Pulsar Astronomy — 2000 and Beyond 
ASP Conference Series, Vol. 202, 2000 
M. Kramer, N. Wex, and R. Wielebinski, eds. 

M e a n , i n d i v i d u a l p u l s e s a n d s p e c t r u m o f G e m i n g a r a d i o 
e m i s s i o n 

V.M. Malofeev a n d 0 . 1 . Malov 

Pushchino Radio Astronomy Observatory, Lebedev Physical Institute, 

142292, Pushchino, Moskow reg., Russia 

A b s t r a c t . T h e m e a s u r e m e n t s of profiles at 102, 87, 59 a n d 40 MHz are 
presented. Geminga shows unique character of radio emission: t h e most 
steep s p e c t r u m , the large changes of pulse widths, phases of pulse time 
of arrival a n d t h e presence of giant pulses. 

After the p r e s e n t a t i o n of our first Geminga observations (Malofeev & Malov, 
1997) we continued t h e investigations of this pulsar a n d present new interesting 
d a t a briefly. T h e m e a s u r e m e n t s were carried out using t h e Large P h a s e d Array 
(Pushchino) at 102 MHz. New observation confirmed t h e t e m p o r a l changes of 
the form, w i d t h a n d t h e pulse phase. A few examples of integrated profiles are 
presented a t F i g . l . T h e integration of 30000 p e r i o d s is not enough t o o b t a i n 
the stable mean profile (two last profiles at F i g . l ) . T h e interpulse separated at 
~ 180° from t h e m a i n pulse is displayed for t h e last series of observations. T h e 
distribution of pulsewidths a n d pulse phases (Fig.2) show a b n o r m a l very broad 
profile at 102 MHz. 

O u r observations at t h e a n o t h e r radio telescope (cross-type) p e r m i t t o find 
the radio emission of Geminga at 40, 60, 87 MHz with similar pecularities men-
tioned above. To u n d e r s t a n d t h e u n s t a b l e form a n d w i d t h of t h e integrated 
profiles we carried out t h e observations of individual pulses or t h e groups of 
pulses. These observations have shown positive results at all frequencies d u r i n g 
a few percentage of the observing time (Fig.3). T h e most impressionable effect 
is t h e existence of t h e giant pulses d u r i n g ~ 0 . 1 % of observing t i m e (Fig.4), 
when the flux density can reach ~ 10 Jy. It is worth noting t h a t giant pulses 
can exist d u r i n g all period, t h e examples are presented a t Fig.4a (the second 
giant pulse) a n d Fig.3a (the first pulse). 

Geminga shows t h e most steep s p e c t r u m among all pulsars. S p e c t r a l index 
is > 5. S p e c t r u m shows low-frequency turnover w i t h a m a x i m u m a b o u t 60 MHz 
(Malofeev - these proceedings). 

A c k n o w l e d g m e n t s . T h i s work was p a r t l y s u p p o r t e d by R F B R ( P r No 
97-02-17372) and INTAS (grant No 96-0154). 

R e f e r e n c e s 

Malofeev V.M., Malov O.I. 1997, N a t u r e , 389, 697. 

241 

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242 Malofeev and Malov 

P\\ ,L I | t l ! vhi 

; • £ < * . ; t w ;X*J £ ^ x o :'•»* 

Phase (deg) 

Fig. 1. Mean pulse profiles in new sorits (a. h. c\. 

The sums of integrated profiles (e. d). 

PIU.NL* (ms) 

};ig. 2. Distributions of 1 lit* pulse-width (a. hi 

and phases of pulse time of arrival (e. d) lor 

main (MP) and imerpulse (IP). 

P l u s c t p u i i ' d s i 

Physt;<(k»(i) 

lig. 3. ft samples of individual pulses ;\\ 11 VIM/un; 
integrated proiiks at 41 Ml iy (hi. Arrows down and up 
are shown pluses ui* the main pulse and ike imcrpulsc. 

Hiasc \tk-y.) 

fig. i I'xampJCK (*f ujoupsof jjSKAit fnilws ;il S"1 N'M/ 

Willi Tiifcyr.UKii o!'? ohscn'injiiiciioiisialifiniJ 55 pcrtsnts 

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