The word 'ἠγέρθη' transliterates into ēgerthē, meaning in its infinitive form 'to rise'. To understand the intended meaning of the word in a specific case we should look both at how the word is used elsewhere in the same work, using a semantic analysis, and at the immediate surrounding context of the narrative, using an informative analysis.
Note also that when I refer to a 'physical' resurrection I refer to the notion that Christ as a body rose from the dead and appeared to His disciples as such. When I refer to a 'spiritual' resurrection I refer to the notion that Christ rose as a spirit, or that Christ's body and spirit 'ascended' into nonphysical reality at the moment of resurrection. The former necessitates a return to physical reality while the latter does not. As such, the latter indicates that when the word 'resurrection' is used, it is generally speaking about a Jesus that is firstly spiritual in nature. So when I refer to 'physical' and 'bodily' I refer to the idea of Christ returning as a body to physical reality, where when I refer to 'spiritual' I refer to the idea of Christ ascending into nonphysical reality, or a reality that transcends the physical. The terms are not so much about what Christ is, but about where and how Christ is. I consider these theories to be the two major ones that you are asking about in your question.
The word 'ἠγέρθη' is used in many other places in the New Testament, and even within other places within Mark. The following are a few examples of the uses of the word within other contexts.
καὶ ἠγέρθη καὶ εὐθὺς...
Ἰωάννην οὗτος ἠγέρθη...
The former refers to a very physical action of 'getting up' and the latter is referring to the idea of John the Baptist 'rising' from the dead after he was beheaded. In both cases I think it is fair to say that the writer considers the word to indicate a more physical sort of connotation than a spiritual one. The first use of the word is rather obviously physical, but the latter is very interesting and precisely supportive of the idea that Mark 16 is using 'ἠγέρθη' in a physical sense. This is because Herod would only be surprised and shocked at the notion of John the Baptist 'rising' if it was bodily, a fact that is reasserted by Herod's claiming in confusion that he 'beheaded' John. Mark uses this same word to describe the possibility of John the Baptist rising bodily from the dead as he does describing the 'rising' of Jesus. And again, keep in mind the matter is not about what Christ is, but about where and how Christ is. The where and how is truly what makes anything the way it is, and this detail is a prime example of the idea that the word in question is referring to a 'physical' thing, insofar as that means truly present and bound by physical law, for that is what is truly surprising Herod. By physical law, John the Baptist should be dead. And in light of the physical law, it'd be shocking if John were present and 'living'. This fact is only surprising if John is living in the way that is subject to the physical world. So we find that this word used to describe Christ's rising is used to describe John's own possible shocking, and so physical, rising. But even overlooking these uses of the word, the word itself is very closely associated with a physical image by its nature, and it is a great stretch to think that it could mean in itself anything 'ultra-spiritual'. The word, in other words, is not descriptive enough to imply a mystical concept of 'spiritual resurrection'. There are other, far more relevant words that Mark would use to describe such an idea if that were indeed the idea he were trying to describe.
With the semantic analysis somewhat covered, we can go on to the informative analysis, or in other words looking at the narrative itself in order to derive what could be meant by the term.
When trying to gather the meaning of a word using the context of narrative information we have to look for details that lead us to believe the word means one thing over another thing. In this case, if we hold to the idea that the word has a physical connotation and intended meaning, we have to look for details that suggest this.
But he said to them, 'Do not be alarmed; you are looking for Jesus of Nazareth, who was crucified. He has been raised; he is not here. Look there is the place they laid him.
Although an angel seems like a very 'spiritual' encounter, we have to look past this to identify what is more strictly spoken regarding Christ. It is here that there is perhaps indication that the Jesus that 'has been raised' has been raised bodily. I say this due to the angel's very practical use of his physical surroundings to refer to the resurrection of Christ. Rather than state something like 'Jesus can be seen by all who believe' or some other spiritual bidding, the angel rather straightforwardly refers the women to the reality of the empty tomb, pointing to 'the place they laid him' in order to confirm that he was in fact not there. This incorporation of physical facts in the angel's speech would seem odd if Christ's 'rise' was anything other than a physical fact itself, and if Christ could not be seen physically as such. But the following detail is even more strikingly supportive of the idea that the writer of Mark was intending 'ἠγέρθη' to be of a physical connotation.
But go, tell his disciples and Peter that he is going ahead of you to Galilee; there you will see him, just as he told you.
