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begelman et al.(1980 ) suggested that multiple blackholes may exist at the center of agn from the existence of merging galaxies .
if there is a multiple blackhole system , we may see an orbital period by a secondary blackhole crossing the accretion disk of the primary or a precession of a jet .
for example , a 12 years periodicity is confirmed in optical data with 100 years for a radio selected blaser oj 287(sillanpaa et al .
also , a periodicity of 23 days for x - ray selected blaser mkn 501 was detected with the tev gamma ray cherenkov detector telescope array ( hayashida et al .
1996 ) and hegra ( eg .
aharonian et al .
1999a ) and with the xray detector _
rxte _ all sky monitor ( asm;levine et al .
1996 ) during a tev flare in 1997 ( kranich et al . 1999 ; nishikawa et al.1999 ) .
there is an observation of radio jet bending in xray selected blasers mkn 421 ( piner et al . ) , mkn 501 ( giovannini et al . 2000 ) with _ vsop _ , which may suggest precession or orbital motion of the jet .
there also may be a long periodicity from a thermal instability in an accretion disk ( honma et al .
1991 ; abramowicz et al .
1995 ) . if we scale the periodicity of 10 sec of blackhole binary grs 1915@xmath0105 ( eg .
morgan et al .
1997 ) to agn of a mass with 10@xmath1 @xmath2 , a periodicity of 100 day is expected .    here , we concentrate on blasers which may have a periodicity from a geometrical origin .
we aim to confirm a periodicity of 23 days for mkn 501 and search for longer periodicities than 1 day for blasers using the _ rxte _ asm archive data with a lomb method .
we used _ rxte _
asm data from january 1996 ( mjd 50087 ) to august 2000 ( mjd 51780 ) , ( 4.6 years ) .
we collected xray selected blasers cataloged by xie et al.(1993 ) from asm archives , as table 1 .
we obtained a series of 90 sec integrated data .
we show the lightcurve of three interesting blasers which show possible periodicities in our analysis , in figure 1 .            here
, @xmath3 is the primary precession period and @xmath7 is @xmath8 , @xmath9 is the primary blackhole mass , @xmath10 is the secondary one , @xmath11 is the separation distance between the two blackholes , @xmath12 is the radius of the accretion disk , and @xmath13 is the orbital inclination angle with respect to the disc .
now , we limit the mass ratio between two blackholes from the detected periodicities , using the above formula . we assume the observed periodicities as precession periods @xmath14 . the two blackhole system with a short orbital period can not be alive for a long time because of gravitational wave emission .
when we assume a typical blackhole separation radius @xmath15 @xmath16100 , the condition of @xmath17 gives an acceptable orbital period of 0.14 cos@xmath18 20 days for @xmath14=140 days .
if we assume the condition with smaller @xmath7 , for example @xmath7=1 , we obtained unacceptable orbital period of 3@xmath19 cos@xmath20 .
we conclude the mass ratio should be very large , typically @xmath21 .
on the otherhand , if we assume observed periodicties as orbital periods , there are two possible models .
one is that we can see the orbital periods by a secondary crossing the accretion disk of the primary or two accretion disk causing a tidal disturbance .
this needs a large mass difference for two blackholes ( sillanpaa et al .
1988;letho & valtonen 1996 ) .
the other is that we can see the orbital period by the orbital @xmath22 motion , which needs two orders mass difference for 23 day periodicity of mkn 501(rieger & mannheim 2000 ) .
it is very interesting that the three blasers with siginificant periodicities are all tev gamma sources ( mkn 421;eg.aharonian et al .
1999b , mkn 501;eg .
aharonian et al .
1999a , pks 2155 - 304;p.m.chadwick et al .
if these periodicities are due to a geometrical effect , we expect a similar periodicity in tev gamma ray intensities .
we searched for such a periodicity using a lomb method with hegra tev published data , for mkn 421 during 1997 - 1998 and for mkn 501 during 1997 - 1999 ( lorenz 1999 ; aharonian 1999b ; aharonoan 2001;kranich 2001 ) .
we confirmed a 23 day periodicity for mkn 501 during the 1997 flare time found by kranich et al.(1999 ) .
however , during 1998 - 1999 , 23 day periodicity was not found for mkn 501 .
a 62 day periodicty was not found for mkn 421 . probably , the sensitivity of tev gamma ray cherenkov detectors may not be enough to detect periodicities except around the large flare of mkn 501 in 1997 .
the good coincidence between periodic blasers and tev gamma ray blasers is remarkable .
we can estimate the chance probability of this coincidence at less than 10@xmath23 .
there may exist a relation between multiple blackholes and an electron acceleration to ultra high energy .
we wish to acknowledge the _ rxte _ asm group for their public data service and xtehelp for a kindness in support .
we also acknowledge the hegra group , especially dr .
d. kranich and dr .
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we have searched for long periodicity in ten x - ray selected blasers with _ rxte _ 
 asm 4.6 years data . 
 we found about 10 - 100 day possible periodicities for three tev gamma ray blasers , mkn 421 , mkn 501 and pks 2155 - 304 .    
 = 0.0 cm = 0.0 mm = 20.0 cm = 0.0 mm = 0.0 mm    * long periodicity of blasers with rxte asm *    s.osone , m.teshima and k.mase    institute of cosmic ray research , universty of tokyo , kashiwa 277 - 8582 , japan