29th International Cosmic Ray Conference Pune (2005) 00
Observation of AGNs with PACT
Bose D. , Acharya B.S. , Chitnis V. R. , Singh B.B. , Vishwanath P. R.(a) Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India
(b) Indian Institute of Astrophysics, Koramangala, Bangalore 560034, India
Presenter: Bose D. ([email protected]
We report our observations on 4 AGNs viz., Mkn 421, Mkn501, IES1426+428 and ON231 belonging to a class
of objects called blazars. The observations were carried out using the Pachmarhi Array of ˇCerenkov Telescopes
(PACT) and span about 5 year period from 2000 to 2004. We discuss our methods of analysis adopted to extract
the gamma-ray signal from cosmic-ray background. We present our results on the emission of TeV gamma
rays from these objects.
AGNs have dominated extragalactic astronomy by virtue of their great luminosities. It is generally accepted
that these AGNs are powered by black holes of mass 10 M . About 10% of all AGNs are more luminous
at radio wavelengths than at optical ones and are, hence, called radio-loud. The radio emission is believed
to originate in the associated jets which are aligned with the poles of the spinning black hole. If the jets
aim straight towards us, both the waves and the durations of outbursts are compressed by a large Doppler
factor. This greatly enhances the power we receive. Such AGNs with jets directed towards us are also called
Blazars. Blazars are characterised by two parts in their Spectral Energy Distributions (SEDs). First part in
SED rises smoothly from radio wavelengths upto a broad peak spanning the range from microwave to infrared
wavelengths and is due to relativistic electrons radiating via synchrotron process. Second part is probably due
to inverse compton scattering of synchrotron photons by the same electrons and is characterised by a peak
in SEDs in hard X-ray- -ray band. On a power plot these SEDs show a two-humped shape . One of the
characteristic features of these blazars is their time variability on scales ranging from hours to years. Blazars
are further subdivided into two classes, BL Lac and optically violent variables (OVVs). BL Lacs are also
classified into two groups, Low-frequency BL Lacs (LBLs) and High-frequency BL Lacs (HBLs). Mkn 421,
Mkn 501, 1ES1426+428, ON231 are examples of high frequency peaked BL Lac objects with -ray emission
extending upto TeV energies. They are found to be in quiescent state most of the time but occasionally they
flare up. In the flaring state often they are the brightest objects in VHE -rays. There are mainly two models
which are proposed to explain the production as well as variability of -rays in these sources. One is called
'lepton model' and the other 'hadron model' depending on the particle that is responsible for the production of
-rays. The HE and VHE -ray observations constrain both the models but do not rule either out. To further
constrain these models and also to understand the astrophysical processes in the environment of these objects
they are being observed extensively by the ground based -ray telescopes and also in other wavelengths. We
have observed these sources with PACT on several occasions. In the following sections we will present our
analysis procedure and results for the data collected on these sources from year 2000 to 2004.
2. PACT Array
Pachmarhi array of ˇCerenkov telescopes (PACT) is located at Pachmarhi in central India (latitude 22 28 N,
longitude 78 25 E, altitude 1075
) . PACT consists of 5
5 array of 25 telescopes spread over an
100m. Each telescope consists of 7 parabolic mirrors of diameter 0.9m with f/d
para-axially. Total reflector area is 4.45 m per telescope. A fast phototube (EMI9807B) of 2 in. diameter
Bose D. et al.
Observation log for Blazars
observation duration (mins.)
Mkn 421 Mkn 501 1ES1426+428
is mounted at the focus of each mirror. All the telescopes are equatorially mounted and are independently
steerable in both E-W and N-S direction within
45 . The movement of the telescopes is remotely controlled
by a low cost control system called Automated Computerized Telescope Orientation System (ACTOS). The
system can orient to the putative source from an arbitrary initial position with an accuracy of (0.003 0.2) .
The array is divided into 4 sectors with 6 telescopes in each. At the center of each sector there is a Field Signal
Processing Center (FSPC) where pulses from individual PMTs of telescopes in a sector are brought through
coaxial cables of type RG213 and processed. High voltage to PMTs are controlled through a high voltage
divider unit (C.A.E.N. model SY170) which is controlled by CAMAC based controller module (C.A.E.N.
model CY117B). A coincidence of 4 out of 6 telescopes generates the event trigger for a sector. Once an event
trigger is generated CAMAC controller initiates the data recording process. A
based PC records TDC
(timing) and QDC (photon density) information of 6 peripheral mirrors of telescopes along with other house
keeping informations for that event. In addition, information relevant to entire array is recorded in the central
Master Signal Processing Center (MSPC) in the control room at the centre of the array. PACT has energy
rays incident in the vertical direction and the corresponding collection area is
Since the year 2000 we have collected data on Mkn 421, Mkn 501, 1ES1426+428 and ON231 using PACT.
