We have performed a multiwavelength campaign on the high red-shift FSRQ PKS 0537-286 during October - November 2006 and February 2008. The automatic optical and near-infrared telescope (REM) and the Gamma-Ray Burst Optical and Near Infrared Detector (GROND) observed the source simultaneously to X-ray and hard X-ray satellite pointings with INTEGRAL/ISGRI, Swift/XRT and RXTE that allowed covering a wide range of energies. At X-ray energies no significant variability was found. The Swift/BAT light curve over two years of survey showed a constant flux level. We find a rather flat high energy spectrum and absorption at soft X-rays in excess to the Galactic value, as previously found in other FSRQ [10][13]. We propose that these features are the signature of bulk Comptonization of soft X-ray photons

Ajello, Marco

Bottacini, Eugenio

Greiner, Jochen

Palazzi, Eliana

Pian, Elena

Rau, Arne

Yoldas, Aybüke Küpcü

Cassiani, Suzani

Repositório Institucional da UFSC

MEMORIAL DE ATIVIDADES ACADÊMICAS SUZANI CASSIANI

Caltech Authors - Main

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 Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it 
 
PKS 0537-286, the high red-shift FSRQ, giving new 
insights into the jet physics 
 
Eugenio Bottacini1, Jochen Greiner 
Max-Planck-Institut fuer extraterrestrische Physik 
Giessenbachstrasse, 85748 Garching, Germany 
E-mail: eub@mpe.mpg.de, jcg@mpe.mpg.de 
Marco Ajello 
Stanford Linear Accelerator Center/KIPAC 
2572 Sand Hill Road, Menlo Park, CA 94025 
E-mail: majello@slac.stanford.edu 
Arne Rau 
California Institute of Technology 
1200 East California Blvd, Pasadena, CA 91125 
E-mail: arne@astro.caltech.edu 
Elena Pian 
Istituto Nazionale di Astrofisica 
Via G. B. Tiepolo, 11, 34143 Trieste, Italy 
E-mail: pian@oats.inaf.it 
Aybüke Küpcü Yoldaş 
European Southern Observatory 
Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany 
E-mail: ayoldas@eso.org 
Eliana Palazzi 
Istituto Nazionale di Astrofisica 
Via Gobetti 101, 40129 Bologna, Italy 
E-mail: palazzi@iasfbo.inaf.it 
 
The 7th INTEGRAL Workshop 
Copenhagen, Denmark 
September 8– 11 2008
                                                 
1
  Speaker 
P
o
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I
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t
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8
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0
6
6
PKS 0537-286, new insights into the jet physics Eugenio Bottacini 
 
     2 
 
 
 
  We have performed a multiwavelength campaign on the high red-shift FSRQ PKS 0537-286 
during October - November 2006 and February 2008. The automatic optical and near-infrared 
telescope (REM) and the Gamma-Ray Burst Optical and Near Infrared Detector (GROND) 
observed the source simultaneously to X-ray and hard X-ray satellite pointings with 
INTEGRAL/ISGRI, Swift/XRT and RXTE that allowed covering a wide range of energies. At 
X-ray energies no significant variability was found. The Swift/BAT light curve over two years 
of survey showed a constant flux level. We find a rather flat high energy spectrum and 
absorption at soft X-rays in excess to the Galactic value, as previously found in other FSRQ 
[10][13].  We propose that these features are the signature of bulk Comptonization of soft X-ray 
photons.  
 