Here we have two details that are compelling in the interpretation of 'ἠγέρθη' as a physical 'rise'. Firstly, the unknown young man tells the women that this risen Jesus shall specifically meet his disciples at Galilee, and that 'he is going ahead' of the women. This language is about as physical as it gets. If Christ was resurrected only in a 'spiritual' sense, in which He had no body or in which his body was already ascended and only disembodied in current form, it seems odd that Christ would be 'going ahead' to a specific province of Galilee. Is he floating there or something? And why is He 'going' to Galilee? If He were spirit would He not simply 'be', which includes 'being' wherever there is a 'there'? Secondly, the angel confirms that the disciples shall 'see' Christ just as Christ assured them. If we recall the nature of Jesus's claim of His own resurrection, as is seen in Mark 8:31, Mark 9:30, and Mark 10:32, we shall recall that His assertion was met with firstly rebuke by Peter, fearful confusion from the disciples, and we are not told how they react the last time. If we can assume anything from the first two reactions, Jesus was meaning that He would rise bodily and appear as such.
Then he began to teach them that the Son of Man must undergo great suffering, and be rejected by the elders, the chief priests, and the scribes, and be killed, and after three days rise again. He said all this quite openly. And Peter took him aside and began to rebuke him.
...' the Son of Man is to be betrayed into human hands, and they will kill him, and three days after being killed, he will rise again.' But they did not understand what he was saying and were afraid to ask him.
It should be noted that from these verses alone we might not be able to tell exactly what Christ meant in saying he shall rise again. We can only infer what he meant through the reaction of the disciples. And also keep in mind that the meaning of the text is in consideration of not only the action of 'rising itself' but in the where and how of surrounding the act of 'rising'. With that said, in analyzing these verses, I doubt the idea of a resurrection that lacked bodily appearance would excite and ignite such a rebuke from Peter and such fearful confusion from the disciples. This is because when Jewish culture at the time generally spoke about death, it was predominantly physical in implication. It thus implies that when Jesus spoke about 'rising up' he was speaking about something that was an antipode to what was meant by physical death. The Greek word used by Jesus 'ἀναστῆναι', meaning 'to raise up', would imply a thing contrary of the potency of physical death, in this case being a bodily 'rising' and appearing to his disciples as such, not simply in the sense of a body transcending matter but in dead matter, subject to physical laws, being 'raised up' itself to become 'living matter'. The point is not in matter reaching a higher plane of existence, but rather in matter subject to death by physical law being regenerated within the same plane of existence. The essence of Christ being subject to the physical world in his resurrected form is necessary in understanding the nature of his resurrection and the text surrounding this account. This would explain the great reaction and hate that Christ generated from those who wished to persecute him and the rebuke and confusion that were found in Christ's disciples. Christ wasn't proposing a friendly and nonthreatening idea of 'spiritual resurrection'. He was speaking to Jews with their cultural understandings of death and life, and to propose that He would die and 'rise again' was rather clearly inferred and meant to mean that Christ would face bodily death and bodily resurrection, both of which were subject to human awareness and physical reality. I think it is rather safe to say Mark is proposing a bodily resurrection.
Skepticism Regarding A Physical Resurrection In Mark
This analysis might stretch a few things here and there, but such is only so because of the massive amounts of other contextual support for this position found in the other biblical source texts. If we were to try to support the position that Mark proposes Christ only rose in a 'spiritual' way the reality is that we have very little reasonable evidence for such a position in Mark itself, and even less of a reason granted the surrounding source texts. In other words, this position is sourced largely from an assumption that is reading meaning into the text rather than allowing the text to speak for itself. Some might go with the idea that Mark supported a spiritual resurrection and that the later Gospels morphed into a physical resurrection. There are several problems with this theory though. As already mentioned, there is no inherent support for this theory within Mark itself, and I would hold that there is no analysis that is better than the one I have already offered. It is also unlikely that the later source text would have formed out of a legend granted the communion between the disciples and the short amount of time allotted between Mark and the other Gospel texts. And more precisely, to believe that the later Gospels were supporting a 'legend' view of Christ doesn't really make sense, granted that such would indicate that the understanding of Christ's resurrection would have began in a more 'mystical' sense and gravitated to a more 'concrete' sense. This is contrary to the nature of legends, and specifically contrary to the history at the time (Christian mysticism grew later in the Church as opposed to earlier). Even more so, the idea that the latter Gospels are supporting a 'legendary' view of Christ is contradictory to what we find within the said Gospels. We do not see signs of legend or any specific agenda to confirm Christ's physical resurrection anymore than we such an agenda in Mark (with the exception of the Resurrection account itself of course). There would be obvious points where such accounts could twist and/or add words to support any such agenda, but where they don't (the spiritual nature of the transfiguration, the same account of Jesus's foretelling of his death and resurrection as Mark, the ascension, etc). With all of this said, I think the skeptic's position on Mark not supporting a physical resurrection is unwarranted and based mostly on metaphysical assumption.