The Cousin R and I band photometric observations of ~ 13' × 13' field in the direction of M31 galaxy have been carried out during 1999-2001 to search for microlensing events using pixel technique. Here we report a microlensing-like event, of which preliminary analysis indicates that it is a long duration (t1/2 ~ 66 days) event

Joshi, Yogesh C.

Narasimha, D.

Pandey, Anil K.

Ram Sagar,

English

Publications of the IAS Fellows

~"11. Astr. Soc. India (2003) 31, 417418 
possible Microlensing Event in the direction of M31 
yogesh C. Joshi', Anil K. Pandeyl, D. Narasimha2, Ram Saga$ 
1 Slate Obsen~atoty Marlortr Peak, N(~itlbri Tal - 263 129, lrrdia 
2 Tam institute of Fur~riclmcrltal Resrtirch, Horni Bhahha Road, Mumbai - 400 005, lndia 
Abstract. The Cousin X and 1 band photometric observations of - 13' x 13' 
field in the direction of M3 1 galaxy have been carried out during 1999-2001 to search 
for microlensing events using pixel technique. Here we report a microlensing-like 
event, of which preliminary analysis indicates that it is a long duration (tllz - 66 days) 
event. 
1. Introduction and Observations 
M31 has been a promising target to search for microlensing events. Consequently a number 
of groups have started observations towards this galaxy, however, analysing the observations in 
the large background of unresolved stars is n cumbersome process. To deal with the problem, 
AGAPE (Baillon et al. 1993) collaboration proposed 'pixel technique' to monitor pixels of the 
CCD rather than the stars themselves. To search for microlensing events, we have also started 
CCD observations in the direction of M31 at the State Observatory, Naini Tal in 1999 using 
2Kx2K CCD at the f/13 Cassegrain focus of 104-cm Sa~npurnanand Telescope. The target field 
(13' x 13'), observed in  Cousins R and I bands, is centered at azow = 0 0 ~ 4 3 ~ 3 8 ~  and 6tooa = 
+41°09'.1, at a distance of about 15 mcmin in the South-East direction from the center of M31. 
An overview of the observations and data reduction are given in Joshi et al. (2001,2003) and the 
details of 'pixel technique' is described by Ansari et al. (1997)- 
2. Preliminary results 
We found few possible microlensing events in our data after three observing seasons. The pixel 
light curve of a possible microlensing event ( ( ~ 2 , ~  = 00 : 43 : 33 .3 ,62~~)  = $41 : 06 : 43.8) is 
shown in Fig. 1. A 7 parameter theoretical P a ~ ~ y f i s k i  fit (1986), yielding same time period ( t i p )  
and maximum mngnificatiall (A,,,) in bath ,4 and I filters, is also plotted with the light curve. 
The event is peaked at tmax - 1910 Days (JD- 245 1534.5) where the Am, is - 1.22. The t112 
of the light curve is esli~nated about 66 Days. At the noise level of typically 300 ADUs against 
amplification of 2000 ADUs at peak flux, the single lens parameters are not well determined, 
Yogesh C. Joshi el a/. 
Days (JD - 2449624.5) 
Figure 1. The pixel light c w e s  of a microlensing candidate in both R and 1 filter detected in our study. The 
continuous line represent the 7-parameter PaczyITski fit. 
however, we are trying to improve the noise level and refined analysis of the candidate event is in 
progress. 
Acknowledgments 
We would like to thank Dr. Giraud-Hiraud Yannick and Dr. Jean Kaplan for their helpful dis- 
cussions. This study is a part of the project 2404-3 supported by Indo-French center for the 
Promotion of Advance Research, New Delhi. 
References 
Ansari, R., Auriere, M., Baillon, P.. et,al. 1997, A&A, 324, 843 
Baillon P. et al., 1993, AtA,  277, 1. 
Joshi, Y.C., Pan&y, A.K., Narasimha, D., Sagar, R., 2001, BASI, 29,531 
Joshi, Y.C., Pandey, A.K., Narasimha D., Sagar, R., Giraud-Hgraud, Y., 2003, A&A, 402, 1 13. 
PaczyiFski B.,1986, A#, 304,l. 


Possible microlensing event in the direction of M31

http://repository.ias.ac.in/65958/1/84_pub.pdf

Possible microlensing event in the direction of M31

Abstract

Similar works

Full text

Available Versions

Publications of the IAS Fellows