1. Introduction 
The spectral energy distribution (SED) of blazars is dominated by non-thermal continuum. 
The relativistic jets producing the typical two hump structure from radio to gamma-rays and 
sometimes to TeV band [11] extend over kpc scale. According to whether jets are observed 
from the side or pole-on, they give rise to radio galaxies or blazar objects [21]. Within this 
framework multiwavelength studies of blazars give a unique insight into the jet physics due to 
emission enhancement through relativistic beaming. These observations over several decades of 
energy started to be carried out more than ten years ago and lead to different emission models. 
But still the question, on how the central super massive black hole (SMBH) transfers its 
gravitational energy to the relativistic moving plasma, is asking to be solved.  
The overall blazar emission is successfully interpreted in the view of the synchrotron and  
inverse-Compton models. The first peak at lower energies is dominated by synchrotron 
radiation, while at higher energies the second component is due to inverse-Compton scattering. 
The prevailing picture of the emission mechanism foresees the emitting plasma to be 
accelerated within the jet. Cooling and acceleration of these relativistic particles leads to 
variability in the measured spectrum caused by shocks within the jet. In this scenario also the 
external components [9] to the jet, like the accretion disk surrounding the central SMBH, play a 
fundamental role, injecting external seed photons scattered by the broad line region (BLR) into 
the jet. 
The importance of high red-shift blazars is related to the evolution studies of SMBH in the 
early Universe. Indeed, their accretion rate is related to the circumnuclear environment that 
should be revealed in terms of spectral emission features in the X-ray energy band. Their high 
energy spectral properties make them suitable candidates for the recently launched FERMI 
(formerly GLAST) gamma-ray mission and thus ideal targets for further probe of gamma-ray 
horizon [19].  
The X-ray spectra of high red-shift blazars are generally hard and exhibit occasionally 
absorption in the soft energy range in excess to that due to the Galactic hydrogen column 
density [22] [24]. 
P
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I
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PKS 0537-286, new insights into the jet physics Eugenio Bottacini 
 
     3 
 
 
2. The observation campaign 
2.1 The source 
PKS 0537-286, at z = 3.104 [23], is one of the most luminous known high red-shift quasar. 
First detected at radio frequencies [5], it was observed at X-rays by the Einstein observatory 
[25] and then studied with ASCA [7] [17], ROSAT [10], XMM [14] and Swift [15]. These 
observations showed an extremely luminous quasar (Lx=10
47
 erg s
-1
 in the 0.1 – 2 keV range). A 
further characteristic is its particularly hard spectrum and a weak iron K α emission and 
reflection features. Moreover Sowards-Emmerd et al. identified PKS 0537-286 as probable 
counterpart of the EGRET source 3EG J0531-2940 [18]. 
2.2 Observations 
The source was proposed to be monitored by INTEGRAL. Due to the fact that the prior  
Swift/BAT light curve over 9 months of exposure [1] was consistent with a constant flux level, 
the INTEGRAL pointings were proposed in non-contiguous time intervals gaining an exposure 
of 1 Ms.The obervations were performed during revolutions: 0493 ,0494, 0549, 0550, 0552, 
0558. These observations were performed with a rectangular dithering pattern. By instrument 
design, only few dither pointings produced a useful JEM-X spectrum of the source being off-
axis for most of the time. The source is only marginally detected with IBIS/ISGRI [12] in the 17 
– 55 keV band. Using the detected count rate, we performed data cleaning. Most recent matrices 
available for standard software were used for spectral analysis. We used 296 science windows 
for a total amount of 981 ksec of exposure time on the source. The source is detected with 
ISGRI at a significance level of 5.6 sigma. Data screening was performed according to the 
median count rate with respect to each science window and their distribution. Due to the low 
detection level a spectrum cannot be fitted. 
The Burst-Alert Telescope (BAT, [3]) on board the Swift satellite is a coded-mask 
telescope operating in the 15 – 200 keV energy range. We selected all observations comprised 
in the time span January 2005 - March 2007. The data were processed using HEASOFT 6.3 and 
following the recipes presented in [2]. The spectrum and the light curve of PKS 0537-286 were 
extracted using the method presented in [1]. 
RXTE All Sky monitor observed PKS 0537-286 for 9.9 ksec, starting from November 1st  
2006. We reduced the data using the standard reduction script REX included in the 
HEAsoft6.0.4 package. 
The X-Ray Telescope [6] on board the Swift observed the blazar on October 27th, 30th, 
31st 2006 and February 10th, 12th 2008. The monitoring campaign was carried  out within five 
observations. Data processing, screening and filtering were done using the FTOOL xrtpipeline 
comprised in the HEASOFT 6.3 distribution.  
Simultaneously to the RXTE and Swift/XRT pointings in 2006, photometry with REM 
was performed in 5 optical energy bands (V, R, J, I, H).  
GROND observed the source  simultaneously to the Swift/XRT pointings in 2007. 
P
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I
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t
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PKS 0537-286, new insights into the jet physics Eugenio Bottacini 
 