Most of these runs were taken with all 4 sectors pointing to the source direction (ON-source). On the same
night background runs (OFF-source) were taken before or after the source runs with all telescopes pointing to a
dark region (a region with same declination as that of source but offset in RA) such that zenith angle coverage
is same as source run. Some of the runs in year 2002 and in 2003 were taken with 2 sectors pointing at the
source and other 2 sectors at a background region. Data were also collected on fictitious sources, in these
cases the source region is an arbitrary one (a region devoid of any known
ray sources). Table 1 summarises
durations for ON-source observation of these blazars. Similarly OFF-source observations were also carried out
for each of them with same durations.
4. Data Analysis and Results
A number of preliminary checks on the data were carried out before doing actual analysis. A large fraction of
data collected ( 50%) were rejected as they were found to be noisy. Telescopes having similar efficiencies
for source and background runs were retained for further analysis. The arrival direction of each shower is
Observation of AGNs.
determined by reconstructing shower front using the relative arrival time of ˇCerenkov front at the telescopes.
This ˇCerenkov photon front is fitted with a plane, the normal to this plane gives the direction of shower axis.
By comparing the observed and expected arrival times of pulses at the telescopes events with bad fits are
rejected. Thus the space angle between the direction of shower axis and the direction of source is obtained for
8 telescopes. The space angle distribution peaks around 1.5 and has a FWHM of 2.5 .
The space angle distribution become narrower and the peak shifts to lower angle as the degrees of freedom
(no. of telescopes with timing information) increases. Space angle distributions of all the source runs are
compared with respective distributions of background runs. For this comparison it is ensured that both source
and background runs have the same zenith angle coverage as well as similar distribution of events as a function
of the no. of telescopes triggered. Further background space angle distribution is normalized with the source
distribution by comparing the shape of the distribution in 2.5 to 6.5 window. We chose this region because
the angular resolution of the array in the estimation of arrival direction is such that we do not expect any
events beyond 2.5 . Beyond 6.5 , the statistics is poor, besides, this region is populated by events with
poor estimation of direction of arrival angles. Normalisation of distributions corresponding to the background
with that of the source is necessary as these two data sets were taken at different times. The normalisation
constant is obtained as follows. We define
where S, B, are the no. of source and background events in th bin. The normalisation constant
is minimum. After normalising the source and background distributions, the
obtained as excess of source events over background in 0 to 2.5 region i.e.
This procedure is tested for fictitious source from which we do not expect to receive any
rays. We get a rate
rays as 0.5 0.7 per minute, which sets the noise level for our
ray signal. The rate of
were calculated for each run or part of a run using the respective duration of observation. Figure 1 gives the
ray rate vs MJD) for all the above mentioned sources from 2000 to 2004.
5. Discussions and Conclusions
Mkn 421 was found to be in flaring state in 2000, 2001 and in 2004 [6, 5], as confirmed by other ground
ray experiments. At present the 'Lepton model' in which Self Synchrotron Compton (SSC) process
is responsible for the production of TeV
rays is the widely accepted model for blazars. One of the features
of this model is a strong correlation between X-ray and
ray emission. Mkn421 was indeed found to be quite
active by RXTE in these periods most of the time. Over the last few years several multiwavelength campaigns
are carried out to study correlations between different wavebands for Mkn421. At present correlation study
between PACT data and data at other wavelengths that are simultaneous with PACT observations is in progress.
Mkn501 was not found in flaring state over the last several years although in the past it was detected in flaring
state . No out-burst is reported so far for 1ES1426+428 and ON231.
All the data available so far, for Mkn421 and Mkn501, suggests strong correlation between X-ray and
But recently Whipple observation has shown a flare where X-ray emission reached the peak a few days after
the TeV emission . This is very significant because if it is true then it will pose a serious challenge to the
Bose D. et al.
Light Curves for Mkn421, Mkn501, 1ES1426 and ON231 from 2000 to 2004.
standard SSC model as well the hadronic model. Therefore to understand the astrophysical processes in these
Blazar class of objects, it is necessary to study correlation between different wavebands through coordinated
multiwavelength campaigns and also on more such objects.
We are grateful to all the members of PACT collaboration for their contributions towards making this project
successful. We thank Prof. P.N. Bhat, S.S. Upadhya, K.S. Gothe, B.K. Nagesh, S.K. Rao, M.S. Pose, P.V.
