−0.14 0.18 0.72/12 2.01×10
1751+288 9772 1.77+0.45
−0.39 0.12
+0.11
−0.09 0.05 0.83/7 1.10×10
1758+388 9711 2.14+1.30
−0.90 < 0.38 0.03 0.70/4 2.84×10
1800+440 10098 1.75+0.17
−0.16 0.04
+0.03
−0.03 0.03 0.98/31 3.36×10
1849+670 9952 2.07+0.31
−0.28 0.17
+0.08
−0.07 0.05 1.65/16 1.71×10
1936−155 9929 2.25+0.60
−0.49 0.24
+0.17
−0.12 0.08 0.50/5 7.15×10
1958−179 8997 1.84+0.29
−0.27 0.16
+0.09
−0.07 0.07 0.90/14 1.95×10
2005+403 11986 1.69+0.29
−0.27 0.50
+0.19
−0.15 0.48 0.88/15 1.98×10
2008−159 9657 1.75+0.13
−0.12 0.14
+0.04
−0.03 0.06 1.08/48 5.71×10
2021+317 4C +31.56 28861 1.96+1.04
−0.65 1.21
+0.95
−0.76 0.52 1.98/4 3.24×10
2021+614 17562 0.87+1.26
−0.88 < 2.01 0.14 0.51/3 2.14×10
2037+511 3C 418 10189 1.70+0.45
−0.38 0.66
+0.37
−0.25 0.54 0.91/11 2.02×10
2136+141 OX 161 10140 1.43+0.28
−0.25 < 0.15 0.06 0.48/11 1.67×10
2201+171 9585 1.85+0.34
−0.30 0.10
+0.09
−0.07 0.05 0.89/7 9.80×10
2216−038 9650 1.82+0.33
−0.29 0.07
+0.08
−0.06 0.06 1.16/12 1.53×10
ACKNOWLEDGMENTS
The authors wish to acknowledge the efforts and contributions of the Swift BAT and MOJAVE teams.
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	X-Ray Observations of MOJAVE and Relevance for GLAST
	Swift X-Ray Survey of the MOJAVE Sample