     4 
 
 
3. X-ray and hard X-ray spectra 
For the Swift/XRT spectra, a power law with a fixed galactic absorption (2.0 x 10
20
 cm
-2
) 
yielded an unacceptable fit. Leaving the absorption value to be fitted freely a substantial 
improvement of the reduced chi-square (0.9) was obtained for each spectrum. The lower limit of 
the Nh-value is 5.3 x 10
20
 cm
-2
, that is well above the galactic value. While the spectral index 
assumes values around 1.5. The absorption parameter is in good agreement within the five 
observations and so does the spectral index.  
It is unlikely that an excess column density is in origin galactic. It would require a factor 
~3.5 of increase in the galactic column density toward the direction of the source. Also the 
intergalactic origin is highly improbable because the line of sight should intercept several 
systems having very high column density. The intrinsic absorber hypothesis is much debated. 
The best evidences for warm absorbers, like O absorption edge and Fe M-shell, are down 
shifted outside our observed range (0.3 – 10 keV), being in the rest frame’s energy band within 
0.5 - 0.9 keV.   
None of the X-ray and hard X-ray observations showed flux variability. We therefore 
fitted all the spectra simultaneously. Figure 2 (left panel) shows the joint spectrum of the 
instruments Swift/XRT, RXTE and Swift/BAT obtained during the multiwavelength campaign. 
A theoretical interpretation to the excess absorption and hard spectral index in the X-ray 
spectra is given by [8] who foresee a peaked seed photon energy distribution. The seed photons, 
arising from the innermost part of the accretion disk and entering the jet through the 
reprocessing in the BLR, are bulk comptonized in the jet. Thus the entire spectrum is the 
contribution of relativistic Compton and bulk Compton, which can be approximated by the sum 
of a power law and black body components. 
Bridging the energy gap between Swift/XRT- and Swift/BAT-data with RXTE, our data 
are very suitable for the determination of the above mentioned spectral features. Therefore we 
fitted in addition to a power law also a black body component gaining an equal good fit result 
(reduced chi-square 0.8 for 142 degrees of freedom) as previously but with better residuals. The 
f-test probability of 97.2% confirms the additional parameter. Figure 1 shows the comparison 
between residuals of the fit of  power law + black body and simple absorbed power law. The 
resulting seed photon temperature of 8.6 keV is in good agreement with the predicted one by the 
authors of the earlier mentioned paper. This high value for the temperature of the seed photons 
is not surprising since in the observer frame it is blueshifted by the bulk Lorentz-factor and the 
Doppler-factor after the scattering. 
A further model describing bulk Comptonization motion is given by [20] whose model is 
self-consistent bulk motion Comptonization rather than the sum of two components (as used 
previously). Again we obtained a good fit with reduced chi-square of 0.9 (with 141 degrees of 
freedom) by fitting the BMC-model. The seed photon temperature of 0.2 keV is in good 
agreement with the one expected, considering a geometrically thin and optically thick accretion 
disc, having surface temperature (multi-color black body) profile as in [16].  
 
P
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PKS 0537-286, new insights into the jet physics Eugenio Bottacini 
 
     5 
 
 
 
E (keV) 
Figure 1: The comparison between the residuals obtained with a power law + black body 
model (lower panel) and a simple absorbed power law model (upper panel) is shown. It is 
apparent that in the latter case the data points at energies larger than 50 keV are better fitted. 
 
The confidence contours of fitted seed photon temperature and alpha-parameter of the 
fitted BMC model are shown at confidence levels of 68%, 90% and 99% (see figure 2, right 
panel). 
 
