Mass of the electron is defined via its rest mass called m0. This is a Lorentz invariant quantity.  Energy of a relativistic electron is E2 = p2c2 + m20c4. This is also called energy momentum relation. When a electron absorbs energy from a photon, the initial energy and momentum of the system (photon + electron) is equal to the final energy and momentum of the system after the interaction is over. That is also called conservation of 4-momentum.

An electron can indeed absorb energy from a photon. Its increased mass will then be in the form of (increased kinetic energy)/c^2.

Is there any proof or validation for this, I looked for it, i didn't find anything. I would be deeply grateful if you can suggest me a source of reference.

Mass of the electron is defined via its rest mass called m0. This is a Lorentz invariant quantity.  Energy of a relativistic electron is E2 = p2c2 + m20c4. This is also called energy momentum relation. When a electron absorbs energy from a photon, the initial energy and momentum of the system (photon + electron) is equal to the final energy and momentum of the system after the interaction is over. That is also called conservation of 4-momentum.

The electron mass is made up of exactly 0.51099907 MeV of energy. In kg, this mass is 9.10938188E-31 kg. If you multiply this mass in kg by the square of the speed of light (299792458 m/s), you will get a value in joules equal to 8.18710414E-14 j, which, , when divided by the unit charge of the electron (1.602176462E-19) will give you the energy value in eV (510998.9027).

Ref: CRC Handbook of Chemistry and Physics, page 11-3

This is what is named the rest mass of the electron. This mass is totally invariant.

When kinetic energy is communicated to the electron, part of this added energy converts to a momentary velocity related mass increment, which is detectable transversally as in excess mass increment. The sum of both is what is called the relativistic mass of the electron. If the electron is stopped in its motion, then all its carrying kinetic energy is communicated to the target and this mass increment vanishes at the same time.

This was first observed by Walter Kaufmann at the beginning of the 20th century:

http://gdz.sub.uni-goettingen.de/dms/load/img/?PPN=PPN252457811_1903&DMDID=DMDLOG_0025

Electrons and positrons can be created when electromagnetic photons of energy 1.022 MeV (twice the energy contained in the invariant rest mass of the electron) graze closely massive particles such as atomic nuclei. Electrons and positrons are totally identical except for the sign of their charges.

This was confirmed at the beginning of the 1930's by Blackett and Occhialini from analyzing recorded cosmic radiation scattering impact traces in a bubble chamber.

I can mathematically, rigorously prove that E does not =mc^2.  So no, there Is  no physically correct experimental relation between E=mc^2 and electron mass. The proof is on my website www.jmkingsleyiii.info

Hi Akash

If you try to understand fundamental particles by searching the internet, you are likely to end up finding dozens of descriptions that more often than not are not grounded on experimentally confirmed properties and often contradictory, intermixed with others that are well grounded.

Very difficult to separate them and identify the correct descriptions.

My advice is for you to get hold of an old undergrad textbook such as Halliday & Resnick "Physics" or "University Physics" By Sears, Zemansky and Young. and read about what is of interest for you. The math level is easy and the descriptions are fine. You can trust them.

Once you get a basic understanding, you will be able to identify by yourself what is good on the internet. You can trust official sources such as the CRC Handbook of Chemistry and Physics.

I put emphasis on old versions of undergrad textbooks, dating back before the 1980's if possible. Nothing new has been discovered about electrons for the past 80 years, so you do not run the risk of being misinformed with these old reference books.

The more recent textbooks are usually not very explanatory on the origin of formally confirmed discoveries. The assume too much prior knowledge on the part of students.

You have mentioned E = mc^2 in which m is a relativistic mass. Biswajoy has mentioned the energy momentum invariant in which m_o is the rest mass and p=mv, where m is a relativistic mass. When photon transfers its energy to electron, its rest m_o does not change but its relativistic mass m does change. Therefore its momentum p and its total energy E also change.

Of course there is. You can use E=mc2 for the hamburger you're eating, for a photon or for an electron.  But in the case of a photon the mass is its momentum (this means that a rest mass doesn't exist for a photon since a stationary photon doesn't exist!), in fact you have:  E = mc2  => m = E / c2 = hc / λ = photon's momentum.

So, the mass of an electron is  m = E / c2  where for "E" you have to consider ALSO its electrostatic field (we say electromagnetic mass). Practically an electron can't exist without its electrostatic field, whose energy is part of its mass-energy.