The MACHO Project LMC Microlensing Results from the First Two Years and the Nature of the Galactic Dark Halo

Details The MACHO Project LMC Microlensing Results from the First Two Years and the Nature of the Galactic Dark Halo The MACHO Project LMC Microlensing Results from the First Two Years and the Nature of the Galactic Dark Halo

1996-06-26

arxiv.org/abs/astro-ph/9606165v1

Astrophys.J. 486 (1997) 697-726

Astronomy and Astrophysics

Astrophysics

Latex, 54 pages, uses aas2pp4.sty and astrobib.sty, with 24 out of 26 Postscript figures in gzipped tar file. 2 extra greyscal

Scientific paper

10.1086/304535

The MACHO Project is a search for dark matter in the form of massive compact halo objects (Machos). Photometric monitoring of millions of stars in the Large Magellanic Cloud (LMC), Small Magellanic Cloud (SMC), and Galactic bulge is used to search for gravitational microlensing events caused by these otherwise invisible objects. Analysis of the first 2.1 years of photometry of 8.5 million stars in the LMC reveals 8 candidate microlensing events. This is substantially more than the number expected ($\sim 1.1$) from lensing by known stellar populations. The timescales ($\that$) of the events range from 34 to 145 days. We estimate the total microlensing optical depth towards the LMC from events with $2 < \that < 200$ days to be $\tau_2^{200} = 2.9 ^{+1.4}_{-0.9} \ten{-7}$ based upon our 8 event sample. This exceeds the optical depth, $\tau_{\rm backgnd} = 0.5 \ten{-7}$, expected from known stars, and the difference is to be compared with the optical depth predicted for a ``standard" halo composed entirely of Machos: $\tau_{halo} = 4.7\ten{-7}$. Likelihood analysis gives a fairly model independent estimate of the halo mass in Machos within 50 kpc of $2.0^{+1.2}_{-0.7} \ten{11} \msun$, about half of the ``standard halo" value. We also find a most probable Macho mass of $0.5^{+0.3}_{-0.2}\msun$, although this value is strongly model dependent. Additionally, the absence of short duration events places stringent upper limits on the contribution of low-mass Machos: objects from $10^{-4} \msun$ to $0.03 \msun$ contribute $\simlt 20\%$ of the ``standard" dark halo.

Affiliated with

Also associated with

No associations

Rating

The MACHO Project LMC Microlensing Results from the First Two Years and the Nature of the Galactic Dark Halo does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with The MACHO Project LMC Microlensing Results from the First Two Years and the Nature of the Galactic Dark Halo, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The MACHO Project LMC Microlensing Results from the First Two Years and the Nature of the Galactic Dark Halo will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-246451