  
Figure 2: Left panel shows the joint spectrum of the instruments Swift/XRT, RXTE and 
Swift/BAT obtained during the multiwavelength campaign. The fit to the data points is an 
absorbed powerlaw of spectral index 1.3. Right panel shows the confidence level contours at 
68%, 90% and 99% of the parameter kT (indicating the temperature of the seed photons) and 
alpha (indicating the efficiency of the Comptonization) of the BMC model [20]. 
 
4. Conclusions 
We have conducted a multifrequency campaign on PKS 0537-286 on five different 
epochs. At X-rays the source showed no flux variability. We probe the spectral flattening for the 
source and show that it is physically associated to it. We detect spectral X-ray features, related 
to bulk Comptonization scattering, predicted by [8]. Furthermore, the spectra can be fitted with 
the bulk motion comptonization model (BMC) [20] gaining a reduced chi-square of 0.9. Thus, 
we find the source's jet to be matter dominated. This finding can have an impact on 
cosmological evolution of blazars. Indeed, Boettcher and Dermer (2002) proposed a scenario 
P
o
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I
n
t
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PKS 0537-286, new insights into the jet physics Eugenio Bottacini 
 
     6 
 
 
where BL Lacs are the final stage of FSRQ [4]. As the accretion power drops with time, less gas 
and dust are left. Thus, FSRQs at high red-shift are expected to be matter dominated. 
 
References 
[1]  M. Ajello et al., 2008, ApJ, 673, 96 
[2]  M. Ajello et al., 2008b, ApJ, 678, 102 
[3]  S. D. Barthelmy et al., 2005, SSRv, 120, 143 
[4]  M.Boettcher, C.D. Dermer, 2002, ApJ, 564, 86 
[5]  J. G. Bolton et al., 1975, Aus. J. Phys. Ap. Suppl. 34, 1 
[6]  D. N. Burrows et al., 2005, SSRv., 120, 165 
[7]  M. Cappi et al., 1997, ApJ, 478, 492 
[8]  A. Celotti et al., 2007, MNRAS, 375, 417 
[9]  C.D. Dermer et al., 1992, A&A, 256, 27 
[10] F. Fiore et al., 1998, ApJ, 492, 79 
[11] G. Fossati et al., 1998, MNRAS, 299, 433 
[12] F. Lebrun et al., 2003, A&A, 411, 14 
[13] J.N. Reeves & M.J.L. Turner, 2000, MNRAS, 316, 234 
[14] J.N. Reeves et al., 2001, A&A, 365, 116 
[15] R.M. Sambruna et al., 2007, ApJ, 669, 884 
[16] N.I. Shakura & R.A. Sunyaev, 1973, A&A, 24, 337 
[17] J. Siebert et al., 1996, A&A, 307, 8 
[18] D. Sowards-Emmerdet al., 2004, ApJ, 609, 564 
[19] F. W. Stecker et al., 2006, ApJ, 648, 774 
[20] L. Titarchuk et al., 1997, ApJ, 487, 834 
[21] C.M. Urry & P. Padovani, 1995, PASP, 107, 803 
[22] M.A. Worsley et al., 2004, MNRAS, 350, 67 
[23] A.E. Wright et al., 1978, 226, 61 
[24] W. Yuan et al., 2005, MNRAS, 358, 4 
[25] G. Zamorani, et al., 1981, ApJ, 245, 357 
 


English

PKS 0537-286, the high redshift FSRQ, giving new insights into the jet physics

P
oS(Integral08)066
 
 
 
 
 Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it 
 
PKS 0537-286, the high red-shift FSRQ, giving new 
insights into the jet physics 
 
Eugenio Bottacini1, Jochen Greiner 
Max-Planck-Institut fuer extraterrestrische Physik 
Giessenbachstrasse, 85748 Garching, Germany 
E-mail: eub@mpe.mpg.de, jcg@mpe.mpg.de 
Marco Ajello 
Stanford Linear Accelerator Center/KIPAC 
2572 Sand Hill Road, Menlo Park, CA 94025 
E-mail: majello@slac.stanford.edu 
Arne Rau 
California Institute of Technology 
1200 East California Blvd, Pasadena, CA 91125 
E-mail: arne@astro.caltech.edu 
Elena Pian 
Istituto Nazionale di Astrofisica 
Via G. B. Tiepolo, 11, 34143 Trieste, Italy 
E-mail: pian@oats.inaf.it 
Aybüke Küpcü Yoldaş 
European Southern Observatory 
Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany 
E-mail: ayoldas@eso.org 
Eliana Palazzi 
Istituto Nazionale di Astrofisica 
Via Gobetti 101, 40129 Bologna, Italy 
E-mail: palazzi@iasfbo.inaf.it 
 