Sudershanan, S. Sharma, K.K. Rao, A.J. Stanislaus, P.N. Purohit, M.A. Rahman, A.I. D'Souza, J. Francis, and
B.L.V. Murthy for their help and support.
 T.C.Weeks, Very High Energy Gamma-Ray Astronomy, IOP (2003).
 Chitnis, V.R. et al., 27th ICRC, Hamburg, OG.2.05, 2793 (2001).
 Gothe, K.S. et al., Indian Journal of Pure & Applied Physics, 38, 269 (2000).
 Majumdar, P. et al., Astroparticle Physics, 18, 333 (2003).
 Aharonian, F. et al., A&A 393, 89-99 (2002).
 Blazejowski, M. et al., astro-ph/0505325 (2005).
 Petry, D. et al., ApJ, 536:742-755 (2000).
Ergebnisdarstellung des Experten-Arbeitskreises „Verdauung und Ausscheidung" Der dritte Expertenarbeitskreis des Forum Wartaweil hat sich zum Ziel gesetzt, das meist nur am Rande behandelte und in der Fachliteratur eher vernachlässigte Thema der Verdauung und Ausscheidung von Menschen mit schwersten Behinderungen und Lebenseinschränkungen transdisziplinär aufzuarbeiten. Folgende Ergebnisse können festgehalten werden: Begegnung mit dem Thema im Alltag Für Eltern ist das Thema „Verdauung und Ausscheidung" ein sehr zentrales, über das sie sich untereinander (z.B. in Elterninitiativen) regelmäßig und intensiv austauschen. Professionelle in Einrichtungen der Behindertenhilfe, die in ihrem pflegerischen Arbeitsalltag mit diesem Thema konfrontiert sind, sprechen ebenso offen und häufig mit Kollegen über dieses Thema. Ein Defizit in der literarischen Aufarbeitung des Themas bestätigen und beklagen alle Teilnehmer der Gesprächsrunde. Die Erschwernisse bei der Nahrungsaufnahme sind ausreichend wissenschaftlich aufgearbeitet und publiziert, die oftmals problematische Ausscheidung, medizinisch im Fachgebiet der (pädiatrischen) Gastroenterologen angesiedelt, findet jedoch nur im Kontext persönlicher Betroffenheit Beachtung. Auch die sonderpädagogische Fachrichtung (Schwerstbehindertenpädagogik) hat sich in noch nicht ausreichendem Maße dieser Thematik angenommen. Gerade Jugendliche mit Verdauungsproblemen aufgrund schwerster Behinderungen können dieses Thema als sehr belastend erleben. Entsprechend finden Gespräche zwischen Pflegenden und zu Pflegenden statt. Die Problematik eines nicht täglich funktionierenden Stuhlganges wird von medizinischer Seite u.U. seltener gesehen, jede Darmausscheidung zwischen drei mal täglich bis zwei mal wöchentlich liegt im Bereich des Vertretbaren. Auch die dauerhafte Einnahme von dosierten Abführmitteln gilt als unbedenklich. In Einrichtungen für Menschen mit schwersten Mehrfachbehinderungen sind die wenigsten Betreuten kontinent, fast alle haben Probleme mit der Ausscheidung, gleichzeitig müssen Wege der (unterstützten) Kommunikation gefunden werden, um den Betroffenen den Ausdruck von Wünschen und Bedürfnissen auch in diesem Bereich zu ermöglichen. Ursachen von Verdauungs- und Ausscheidungsproblemen bei Kindern mit Behinderungen Verdauungs- und Ausscheidungsprobleme von Kindern mit schweren Körper- und Mehrfachbehinderungen können durch die Addition unterschiedlicher Ursachen zustande kommen:
Cerebral Cortex Advance Access published August 13, 2014 The Fault Lies on the Other Side: Altered Brain Functional Connectivity in PsychiatricDisorders is Mainly Caused by Counterpart Regions in the Opposite Hemisphere Jie Zhang1,2,†, Keith M. Kendrick3,†, Guangming Lu4,2 and Jianfeng Feng1,2,5 1Centre for Computational Systems Biology, Fudan University, Shanghai 200433, PR China, 2Fudan University – Jinling HospitalComputational Translational Medicine Center, Jinling Hospital, Nanjing University School of Medicine, Nanjing 210002, PR China,3Key Laboratory for Neuro Information, University of Electronic Science and Technology of China, School of Life Science andTechnology, Chengdu 610054, PR China, 4Department of Medical Imaging, Jinling Hospital, Nanjing University School ofMedicine, Nanjing 210002, PR China and 5Department of Computer Science, University of Warwick, Coventry, UK