The 7th INTEGRAL Workshop 
Copenhagen, Denmark 
September 8– 11 2008
                                                 
1
  Speaker 
P
oS(Integral08)066
PKS 0537-286, new insights into the jet physics Eugenio Bottacini 
 
     2 
 
 
 
  We have performed a multiwavelength campaign on the high red-shift FSRQ PKS 0537-286 
during October - November 2006 and February 2008. The automatic optical and near-infrared 
telescope (REM) and the Gamma-Ray Burst Optical and Near Infrared Detector (GROND) 
observed the source simultaneously to X-ray and hard X-ray satellite pointings with 
INTEGRAL/ISGRI, Swift/XRT and RXTE that allowed covering a wide range of energies. At 
X-ray energies no significant variability was found. The Swift/BAT light curve over two years 
of survey showed a constant flux level. We find a rather flat high energy spectrum and 
absorption at soft X-rays in excess to the Galactic value, as previously found in other FSRQ 
[10][13].  We propose that these features are the signature of bulk Comptonization of soft X-ray 
photons.  
 
1. Introduction 
The spectral energy distribution (SED) of blazars is dominated by non-thermal continuum. 
The relativistic jets producing the typical two hump structure from radio to gamma-rays and 
sometimes to TeV band [11] extend over kpc scale. According to whether jets are observed 
from the side or pole-on, they give rise to radio galaxies or blazar objects [21]. Within this 
framework multiwavelength studies of blazars give a unique insight into the jet physics due to 
emission enhancement through relativistic beaming. These observations over several decades of 
energy started to be carried out more than ten years ago and lead to different emission models. 
But still the question, on how the central super massive black hole (SMBH) transfers its 
gravitational energy to the relativistic moving plasma, is asking to be solved.  
The overall blazar emission is successfully interpreted in the view of the synchrotron and  
inverse-Compton models. The first peak at lower energies is dominated by synchrotron 
radiation, while at higher energies the second component is due to inverse-Compton scattering. 
The prevailing picture of the emission mechanism foresees the emitting plasma to be 
accelerated within the jet. Cooling and acceleration of these relativistic particles leads to 
variability in the measured spectrum caused by shocks within the jet. In this scenario also the 
external components [9] to the jet, like the accretion disk surrounding the central SMBH, play a 
fundamental role, injecting external seed photons scattered by the broad line region (BLR) into 
the jet. 
The importance of high red-shift blazars is related to the evolution studies of SMBH in the 
early Universe. Indeed, their accretion rate is related to the circumnuclear environment that 
should be revealed in terms of spectral emission features in the X-ray energy band. Their high 
energy spectral properties make them suitable candidates for the recently launched FERMI 
(formerly GLAST) gamma-ray mission and thus ideal targets for further probe of gamma-ray 
horizon [19].  
The X-ray spectra of high red-shift blazars are generally hard and exhibit occasionally 
absorption in the soft energy range in excess to that due to the Galactic hydrogen column 
density [22] [24]. 
P
oS(Integral08)066
PKS 0537-286, new insights into the jet physics Eugenio Bottacini 
 
     3 
 
 
2. The observation campaign 
2.1 The source 
PKS 0537-286, at z = 3.104 [23], is one of the most luminous known high red-shift quasar. 
First detected at radio frequencies [5], it was observed at X-rays by the Einstein observatory 
[25] and then studied with ASCA [7] [17], ROSAT [10], XMM [14] and Swift [15]. These 
observations showed an extremely luminous quasar (Lx=1047 erg s-1 in the 0.1 – 2 keV range). A 
further characteristic is its particularly hard spectrum and a weak iron K α emission and 
reflection features. Moreover Sowards-Emmerd et al. identified PKS 0537-286 as probable 
counterpart of the EGRET source 3EG J0531-2940 [18]. 
2.2 Observations 
The source was proposed to be monitored by INTEGRAL. Due to the fact that the prior  
Swift/BAT light curve over 9 months of exposure [1] was consistent with a constant flux level, 
the INTEGRAL pointings were proposed in non-contiguous time intervals gaining an exposure 
of 1 Ms.The obervations were performed during revolutions: 0493 ,0494, 0549, 0550, 0552, 
0558. These observations were performed with a rectangular dithering pattern. By instrument 
design, only few dither pointings produced a useful JEM-X spectrum of the source being off-
axis for most of the time. The source is only marginally detected with IBIS/ISGRI [12] in the 17 
– 55 keV band. Using the detected count rate, we performed data cleaning. Most recent matrices 
available for standard software were used for spectral analysis. We used 296 science windows 
for a total amount of 981 ksec of exposure time on the source. The source is detected with 
ISGRI at a significance level of 5.6 sigma. Data screening was performed according to the 
median count rate with respect to each science window and their distribution. Due to the low 
detection level a spectrum cannot be fitted. 
The Burst-Alert Telescope (BAT, [3]) on board the Swift satellite is a coded-mask 
telescope operating in the 15 – 200 keV energy range. We selected all observations comprised 
in the time span January 2005 - March 2007. The data were processed using HEASOFT 6.3 and 
following the recipes presented in [2]. The spectrum and the light curve of PKS 0537-286 were 
extracted using the method presented in [1]. 
RXTE All Sky monitor observed PKS 0537-286 for 9.9 ksec, starting from November 1st  
2006. We reduced the data using the standard reduction script REX included in the 
HEAsoft6.0.4 package. 
The X-Ray Telescope [6] on board the Swift observed the blazar on October 27th, 30th, 
31st 2006 and February 10th, 12th 2008. The monitoring campaign was carried  out within five 
observations. Data processing, screening and filtering were done using the FTOOL xrtpipeline 
comprised in the HEASOFT 6.3 distribution.  
Simultaneously to the RXTE and Swift/XRT pointings in 2006, photometry with REM 
was performed in 5 optical energy bands (V, R, J, I, H).  
GROND observed the source  simultaneously to the Swift/XRT pointings in 2007. 
P
oS(Integral08)066
PKS 0537-286, new insights into the jet physics Eugenio Bottacini 
 
     4 
 
 
3. X-ray and hard X-ray spectra 
For the Swift/XRT spectra, a power law with a fixed galactic absorption (2.0 x 1020 cm-2) 
yielded an unacceptable fit. Leaving the absorption value to be fitted freely a substantial 
improvement of the reduced chi-square (0.9) was obtained for each spectrum. The lower limit of 
the Nh-value is 5.3 x 1020 cm-2, that is well above the galactic value. While the spectral index 
assumes values around 1.5. The absorption parameter is in good agreement within the five 
observations and so does the spectral index.  
It is unlikely that an excess column density is in origin galactic. It would require a factor 
~3.5 of increase in the galactic column density toward the direction of the source. Also the 
intergalactic origin is highly improbable because the line of sight should intercept several 
systems having very high column density. The intrinsic absorber hypothesis is much debated. 
The best evidences for warm absorbers, like O absorption edge and Fe M-shell, are down 
shifted outside our observed range (0.3 – 10 keV), being in the rest frame’s energy band within 
0.5 - 0.9 keV.   
None of the X-ray and hard X-ray observations showed flux variability. We therefore 
fitted all the spectra simultaneously. Figure 2 (left panel) shows the joint spectrum of the 
instruments Swift/XRT, RXTE and Swift/BAT obtained during the multiwavelength campaign. 
A theoretical interpretation to the excess absorption and hard spectral index in the X-ray 
spectra is given by [8] who foresee a peaked seed photon energy distribution. The seed photons, 
arising from the innermost part of the accretion disk and entering the jet through the 
reprocessing in the BLR, are bulk comptonized in the jet. Thus the entire spectrum is the 
contribution of relativistic Compton and bulk Compton, which can be approximated by the sum 
of a power law and black body components. 
Bridging the energy gap between Swift/XRT- and Swift/BAT-data with RXTE, our data 
are very suitable for the determination of the above mentioned spectral features. Therefore we 
fitted in addition to a power law also a black body component gaining an equal good fit result 
(reduced chi-square 0.8 for 142 degrees of freedom) as previously but with better residuals. The 
f-test probability of 97.2% confirms the additional parameter. Figure 1 shows the comparison 
between residuals of the fit of  power law + black body and simple absorbed power law. The 
resulting seed photon temperature of 8.6 keV is in good agreement with the predicted one by the 
authors of the earlier mentioned paper. This high value for the temperature of the seed photons 
is not surprising since in the observer frame it is blueshifted by the bulk Lorentz-factor and the 
Doppler-factor after the scattering. 
A further model describing bulk Comptonization motion is given by [20] whose model is 
self-consistent bulk motion Comptonization rather than the sum of two components (as used 
previously). Again we obtained a good fit with reduced chi-square of 0.9 (with 141 degrees of 
freedom) by fitting the BMC-model. The seed photon temperature of 0.2 keV is in good 
agreement with the one expected, considering a geometrically thin and optically thick accretion 
disc, having surface temperature (multi-color black body) profile as in [16].  
 
P
oS(Integral08)066
PKS 0537-286, new insights into the jet physics Eugenio Bottacini 
 
     5 
 
 
 
E (keV) 
Figure 1: The comparison between the residuals obtained with a power law + black body 
model (lower panel) and a simple absorbed power law model (upper panel) is shown. It is 
apparent that in the latter case the data points at energies larger than 50 keV are better fitted. 
 
The confidence contours of fitted seed photon temperature and alpha-parameter of the 
fitted BMC model are shown at confidence levels of 68%, 90% and 99% (see figure 2, right 
panel). 
 
 
 
Figure 2: Left panel shows the joint spectrum of the instruments Swift/XRT, RXTE and 
Swift/BAT obtained during the multiwavelength campaign. The fit to the data points is an 
absorbed powerlaw of spectral index 1.3. Right panel shows the confidence level contours at 
68%, 90% and 99% of the parameter kT (indicating the temperature of the seed photons) and 
alpha (indicating the efficiency of the Comptonization) of the BMC model [20]. 
 
4. Conclusions 
We have conducted a multifrequency campaign on PKS 0537-286 on five different 
epochs. At X-rays the source showed no flux variability. We probe the spectral flattening for the 
source and show that it is physically associated to it. We detect spectral X-ray features, related 
to bulk Comptonization scattering, predicted by [8]. Furthermore, the spectra can be fitted with 
the bulk motion comptonization model (BMC) [20] gaining a reduced chi-square of 0.9. Thus, 
we find the source's jet to be matter dominated. This finding can have an impact on 
cosmological evolution of blazars. Indeed, Boettcher and Dermer (2002) proposed a scenario 
P
oS(Integral08)066
PKS 0537-286, new insights into the jet physics Eugenio Bottacini 
 
     6 
 
 
where BL Lacs are the final stage of FSRQ [4]. As the accretion power drops with time, less gas 
and dust are left. Thus, FSRQs at high red-shift are expected to be matter dominated. 
 
References 
[1]  M. Ajello et al., 2008, ApJ, 673, 96 
[2]  M. Ajello et al., 2008b, ApJ, 678, 102 
[3]  S. D. Barthelmy et al., 2005, SSRv, 120, 143 
[4]  M.Boettcher, C.D. Dermer, 2002, ApJ, 564, 86 
[5]  J. G. Bolton et al., 1975, Aus. J. Phys. Ap. Suppl. 34, 1 
[6]  D. N. Burrows et al., 2005, SSRv., 120, 165 
[7]  M. Cappi et al., 1997, ApJ, 478, 492 
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MEMORIAL DE ATIVIDADES ACADÊMICAS SUZANI CASSIANI

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